Soil Conservation Service of N,S.W.

Glossary of Termsused in

Soil Conservation

F. D. HoughtonP. E. V. Charman

1986

Published by theSoil conservation Service of N.S.W.

under the Authority of theHon. J. R. Hallam, M.L,C.

Minister for Agriculture and Minister for Lands,for and on behalf of the

Standing Committee on Soil Conservation.

ISBN 07305 15257

60320-15204-1

3

Glossary of Termsused in

Soil Conservation

Minister's Foreword

With the growing recognition of soit degradation as a national problem, therehas developed a need in recent years for standardisation of soil conservationterminology across Australia. The Soil Conservation Service recognised thisneed in the late seventies, and began to assemble a fite of terms withdefinitions and explanations firstly aimed al meeting its own requirements.

Subsequently the first dratt glossary was put to the Standing Committee onSoil Conservation who adopted it as a basis for the development of a nationaldocument. Since then all Australian soil conservation organisations haveassisted with constructive comment on two drafts, and thus the major steptowards a common soit conservation terminology has been taken.

The Soil Conservation Service is now pteased to publish this glossary on behalfof the Standing Committee on Soil Conservation. There are clearly manyadvantages in the rationalisation of terminology between States and I thuscommend this most useful glossary to all those with an interest in theprotection of the nation's soil resources.

J. A. HALLAM, M.L.C.Minister for Agriculture and Minister for Lands

5

Preface to First Draft

This glossary has been produced in response to a needwhich has been felt during lhe widening of Serviceactivities in lhe seventies and eighties. A number ofattempts have been made to produce a soilconservation glossary during lhe Services history. Earlyvolumes of the journal listed a limited number of itemsin an atlempt to standardise what was then a newterminology in Australia. A number of terms werecollecled from soil conservationists in the early sixties,but were deslined lo remain on file.

The initiative for the present volume came trom anumber ot exchanges between various officers in 1976,which resulted in the start of a collection of definitionsconsidered appropriate for Service use, However, noreal commitment was made to sort them out until 1982,but in the intervening years our collection graduallygrew. The Service's increasing involvement in urban soilconservation, mining rehabilitation and conservationtillage in recent years, and glossaries produced in theseareas of technology, have added scope to the presentwork and have urged us on, The main impetus,however, has been the recognition of a need for thestandardisation of terminology at a time when theService's interaction with other organisations andauthorities is increasing so rapidly.

This first edition of the glossary is a DRAFT only, to beused internally until 31st December1983. During thistime review and constructive comment are invited,including an indication of additional terms which shouldbe included. We are interested to learn of technicaldeficiencies as well as unsatisfactory layout orinadequate supporting information.

lt is possible that during the review period supplementswill be issued which will also be considered in the finalassessment before printing. We are keen to receivephotographs and/or diagrams which may be useful inthe tinal document. Another idea which we have in mindis to include an appendix for terms which are strictly"in-Service".

6

Our approach throughout the glossary has been notonly to achieve standardisation and rationalisation ofdetinitions, but also to provide useful additionalinformation on each term. This applies particulary to themore important soil conservation terms and those wherewe felt there had been some confusion in definition orinterpretation. We acknowledge the fact that someareas of technology appear to have been given greaterattention than others, This not only reflects our owninterests but also areas where we felt a special effortwas necessary. We also acknowledge that some areasmay have been given inadequate attention at thisstage.

We have used a wide variety of source material whichis recorded in the reference list, and which is herebyduly acknowledged. A number of officers have been ofconsiderable assistance to us in commenting onprevious drafts, giving us definitions, and acting as"sounding boards" for our own. Mrs Jenny Perry hashandled the whole exercise on the word processor andher patience and diligence have been muchappreciated.

Terminology is something that ¡s always changing,particularly in a 'dynamic subject such as soilconservation. We would like to think that this glossarywilt represent a new basis for communication betweensoit conservationists. Indeed, we hope that the firstmajor edition will be endorsed by the StandingCommittee on Soil Conservation as a starting point forthe standardisation of soil conservation terminology inAustralia. In the interim, however, our main hope is thatit will prove useful to people involved in soilconservation at all levels.

P. D. HOUGHTONP. E. V. CHARMAN

July, 1983.

Preface to Second Draft

Since the production of the first draft, the glossary hasbeen in use in the Soil Conservation Service of N.S.W,,and copies were also made available to soilconservation organisations in other States. Thus therehas been widespread opportunity for comment onexisting definitions and ommissions. The contribution bymany people from both N.S,W. and other States hasbeen very much appreciated. This second draftincorporates as much of the comment as possible andalso a large amount of additional material.

Standing Committee on Soil Conservation has endorsedthe production of the glossary as a national document.and we have therefore made every effort toaccommodate interstate perceptions of variousdefinitions and also inctude terms specific to particularStates. The tillage machinery terms (Grevis'James andKamel, 1g77) are currently'being revised by O.D,P.I. andwill be included in the final document.

lt is intended that this second draft be issued for alimited period only, to seek further comment prior tofinal printing. We do not envisage any major changesor the addition of much more material, except fordiagrams and photographs where appropriate. Howeverwe will attend to any serious ommissions brought to ourattention. For these reasons we would appreciate anyfinal comments to be sent in by 30th June, 1985.

P. D. F-1OUGHTONP. E. V. CHARMAN

December, 1984.

7

Preface to This Edition

The final phase of work on this publication has beenundertaken following comment on the second draft byall soil conservation organisations in Australia andC,S.I,R.O, Division of Soils, We are grateful for theinterest shown by all these groups, and to the manyindividual officers who have assisted us with theircomments, Particularly we owe our thanks to the SoilConservation Services Branch ot the QueenslandDepartment of Primary Industries who contributed theconservation tillage machinery terms. These were basedon the 1977 glossary of I. GrevisJames and T. Kamel.who again cooperated by undertaking its Furtherreview.

The number of glossary entries added at this stage hasnot been great, being restricted to about seventy terms.The main addition has been by way of photographswhich come from both N.S.W. and Queensland soilconservation sources.

We are indebted to Mrs Jenny Perry who has typed alldrafts of the glossary since its inception, originally onconventional typewriter and more recently on the wordprocessor. Our sincere thanks are also due to Mr L. E.S. Coxen and Miss K. Russell of Queensland D.P.l whoproduced the photographs of tiRage machinery onbehalf of that organisation.

Finally we owe our thanks to the members of theStanding Committee on Soil Conservation who havesupported the development of this glossary, which wehope will make a substantial contribution to soitconservation in Australia.

P. D. HOUGHTONP. E. V. CHARMAN

December, 1985.

REFERENCES

ALLABY, M. (1917)'Dictionary of the Environment."

Macmillan Press Ltd. London, U.K.

ANON (1962)'Dictionary of Geological Terms,"

Dolphin Reference Books, New York, U.S.A.

ANON (1967)"G/ossary of Soil and Water Terms"Special Publication SP.04-67. American Society ofAgricultural Engineers, Michigan, U.S.A.

ANON (1970)"Glossary of Soil Science Terms,"Soil Science Society of America, Madison, U.S.A.

ANON (1975)"Terminology and Definitions for Soil Tilla ge and So//-Tool Relationships"Yearbook of American Society of Agricultural Engineers,Michigan, U.S.A.

ANON (1976)"Glossary of Terms in Soif Science."Canada Department of Agriculture, Ottawa, CAN,

ANON (1979)"Our Land Resources."National Waler and Soil Conservation Organisation,Wellington, N.Z.

ANON (1982)"Resource Conservation Glossary."Soil Conservation Society of America, Ankeny, USA.

AVEYARD, J. M. and CATHCART, R. J. (1982)"Design Manual for Soil Conservation Works.'Soil Conservation Service of N.S.W., TechnicalHandbook No. 5, Sydney AUST.

BECKMANN, G. G., CRACK, B. J. and PREBBLE,R. E. (1976)

"Supplementary Glossary of Soil Science Terms as usedin Australia."Publication Number 6. Australian Society of Soil ScienceIncorporated, St. Lucia, AUST.

BERGSMA, E (1984)"G/ossary of Terms of Soil Erosion and Conservation"

(DRAFT ONLY). International Society of Soil Science,Wageningen, THE NETHERLANDS.

BURTON, J. R. (1965)"Water Storage on the Farm, 'Vot. I.Water Research Foundation Bulletin No. 9 Sydney,AUST.

CHARMAN, P. E. V. (Ed.) (1978)"Soils of New South Wales Their Characterisation.Classification and Conservation."Soil Conservation Service of N.S.W. TechnicalHandbook No. 1, Sydney AUST.

CHOW, V. T. (Ed.) (1964)"Handbook of Applied Hydrology."McGraw-Hill Book Co.. New York, U.S.A.

8

GARVIN, R. J., KNIGHT, M. R., and RICHMOND, T.J. (1979)

"Guidelines for Minimising Soil Erosion andSedimentation from Construction Sites in Victoria."Soil Conservation Authority of Victoria, TechnicalCommunication 13. Melbourne, AUST.

GLENDINNING, J. S. (Ed.) (1981)"Fertiliser Handbook."Australian Fertilisers Ltd., North Sydney, AUST,

GRE VIS-JAMES, I. W. and KAMEL, T. R. (1977)"Conservation Tilla geA Glossary of Selected Terms."Queensland Department of Primary Industries, BrisbaneAUST,

HANNAN, J. C. (1978)"Extractive Industries Handbook for SoilConservationists."Soil Conservation Service of N.S.W., Sydney, AUST.

IBRAHIM, K. (1915)"Glossary of Terms used in Pasture and Range Survey.Research, Ecology and Management."Food and Agriculture Organisation ol the U.N., Rome,ITALY.

McDONALD R. C., ISBELL, R. F., SPEIGHT, J. G.,WALKER, J. and HOPKINS, M. S. ('EM) /4(41

"Austral ian Soil and Land Survey'Field Handboog.Inkala Press, Melbourne, AUST.

MORSE, R. J., ATKINSON, G. and CRAZE, B."Soil Data Card Handbook."Soil Conservation Service ol N.S.W, TechnicalHandbook No. 4, Sydney, AUST.

NORTHCOTE, K. H. (1979)"A Factual Key for the Recognition of Australian Soils."Rellini Technical Publications, Adelaide, AUST.

NORTHCOTE, K. H. and SKENE, J. K. M. (1972)"Australian Soils with Saline and Sndic Properties."C.S.t.R.O, Melbourne, AUST.

OUILTY, J. A., HUNT, J. S- and HICKS, R. W. (1978)"Urban Erosion and Sediment Control,"Soil Conservation Service of N.S.W. TechnicalHandbook No. 2. Sydney, AUST.

ROWE, R. K., HOWE, D. F. and ALLEY, N. F. (1981)"Guidelines for Land Capability Assessment inVictoria,"Soil Conservation Authority of Victoria, Melbourne,AU ST.

STACE, H. C. T., HUBBLE, G. D., BREWER, R.,NORTHCOTE, K. H.. SLEEMAN, J. R., MULCAHY,M. J. and HALLS WORTH, E, G. (1968)

"A Handbook of Australian Soils.".ReLlim Technical Publications, Glenside, South Australia,AUST.

STEPHENS, C. G. (1962)"A Manual of Australian Soils"CS.I,RO, Melbourne, AUST,

WISCHMEIER, W. H. and SMITH, ,D. D. (1918)"Predicting Rainfall Erosion Losses."Agriculture Handbook No, 537, U.S. Department ofAgricullure. Washington D.C.. U.S.A.

Introduction

The text of each definition in this glossary has generallybeen written with a minimum of scientific jargon.Definitions drawn from a scientific source have thereforebeen modified to some extent where this wasconsidered necessary. However, compatability withexisting glossaries used in Austratia has beenmaintained wherever possibte. The aim has been toexpress definitions and explanations in a straight-forward styte acceptable to the practising soilconservationist.

Terms are listed in alphabetical order. Each term hasbeen classified. tor the purpose of definition, into oneof the following categories, according to the context inwhich it is detined:

agrAgronomyalpAlpine

csdCoastal Sand DrittongEngineeringforForestry

genGeneralhydHydrologylevLand EvaluationlimLandlorm

mmMiningran-iRange ManagementrmsRemote SensingsotSoil SciencestrStructuratsurSurveyingurbUrban

lt witt be noted that some terms are defined under morethan one of the above categories (e.g. CREST).

Cross-referencing has been used extensively. Wheretwo synonymous terms are in use the definition is listedunder the preterred term, and the alternative is shown

g

in brackets e.g. FILTER STRIP (DESILTtNG AREA)(str). The alternative term is also listed separately, witha reference back to the preferred term.

e.g. DESILTING AREA (str)

Syn. FILTER STRIP.

Key terms used in a definition, which can themselvesbe found in the glossary, are printed in italics. Wherea term is defined as part of another delinition, the termis put n CAPITALS, within that definition, and a cross-reference is made thus:

e.g. CHEMICAL FALLOWING (agr)

See FALLOWING.

Where additional useful information in relation lo a termcan be found elsewhere in the glossary, the cross-reference is of the form: See also

at the end of the text of thedefinition. The additional information may include aphotograph or diagram.

Where attention needs to be drawn to the definition ofa term closely related to the one being defined, thecross-reference is ot the form: Cf

also at the end of the text of the definition.

Antonyms tor terms are identified thus Ant.

Acceptable abbreviations are listed in the glossary, forwhich primary entries contain full stops betweenconstituent letters to show that they are abbreviations,e.g. U.S.L.E. The terms they represent will be foundlisted separately with the normally used abbreviationsin brackets, e.g. UNIVERSAL SOIL LOSS EQUATION(USLE).

A, A1, A2 HORIZON (sol)

See SOIL PROFILE.

A.H.D. (sur)

See DATUM.

A.P.I. (mis)

Syn. AERIAL PHOTOGRAPH INTERPRETATION.

ABANDONED MINE (DERELICT MINE) (mm)

A mine which has been inactive for some considerabletime and for which no title is current or where the leasehas been cancelled.

ABNEY LEVEL (sur)

See LEVEL.

ABRASION DETACHMENT (gen)

See DETACHMENT.

ABSORPTION AREA (gen)

Syn. WATER DISPOSAL AREA.

ABSORPTION BANK (str)

See BANK.

ACCELERATED EROSION (gen)

See EROSION.

ACCEPTABLE OUTLET (str)

Syn. STABLE OUTLET.

ACCRETION (csd)

Gradual addition of sand to a beach or lake shorelineduring periods of light on-shore wind and/or loweredsea level.

ACID SOIL (sol)

A soil giving an acid reaction throughout most or all ofthe soil profite (precisely. helow a pH of 7.0; practically,below a pH of 6.5). Generally speaking, acid soilsbecome a problem when the pH drops below 5.5. Atthis level, and particularly below 5.0, the followingspecific problems may occur - aluminium toxicity,manganese toxicity, calcium deficiency and/ormolybdenum deficiency. Such problems adversely affectplant growth and root nodulation, which may result ina decline in plant cover and increase in erosion hazard.

The term is frequently used to describe soils withacidity problems as above.

Correction of the acidity is normally carried out by theapplication of appropriate amounts ot lime to bring thesoil pH to a level of 6.0 - 6.5.

See also pH.

11

ACIDITY (sol)

The chemical activity of hydrogen ions in soil expressedin terms ol pH. See also ACID SOIL, pH,

ACTIVE RECREATION (urb)

A level of land development which provides for ovals,camp sites or other activities requiring extensiveclearing or levelling for facilities, Cf. PASSIVERECREATION.

See also RECREATIONAL CAPABILITYCLASSIFICATION.

ADSORPTION (sol)

The interaction of ions with the surfaces of soilmaterials, particularly with organic matter and inorganiccolloidal substances comprising part of the clay fraction.In this way nutrients in solution, made up of ions,become attracted to sites on soil particles with anopposite charge.

AEOLIAN (If m)

A term applied to deposits of soil materials transportedand/or arranged by wind.

AERIAL PHOTOGRAPH (rrns)

Any photograph taken of the surface of the earth fromfixed wing aircraft, helicopters, balloons or spacecraft.There are two categories of aerial photography:

Vertical . where an attempt is made to keep theoptical axis of the camera perpendicular to the earth'ssurface. If the axis is exactly vertical, the photo iscalled a truly vertical photo and therefore containszero TILT. However, in practice it is impossible tokeep the camera axis vertical and small tilts of lessthan 3 degrees are tolerated, The resultant photos arereferred to as near vertical and may be regarded asequivalent to truly vertical for most photointerpretation purposes.

Oblique where the optical axis is deliberately tiltedaway from the vertical. If it is tilted sufficiently toinclude the horizon, the photo is called a high obliqueand it the horizon does not appear, it is called a lowoblique. Oblique aerial photographs cover moreground area than vertical aerial photographs exposedat the same altitude.

AERIAL PHOTOGRAPH INTERPRETATION(API) (rms)

A technique of obtaining information from aerialphotographs, principally applied to the techniquesinvolving the stereoscopic viewing of the photographs.This method enables the evaluation of terrain in threedimensions. lt is basically a deductive process thatrequires conscious or subconscious consideration of theelements of the image. The quality, reliability andefficiency of any interpretation are dependent on thepersonal experience and expertise of the interpreter.The acquisition ol such knowledge, either by fieldexamination to establish ground truth, or by the studyof available maps and reports, should, therefore beconsidered an essential part of any photo-interpretationjob.

AERIAL PHOTOGRAPH INTERPRETATION(Continued)

API involves three basic steps:

examine the photographs o get a three-dimensionalperception:

idenlify ground conditions by observing certainelements appearing in lhe pholographs: and

analysing specific problems by the association ofground conditions with one's backgroundexperience.

No other technique can provide a three-dimensionaloverview of the terrain from which the inter-relations oftopography, drainage, surface cover, geologic materials,and human activities on the landscape can be viewedand evaluated. (Reference: Rib, F-IT, and Liang, T.Recognition and Identification. In Landslides : Analysisand Control, Transportation Research Board, NationalAcademy of Sciences, Washington D.C., U.S.A., SpecialReport 176, Chapter 3. 1978).

AEROBIC (soi)

Describes soir condifions in which tree oxygen isplentiful and chemicalfy, oxidising processes prevail.Such conditions are usually found in well-drained soilswith good soil structure. Ant. ANAEROBIC.

AFFORESTATION (for)

The establishment of a forest on land that has notpreviously, or not recently, been timbered. Cf.REAF FOR E STATION.

An a/cove formed as a result of a landslide.

't,.

12

a -' -t--t- Z-,rÇ)L(

t - ,1 TZr'- -

AGGRADATION (gen)

The process of building up of surfaces, such asstreambeds or floodplains, by the deposition ofsediment and/or colluvium,

AGGREGATE (gen)

A cluster of particles, held together by inter-particleforces or bonds. The term is also used to mean roadgravel. See atso SOIL AGGREGATE.

AGROFORESTRY (agr for)

The integration of commercial tree growing into theoperation of a farming enterprise. t involves thecommercial utifisafion of native frees as welt as theplanting and management of quicker-growing freesthrough afforestation, The aim is to ensure a long termviable enterprise based on timber and limber products,as part of the overall farm operation,

AGRONOMY (agi-)

The study of land management and associatedpractices for the establishment, growth and use ofcrops and pastures Involves an understanding of soils,land. climate, plant characteristics and animalhusbandry in relation to crop and pasture production,

AIR SEEDER (eng)

See DRILL.

ALCOVE (If m)

A moderately inclined to very steep open depressionwith concave cross-section, such as the recess createdin a hi//slope as the result of a slump,

ALKALINE SOIL (sol)

A soil giving an alkaline reaction throughout most or allo! the soil profile (precisely, above a pH of 7.0;practically, above a pH of 8.0). Many alkaline soils havea high pH indicated by the presence of calciumcarbonale, and are suitable tor agriculture. However,others are problem soils because of salinity and/orsodicity. Soils with a pH above 9.5 are generallyunsuitable for agriculture. See also SODIC SOIL, SALINESOIL, pH.

ALKALINITY (sol)

The chemical condition of soil with a pH greater than7.0. Often associated with saline soils and sodic soils.See also pH.

ALLUVIAL (Ifni, sol)

Describes material deposited by, or in transit in, flowingwater. See also ALLUVIUM.

ALLUVIAL FAN (Um)

An accretion of sediments in a flowline characterisedby radial slope lines inclined away from a point, givingit a typical fan' shape Such deposits may build up toeventually block and divert flows.

ALLUVIAL PLAIN (If m)

A large flat area of alluvium. Although it includesfloodplains, the preferred use of the term is to describeformer floodplains where there is no recentaccumulation of sediment,

ALLUVIAL SOIL (sol)A soil developed from recently deposited alluvium,normally characterised by little or no modification of thedeposited material by soil-forming processes,

'particularly with respect to soil horizon development.

ALLUVIUM (tim, sol)

An extensive stream-laid deposit of unconsolidatedmaterial, including gravel, sand, silt and clay. Typicallyit forms lloodplains that develop alluvial soils,

ALPINE (gen)

Describes the area above the timber line inmountainous terrain which is determined by theoccurrence of low temperatures. In Australia, thedominant vegetation consists of a snowgrass-herbcommunity.

AMELIORANT (sol)

Syn. SOIL AMELIORANT.

ANAEROBIC (sol)

Describes soil conditions in which free oxygen isdeficient and chemically, reducing processes prevail.Such conditions are usually found in waterlogged orpoorly drained soils in which water has replaced soil air.Ant. AEROBIC.

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ANGLE OF REPOSE (eng)

The stable angle between the horizontal and themaximum slope that loose material assumes throughthe influence of gravity.

ANIONIC BITUMEN EMULSION (gen)

See BITUMEN EMULSION.

ANNUAL CROPPING (agr)

A cropping system where one crop per year is grownon the same piece of land,

ANNUAL EXCEEDANCE PROBABILITY(hyd)

The chance that a particular storm or flood event willbe equalled or exceeded in any year, expressed as apercentage. lt is the reciprocal of return period. Forexample, a 20 year return period is equivalent to a 5per cent annual exceedance probability.

ANNUAL PASTURE (agr)

See PASTURE.

ANNUAL PLANT (agr)

A plant which completes its life cycle and dies withinone year or less. The lite cycle includes production ofroots, stems, leaves, flowers and finally seed for furtherregeneration. Cf. BIENNIAL PLANT, PERENNIAL PLANT.

ANTECEDENT MOISTURE CONTENT (sol)

The moisture content of a soil prior to a rainfall event.It has an important influence on the liketihood of runoffoccurring as a result of subsequent rainfall, becauseantecedent moisture restricts the amount of infiltrationwhich can take place.

ANTI-SEEP COLLAR (eng)

Syn. COLLAR,

ANTI-VORTEX DEVICE (eng)

A device, usually a vertical or horizontal plate, placedat the entrance of a pipe to prevent the formation of avortex (whirlpool effect) in the water at the pipeentrance.

APEDAL (soI)

Describes a soil in which none of the soil materialoccurs in the form of peds in the moist state. Such asoil is without apparent structure and is typicallymassive or single grained. When disturbed it separatesinto primary particles or fragments which may becrushed to primary particles. Ant. PEDAL.

APRON (eng)

A layer of concrete, stone, timber, or other relativelypermanent material placed at the entrance or outlet ofa hydraulic structure, such as a culvert or chute, in thechannel bed, to protect the structure against erosion.

An apedal soil section - peds are not evident.

AOUIFER (sol)

A porous soil or geological formation, often lyingbetween impermeable sub-surface slrata, which holdswater and through which water can percolate slowlyover long distances and which yields ground water tosprings and wells. Aquifers may, however, beunconfined and the water level subject to seasonalinflow. An AQUITAnO is also a groundwaterbearingformation but is insufficiently permeable to transmit andyield water in usable quantities.

AQUITARD (gen)

See AQUIFER.

ARABLE (agr)

Describes land suitable for the economic production ofcrops, usually involving regular cultivation.

ARID (ram)

Refers to climates or regions which lack sufficientraintau for crop production or extensive sown pastures.Usually defined as a climate with annual average rainlallless than 250 mm (10 inches). See also SEMI-ARID.

ARMOURING (gen)

The process of development of a layer of coarseparticles on the surface of a soil which is capable ofprotecting the soil below from wind or flowing water.

ARMOURING LAYER (gen)

A layer of particles, some of which may be in theprocess of being moved by erosive forces, but whichare deep enough to prevent access of Ihe moving windor water Io the soil below. lt protects the underlying soiluntil il is broken by stock trampling or cultivation or untila stronger erosion event removes il.

14

ASPECT (Ifm)

The direction that a slope faces, measured at rightangles lo the contour.

ASSAY (mm)

The determination of the total amount of one or moreconstituents of a rock or ore.

ASSOCIATION (ram, alp)

A stable plant community of definite composition,presenting a uniform appearance and growing in moreor less uniform habitat conditions.

ASSOCIATION (rms)

The identificalion of an image on an aerial photographby inference; that is, certain features can be inferredas occurring by the presence of other readily identifiableleatures. For example, in some areas soil types can bedetermined from vegetation types, the latter being themore readily identifiable features from the aerialphotographs.

ASSOCIATION (sol, lev)

Syn. SOIL ASSOCIATION.

ATTERBERG LIMITS (sol)

The soil waler conlents al the solid/plastic and plasticiliquid boundaries. Atterberg limits are based on theconcept that a fine-grained soil can exist in any of threeslates depending on ils water conlenl. Thus, on theaddition of waler, a soil may proceed from the solidstate through to the plastic and finally liquid states. Thewater contents at the boundaries between adjacenlslates are termed the plastic limit and the liquid limit,Water content is expressed as a percentage of theoven dry weight of soil.

PLASTIC LIMIT (PL)

The plaslic limit of a soil is the water content atwhich the soil passes from the solid to the plastic

state. It is arbitrarily defined as the lowest watercontent at which the soil can be rolled into threads3 mm in diameter without the threads breaking intopieces. (Australian Standard AS 1289.02.1 - 1977)

LIOUID LIMIT (LL)

The liquid limit of a soil is the water content atwhich the soil passes from the ptastic to the liquidstate. lt is arbitrarily defined as the water contentat which two halves of a soil cake will flow togetherfor a distance of 12 mm along the bottom of thegroove separating the two halves, when dropped25 times trom a distance of 10 mm at the rate of2 drops/second, using standard apparatus. (AS1289.01.1 - 1977)

PLASTICITY INDEX (Pl)

The plasticity index of a soil is the numericaldifference between the plastic limit and the liquidlimit. (AS 1289.03.1 - 1977)

These limits are used to categorise soil materials interms of their likely engineering behaviour at differentmoisture contents such as in building or roadfoundations, Prior to earthwork construction, theirdetermination assists the specification of requiredcompaction levels, batter slopes and optimum moisturelevels for construction. See also UNIFIED SOILCLASSIFICATION SYSTEM, PLASTIC, SOILPLASTICITY, LINEAR SHRINKAGE.

AUSTRALIAN HEIGHT DATUM (sur)

See DATUM.

AUTECOLOGY (gen)

The study of relationships between a single species andits environment. Cf. SYNECOLOGY.

AUTOMATIC LEVEL (sur)

See LEVEL.

AVAILABLE NUTRIENT (sol)

The portion of any element or compound in the soil thatcan be taken up and assimilated by plants to enhancetheir growth and development. See also PLANTNUTRIENT.

AVAILABLE SOIL WATER (sol)

That part of the water in the soil that can be absorbedby plant roots. The amount of water held between themoisture content prevailing at any point in time and themoisture content at which plant growth ceases.

Plants have difficulty extracting moisture when theavailable soil water approaches wilting point. Where soilmoisture can be controlled, the aim is to maintain it ata level where it can be readily extracted by plants, thatis to prevent moisture depletion below about 50 percent of the available range. See also FIELD CAPACITY.

AVAILABLE WATER-HOLDING CAPACITY(sol)

The amount of water in the soil, generally available to

15

plants, that can be held between field capacity and themoisture content at which plant growth ceases.Sometimes also known as the PLANT-AVAILABLEWATER CAPACITY.

AVALANCHE (gen)

A form of mass movement that results in acharacteristic long and narrow track down the steepslopes on which it typically occurs. Downhill motion isextremely rapid and it may occur under a variety ofmoisture conditions.

AVALANCHING (ram, cad)

The process of self-perpetuation that increases theintensityand severity of wind erosion down-wind. lt maybe initiated by sa/tation whence the particles, as theyhit the ground, dislodge more particles resulting in acumulative effect down-wind,

B, B1, B2,HORIZON (sol)

See SOIL PROFILE.

BACK-PUSH BANK (Str)

See BANK.

BACKPLAIN (11m)

A large flat area comprising the part of a tloodp fainaway from the watercourse beyond the /evee. It is oftencharacterised by a high water table, fine sediments, andthe presence of swamps or lakes.

BACKSIGHT (sur)

The first sight taken after setting up a level. A backsight is taken to a bench mark at the start of levellingand then to change points at each subsequentinstrument set up. See also FORESIGHT,INTERMEDIATE SIGHT.

BACKWATER (agi)

A strep cropping term for surface water backed up byvegetated strips, typically on country of less than oneper cent slope. Runoff is retarded as it moves throughthe vegetated strips with the result that velocity is alsoreduced on the cultivated strips above, provided thatthe strips are not too wide. See also STRIP WIDTH.

BAND SEEDING (agr)

Drilling seed and fertiliser in the one operation inseparate but adjacent bands,

BANK (tfm)

Syn. STREAMBANK.

BANK (Str)

A constructed earth embankment, incorporating achannel on the upslope side, typically traversing a slopeto control and/or prevent the erosion of that slope. Thisis achieved by intercepting, diverting or storing runoffinstead of permitting it to flow uninterrupted down thestope. The purpose of each bank is to increase the timeof concent ration of runoff and to control its volume andvelocity so that serious erosion will not occur.

Where a series of banks is constructed it is possible,particularly in an arable situation and depending on thebank design criteria used, that some interbank erosionwill occur. Complementary land management practicessuch as contour farming and conservation ti/fa gecarried out between the banks should then aim toprevent such erosion. Banks should be maintained toconform with their designed purpose.

Apart from banks built for the above purposes there arealso a number of banks designed for other morespecific purposes such as waterspreading.

Two basic construction methods are used. ACONVENTIONAL BANK is constructed by moving thesoil downslope so that the excavation or channel isimmediately above the bank. A BACK-PUSH BANK isconstructed by moving the soil upslope so that theexcavation is immediately below the bank. These areconstructed where it is necessary to retain undisturbedvegetation on the upslope side, such as in criticaldisposal situations on highly erodible soils.

General purpose soil conservation banks commonly inuse are:

Level banks on grazing land.

16

LEVEL BANK (CONTOUR BANK)

A bank that is constructed along the true contour,its channet being level, and which discharges ateither or both ends depending on designrequirements. Typically used on grazing land.

ABSORPTION BANK (PONDAGE BANK)

A level bank with a turn-up at each end designedto pond water to a pre-determined depth. Notnormally used on impermeable soils or on arableland because of the undesirable effects of pondedwater in the cropping situation. When designed tointercept inter/low the term INTERCEPTOR BANKmay be used.

GRADED BANK (GRADE BANK)

A bank buitt with a design fall along the channel,to allow water to flow in a specified direction.Primarily used on arable land, but atso on grazingland to some extent. Design grades normally rangefrom 0.1 to 0.5 per cent depending on soil typeand design requirements. Some very long bankswould be progressively increased in capacity, inorder to handle the large flows which developtowards the outlet end.

DIVERSION BANK

A bank specifically designed to divert water,normatly to protect a cultivated area, a gully,eroded area, work or facility below, or to carryrunoff to or from a dam or waterway away from thenatural drainage line. Such banks are typicallygraded.

Special-purpose soil conservation banks commonlyin use for waterspreading, and collectively called

GAP SPREADER BANK

A level bank constructed to allow waler to bespread by a series of gaps in the bank. Excavationfrom below creates a level channel into whichwater flows through the gaps, and from which it

Ir

'ir

DIVERSION SPREADER BANK

A bank that collects water from high runoff-producing areas and diverts and spreads out theflow to increase the production from a limited area

Source of runoff

Che1 bank

GAP ABSORPTION SPREADER BANK

A series of related absorption banks constructedon the same contour which allow water to bespread via the gaps between them. Excavation

t t

Channel

t

N.B. For further description of these three special-purpose banks refer Ouìlty JA. 1972. J. Soil Cons.N.S.W. 28

60320- 15204-2

17

Runoff-e,

WATERSPREADING BANKS, are:

spreads evenly over land downslope. Such banksare normally used in marginal arable areas, wherelarge amounts of runoff are to be controlled andsoils are relatively impermeable. Cf. GAPABSORPTION SPREADER BANK.

'I,BankGap Wo.wo./

I I i

from below creates level channels into which runoffwater flows through the gaps when the banks arefull, and from which it spreads evenly over landdownslope. Such banks are normally used inmarginat arable areas, Cf. GAP SPREADER BANK.

S'%in:a,.In in,,

t I - t t

downslope. Such banks normally consist of adiversion bank and a gap spreader bank joined bya continuous channel. They are particularly suitablefor use in marginal arable areas.

BANK (Continued)

Special purpose soil conservation banks commonlyin use for other purposes are:

CHECK BANK

A short level bank constructed lo stow and spreadflows from other structures.

TRAINER BANK

A hank constructed to prevent flows fromspreading or to direct runoff away Irom an -

undesirable location and/or towards a stable outlet.Such a bank is designed so that runoff flows onnatural vegetation and will only be guided orcontained by it. The grade may be relatively steepas the bank may have to run partty across ordirectly up and down the slope.

WATERWAY BANK

A bank constructed at the side(s) of a waterwayto retain runoff within the designed width. Suchbanks normally run directly up and down the slope.

PROTECTIVE BANK

A temporary bank constructed to prevent runoffflowing onto an unstable area. Once the area hasbeen stabilised, typically by the establishment ofan adequate vegetative cover, the bank may be

18

removed, Such a bank is particularly uselul at theinlet of a constructed earth channel or waterwayto prevent runoff entering until vegetation isestablished, In such cases the runoff must betemporarily diverted to a stable outlet at anotherlocation.

Banks can be further characterised by their cross-sectional shape which will depend upon land use,topography, soils and other design criteria:

BROAD-BASED BANK (ROLLOVER BANK)

A low profile bank with smoothed cross sectionand gentle batters which are weil compacted. Theshape enables travel across them and tillage alongtheir length with agricultural machinery. Suchbanks should be constructed so that the crosssections are not curved, to facilitate even sowingdepths along each face. They are particutarlysuited to arable lands of slope 2-6 per cent and tosituations where easy access is required. Slopesfrom 6 to 10 per cent may necessitate shorterbatter lengths which may not be suitable for thewider types of agricultural machinery.

Broad-based banks are also well suited tosituations where expansive soils occur,

A broad-based bank. Cultivation ot both bank andchannel is possible.

RIDGE TYPE BANK (PEAK TYPE BANK)

A narrowbaed bank having a more or lesstriangular cross section. Particularly suited to thehandling of large volumes of runoff and usedfrequently on slopes in excess of 10 per cent.

Ridge type banks.

In the design of banking systems there may beone or more KEY BANKS. A key bank is one whichhas a specific localion to achieve a special result.For example it may be a bank to collect discharge(rom a culvert at a property boundary and divert itto a waterway. To do this effectively it must collectthat discharge as close as possible to theboundary and hence variation in its location will belimited. This bank becomes a key bank in thesystem and other banks should be spaced up ordown slope from it. The location of such banksshould be established before planning others.

19

BANK CAPACITY (Str)

The calculated or actual volume or discharge rate of asoil conservation bank. For a graded bank the importantdesign requirement is for the bank to safety carry thedesign peak discharge! and this represents the bankcapacity. For an absorption bank the important designrequirement is for the bank lo hold a certain volume ofrunoff without overtopping, and this represents the bankcapacity. See also DESIGN CAPACITY.

BANK SPACING (sfr)

The actual distance along the ground between adjacentsoil conservation banks! used particularly when lalkingto landholders. See also HORIZONTAL INTERVAL.VERTICAL INTERVAL.

BANKING SYSTEM (str)

A scheme involving the construction of a series of soilconservation banks to control erosion over a large area.Such a system is frequently integrated with a numberof gully control structures and/or waterways. In somecircumstances a parallel banking system allows foreasier cultivation between the banks.

BAR (csd)

An offshore ridge of unconsolidated material submergedby high tide, lying al the mouth of a river or a shortdistance from and parallel to the beach. Bars tend toform in beach systems following periods of beacherosion and represent a temporary storage of beachsand which is returned during ensuing light weather,

A banking system incorporating graded banks,waterways and a gully control structure.

BAR (If m)

An elongated gently to moderatety inclined low ridgeof unconsolidated sediment built up by channeltedwater flow. Typicatty occurs as part of a streambed asa resutt of tocafised retardance to ftow, causingdeposition of sediment.

BARE FALLOWING (agr)

See FALLOWtNG.

BASAL COVER (ram, agr)

The proportion of the ground surface actually coveredor occupied by the stem or stems of a ptant at groundtevel, expressed as a percentage. Cf. COVER.

BASE FLOW (hyd)

See TRICKLE FLOW.

BASE PLATE (sur)

A metal plate with a central high point on which thestaff is placed at change points, where necessary,during levelling.

BASIN (hyd)

The area drained by a river. The term is also used todescribe an area which, when surrounded byembankments, may be flood irrigated.

BATTER (str)

The excavated or constructed face of a dam wail,embankment or cutting! produced as a result ofearthmoving operations involving cutting and filling.

In describing batter grade. 1:3 or lin 3 means a fall (orrise) of i vertical metre in a horizontal distance of 3metres.

Conventional bank and back-push bank batters.

NATURAL

A Y URA

N°2BAIT E R

(uphill batter)

N°3BATTER(downhill

batter)

20

CHANNEL FLOOR

Batters created in the construction of soil conservationbanks are identified by numbering them 1, 2 and 3 onthe basis that the No. 2 batter is always the water-bearing lace of the embankment and the No, i batteris the excavation batter. Thus, on a conventional bankthe No. 1 batter is upslope of the embankment the No.2 batter is the uphilt side of the embankment (uphitlbatter) and the No. 3 batter is the downhill side of theembankment (downhill batter). On a back-push bankthe No. i batter is downslope of the embankment butthe embankment batters are numbered similarly tothose of a conventional bank, i.e. the No. 2 and 3batters are the uphill and downhill batters respectively.

Batters created in the construction ol gully controlstructures and dams are also identified by numberingthem 1, 2 and 3 on the basis that the water-bearingface is the No. 2 batter, viz:

* No. 1 batter the excavation batter typically tormedon the upstream of the ftoor of the storage. In thiscase it is denoted the upstream excavation batter.

No. 2 batter the batter typically formed by thecombination of the exposed face on the downstreamside of the floor excavation (downstream excavationbatter) and the constructed face on the upstreamside of the embankment (upstream embankmentbatter). lt is always the batter which causes the waterto pond.

- No. 3 batter . the batter formed on the downstreamside, or outside, of the embankment and denoted thedownstream embankment batter.

The above descriptors tor GCS and dam batters areparticularly applicable to structures with straight orcurved embankments. For square or oblong structuresthe batters associated with the side embankmentsshould be identified as left or right looking downstream.in conjunction with the numbering system (e.g. left handNo. 2 batter).See also CUT BATTER, FILL BATTER, DAM.

N°] BATTER(excavation batter)

N°3BATTER

(downhill batter)

SURFACE

Conventional Bank

Eo UND BackPush Bank

SURFACE

M

'C'

-

Vt,

-V

,

-- o '4

A rocA-grouted battei drop-down.

BATTER DROP-DOWN (eng)

A constructed and stabitised drain to carry runoff downa batter, typicatty down the tine of greatest stope.

BATTER STABILISATION (gen)

The process of stabilising batters and their environs.This may invotve vegetative and/or structurat measures.

Revegetation ol exposed batters may be achieved byusing grasses and legumes sown by hand, seed drittsor hydroseeders, with or without special mulches suchas hay and bitumen emulsion, or various types ofnetting. n certain situations revegetation may invotvesodding or sprigging. Stabitisation of unstabtemateriats, particutarty batters subject to massmovement, may require the use of trees such as witlowsor poptars to provide more deep rooted stabitity.

Masonry measures may inctude revetments, gabionsand concrete waUs. Special attention is needed indesigning drainage systems, inctuding the use ofberms, to provide protection ot the batter surfaceagainst erosion by concentrated runoff. To assiststabilisation, batter slopes shoutd be constructed to anangte tess than the angle of repose.

J

21

naL

aa. ,q'3

4$ -"s

-,: b...

BEACH (Um, csd)

A gentle or moderatety stoping shore at the margin ofa sea or take, tormed by waves or tides. Generattycovered by loose granutar materials, but can becomposed of a wide range of materiats from boutdersto sitts. A beach is tateratty extensive retative to itswidth.

BEACH FACE (11m, cad)

The section of the beach normalty exposed to the actionof wave uprush.

BEACH RIDGE (FULL) (11m, cad)

A long tow, mear, even-crested rise built up by waveaction at a former shoreline, Such ridges are usuallymodilied by the wind and may occur singly or in aseries of parallel ridges,

BEACH SCARP (Um, cad)

A laterally extensive precipitous tace along a beach ordune formed by erosive wave action where sand fallsaway under the inlluence of wave-assisted massmovement,

I ,. ,-_

BED (tim)

A variously shaped channel floor which normally carrieslhe flowing water within the channel.

BEDLOAD (gen)

The sediment lhat moves by sliding, rolling or boundingon or very near the bed of a channel due to the actionof flowing water. lt is moved mainly by traclive and/orgravitalionat forces, but at velocities less than thesurrounding flow. Cf. SUSPENDED SEDIMENT.

BEDROCK (COUNTRY ROCK) (sol)

Solid rock underlying the soil profile or other surfacematerials. lt does not necessarily represent the parentmaterial of the overlying soil.

BELT TRANSECT (ram, agr)

A strip of vegetation along which and in which plantsare mapped and/or other quantitative measurementssuch as cover are recorded. See also LINE TRANSECT,POINT TRANSECT.

BENCH (eng)

Syn. BERM.

BENCH (mm)

A strip of relatively level earth or rock breaking thecontinuity of a slope.

BENCH (lfm)

A small flat area breaking the continuity of a hillslope.Benches are usually associated with flat-lying strata.

BENCHMARK (sur)

A fixed point of reference used in levelling.

BENCHMARK SITE (ram)

A fenced off area of land used as a reference in theassessment of range/and condition. Benchmark sitesare usually selected on the basis of having beenrelatively unaffected by grazing activities, as aconsequence of distance from drinking water orinaccessibility to stock.

BENTONITE (sol)

A clay usually formed by the weathering of volcanic ash,and which is largely composed of montmoriflonite typeclay minerals. t has great capacity to absorb water andswell accordingly. For this reason t is used to sealdams and/or earth embankments built of coarsematerials or which contain a coarse textured seamcausing them to leak.

BERM (csd)

A level area of loose sand between the upper limit ofthe swash zone and toe of the toredune, formed trommarine deposition.

22

BERM (BENCH) (eng)

A constructed ledge formed at one or more levelsbetween the top and bottom of a batter. Its purpose isto intercept runoff and reduce slope instability.

BERM (str)

A constructed ledge on the excavation batter of a damor tank which increases the storage capacity and/orenables the entrapment of debris before water entersthe storage. The latter is achieved by inclining the bermoutwards.

The term is also applied to a structure used in bordercheck irrigation to prevent sideways flow of water.

BERM DRAIN (eng)

See DRAIN.

BIENNIAL PLANT (agr)

A plant whose tile cycle extends for two years. The firstyear it produces roots, stems and leaves. In the secondyear it flowers, produces fruits and seeds for futureregeneration, then dies. The term is also used looselyto describe short-lived perennial plants which rarelypersist more than two years in sown pasture, such asred clover. Cf. ANNUAL PLANT, PERENNIAL PLANT.

BIFURCATION (gen)

Division into two branches. In a soil conservationcontext, it is used to describe the formation of twogullies from one, due to the inflow of runoff to a gullyhead from two separate sources.

BIOLOGICAL FERTILITY (soI)

See SOIL FERTILITY.

BIOMASS (agr)

The quantity of living material present at a given timewithin a given area, such as the weight of vegetativematter removed by clipping a quadrat. Total biomasswithin an area would include all living material, whetherof plant or animal origin.

BITUMEN (gen)

A viscous hydrocarbon mixture commercially obtainedfrom the destructive distillation of primary energysources such as coal and crude oil. It retains a 'solid'character under normal air temperatures and forapplication must be heated. For soil conservationpurposes bitumen emulsions are used in stabilisationprograms.

BITUMEN EMULSION (gen)

A mixture of bitumen, emulsifying agent, stabilisingagent and water which has low viscosity and may beapplied without heating. Its production does not createany chemical change in the bìturnen, but the physicalstate is altered so that it is no longer a homogeneousmass but a series of minute particles, each coated withthe emulsifying agent to keep them apart andsuspended in the water.

Bitumen emulsions are applied lo disturbed soilsurfaces to provide immediate stabilisation, Whenapplìed, typically by spraying, the emulsion breaks (Le.sets and turns from brown to black) and bitumenparticles merge together again as the water is absorbedor evaporates. The rate of break can be varied,depending on the emulsitying and stabilising agentsused, to suit climatic conditions and the purpose forwhich the emulsion is used. Where a rapid set isrequired as ¡n road sealing, FAST-BREAKING BITUMENEMULSIONS are used. Conversely SLOW-BREAKINGBITUMEN EMULSIONS are used where a longer timespan prior to complete set is required. Such emulsionsare typically used in conjunction with stabilisation whererevegetation is required.

Two types ot bitumen emulsion are recognised:

CATIONIC BITUMEN EMULSION

This emulsion is acid in nature and the bitumenparticles which are in suspension carry a positivecharge. The acidity is a function of the type ofemulsifiers used.

Emulsions of this type are favoured for road sealingdue to the attraction of the positive particles toroad base aggregates. They are rarely used inAustralia for soil conservation purposes althoughslow-breaking types can be useful on certain soilswhich carry negatìve charges.

ANIONIC BITUMEN EMULSION

This emulsìon is alkaline in nature and the bitumenparticles which are in suspension carry a negativecharge.

Emulsions of this type are favoured for soilconservation purposes and slow-breaking anionicbitumen emulsions are commonly used in soil andbatter stabilisation programs. Seed germination,especially in cold conditions, is promoted sinceground temperatures are increased due to theblack surface and added heat generated from thesoil below, Due to the heat, moisture rises underthe bitumen and assists germination. Frosts aretess likely to have an effect on the seed. Plantgrowth is enhanced and less seed lost by windand water erosion because of the protectivebitumen cover and therefore a much denser swardis obtained.

BLADE (eng)

A large wingshaped fi/lago tool fitted to blade ploughs.It is designed tor sub-surface titlage with minimumsurface disturbance and minimum residue incorporation.Sizes range from 1500 to 2100mm with a 75° includedangle being usual. Cf. SWEEP,

BLADE PLOUGH (erg)

A heavy duty tillage implement fitted with b/ades forboth primary and secondary ti//age. Blade sizes rangefrom 1500 fo 2100 mm and the blade angle is normally75° (blade angle is the included angle between the twowings of the blade). Usually shear-pin protection onlyis provided. The complete implement may have aconventional frame or comprise several modules eachwith a single tine and blade, Modular units are mostsuitable where ground obstructions are expected.

23

Owing fo the arge effective c/earance and fine /atera/spacing the residue handling capacity of this type ofimplement is greater than that of most other titlageimplements. Blade ploughs cause little disturbance ofthe surface soil and incnrporate a minimum of residue,and are therefore widely used in conservation tillageprograms.

A blade plough.

BLADING OFF (for)

The removal of surface soil from a snig track or road inorder to expose a drier andjor firmer surface to allowits use by machinery.

In a broader context the term "btading" describes asimilar function whereby surface soil is removed, roughsurfaces made trafficable, or earth windrows removedto facilitate cross fa/I drainage, during frail constructionand maintenance.

BLEACHING (sol)

The near-white colouration of an A2 horizon which hasbeen subject to chemical depletion as a result of soit-forming processes including eluviaf ion. The colour isdefined for all hues as having a value of 7 or greaterwith a chroma of 4 or less, on dry soils. CONSPICUOUSBLEACHING means that 80 per cent or more of thehorizon is bleached, whereas SPORADIC BLEACHINGmeans that less than 80 per cent of the horizon isbleached, with affected portions appearing irregularlythrough the horizon, See also SOIL COLOUR.

BLOCK GLIDE (gen)

See LANDSLIDE.

BLOWOUT (If rn csd, alp)

A closed depression formed in the land surface as aresult of wind erosion removing material and depositingit in an accumulation adjacent fo the resulting trough.

In a beach situation such blowouts develop where thevegetative cover of a dune is removed and exposedsand is transported tandward by prevailing on-shorewinds. As a blowout proceeds through the dunes itdevelops an advancing front of loose sand and trailingarms which are hetd back by boundary vegetation.Blowouts which remain unchecked thus ultimately formparabolic or 'U' dunes which are found disrupting thecoastal dune ridge system.

BLOWOUT (Continued)

In an alpine situation, such blowouts may develop inalpine humus soils,

BOLUS (sol)

A small handful of soit which has been moistened andkneaded into a soil ball which just fails to stick to thefingers. The behaviour of the bolus and of the ribbonproduced by pressing it between thumb and forefingercharacterises soi/ texture.

BOOT (eng)

A hollow component attached to a soil opener andthrough which seed and/or fertiliser are conveyed fromthe sowing tube to the soil. lt comprises part of the soilopener at its lower end.

BORD AND PILLAR (mm)

A system of underground coal mining consisting of anetwork ot parallel and intersecting drives orpassageways (bords) separated by solid blocks of coalor pillars.

BORROW AREA (BORROW PIT) (gen)

An area or excavation from which soil, clay, sand, rockor gravel has been extracted tor a specific purpose. Thematerial extracted is typically employed for damconstruction, road construction, filling or topsoiling.

BORROW PIT (gen)

Syn. BORROW AREA.

BOX CULVERT (eng)

See CULVERT.

BOX INLET DROP SPILLWAY (eng)

See SPILLWAY.

BOX-CUT (PORTAL CUT) (eng, mm)

A relatively narrow but deep excavation, with steeplaces on three sides, sunk to allow access tounderground workings. Also refers lo the initialexcavation for an open-cut mine.

BREAKOUT FORCE (eng)

The horizontal force applied at the tip of a tine whichwill just cause rotation of the tine mechanism about itspivot point. The magnitude of the breakout force givesari indication of the severity of duty for which the tineassembly is suitable.

BROAD-BASED BANK (str)See BANK.

BROADCAST SEEDING (agr)

Scattering seed on the soil surtace as contrasted tosowing into the soil in rows by drilling. See alsoSEEDING.

24

BROWSE (TOPFEED) (ram)

Twigs or shoots, with or without attached leaves, ofshrubs, trees or woody vines available for grazing bylivestock.

BROWSE LINE (ram)

A line marking the height to which browse from shrubs,trees or vines has been removed by animals.

BRUSH (gen, cad)

Vegetative matter in the form of small branches witheaves and seeds intact, which is laid on top ofdisturbed ground to provide a mulch, to act as a trapfor soil and seed. and/or to provide a seed source. ltis especially used as a means of introducing nativeseed to disturbed areas and as a trap for wind-blownsand in coastal sand drift control. Where brush is usedas a surface cover it is often referred to as brushmatting, as opposed to brush fencing where thebranches are closely packed to form a vertical barrier,

BUFFER CAPACITY (soi)

The ability of a soil to resist changes in pH. Thebuffering action is due mainly to the properties of clayand fine organic matter. Thus, with the same pH level,more lime is required to neutralise a clayey soil than asandy soil, or a soil rich in organic matter than one lowin organic matter,

BUFFER STRIP (for)

Syn, FILTER STRIP.

BUFFER STRIP CROPPING (agr)

See STRIP CROPPING.

BUFFER ZONE (csd)

A strip of coastal land of nominal width, maintained inan undeveloped state, adjacent to the coastline, as aprotection against irreparable damage during periods ofcoastline recession. See also SETBACK.

BUFFER ZONE (gen)

Any area ot land used or designed to isolate one areaof land from another so that adverse effects arising fromone area do not affect the other. For example:

- A buffer zone around a mine site intended toreduce the effects ot noise, dust etc. on adjacentlandholders.

A buffer zone at the outflow of a creek orwaterway designed to spread the water beforeit enters a strip cropping system.

BULK DENSITY (sol)

The mass of dry soil per unit bulk volume. The bulkvolume is determined before drying to constant weightat 105 degrees celsius. The unit of measurement isusually grams per cubic centimetre.

Bulk density is a measure of soi/ porosity, with lowvalues meaning a highly porous soil and vice-versa, It

does not, however, give any indication of the number,sizes, shapes, distribution or continuity of soil pores.

This parameter is also used as an indicator of thestructural condition of a soit, with low values indicatinga better state of aggregation than high values. Therange for soils in natural condition would typically befrom t to 2 9/cm3.

BULKING FACTOR (mm)

The degree to which spoil swells in volume as it isexcavaled. lt may involve an increase of up to 35 percent in a typical dragline operation. The increase involume is due lo a loosening of the material and aconsequent increase in pote space.

The bulking factor needs to be taken into account whenplanning rehabililalion programs, to allow forconsolidation and/or compaction.

BURIED SOIL (PALEOSOL) (sol)

One or more layers of soil which were formerly at thesurface but which have been covered by a more recentdeposition, usually to a depth greater than thethickness of the so/urn,

BYWASH (Str)

See SPILLWAY.

C HORIZON (Sol)

See SOIL PROFILE.

CADASTRAL MAP (lev)

A map showing legal survey boundaries, portion andplan numbers, parish and county names andboundaries. The cadastral patlern is that arrangementof survey boundaries that defines ali separate parcelsof land, usually for the purpose of describing andrecording ownership and tenure.

CALCAREOUS (sol)

Refers to materials, particularly soils, containingsignificant amounts of calcium carbonate. Describesrocks composed largely of, or cemented by, calciumcarbonate. A calcareous soil is one containingcarbonate in sufficient quantity to effervesce visiblywhen Ireated with cold dilute (N) hydrochloric acid,

CANOPY (lam, for, alp)

The uppermost vegetation layer consisting of crowns oftrees or shrubs in a forest or woodland.

CANOPY COVER (ram, for)

The proportion of the ground surface covered bycanopy.

25

CAPILLARY FRINGE (sot)

The zone above the waler table in an unconfinedaquifer where Ihe formation is saturated but the waterin the zone is al less than atmospheric pressure.

CAPILLARY POROSITY (sol)

See SOIL POROSITY.

CARRYING CAPACITY (ram, agr)

The maximum stocking rate possible which grazing landcan support throughout the greatest period of stresseach year. Cf. GRAZING CAPACITY.

CATCH DRAIN (str)

See DRAIN.

CATCHMENT (gen)

The source area for runoff flowing to a particular point.Cf. WATERSHED.

CATCHMENT (Ifni)

That area determined by topographic features withinwhich rainfall will contribute to runoff at a particularpoint under consideration.

CATCHMENT DRAIN (Str)

See DRAIN,

CATENA (sol)

A repetitive sequence of soils generally of similar ageand parent material, encountered between hillcrestsand the valley floor,

The soils in the sequence occur under similar climaticconditions, but have different characteristics due tovariation in relief, drainage and the past history of theland surface. Such variations are normally manifest indifferential transport of eroded material and theleaching, translocation and re-deposition of mobilechemical constituents,

In soil mapping, the use of this term has been largelyreplaced by the more general term toposequence.

CATION EXCHANGE CAPACITY (sol)The total amount of exchangeable cations that a soilcan adsorb, expressed in centimoles of positive chargeper kilogram of soil, Cations are positive ions such ascalcium, magnesium, potassium, sodium, hydrogen,aluminium and manganese, these being the mostimporlanl ones found in soils, Cation exchange is theprocess whereby these ions interchange between thesoil solution and the clay or organic matter complexesin the soil. The process is very important as it has amajor controlling effect on soil properties and behaviour,stability of soil structure, the nutrients available for plantgrowth, soil pH, and the soil's reaction to ferlilisers andolher ameliorants added lo the soil.

CATIONIC BITUMEN EMULSION (gen)See BITUMEN EMULSION.

CAUSEWAY (eng)

A roadway across a watercourse or tidal water, speciallyconstructed to resist the effects of submergence.

CEMENTED (sol)

Describes soil materials having a hard, brittleconsistency because the particles are held together bycementing substances such as humus, calciumcarbonate! or the oxides of silicon, iron and aluminium.The hardness and brittleness persist even when the soilis wet. CI. INDURATED.

CENTRAL PERSPECTIVE (rms)

See ORTHOPHOTO.

CHANGE POINT (TURNING POINT) (sur)

A point on which the staff has been observed and onwhich il is then held whilst the level is being movedduring levelling. II can be a peg, base plate, rock orany readily identified and firm point. See alsoBACKSIGHT, FORESIGHT, INTERMEDIATE SIGHT.

CHANNEL (gen)

A passage in which water is confined sufficiently totemporarily hold it or allow it to flow from one place toanother! given sufficient head between them. Typicallyit comprises a floor (or bed), which carries the flowingwater and sides (or banks) which confine it.

A channel may be constructed (e.g. conduit, drain),natural (e.g. stream, river), or occur as an indirect

26

consequence of human land use activities (e.g. nil,gully).

CHANNEL BENCH (11m)

A level area within the defined banks of a watercourse,Under natural conditions it may be an incipientfloodplain.

CHANNEL IMPROVEMENT (gen)

The upgrading of the flow characteristics of a channelby clearing, excavation, realignment, shaping, lining, orother means, in order to improve its water-carryingcapacity and stability.

CHANNEL STABILISATION (gen)

The implementation of appropriate vegetative and/orstruclural measures Io prevent or mitigate erosion in achannel. See also CHANNEL IMPROVEMENT,STABILISATION.

CHANNEL STOP (sir)

A vertical spacer in a large storage bank to limit waterloss should the bank fail at any point.

Extensive channel stabilisation works.

The fencing pattern entraps sediment, and encouragesgrowth of vegetation to improve channel stability.

CHECK BANK (str)

See BANK.

CHECKERBOARD FURROWING(CHECKERBOARD PLOUGHING) (ram)

A squared pattern of furrows created on generally flatland to reslricl the effects of wind and water erosionand to allow revegetation to occur. Such a treatment isused in semi-arid and arid rangeland areas wherescalds are a problem. The squared areas represent ameans of waterponding whereby water, soil and seedcan be held within both the furrows and the squaresenclosed by the furrows. The whole area then has agreatly improved chance. of becoming revegetated,stable and productive.

CHECKERBOARD PLOUGHING (ram)

Syn. CHECKERBOARD FURROWING.

CHEMICAL FALLOWING (agr)

See FALLOWING.

CHEMICAL FERTILITY (sol)

See SOIL FERTILITY.

CHISEL PLOUGH (eng)

A tillage implement used mainly for primary ti//age atdepths up to 200 mm. Heavy duty tines are arrangedat an overall tine spacing of 300 to 350 mm, andattached to a heavy frame, The usual tine cross-sectionis such that the lateral dimension is greater than the

27

Checkerboard turro wing. Note the growth of vegetation inthe furrows.

longitudinal dimension, The implement can be used witha range of tillage tools from narrow points to sweeps,making it also adaptable to secondary tilla ge needs.Breakout force is usually in the range 1.3 to 5 kN.

CHISEL PLOUGHING (agr)

A primary tilla ge operation involving breaking orloosening the soil, without inversion, using heavy dutyfined machinery with chisel shaped points. The practicereduces compaction, breaks up shallow pans andpromotes infiltration of water into the soil, particularlywhen carried out on the contour, Operating depthwould not typically exceed 200 mm. See also RIPPING.

-A chisel plough, litted with sweeps.

CHuTER (mm)

Coarse-grained rock fragments and carbonaceousmaterial discarded alter the first washing and screeningof coal. It is separated from the coal by means ofdifferences in specific gravity and commonly disposedof in a dry state into dumps or abandoned open-cutmines.

CHROMA (sol)

See SOIL COLOUR.

CHROMATIC ABERRATION (rms)

A tactor which nay affect tone and texture of aerialphotographs. It is caused by the different refractivequalities of the various colours that make up white tight.As tight rays pass through the tens of the camera, bluelight is refracted more than red tight and this results inthe two colours faiting to come into focus at a commonpoint.

Theoretically, this means that detail cannot be imagedperfectly sharply on the negative and this could affectthe tonal and textural qualities. In modern surveycameras, the effects of chromatic aberration arecompensated by using multiple converging anddiverging tens assemblies.

CHUTE (str, eng)

The steeply inclined section ot a flume or other similarhydraulic structure, between the inlet and outlet, thatconveys the flows directly from one level to another.See also DROP STRUCTURE.

CHUTE SPILLWAY (eng)

See SPILLWAY.

CIRQUE (Ifni)

A gently inclined to precipitous closed depression ofconcave cross-section excavated by ice,

CLAY (sot)

Soil material consisting of mineral particles less than0.002 mm n equivalent diameter. This generattyincludes the chemically active mineral part of the soil.Many of the important physical and chemical propertiesof a soit depend on the type and quantity of clay itcontains. Three broad classes of clay type arerecognised, namely montmorülonite, kaolinif e and i/lite.

When used as a soif texture group such soil containsat least 35 per cent clay and no more than 40 per centsilt. See also SOIL TEXTURE.

CLAY LOAM (sol)

A soil texture group representing a welt-graded soitcomposed of approximately equal parts by weight ofctay. silt and sand. See also SOIL TEXTURE.

28

CLAYPAN (sol)

A pan made up of a concentration of dense clays inthe subsoil, The term is also used for the impermeableclay surface produced as a result of scalding, althoughthis usage is colloquial.

CLEAR FELLING (for)

The cutting down of an entire forest stand in onecutting operation.

CLEARING (for)

The removal of trees and shrubs from land to enablefurther land development. Such development mayinclude agricultural or urban land uses or the plantingof other tree crops. Cf, FELLING. See also PERMANENTCLEARING, TEMPORARY CLEARING.

CLIFF (lfm)

A high, precipitous face, typically of exposed bedrock,resulting trom the undercutting and collapse ofpreviously exposed surfaces.

CLINOMETER (sur)

See LEVEL.

CLOD (sol)

A large compact and coherent soll aggregate producedartificially, usually by ploughing or digging soils that areeither too wet or too dry for normal tillage operations.Cf, PED.

CLOSED MINE (DISUSED MINE) (mm)

A mine which, although currently inactive, is still ownedor leased by a mining company and could be re-openedfor mining.

COAST (If m)

The strip of land, of indefinite width, that extends fromthe seashore inland to the first major change in terrainand/or geology.

COASTAL EROSION (csd)

Loss of sand, soil and rock material to the sea inresponse to wave action,

COASTAL RECESSION (csd)

Net loss of sand from the beach in response to off-shoresand movements.

COASTAL SAND DRIFT (csd)

A broad term used to refer to the erosive processesaffecting beach areas and related to the excessivemovement of sand due to the instability of dunesystems. The main cause of the drift is tack otstabilising vegetation on the dunes which makes themhighly susceptible to wind erosion,

Severe coastal erosion.

C000MINANT (gen)A term used to indicate the joint dominance of two ormore members of a grouping, over the other members.Typically used when mapping soils, vegetation, andother land resources,

COFFEE ROCK (sol)

A type of brownish sand-rock formed where iron oxidesand organic matter which have leached through the soilprofile, are precipitated at, or above, a fluctuating watertable, A typical leature ol some older coastal sands inwhich podzols have formed.

COHERENCE (sol)

Syn. SOIL COHERENCE.

COKE BREEZE (mm)

Waste product from coke production.

COLLAR (ANTI-SEEP COLLAR) (eng)

A flange fitted round a pipe to prevent seepage ofwater along the outside of the pipe. Typically used indams to prevent seepage along the outside of pipespassing through the wall,

COLLIERY (mm)

A large coal mine including associated surface works,

COLLIMATION TEST (TWO PEG TEST) (sur)

A test to check whether the line ot sight - line ofcollimation - through the telescope of a /evel ishorizontal when the vertical axis is truly vertical. The

29

level is centrally located between two points,approximately 100 metres apart, and staff readings aretaken to determine the true height difference. lt is thenset up about 3 metres from one of the points. Staffreadings are again taken and a new height differencecalcurated, Any variation between this difference andthe true difference is the collimation error. A collimationerror of less than 0.02 metres in 100 metres isacceptable for general soil conservation purposes.

COLLOIDAL MATERIAL (sol)

The finest clay and organic material with a particle sizegenerally tess than 1& mm in diameter. Such materialrepresents the finest particles removed in an erosionevent,

and as such remains permanently in suspension, unlesssubject to flocculation.

COLLUVIAL (11m, sol)

Describes material transported largely by gravity. Seealso COLLUVIUM, MASS MOVEMENT, CREEP.

COLLUVIUM (If m, sol)

Unconsolidated soil and rock material, moved largely bygravity, deposited on lower slopes and/or at the baseof a slope. Cf. ALLUVIUM. See also COLLUVIAL, MASSMOVEMENT, CREEP. TALUS and SCREE.

COMBINE DRILL (eng)

See DRILL.

COMMUNITY (alp, ram)

A naturally occurring group ot plants occupying acommon location. The term s employed when it is notnecessary or desirable to use a more specificdesignation.

COMPACTION (eng, Str)

The process of increasing the density of a material byremoving air and inducing the closer packing of itsparticles. This may be achieved by rolling, tamping orother mechanical means, and leads to a reduction inthe porosity of the material.

Optimum compaction of earthworks is dependent onthe moisture content of the material and is particularlyimportant in the control of seepage and earthworktunnel/ing. Cf. CONSOLIDATION.

COMPACTION (sol, agr)

The process whereby the density of soils is increasedby tillage, stock trampling and/or vehicutar traffic, oftenresulting in the formation of plough-pans. Suchcompaction gives rise to Lower soil permeability andpoorer soit aeration with resultant increases in erosionhazard and lowered plant productivity. Deep tippingand conservation ti//age are used to alleviate thecondition.

COMPARTMENT (for)

A management area within a commercial forest whoseboundaries are generally defined by forest roads, tracksor firebreaks.

COMPASS (sur)

An optical or prismatic hand-held instrument used todetermine the magnetic meridian through a point. Acompass with a graduated circle is used to readmagnetic bearings.

CONCRETION (sol)

Syn. NODULE,

CONDUIT (eng)

A constructed closed channel or pipe, lined withconcrete or similar material, for the conveyance ofwater.

CONE (If m)

A hi/lock with a circular symmetry, commonly built up'by volcanism.

CONSERVATION (gen)

The management of human use of the biosphere sothat it may yield the greatest sustainable benefit topresent generations white maintaining its potential tomeet the needs and aspirations of future generations.Thus conservation is positive, embracing preservation,maintenance! sustainable utilisation, restoration, andenhancement of the natural environment. Livingresource conservation is specifically concerned withplants, animals and micro-organisms, and with thosenon-living elements of the environment on which theydepend. Living resources have two important propertiesthe combination of which distinguishes them from non-living resources: they are renewable if conserved; andthey are destructible if not.

This definition is taken from the National ConservationStrategy tor Australia (1983) and is consistent with thatof the World Conservation Strategy (1980).

30

CONSERVATION FARMING (gen)

A system of farming which involves using the land inaccordance with its capability and suitability andmanaging the tand in accordance with the principles ofconservation, Such a system would include contourtarming, conservafion ti//age, crop and pasture rotation,judicious stocking management, pasture improvement,strip cropping, and soil/water conservation works andpractices where appropriate. The aim of the system isto farm in such a way as to conserve soil, water andenergy resources, whilst ensuring continued farmproductivity and economic viability.

CONSERVATION TILLAGE (agr)

A tillage system that creates a suitable soil environmentfor growing a crop and that conserves soil, water andenergy resources. The essential elements of such asystem are reduction in the intensity of tillage, andretention of plant residues.

CONSISTENCE (sol)

Syn. SOIL CONSISTENCE.

CONSOLIDATION (mm)

The process of reducing the volume of wet material.such as slurry by gradual drainage.

CONSOLIDATION (str)

The process whereby a newly formed earthen structure-reduces its volume by natural settling. Cf.COMPACTION.

CONSPICUOUS BLEACHING (sol)

See BLEACHING.

CONSTRUCTED WATERWAY (str)

See WATERWAY.

CONTACT HERBICIDE (agr)

See HERBICIDE.

CONTINUOUS CULTIVATION (SUCCESSIVECROPPING) (agr)

The repeated growing of crops requiring tillage, on thesame parcel of land without an intervening pasturephase. Crops are usually grown annually, but may begrown more often in favourable seasons, Cf. REGULARCULTIVATION, OCCASIONAL CULTIVATION.

CONTOUR (gen)

An imaginary line on the surface of the earth connectingpoints of the same elevation. Such lines drawn on mapsare used to portray' the shape of the land surtace.

CONTOUR BANK (sIr)

See BANK.

CONTOUR DITCH (str)

A level excavated channel designed to hold and spreadwater on low slope country. The waler accumulates andspreads along the length of the ditch, before spilling ona broad, even front. Typically used on marginal arableland of slope less than 3 per cent, and constructedusing a disc plough or grader blade. Also serves as aguide for contour farming. Normally dish-shaped incross-section and ol approximate dimensions 15-30cmdeep and 2-2.5 m wide. Cf. CONTOUR FURROW,

CONTOUR DRAIN (str, eng)

See DRAIN,

CONTOUR FARMING (gen)

The performance of farming operations such as tillage,sowing and harvesting on the contour, largely for thepurpose of reducing erosion hazard.

CONTOUR FURROW (PASTURE FURROW)(str)

A small level channel designed to hold water onmoderately steep grazing land, Such furrows aim toincrease the retention of rainfall on the land, therebyreducing runoff and erosion hazard and increasingpasture productivity, Constructed using single furrowmouldboard or disc ploughs, graders, modified rippersor specially designed implements. A treated area wouldhave a series of such furrows down the slope atintervals which are calculated according to slope andrainfall data. Cf. CONTOUR DITCH,

.-.

31

CONTOUR GRASS STRIPS (agr)

See STRIP CROPPING.

CONTOUR INTERVAL (gen)

The vertical distance between two contours,

CONTOUR PLOUGHING (gen)

The performance of ploughing on the contour, largelyfor the purpose of reducing erosion hazard.

CONTOUR RIPPING (sir)

Ripping that is carried out on the contour to promoteinfiltration of water into the soil thereby reducing runoftand consequent erosion hazard.

CONTOUR SILL (str)

See SILL.

CONTOUR STRIP CROPPING (agr)

See STRIP CROPPING.

CONVENTIONAL BANK (sir)

See BANK.

Contour ploughing.

The photo shows the pattern typically produced bycontour farming practice.

CONVENTIONAL CULTIVATION (agr)

Syn. CONVENTIONAL TILLAGE.

CONVENTIONAL SPILLWAY (Str)

See SPILLWAY.

CONVENTIONAL TILLAGE(CONVENTIONAL CULTIVATION) (agi)

A lillage system using cultivation as the major meansof seedbed preparation and weed control, andtraditionally used for a given crop in a givengeographical area, Typically includes a sequence of soilworkings, such as ploughing, discing and harrowing, toproduce a fine seedbed, and also the removal of mostof the plant residue from the previous crop. In thiscontext the terms cultivation and tillage aresynonymous, with emphasis on soil preparation.

CORE (Str)

The central compacted mass of impervious soil materialincorporaled in an earth embankment to preventseepage through it.

CORE TRENCH (str)

The excavation which is filled with impervious corematerial in the construction of an earth embankment,

32

CORRASION (sol)

That part of natural erosion processes in which earthand rock materials are worn away due to their abrasionwhen carried n flows of water, air or ice.

CORRECTION AREA (agi)

A triangular area which may have to be incorporatedinto a strip cropping plan to allow for variation incontours. Where contours are markedly uneven,successive sets of strips down the slope cannot be putin parallel and a triangular correchon area betweenthem is unavoidable.

COSTEAN (mm)

A shallow, steep-sided trench cut across the line of anorebody or deposit to expose it during prospectingoperations.

COULTER (eng)

A ti//age tool which cuts plant material and soil aheadof another tool. The most common kind of coulter is thedisc coulter of which there are four main types:

Plain - a simple flat disc.

* Scafloped - a simple flat disc with notches cutaround the rim.

Rippled cou tier. Fluted coutter.

Plain coy/ter. Scalloped cou/ler.

Rippled - a disc where the rim is displaced axiatyin a wavy form with a maximum displacement ofabout 10 mm.

* Fluted as above, but with a maximumdisplacement greater than 20 mm,

Knife coulters are vertically mounted fixed blades whichperform a similar function in special circumstances.

COUNTRY ROCK (mm)

Rock of no commercial value surrounding andpenetrated by an orebody or mineral veins.

COUNTRY ROCK (sol)

Syn. BEDROCK.

COVER (ram, agr)

The proportion of the ground surface covered, over agiven area, by the combined aerial and basal parts ofplants, litter and mulch, expressed as a percentage ofthe given area. Cf. BASAL COVER. See also FOLIARCOVER.

COVER (gen)

Vegetation or other materiál providing protection to theground surface against erosive agents. See atsoGROUND COVER.

COVER CROP (agr)

A temporary vegetative cover which is grown to provideprotection for the soil and the establishment of plants,particularly those which are stow to establish. The latterare introduced by undersowing and in due courseprovide permanent vegetative cover to stabilise the areaconcerned. The term can include an INTERMEDIATECROP which can be removed by the use of selectiveherbicides.

CRABHOLE GILGAI (If m, sol)

See GILGAI.

CRATER (11m)

A steep to precipitous closed depression excavated byexplosions due to volcanism, human action, or impactot an extraterrestrial object.

CREEK (gen)

See WATERCOURSE.

CREEP (gen)

A general term used to describe more or lessimperceptible transportation of soil particles under theinfluence of various erosive agents. Three types ofcreep are commonly recognised:

GRAVITATIONAL CREEP

Creep associated with mass movement. It rangesfrom surficial SOIL CREEP to deep seatedmovements related to deformation that continuesunder constant stress. (Refer: Varnes, D.J, Slope

60320-15204-3

33

Movement Types and Processes. In LandslidesAnalysis and Control, Transportation ResearchBoard, National Academy of Sciences, WashingtonD.C., U.S.A. Special Report 176, Chapter 2, 1978.)

SURFACE CREEP

The rolling or sliding of larger particles along theground under the influence of wind. These particlesare too heavy to be tif ted, but are moved by theimpact ot saltating particles. Clay aggregates andcoarse sand moved in this way are usuallybetween 0.5 and 2.0 mm in diameter. See alsoWIND EROSION, SALTATION.

SOLIFLUCT ION

Creep associated with frequent freeze and thawactivity. In areas of perennially frozen ground it isknown as GELIFLUCTION.

CREST (csd)

The top section of a dune.

CREST (eng)

The overflow section of a weil or similar structure.

CREST (Ifm)

A landform that stands above all, or almost all, pointsin the adjacent terrain. It is characteristically smoothlyconvex upward.

CREST (str)

The top section of an earth embankment, bank or dam.

CRIB BLOCK (sir, eng)

A form of prefabricated wall construction, usually ofconcrete or timber, used to shore up unstable batters.

CRITICAL AREA (gen)

A site affected by serious erosion whose treatment isessential to the successful control of erosion in thesurrounding area,

CRITICAL DEPTH (hyd)

The depth of critical flow, Symbol: d, Unit: metres,

CRITICAL FLOW (hyd)

See FLOW.

CRITICAL SURFACE BARRIER RATIO(gen)

See SURFACE BARRIER RATIO.

CRITICAL VELOCITY (hyd)

The velocity of critica/ flow, Symbol: V, Unit: metres/second,

CROP RESIDUE (agr)

The portion of a plant or crop left in the field afterharvest, Cf. STUBBLE.

CROP ROTATION (agr)

The growing of different crops and pasture in recurringsuccession on the same parcel of land with a view toincreasing soil fertility and structural stability, andreducing plant disease and soil erosion hazard. Thelatter can be achieved particularty when crop rotationis integrated into a system of strip cropping on suitableslopes.

CROP-LINE (miii)

Tne surface trace or line marking the position at whicha coal seam or stratified orebody is exposed at theearths surface.

CROSS BANK (for)

A hump of earth constructed across a snig track,outrow, tog dump or road so that runoff is baulked andeffectively diverted from it. Waste material such as barkshould not be used. Such a bank s designed to handlelarger anticipated flows than a cross drain. Sometimesknown colloquially as a "whoa boy".

CROSS DRAIN (sfr, eng)

See DRAIN.

A frat/icable cross bank which provides effect ivedrainage.

34

CROSS SLOPE (gen)

The slope of the land's surface at rightangtes to thegenerat direction of the main slope.

CROSSFALL DRAINAGE (for, gen)

Drainage which occurs when the surface of a road, trailor other access-way has sufficient cross slope to causewater to flow' across and off the surface, rather thanalong it. Where the water flows into the hillside it istermed INFALL, and where ftow is away from the hillsideit is termed OUTFALL.

The minimum cross slope required to achieve suchcrossfall drainage is 1:25, For safety reasons themaximum crossfall used should generally not exceed1:tO.

CROWN COVER (ram, alp)

The percentage of a given area of land occupied byforest or woodtand that has cover provided by treecrowns. Cf. CROWN DENSITY. See also CANOPY.

CROWN DENSITY (ram, alp)

The percentage ol a given area of land occupied byforest or woodland that has a complete crown cover,See also CANOPY.

CRUMB (sol)

A soft, porous, more or less rounded soi! aggregatefrom 1 to 5 mm in diameter. See also CRUMBSTRUCTURE, SOIL STRUCTURE.

CRUMB STRUCTURE (sol)

A soil structural condition in which most of the soi/aggregates are soft, porous and more or less roundedunits from i to 5 mm in diameter. The typical surfacecondition of medium-textured soils recently cultivatedafter a period of well-managed pasture.

CRUSTING (sol)

See SURFACE SEALING.

CULTIVATION (agi')

The growing c' crops requiring the mechanicalpreparation of the soil. lt typically involves a series ofsoil workings for seedbed preparation.

While the term is often used synonymously with tilla ge.it also embraces the broader concept of cropproduction as distinct from just soil preparation. Pastureproduction is not regarded as part of this broaderconcept.

CULVERT (eng)

One or more adjacent enclosed conduits for coveyingrunoff under a roadway or other structure. When theconduits are of rectangular cross-section the culvert isknown as a BOX CULVERT.

CUMEC (hyd)

A term used for rates of flow, representing the unit ofcubic metres per second. In written communications itshould be set out in full or abbreviated to m3/s.

CUT (sir)

Portion of land surface from which material has beenremoved by excavation during earthmoving operations.

CUT AND FILL (sir)

A process of slope modification in which soil isexcavated from along one section of a slope and usedto construct an embankment below, See also BAUER,CUT BATTER, FILL BAUER,

CUT BAiTER (str)An exposed surface left by excavation duringearthmoving operations. See also BATTER, CUT ANDFILL.

CUT FACE (Ifm, sir)

A slope excavated during earthmoving operations. Seealso DISTURBED TERRAIN.

CUT-OFF TRENCH (eng)

The excavation for a cut-off wail.

CUT-OFF WALL (eng)A watertight barrier for preventing seepage ormovement of water under or past a structure,

Usually a masonry wall, co/lar or core of imperviousmatenal, intended to reduce percolation of water along

35

otherwise smooth surfaces or through porous strata,

Other functions may include providing anchorage of ahydraulic structure against downhill sliding, andproviding protection against structural damage due toscouring at the inlet or outlet.

CUT-OVER SURFACE (Ifm, Str)

A level area excavated during earthmoving operations,See also DISTURBED TERRAIN.

CYCLIC SALT (sol)

Salt deposited on soils from wind or rainfall, Near thesea or inland salt lakes, where the amounts depositedare likely to be significant, such salt may subsequentlybe leached into the soU and take pari in variouschemical processes there.

D HORIZON (sol)

See SOIL PROFILE.

DAM (gen)

A barrier, embankment or excavated earth structure,generally built in or near a tlowline, which has theprimary function of impounding water for storage. Thestored water is used for such purposes as stockwatering, domestic supply, irrigation and firefighting.

Dams used for water conservation on the farm arenormally built of compacted soit and are called earthdams,

Dams may also be used in conjunction with thediversion of water, creation of a hydraulic head,sediment retention or for soil erosion control, When theirprimary function is for gully erosion control the termgully control structure is used. When their primaryfunction is for sediment retention the term sedimentbasin is used.

The siting of a dam may depend on; the availability ofwater-holding materials which are also suitable forconstruction purposes; the achievement of a highstorage/excavation ratio; the need to locate it near awater source; the location of fencing and the possiblerole of the structure as a watering point for stock; and/or the need to locate it in relation to buildings to besupplied with water, areas to be irrigated, or areas tobe protected in fire situations,

The design of such a structure is dependent on; itslocation; the size of the catchment above it and theassociated land use; availability of a suitable site for thespillway and disposal of overflow; the nature of the siteselected and the construction materials available there:and/or its relationship to soil conservation structures.

DAM (Continued)

The construction of a dam involves on-site considerationof: the nature of the site chosen: the nature andmoisture content of soit materials avaitabte if used inconstruction: the conditions occurnng at the time ofconstruction: and the equipment avaitable in relation tothe size of structure required. Important factors in theconstruction of an effective earth dam inctude:compaction of the materiat in the wall at or nearoptimum moisture content: keying of the watt by wayof a core trench in suitable materiat: topsoiting andseeding of the finat watt and surrounding areas abovelop water level: and adequate spillway installation. Cf.TAN K.

DATUM (sur)

A fixed surface to which heights are referred.STANDARD DATUM relates to Mean Sea Level and wasthe traditional datum to which major surveys andtopographical maps were retated. Currently,AUSTRALtAN HEIGHT DATUM (AHD) is the nationallyadopted datum surface. It was derived from theadiustment of a continental levelling network whichinctuded tidal gauges hetd fixed at the values of MeanSea LeveL The maximum difference in New SouthWates between Standard Datum and AND isapproximately 0.06 metres.

DEAD ROD (eng)

See ROD WEEDER.

An earth dam used for soil and water conservation.

#'. z -M_,-- 'ts , ,- '"

-k-

't

36

DEBRIS (sol)

Loose and unconsotidated material arising from thedisintegration of rocks, soit, vegetation or other materialtransported and deposited in an erosion event. lt isgenerally surficial and contains a significant proportionof coarse material.

tn the classification of mass movement, debris refers tomaterial n which 20 to 80 per cent of the fragmentsare greater than 2 mm in size and the remainder of thematerial is less than 2 mm. This distinguishes it fromearth type movements, where about 80 per cent ormore of the material must be smatter than 2 mm in size,(Shroder, JE. Landslides of Utah. Utah Geological andMineralogical Survey Bulletin, No. 90, 1971.) Cf.DETRITUS.

DECREASER (ram)

A term used to describe a plant species, theabundance ot which shows a negative correlation withgrazing pressure on a particular soit - vegetationassociation. Ant. INCREASER. See also INDICATORSPECIES.

DEEP LEADS (mm)

Mineral deposits, originally deposited by alluvialprocesses, buried beneath a considerable thickness ofsoil or rock.

DEEP RIPPING (agr)

See RIPPING.

-t 's'.4.-,."--t :..J"t.: .-1.r

4

DEFLATION (soi)

The removal of tine particles from soil by wind.

DEFLOCCULATION (soi)

The process by which masses of colloidal, or very fineclay particles or 'flocs, separate in water into theirconstituent particles which go into suspension. ltdepends on the balance between exchangeable cationson the clay and in sotution and on the overall ionicstrength of the solution. Clays high in sodiumdeflocculate readily. Ant. FLOCCULATION. See alsoSODIC SOILS, DISPERSIBLE SOILS.

DEGRADATION (gen)

Decline in the quality of natural resources commonlycaused by human activities, See also LANDDEGRADATION, SOIL DEGRADATION.

DELTA (Ifm)

An extensive area of alluvial material formed where ariver enters a large body of quieter water, such as asea or lake. It is typically triangular in shape, and maybe traversed by distributary channels.

DENUDATION (gen)

The process whereby animal. and plant lite ¡n an areais seriously reduced by physical, chemical or bioticfactors.

DENUDATION (Ifni)

The process whereby the surface of the earth is wornaway or eroded.

DEPOSITION (gen)

Loose material accumulated as a result of a reductionin the velocity of the transporting agent. Cf.SEDIMENTATION.

DEPOSITIONAL SITE (ifni)

An area where the processes of lateral surfacemovement and sorting are dominant. Sub-surface in situprocesses are minimal or absent at these sites.Examples of depositional sites include /oaf s/opes,drainage plains and /loodplains.

DEPRESSION STORAGE (gen)

The amount ot water stored in depressions in the landsurface. It results from runoff which collects in suchdepressions and therefore does not contribute tooverland flow lower down the catchment, See alsoRUNOFF COEFFICIENT.

DERELICT MINE (mm)

Syn. ABANDONED MINE.

DESIGN CAPACITY (sir)

The calculated volume and/or discharge rate of a soilconservation structure. It is based on a given set of

37

hydrological conditions applicable to the site and therequirements of the structure, e.g. water storage ordiversion. Following its construction a structure'scapacity should be checked to ensure it meets thedesign requirements. If the design capacity is notachieved, the structure may tail.

DESIGN LIFE (str)

The period of time for which a soil conservationstructure is designed to perform its intended function.

DESIGN PEAK DISCHARGE (hyd)

The maximum discharge, calculated for a given set ofhydrological conditions, which is used in the design ofa hydrologic structure that can cope with thoseconditions. (Symbol: O, Units: m3/sec). See alsoRATIONAL FORMULA.

DESIGN RAINFALL INTENSITY (hyd)

The calculated rain/all intensity tor a selected designreturn period and design storm duraf ion, determined toenable design of a hydrologic structure.

DESIGN RETURN PERIOD (hyd)

The re/urn period selected in order to design speciticsoil conservation or hydrologic structures in relation totheir desired lifetime and the acceptable probability ofthe structure not failing within this period. For example,a graded bank may be designed to handle a once infive year storm. A more severe event may causedamage, but it could be more expedient and/oreconomic to repair this than to build a larger bank inthe first place. A gully control structure would normallybe built with a much longer design return period (e.g.2050 years).

DESIGN STORM DURATION (hyd)

The storm duration selected in order to design speciticsoit conservation or hydrologic structures, normallytaken as being equal to the time o/ concentration of thecatchment concerned.

DESILT (gen)

To remove sediment from water storage and soilconservation structures. It is a necessary maintenanceprocedure in instances where the accumulation ofsediment affects the capacity or efficiency of astructure.

DESILTING AREA (Str)

Syn. FILTER STRIP.

DESIRABLE (lam)

A term used to describe a native plant species or usetulintroduced plant which provides grazing value or soilstability to a particular soil'vegetation association, Seealso INDICATOR SPECIES.

DESTOCKING (ram, gen)

The removal of stock from a grazing area tor anindefinite period.

DETACHABILITY (sol)

Syn. SOIL DETACHABILITY,

DETACHMENT (gen)

The breaking away from the soil mass, or from clodsand large peds, of small soil particles capable of beingmoved by erosive processes. ABRASIONDETACHMENT results from the action of wind-borneparticles.

DETACHMENT CAPACITY (gen)

The ability of water or wind to detach and entrain soilparticles from the soil mass over which it is moving.

DETENTION BASIN (RETARDING BASIN)(eng, urb)

The pondage of a large detention structure.

DETENTION STORAGE (eng, urb)

The amount of water temporariry stored by a detentionstructure for a given runoff event.

DETENTION STRUCTURE (RETARDATIONSTRUCTURE) (eng, urb)

A structure used to temporarily hold storm runoff inorder to reduce peak flows. Such a structure mayincorporate excavated, constructed or natural

Typical die-back of eucalypts showing defoliation andre growth.

38

landscape features. The ponded water is allowed todrain at a controlled rate during and after the runoffevent, thereby emptying the structure in readiness forthe next event. Where large volumes of water aretemporarily stored, the pondage is commonly referredto as a detention basin. Cf. RETENTION STRUCTURE,

DETRITUS (sol)

Loose material arising from the mechanical weatheringof rocks and transported and deposited in an erosionevent. Cf. DEBRIS.

DIE-BACK (for)

A general name for a significant decline in tree health,lt mainly affects native trees and is caused by a varietyof agents including insect attack, phytophthera disease,pollution from industrial development and other changesin the environment caused by human activity. In someareas these problems have caused widespread treedeaths, resulting in serious environmental concern andstimulating wide interest in tree planting.

DIFFERENTIAL LEVELLING (sur)

See LEVELLING.

DIRECT DRILLING (agr)

A minimum tilia ge practice in which a crop or pastureis sown directly into unfilled soil. Stubble or pastureresidue may be reduced by burning or grazing, orretained, Weed control and the reduction of competitionfrom pastures may be achieved by grazing, burning orherbicides. It is typically practised in mixed farmingareas with reliable rainfall. Cf. NO-TILLAGE,

DIRECT SEEDING (agr)

Field seeding of any plant species normallytransplanted as seedlings. Cf. DIRECT DRILLING.

DISC CULTIVATOR (eng)

A primary or secondary tilla ge implement which usesa series of heavy duty steel discs to cut and penetratesoil and residue. Disc sizes are in the range 610 to 660mm diameter and machìne weight per disc is in therange of 60 to loo kg, Such implements are made ineither a tandem or offset configuration and arecommonly known as tandem discs or oftset discs"respectively.

Disc implements generally cause substantial inversionof soil and burial of crop residue. They are also moreaggressive in terms of their effect on soil structure, Forthese reasons they are not widely recommended foruse in conservation tillage systems. However, they areuseful where break-up and incorporation ot residue isa specific requirement, as may be the case in doublecropping.

DISC DRILL (eng)

See DRILL.

DISC HARROW (eng)

A secondary filfa ge implement, made in either the offsetor tandem configuration. Disc sizes are in the range of460 to 550 mm in diameter, and machine weight perdisc is in the range of 40 to 60 kg.

DISC OPENER (eng)

See SOIL OPENER.

DISC PLOUGH (eng)

A primary fill age implement using large concave discsto invert soil and incorporate residue. Disc sizes rangefrom 710 to 860 mm in diameter and machine weightper disc is tOO kg or greater.

On mounted disc ploughs the discs are individuallymounted and inclined backwards from the vertical anddisc angles are adjustable. On "reversible" models thedisc mounting can be rotated about a vertical axis to

39

allow soil to be thrown to either side of the plough. Onone-way models this facility is not available and soil isalways thrown in one direction.

A mounted disc plough.

A trailing one-way disc plough.

DISCHARGE (hyd)

The instantaneous flow rate at a specific location in aflow line or hydrologic structure. Specifically it relatesto the volume of water flowing through a cross sectionof the flowline or structure in unit time. Symbol: O,Units: m3/s.

DISCHARGE CURVE (hyd)

Syn. RATING CURVE.

DISCING (agr)

Tillage of the soil with a disc-type implement such asa disc plough or disc harrow,

A mounf ed disc harrow in fhe offset conliguraf ion.A trailing offset disc plough.

DISPERSIBILITV (sol)

Syn. SOIL DISPERSIBILITY.

DISPERSIBLE SOIL (sol)

A structurally unstable soil which readily disperses intoits consliluerit particles (clay, silt, sand) in waler. Highlydispersible soils are normally highly erodible and arelikely to give problems related to held and earthworktunnelling. See also SOIL DISPERSIBILITY, SODIC SOIL.

DISPERSION PERCENTAGE (sol)

A measure of soi/ dispersibihity representing theproportion of clay plus fine sill (<.005 mm approx.) ina soil which is disersible, expressed as a percentage.lt is determined in the laboratory by comparing theamount of fine material, in a soil sample, dispersed bya 10 minute shaking in waler, to the amount dispersedby a 120 minute shaking in water containing dispersant.Highly dispersible clays have a high dispersionpercentage. See also SOIL DISPERSION.

DISSIPATOR (eng)

Syn. ENERGY DISSIPATOR.

DISTORTION (rms)

A feature of an aerial photograph r&ated principally toits central perspective such that the position of imageson the photo are altered from their true relativepositions. Radial displacement increases towards theedges of the photo, thus, the closer to the edge of thephoto the greater the distortion.

PERSPECTIVE DISTORTION is caused when the eyesof the observer are moved away from the central pointof a stereo- pair. This has the effect of exaggeratingslopes facing away from the stereo-centre anddecreasing those that face towards it. HEIGHTEXAGGERATION is a distortion in the stereo-pair duelargely to the small ratio of eye base to flying height.

DISTROMETER (hyd)

An electronic instrument used to measure the sizedistribution of raindrops. Typically comprises a conicalsensor which produces an electrical output related todrop velocity and mass. This output is electronicallyrecorded for subsequent analysis.

DISTURBED AREA (gen)

An area which is susceptible to erosion because thevegetative soil cover has been removed or altered. Thismay be accompanied by mixing or removal of some soilhorizons. Cf. DISTURBED TERRAIN.

DISTURBED TERRAIN (lfm)

An area of land in which the components have beenpermanently altered from their original state as a resultof human activities, It includes mining or quarrying pitsand construction sites. Artificial /and!orms may bespecficalIy created on disturbed terrain to serve variousconstruction purposes. Such landlorms includeembankments, mounds, cut laces, cut-òver surfacesand li/I tops.

40

- DISUSED MINE (mm)

Syn. CLOSED MINE.

DIVERSION BANK (str)

See BANK.

DIVERSION CHANNEL (str)

An earth channel traversing a slope designed to protectadjacent lower slopes or development works byintercepting surface water and diverting it to a stableoutlet. The channel may have a minor ridge on its towerside to help contain ftows. Where flows are too large tobe contained by a simple channel, a diversion bank isconstructed.

Diversion channels should be parabolic or trapezoidalin cross section to permit maintenance of theirprotective vegetative cover. Such channels are typicallygraded.

DIVERSION DRAIN (str, eng)

Syn. CATCHMENT DRAIN

DIVERSION SPREADER BANK (str)See BANK.

DOT GRID (lev)

A transparent medium, typically film positive, withregularly spaced dots used as an overlay to aphotograph or map for determining areas.

DOUBLE CROPPING (agr)

A cropping procedure whereby two crops are grown inone year on the same piece of land.

DRAIN (gen, str, eng)

A channel for the purpose of interception and removalof excess surface or sub-surface water to a stableoutlet,

Surface drains, excavated for runoff control and incommon use for soil conservation purposes are:

BERM DRAIN

A drain along a constructed ledge between the topand bottom of a batter. See also BERM (eng).

CATCH DRAIN

A drain adjacent to a batter or embankment for thepurpose of intercepting runoff flowing onto or awayfrom it.

CATCHMENT DRAIN tDI VERSION DRAIN)

A drain extending beyond the natural catchmentof a dam in order to augment the supply of runoffto it.

CONTOUR DRAIN

A drain excavated along the contour.

CROSS DRAIN

A drain of various form that baulks the flow ofwaler down a road, trait or other access-way anddiverts it across the roads surface. Cross drainsare required where runoff cannot be controlled bycrosstall drainage. Cf. CROSS BANK.

MITRE DRAIN (SPUR DRAIN)

A drain to conduct runoff from a road shoulder toa disposal area away from the road alignment.

OPEN UNLINED DRAIN

An open drain with no stabilising material toprotect ìts floor or sides.

RESIDUAL FLOW DRAIN

A drain designed to carry trickle flows, such asmight be used in conjunction with a strip croppingscheme.

SEEPAGE INTERCEPTOR DRAIN

A drain with a channel cut deep enough tointercept sub-surface seepage, and convey it to asate outlet. When used in conjunction with a bankon the upslope side it is known as a REVERSESBANK SEEPAGE INTERCEPTOR DRAIN. Thissytem allows surface runoff to be safely dealt withas well as enhancing the drainage of shallowseepage water.

SPOON DRAIN

A drain with semi-circular crosssection having noassociated ridge of soil. lt's capacity is sotelydefined by the excavated channel dimensions, andit is only effective on low slopes.

TABLE DRAIN

The side drain of a road running adjacent andparallet to the shoutders, and comprising part ofthe road formation, Its purpose. when properlystabilised, is to conduct runoff safely away from theroad area. Usually associated with mitre drains.

TANK DRAIN

A drain used to intercept runoff and teed it into atank,

WINDROW DRAIN

A drain formed by a windrow along the edge of atrail, which may be useful in directing runoff flowingacross the trail to a stable outlet,

Sub-surlace drains provide a channel for free watermovement through the soil. They are generallyused where site draina ge is poor or where highwatet tables are a problem. Several common typesare:

MOLE DRAIN

An unlined drain used for draining clay soils. Thechannel is formed by pulling a torpedo-shapedcylinder through the subsoil, and only lasts as longas the clay material surrounding the hole remainsstabte.

41

RUBBLE DRAIN

A drain formed by placing gravel, broken rock orconcrete, or similar material, in an excavatedtrench and covering it with soil.

TILE DRAIN

A lined drain formed by placing a pipe along thebottom of an excavated trench and covering it withsoil. Such pipes are usually made of pervious clayor perforated plastic and are bedded in anenvelope of coarse sand.

INTERCEPTOR DRAINS are specifically utilised tointercept flowing water and may be either asurface or subsurface drain or a combination ofboth.

DRAINAGE (gen)

The interception and removal of excess surface and/orsubsurface water Irom land, using artificial or naturalmeans. See also SITE DRAINAGE, INTERNALDRAINAGE.

DRAINAGE DEPRESSION (If m)

A level to gently inclined, shallow, open depression withsmoothly concave cross-section. rising to moderatelyinclined hillslopes, that conveys runoff only during orimmediately after periods of heavy rainfall, Drainagedepressions typically occur at the upstream end of aflow path within any given catchment. They arecommonly eroded or aggraded by sheet wash butbecause ot their tendency to concentrate flows, thepotential for gully erosion may also be high.

Drainage depressions may be subject to seasonalwaterlogging or spring activity and vegetation typeoften indicates a wetter micro-environment than thesurrounding country.

DRAINAGE EASEMENT (urb)

A corridor through private land, that is reserved andcontrolled by a local government authority, facilitatingstormwater flows, lt typically follows a natural flow pathand incorporates a natural or constructed open channelof defined capacity, based on catchmentcharacteristics, and an adjacent floodway to carryexcess flows. Natural channels may require channelimprovement to provide stability and enable efficientmaintenance programs to be adopted. Buildings, fencesor other structures should not encroach onto theeasement, so that it can provide for unimpeded (low ofstorm runoff. Ideally, the channel and floodway shouldbe formed and stabilised before any major developmentoccurs in its catchment. See also DRAINAGE RESERVE,

DRAINAGE LINE (gen)

A channel down which surface water naturallyconcentrates and flows, conveying water only duringand/or immediately after periods of heavy rainfall.Drainage lines may be stable, as in a well-grasseddepression, or unstable, as in an active gully. Stabledrainage lines are olten used in association with soilconservation programs for water disposal.

DRAINAGE PLAIN (Ifm)

A longitudinally extensive, level or gently inchned areaof sediment, adjacent to a drainage line, built up byalluvial deposition during the current regime of thedrainage tine. Such areas are subject to periodicoverland flow of water, may be subject to seasonalwaterlogging and have vegetation types that oftenindicate a wetter micro- environment than thesurrounding country.

DRAINAGE RESERVE (uit)

A dedicated public reserve incorporating a natural orconstructed open channel that carries stormwater flows.The channel must have a defined capacitycommensurate with expected flows and an adjacentfloodway to carry excess flows. Natural channels mayrequire channel improvement to provide stability andenable efficient maintenance programs to be adopted.Buildings, fences or other structures should notencroach onto the reserve, so that it can provide forunimpeded flow of storm runoff. Ideally, the channel andfloodway should be formed and stabilised before anymajor development occurs in its catchment.

As an alternative to piping and masonary channels,vegetated drainage reserves and vegetated drainageeasements have significant advantages in regard tocost, capacity and potential for detention storage. Flowvelocities are usually low, resulting in a longer time o!concentration and lower flood peaks downstream. Theyalso encourage filtration and/or settlement of pollutants,washed from urban areas, which may flow throughstormwater pipes or lined channels.

DRAWDOWN (eng)

Lowering of a water surface resulting from a withdrawalof water. Can be applied to open channel flow, a watertable or stored water in a dam.pr

42

DRIFT (gen)

Material moved by wind action and subsequentlydeposited in sheltered areas.

DRIFT (mm)

A passage driven through country rock to gain accessto a mineral seam or vein. Cf. DRIVE.

DRILL (SEEDER) (eng)

A sowing machine which can simultaneously insert seedand fertiliser into the soil, via a number of soi/ openers,but which does not have separate cultivating tines ordiscs. Hoppers with a series ot individual metering unitsare fitted to supply and meter seed and fertiliser to thesoil openers via sowing tubes and boots.

A number of drill types are available. The main ones aredescribed hereunder:

AIR SEEDER

A type of combine drill using an air distributionsystem to deliver seed and fertiliser to the sowingtines. Air seeders are usually based on fie/dcu/tivators and the working width is seldom lessthan six metres. The system comprising the airsupply unit, seed and fertiliser hoppers andmetering units may be supported on the cultivatortrame or on its own wheels.

Dritt sand encroaching on stable vegetation.

An air seeder in travelling mode.

COMBINE DRILL

A drill which not only applies seed and fertiliser,but also cultivates the soil to a shallow depth.Tines or discs may be fitted to the drill, and theyare usually fixed on a 180 to 250 mm spacing forsowing. Spring release tines are most commonlyused tor this purpose.

A combine drill.

DISC DRILL

A drill fitted with disc openers, Apart from the saitopeners the disc drill is similar in configuration tothe combine drill.

PRESSWHEEL DRILL

A drill whose weight is partially supported bypresswheels which fotlow the individual soilopeners. Commonly made in 2.4 metre widemodules attached side by side, which improvesthe contour - tollowing ability of the drìll.

TRASH SEEDER

A combine drill with greater effective clearance,greater distances between ranks and greaternumbers of ranks compared with traditionalcombine drills. Tine and sowing assemblies can bemoved to allow greater row spacing and teadingcoulters and trailing presswheels can be bolted onas required. These machines are designed to meetthe needs of conservation tiltage systems.

43

A presswheel drill.

A trash seeder.

TRIPLE DISC DRILL

A drill fitted with leading vertical coulters to cutthrough residue, toltowed by double-disc openerswith tubes dropping seed and fertiliser into the V-shaped groove formed by the two discs, Suitabtefor sandy soifs and sowing into pasture sod.

UNIT PLANTER

A drill for sowin seed and fertitiser (optional) intoan individual row. The machine usually comprisesa soil opener, seed and fertiliser metering anddelivery components and a presswheel. Somemodels also include depth gauging wheets and arange ot openers and presswheels to suit differentcrop and soil conditions. Several unit planters arenormally used together on independent mountingsto make up a multiple row machine suitable for no-tillage operations. The term no-till planter is oftenapplied to these machines. A PRESSWHEELPLANTER UNIT is a unit planter without theindividual seed and fertiliser metering units. Mostmodels utilise an air seeder for seed and fertilisermetering and delivery, and are made with tineopeners.

DRILLING (agr)

A procedure whereby a crop or pasture is sown usinga machine that inserts seeds into the soil. Fertiliser maybe applied simultaneously by the same machine. Cf.SOWING.

DRILLING (eng)

An operation to locate and develop underground watersupplies, orto determine the characteristics of subsoil

DRILLING (Continued)

or underground geological formations for a variety ofpurposes, including investigation of siles for earth damsor lanks.

A unit plantet.

A presswheel planter unit.

DRIVE (mm)

A level passageway along the line ot a mineral seam orvein. Cf. DRIFT.

DROP INLET (eng)

A drop structure forming the entrance section to anyhydraulic structure.

DROP INLET CHUTE SPILLWAY (eng)

See SPILLWAY.

DROP INLET CULVERT (eng)

A culvert which incorporates a drop structure al ilsentrance.

DROP INLET PIPE SPILLWAY (eng)

See SPILLWAY.

it,

44

DROP SPILL WAY (eng)

See SPILLWAY.

DROP STRUCTURE (eng)

A hydraulic structure for allowing water to fall to a lowerlevel.

The term may be applied to an enlire structureincorporating an mIel, drop and outlet, which facilitatesthe entry and exit of water between Iwo levels withoutcausing erosion: or to a section of a hydraulic structuresuch as in a drop inlet culvert,

The drop is typically vertical but may be inclinedprovided the nappe does not touch the structure.Where a nappe is not formed the structure is referredto as a chute,

For soil conservation purposes a drop structure shouldinclude an energy dissipator.

'4 -

- a

A sand-cement bag drop structure,

DRY SAND FLOW (gen)

See EARTHFLOW.

DRYLAND (agr)

Describes land degradation or land use not involvingirrigation. For example, dryland salting or dryland wheatproduction.

DRYLAND SALTING (gen)

See SALTING,

DUMP GYPSUM (sol)

See GYPSUM.

DUMPY LEVEL (sur) See LEVEL.

DUNE (csd, Ifrn)

A moderately inclined to very steep ridge or hillock builtup by wind action, Dune formation may be initiated bythe entrapment ot transported material by wind-reducing vegetation or structures

HIND DUNES

Relationships between the val ious dune types.

Various types of coastal dunes recognised are:

INCIPIENT DUNE

An area above the swash zone which hasdeveloped a slight convexity of profile from theaddition of wind- blown sand. lt is the first stagein the development of a new foredune, whichgenerally is encouraged by the growth of primarystabilising species.

FOREDUNE (PRIMARY DUNE)

The first dune immediately landward of. andparallel to, the beach: ridge and built up by on-shore winds. lt is the most seaward location ofsand-trapping vegetation.

FRONTAL DUNE

A toredune which has endured to develop a coverof permanent vegetation but remains exposed tounobstructed on-shore winds.

SECONDARY DUNE

A dune immediately landward of the foredune,

RIND DUNE

Any dunal area landward of the frontal dune,including the secondary dune.

Series of parallel dunes are known as DUNE RIDGES.In the coastal environment dune ridges develop duringperiods of sea-level fall.

Dunes are normally linear in form. However, when ablowout proceeds unchecked a U-shaped dune results.This is known as a PARABOLIC DUNE (U-DUNE). Seealso LUNETTE.

DUNE-BUILDING FENCE (csd)A brush fence or similar structure designed andinstalled to trap drifting sand and create a dune. Thedune so formed can subsequently be stabilised withvegetation.

45

INTERDuNE INTERDuNESWALE SWALE

SECONDARYDuNE

FRONTALDUNE

DUNE RIDGES (csd)

See DUNE.

DUNE SHAPING (cad)

The mechanical rebuilding of dunes in order to createa shape, size and orientation to facilitate theirpermanent stabilisation with vegetation.

DUNEFIELD (lfm)

A level to rolling landform of low relief without streamchannels, built up or locally excavated, eroded oraggraded by wind action. Components include dunes,swales and blowouts,

DUPLEX SOIL (sol)

A soil in which there is a sharp change in sou fexturebetween the A and B horizons (e.g. loam overlyingclay). The soil profile is dominated by the mineralfraction with a texture contrast of 1½ soil texturegroups or greater between the A and B horizons,Horizon boundaries are clear to sharp. The texturechange from the bottom of the A horizon to the top ofthe B horizon occurs over a vertical distance of 10 cmor less. See also SOIL PROFILE, PRIMARY PROFILEFORM, GRADATIONAL SOIL, UNIFORM SOIL,

DUST (gen)

Comprises a wide range of fine materials, including soilmaterials, which can be transported over long distancesby wind. As wind velocity or air turbulence decreases,the larger and heavier particles settle, whereas manyol the smallest particles are ¡n almost permanentsuspension. The suspension fraction in wind erosion isgenerati y accepted as being less than 100 pm in size,

In a soil conservation context, a dust storm or dustcloud is the manifestation of a major wind erosion eventin which soil materials comprise the majority of the dustin suspension,

H.W,M,

BEACH

E.D.M. (EDM) (sur)

A commonly used abbreviation for electromagneticdislance measurement, which determines distanceusing radio or light waves, Lightweight EDMinstruments can be used efficiently under idealconditions for distances as short as 20 metres and astong as 3 kilometres. Larger instruments using lightwaves or microwaves can be used at much greaterdistances.

E.S.P. (ESP) (sol)

Syn. EXCHANGEABLE SODIUM PERCENTAGE.

EARTH (sol)

A general term commonly used to describe a range ofsoil materials. In pedological terms, it is used todescribe great soif groups such as Black Earths andRed Earths. The term also refers to gradational soilswith an earthy fabric in their B horizons.

In the classification of mass movement earth refers tomaterial in which about 80 per ceni or more of theparticles are smaller than 2 mm in size. Thisdistinguishes it from debris type movements whichcontain 20 to 80 per cent of fragments greater than 2mm. (Refer: Shroder, J.F. Landslides of Utah. UtahGeological and Mineralogical Survey Bulletin, No. 90,1971.) As part ot the classification, earth can besubdivided on the basis of ils constituent separates,ranging from non-plastic sand to highly plastic clay.

EARTHELOW (gen)

A category of mass movement involving earth materialsand movement resembling that of a viscous fluid.Earthflows occur under a variety of moisture conditionsand dìsptacement varies from extremely stow toextremely rapid. Accelerated movement is oftenassociated with moisture content increases. They mayoccur on a wide range of slope gradients.

Nomenclature of earthftows is commonly based on thedominance of particular separates within or composingthe earth material, and their moisture content, such as:

Eart hf/ow resa/fin g from overclearing.-

aç

46

DRY SAND FLOW

Occurs under dry conditions in non-plastic sortedsands and is typified by the 'flow' of sand resultingfrom disturbance of a sand dune,

WET SAND FLOW

Occurs under wet conditions in non-plastic sortedsands and is typified by the flow' of sand followingthe collapse of a beach ridge by wave action.

MUDF LO W

Occurs under very wet conditions in plastic clay-type materials. Mudftows typically result whenwater is suddenly applied to an area where asuitable load of unconsolidated ctayey material isavailable, especially in the absence of a goodvegetative cover.

EARTHWORK (str)

An earthen structure designed and constructed for thepurpose of interception, diversion, retention, detentionand/or safe disposal of runoff, or any similar soilconservation purpose. The term may also be applied tothe physical re- orientation of land surface materials bymechanical means to facilitate soil erosion control orprevention.

EARTHWORK TUNNELLING (PIPING) (eng,str)

The process of tunne/ erosion as it occurs inconstructed earthworks. Results from the use ofdispersible soils in such earthworks and their post-construction de flocculation. The continued removal ofsoil material through the tunnels so formed can lead tothe serious leaking of the structure and its eventualcollapse. The use of permeable soil materials, and thosesubject to cracking, may also lead to or accentuate theproblem.

Failure to achieve sufficient compaction duringconstruction and/or to incorporate appropriate soilameliorants are the main reasons for the initiation ofearthwork tunnelling. See also PHREATIC LINE.

ECOLOGY (gen)

The study of relationships between living organisms andtheir environment. See also AUTECOLOGY,SYNECOLOGY,

EDAPHIC (sol)

Pertaining to the soil.

EFFECTIVE CLEARANCE (eng)

The vertical distance measured from the lowest pointon the cutting edge of any tillage too/ up to any partof the tillage implement potentially obstructive tovegetation or residue flow through it, This measurementgives a clear indication of the implement's residuehandling capacity. Cf. UNDER-FRAME CLEARANCE.

EFFECTIVE SOIL DEPTH (sol)

The depth of soil material thai plant roots can penetratereadily to obtain water and plant nutrients. lt is thedepth to a ayer that differs sufficiently from theoverlying material in physical or chemical properties toprevent or severely retard the growth of roots.

EFFLUENT (hyd)

The discharge or outllow of water from ground or sub-surface storage.

EFFLUENT (urb)

The fluids discharged from domestic, industrial andmunicipal waste collection systems, or other treatmentfacilities,

ELECTRICAL CONDUCTIVITY (sol)

A measure of the conduction of electricity through wateror a water extract of soil. Il can be used to determinethe soluble salts in the extract and hence soil sa/mity.The uniI of eleclrical conductivity is the siemens andsoil salinity is normally expressed as millisiemens percenlimetre al 25°C. (Symbol: E, Units: ms/cm).

Conductivity values of 1.5 (for a 1:5 soil:watersuspension) or 4.0 (for a saturation extract) indicate thelikely occurrence of plant growth restrictions. See alsoSALINE SOIL,

ELECTRONIC TACHEOMETER (sur)

A surveying instrument which combines the functionsof a theodobte, electronic distance measurement anda microprocessor, The horizontal and verlical circles areelectronically scanned, The instrument is capable ofdisplaying horizonlal and vertical circle values as wellas slope distances, and horizontal/vertical componentsof slope distance. These displayed values can also bestored in an electronic data recorder connected to theinstrument.

ELUTRIATOR (sol)

An instrument which lifts particles from a fluidised bedof dry soil in a rising currenl of air. By changing the rateof lift, particles of different sizes may be separated toenable soil to be characterised by particle sizedistribution orto determine the proportion of suspensionfraction capable of being mobiUsed during wind erosion.This process is called elutriation.

47

ELUVIATION (sol)

The downward removal of soil material in suspension,or in solution, from a layer or layers of a soil. The lossof material in solution is described by the term leaching.Some of the eluviated materials are typically depositedin lower layers or horizons, Cf. ILLUVIATION.

EMBANKMENT (lfm, Str)

An artificial elevation of earth, longer than it is wide,typrcally construcled for the purpose of controlling theflow of, or storing water as in a bank or dam, See alsoDISTURBED TERRAIN.

EMERGENCY SPILLWAY (Str)See SPILLWAY,

EMERGENCY TILLAGE (agr)

See WIND RIDGING,

EMERSON'S AGGREGATE TEST (sol)A classification of soil aggregates based on theircoherence in waler, Small dry aggregates are placedin dishes of distilled water and their behaviourobserved, The conditions under which they slake, swelland disperse allows the different aggregates to beseparated into eight classes, The test is particularlyvaluable in a soil conservation context as it grades soilaggregates according Io their stability in water.

The lest uses natural peds, with the first separationbeing based on slaking. Those aggregates which donot slake are placed in class 7 if they swell and in class8 if they do not.

Of those which do slake, which form the majority ofsoils, those which show complete soil dispersion areplaced in class i and those showing only partialdispersion are placed in Class 2. Those showing nodispersion are remoulded al field capacity and re-immersed in waler.

Aggregates which disperse after remoulding are placedin class 3 and those which do not are further separatedby the presence or absence of carbonate or gypsum.Those with carbonate or gypsum fall into class 4 whilethose without are made up into a 1:5 suspensionaggregates/water, Those soils which then showdispersion are placed in class S and those which showflocculation fall into class 6.

(Reference:Emerson W.W. (1967) Aust. J. Soil Res. 5 47A classification of soil aggregates based on theircoherence in water.)

In general the degree of stability of soils increases fromclass 1 through to class 8. In a soil conservationcontext, t may be useful to further subdivide classes2 and 3 according lo the degree of dispersionobserved,

END WALL (eng)

A cut-oil wall at the outlet of a hydraulic structure, Itsprimary purpose is to prevent undercutting by flowsleaving the structure.

ENERGY DISSIPATOR (DISSIPATOR) (eng) EROSION (gen)A structure used to absorb excess kinetic energypossessed by flowing water. This energy is acquired bythe water when its velocity is high, such as in a chuteor over a weit. Energy dissipators are incorporated intothe design of hydraulic structures to reduce turbulenceand the erosive power of fast-moving water.

ENTRAINMENT (sol)

The process by which detached soil particles are drawninto the flow of air or water during an erosion event.

EPHEMERAL (hyd)

Describes a watercourse, or portion thereof, that doesnot flow at alt times. lt generally only flows in directresponse to precipitation. lt receives little or no waterfrom springs and no long continued supply from snowor other sources. Its channel is at all times above thewater table.

ERODE (gen)

To wear away the land. In a soil conservation contextthe main active tactors responsible are rainfall, runningwater and wind, and these are called erosive agents.

ERODIBILITY (gen)

Susceptibility to erosion. See also SOIL ERODIBILITY.

ERODIBILITY INDEX (sol)

A quantitative expression of soil erodibility based onmeasured soil properties. See also SOIL ERODIBIUTY.

ERODIBLE (gen)

Susceptible to erosion, The term is typically applied tosoils

A dusf storm resulting from wind erosion.

48

The wearing away of the land by running water, rainfall,wind, ice or other geological agents, including suchprocesses as detachment, entrainment, suspension,transportation and mass movement.

NATURAL EROSION (GEOLOGIC EROSION)

Erosion occuring under natural environmentalconditions, undisturbed by humans, and occurringover long geologic periods,

ACCELERATED EROSION

Erosion much more rapid than natural erosion,primarily involving the loss of soil material from theland as a result of the influence of human activities.

SOIL EROSION

The detachment and transportation of soil and ilsdeposition at another site by wind, water orgravitational effects. Although a component ofnatural erosion, it becomes the dominantcomponent of accelerated erosion as a result ofhuman activities, and includes the removal ofchemical materials.

WAVE EROSION

An erosion process in which soil is detached andtransported from the land by the action of waves.It is typically associated with coastal areas and isthus often referred to as coasta/ erosion. However,wave erosion may occur at the margin of any waterbody, such as a retention structure or dam.

WIND EROSION

An erosion process in which soil is detached andtransported from the land surface by the action ofwind, Where the removal of a fairly uniform layerof soil from the land surface occurs the term sheeterosion may be used. Transport of wind-blownparticles occurs by suspension, saltation or surfacecreep.

%

Sheet and (ill erosion ai arable land.

WATER EROSION

An erosion pricess in which soil is detached andtransported from the and by the action of rainfall,runoff, seepage and/or ice.

The tollowing terms are used to describe differenttypes of water erosion:

SPLASH EROSION (RAINDROP EROSION)

The spattering of soil particles caused by theimpact of raindrops on the soil. The loosenedparticles may or may not be subsequently removedby runoff. An important component of sheeterosion. See also RAINDROP SPLASH.

SHEET EROSION

The removal of a fairly uniform layer of soil fromthe and surface by raindrop splash and/or runoff.No perceptible channels are formed.

N.B, The term may also be applied with respect towind erosion,

RILL EROSION

The removal of soil by runoff from the land surfacewhereby numerous small channels, generally up to30 centimetres deep, are formed. Typically occurson recently disturbed soils. See atso RILL.

60320-15204-4

49

GULLY EROSION

A complex of processes whereby the removal ofsoil is characterised by large incised channels inthe landscape. Such channels are generally morethan 30 centimetres in depth. The severity of gullyerosion may be recorded as minor, moderate,severe or very severe,

Minor nd moderate gully erosion are related to thedensity of gullies within the primary drainage linesover a specified area. With minor gully erosion.gullies are generally discontinuous, and withmoderate gully erosion they are generallycontinuous. When branching of the gullies awayfrom the primary drainage line occurs, the severecategories are used. Three categories of gullydepth may be recorded: <1.5 m, 1,53 m, >3 m.See also GULLY,

GuVy erosion processes may include:

Removal of soil from the land surface byconcentrated runoff with sufficient volume andvelocity to cut large channels,

*Dispersion of unstable subsoils due toseepage followed by the cotlapse of surfacesoil into the void so formed.

HEAD WARD EROSION

Gully enlargement in an upstream directiondue to incision by concentrated runoff and theformation of a waterfall and splash pool

EROSION (Continued)

An aerial view of very severe gully erosion.

Gully erosion resulting from dispersion of unstablesubsoils.

leading lo undercutting and slumping of thegully head. This process may be accentuatedby lhe effects of sheel and splash erosion,and subsurface seepage. *

LATERAL EROSION

Gully enlargement in a lateral direction due toincision by concentrated runoff entering at the S.gully sides and/or by undercutting andslumping and/or by sheet, nIl and splasherosion of the gully sides.

STREAMBANK EROSION

The removal of soil from streambanks by the directaction of stream flow, and/or wind/wave action.Typically occurs during periods of high flow.

TUNNEL EROSION (TUNNELLING)

The removal of sub-surface soil by water while thesurface soil remains relatively intact. An erosionprocess in which water seeps into dry soil causingsoil dispersion and/or slaking of soil particles intosuspension. The dispersed soil is then removed byseepage until the seepage path takes the form ofa tunnel. The process continues as more watercomes into contact with fresh dry soil.

50

Such a tunnel usually outlets in the side of a gully,batter or earth wall, or at the ground surface lowerdown a slope. The tunnel normally collapses in duecourse and a gully is formed.

The process can occur in soils in their natural fieldsituation or in constructed earthworks. The soilsinvolved are normally highly dispersible.

See also FIELD TUNNELLING, EARTHWORKTUNNELLING.

i

Tunnel erosion.

a

Active gully enlargement due to lateral erosion

Streambank erosion - note undercutting on outside curveand deposition on inside curve.

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EROSION CONTROL MEASURES (gen)

Those activities based oni structura! works, vegetationmanagement, tillage operations and/or other farmmanagement options designed primarily to achievecontrol ot soil erosion,

EROSION HAZARD (gen)

The susceptibility of a parcel of land to the prevailingagents of erosion. t is dependent on a combination ofclimate, landtorm, soil, land use and land managementfactors. The qualitative categories of erosion hazardused are low, moderate, high, very high and extreme.

Low erosion hazard is associated with a combinationof the above factors that results in no appreciableerosion damage occurring during or after thedevelopment of the particular land use underconsideration. Soit conservation management shouldhowever, include simple practices, such as topsoilingand conservation tillage where appropriate.

Moderate erosion hazard implies that significant erosionmay occur during development of the particular landuse. Provided appropriate soil conservation measuresare adopted during development both short term andlong term erosion problems may be avoided,

High erosion hazard implies that significant erosion willoccur during development ot the particutar land use andthat appropriate erosion control measures are neededto minimise long-term erosion problems. Control of shortterm erosion could be provided by simple soilconservation measures but long-term erosion controlwould involve intensive measures,

Very high erosion hazard implies that significant erosionwill occur during development and after the land useis established, even with intensive soil conservationmeasures. Such an erosion hazard infers that planningwill need to carefully consider the balance between theprobability of long-term erosion damage and themaintenance or repair needed to ensure the viabitity ofthe land use.

Extreme erosion hazard implies that erosion will occurto such an extent that economic control utilisingconventional soil conservation measures is impractical.If imptementation of the land use is imperative, detailedengineering. geotechnical and/or other appropriatestudies will be necessary to ascertain its viability.

Cf. SOIL ERODIBILITY. EROSION RISK.

EROSION MITIGATION (gen)

Reduction in (he severity of erosion. A general termused to embrace all those activities, including specificsoil conservation activities, aimed at the control of soilerosion and the reduction of its impact on all forms ofland use.

51

EROSION RISK (gen)

The intrinsic susceptibility of a parcel of land to theprevailing agents of erosion. lt is dependent on acombination of climate, landform and soil factors.

Determination of erosion risk differs from thedetermination of erosion hazard in that landmanagement factors are ignored. Thus, the relativedifference between various parcels of land is tesssusceptible to change due to technologicalimprovements in land management practices.

EROSION SURVEY (lev)

The systematic examination, description, classificationand mapping of existing soil erosion within an area.Although other land resource aff ribotes and/or otherelements of the land may be mapped during the survey,its principal function is to describe, classify and mapsoil erosion to show the extent of degradation of thesoit resources. Such a survey also provides someindication of the erodibilif y of different soil types.

EROSION-RESISTING CROPS (agr)A strip cropping term for those crops with goodcapability for stowing and spreading the overland flowot runoff.

EROSIVE (gen)

Tending to produce erosion. lt appties to factors whichact, or can act, on the soil or other materials to causeerosion, but is not a property of the material itself.Therefore, the term refers to the active agents oferosion such as rainfall, running water and wind.

EROSIVE VELOCITY (gen)

Velocity of the erosive agent necessary to causeerosion of the material in question.

EROSIVITY (gen)

Potential ability to cause erosion. The amount of erosionat a site is dependent on the erosivity of the erodingagent - rainfall, running water, wind, etc. The term iscommonly applied to rainfall.

ESCARPMENT (lin,)

A steep to precipitous tandform comprising a linearlyextensive, straight or sinuous inclined surface whichseparates terrains at different altitudes. The uppermargin is commonly marked by a precipitous tace,revealing the exposed geological strata, below whichtalus Or scree occurs.

Escarpments are unstable due to their mode offormation and have a high potential for mass movementas well as the hazard of rockfall. Plateaux frequentlyoccur above escarpments.

ESTUARINE FLAT (11m)

An area of relatively fiai land formed by deposition inan estuary and exposed only at low tide.

ESTUARY (If rn)

An open drainage depression adjacent to the sea,typically at the mouth of a river, into which the tideebbs and flows. Tide movements accentuate erosionand continually modify the drainage channels within theestuary.

EVAPORATION PAN (gen)

Syn. EVAPORIMETER,

EVAPORIMETER (EVAPORATION PAN)(gen)

A shallow open container from which daily changes inwater level are used to calculate natural evaporationfrom a free water surface. Allowance is made for anyaddition of rainfall which occurs. The Bureau ofMeteorology's standard for this purpose is the U.S.Class A Pan, which is 1.2 metres in diameter and 25centimetres deep. The water level is adjusted daily toa depth of 19 centimetres. See also PANEVAPORATION.

An eMpor/meter with two met re anemometer to assistinter pretation o! evaporation data.

EVAPOTRANSPIRATION (agr)

Removal of moisture from soil by evaporation plustranspiration by plants growing in that soil. lt ismeasured at a specific site over a specitic period oftime.

52

EXCHANGE CAPACITY (sol)

The total ionic charge of a soil, expressed in centimolesof charge per kilogram of soil. Ils numerical value isidentical to the value expressed ¡n milliequivalents per100 grams of soil. See also CATION EXCHANGECAPACITY, ADSORPTION.

EXCHANGEABLE SODIUM PERCENTAGE(ESP) (sol)

The proportion of the cation exchange capacityoccupied by sodium ions, expressed as a percentage.Sod/c soils are calegorised as those with an ESP from6to 14%, strongly sodic soils are those with an ESP of15% or more. Soils with a high ESP are typicallyunstable and as a consequence have high erodibilityand often present problems in soil conservationearthworks. See also SOIL DISPERSIBILITY,DISPERSIBLE SOIL.

EXCLOSURE (ram)

An area of range/and from which domestic and/ornative animals are excluded for the purpose of studyingthe effects of no grazing on vegetation. Such an areamay range in size from a few square metres tohundreds of hectares.

EXPANSIVE SOIL (SWELLING SOIL) (sol)

A soil which significantly changes its volume withchanges in moisture content. lt typically cracks whendrying out, and expands on wetting. The shrinking!swelling characteristic is normally due to the presenceof montmori//onitelype clays in the soil, and ischaraclerised by testing for linear shrinkage.

This characteristic can be detrimental to such structuresas masonry walls, roads, buildings and soil conservationearthworks, unless appropriate precautions are taken.See also SHRINK-SWELL POTENTIAL.

EXTENDED PRINCIPAL PROFILE FORM(sol)

See PRINCIPAL PROFILE FORM,

EXTENSIVE BUILDING COMPLEXES (urb)

A level of urban development which provides for theconstruction of commercial centres, such as offices andshopping malls, industrial centres or sporting facilities,which require arge scale clearing and levelling for broadareas of floor space and/or parking bays. See alsoRESIDENTIAL DEVELOPMENT,

FABRIC (sol)

Syn, SOIL FABRIC.

FACTUAL KEY (sol)

The alpha-numeric coding system for recognition andclassification of Australian soils based on observablesoil profile features. lt has a hierarchical structure whichuses the bifurcating principle to successfully separateoui primary profile forms, subdivisions, sections, classesand principal pro file forms. The soil profile features usedinclude soil texture, colour, structure, pH, presence ofpans, consistence, coherence and other specialfeatures related to both A and B horizons. Additionalfeatures may be added to give an extended principalprofile form,

(Reference: Norlhcole, K,H, A Factual Key for theRecognition of Australian Soils, Rellim, 1979.)

A description of Australian soils based on The FactualKey is presented in Norlhcote el al. 1975, "ADescription of Australian Soils", Wilke and Co. Ltd., Vic.

FALL-IN (mm)

Subsidence and/or cracking of the ground surface asa result of roof collapse in an underground mine.

FALLOWING (agr)

The management practice' of leaving land in anuncropped siate tor a period of time prior to sowinganother crop. Ils purpose is to allow for theaccumulation and retention of water and mineralisednutrients in the soil, and generally lo also allow for weedcontrol. Fallowing may not necessarily involve filfa ge,but in Australia the term is usually understood to do so.BARE FALLOWING involves stubble removal and weedconlrol by tillage. CHEMICAL FALLOWING involves notillage, weeds being controlled by herbicides. Fallowlenglh may vary from about 1-5 months (short), 6-12months (medium) and up to 20 months or more (longfallow). Concepts of fallow length vary widely aroundAustralia, depending on the climate and crops underconsideration.

FARM PLAN (1ev)

Syn. SOIL CONSERVATION FARM PLAN.

FAST-BREAKING BITUMEN EMULSION(gen)

See BITUMEN EMULSION.

FELDMARK (FJAELDMARK) (alp)

An open alpine communif y of dwarf flowering plants,mosses and lichens, subject lo extremes of cold andwind.

FELLING (for)

The term used to describe the cutting down of trees.lt may incorporate the complete up'rooting of sometrees. See also CLEAR FELLING.

53

FERTILISER (agr)

Any substance, natural or manufactured, added lo thesoil to supply essential plant nutrients for plant growth,and thereby either maintain or increase the general levelof crop yield and pasture productivity. A straightfertiliser supplies only one major nutrient element (i.e.N, P or K). Mixed fertilisers are physical mixtures oI twoor more straight lertilisers, whereas compound fertiliserscontain two or more of the major elements and aremanufactured by chemical reaction. See also PLANTNUTRIENT.

FERTILISER ANALYSIS (agr)

A statement ot the effective composition of a lerliliser.The contents of nitrogen (N), phosphorus (P) andpotassium (K) are generally given in terms of thepercentage content ol each element. For example,12:12:18 fertiliser contains t2 per cent nitrogen, 12 percent phosphorus and 18 per cent potassium.

Information on other nutrients and additives such astrace elements and insecticides may also be given.

FERTILITY (sol)

Syn. SOIL FERTILITY.

FIELD CAPACITY (WATER-HOLDINGCAPACITY) (sol)

The amount of water held in a soil after any excess hasdrained away following saturation. Expressed as apercentage of the oven dry weight of the soil. As ageneral rule, soils are considered to be al field capacityafter draining for 48 hours. Cl. AVAILABLE WATER-HOLDING CAPACITY. See also SOIL WATERPOTENTIAL.

FIELD CULTIVATOR (TINED CULTIVATOR)(eng)

A light secondary tilla ge implement used al depths ofup to 130 mm on tilled soils. Light duty lines arearranged on an overall line spacing ranging from 115to 230 mm, Breakout force is usually in the range 0.3lo 1.0 kN. Field cultivators are widely used with airseeder systems for sowing grain crops.

A held cultivator in travelling mode.

FIELD STRIP CROPPING (agr)See STRIP CROPPING.

FIELD TUNNELLING (gen)

The process of tunnel erosion as ¡t occurs ¡n the field.Usuafly occurs in soils with unstable A2 or B horizonsas a result of flow into cracks, stump holes, rabbitburrows, or other surface irregularities. The downwardmovement of water into the unstable layers, and itssubsequent lateral movement, creates sub-surfacetunnels through which further water and soil material ismoved to an outlet downslope or in the side of a gully.Eventually the surface soil collapses into the enlargedtunnel and a gully is formed. Cf. EARTHWORKTUNNELLING.

FILL (Str)

Material used to raise the surface of an area to adesired level prior to or during earthmoving operations.Usually made up of soil and/or rock material, but mayalso be solid waste.

FILL BATTER (str)

An exposed surface created during earthmovingoperations by deposition of fill, See also BATTER, CUTand FILL.

FILL TOP (11m, str)

A flat built up during earthmoving operations. See alsoDISTURBED TERRAIN.

FILTER BLANKET (str)A layer of sand and/or gravel designed to prevent themovement of fine-grained soils through protectivelinings of channels or batters. For example, a filterblanket placed beneath rip-rap used to stabilise a batterwill reduce movement ot the underlying soil into andthrough the rip-rap. Cf. FILTER CLOTH.

FILTER CLOTH (str)

A synthetic material which allows water to pass throughil but not soil particles. The size of soil particles heldback depends on the mesh size of the material. Its mainuse is to provide a protective lining for earth structures,battes or channels. Cf. FILTER BLANKET.

FILTER DAM (str)

A barrier, embankment or other similar structure, builtof 'pervious materials, such as stones or gabions, andlocated in drainage lines to filter out and store thesediment carried in passing flows. See also SEDIMENTTRAP.

FILTER STRIP (BUFFER STRIP) (for)

A strip of permanent vegetation at least 20 metres widealong each side of a drainage line or banks of awatercourse to retard the lateral flow of runoff, causingdeposition of transported material and thereby reducingsediment movement,

FILTER STRIP (DESILTING AREA) (str)

A strip of permanent vegetation located above dams,diversions and other structures to retard the flow ofrunoff and cause deposition of transported material,

54

thereby reducing sediment toad in the runoff. They maybe contour strips located on long slopes to interceptoverland flow, unmown bands across waterways tointercept flows, or buffer zones around stormwaterinlets. The flatter and wider these strips, the moresediment they will retain. Also applied to strips ofvegetation used to restrict the off-site effects of winderosion.

FINAL VOID (mm)

The excavation remaining at a strip or open-cul minewhen the mining operation has ceased, Because mininghas ceased there is no adjacent material for back-filling.If back- filling is required, material must be carted fromthe out of pit emplacement or obtained from otherexternal sources. The final void is sometimes used asan area to dump mine waste materials prior torehabilitation, for water storage, orto permit access tounderground workings.

FIREBREAK (for, gen)

A cleared or ploughed strip within agricultural orforested land designed to prevent or halt the spread offire. It may also double as a farm track or forest road,Often subject to erosion on steep terrain or erodiblesoils.

FJAELDMARK (alp)

Syn. FELDMARK.

FLAIL SLASHER (eng)See SLASHER.

FLAT (11m)

A general term defining a landform which is neither acrest nor a depression and that is level or very gentlyinclined. See also SLOPE.

FLOCCULATION (sol)

The process by which colloidal or very fine clayparticles, suspended in water, come together into largermasses or loose 'flocs' which eventually settle out ofsuspension. They are easily redispersed, Flocculationdepends on the balance between exchangeable ions onthe clay and those in solution and on the overall ionicstrength of the solution. Ant. DEFLOCCULATION.

FLOOD FREQUENCY (hyd)

See RETURN PERIOD,

FLOOD-OUT (11m)

A flat spreading radially away from a point on the edgeof a stream channel, showing evidence of rapiddeposition of sediment from overbank flow.

FLOODPLAIN (lfm)

A large flat area, adjacent to a watercourse,characterised by frequently active erosion andaggradation by channelled or overbank stream flow,Such areas result from, and are subject lo. inundationby floodwaters. Components may include streamchannel, /evee and backplain. See also ALLUVIALPLAIN.

FLOODWAY (eng)

A long low section in a road which attows ftood watersto ftow across it.

FLOW (hyd)

The movement of a ftuid trom one point to another. tna soil conservation context the term is normatly appliedto the movement of water over a surface or in achannel. Various types of flow are defined as follows:

STEADY FLOW

Flow ¡n which the depth and velocity remainconstant with respect to time.

UNSTEADY FLOW

Flow in which velocity changes either in depth orin direction with respect to time.

UNIFORM FLOW

Flow in which the depth and velocity remainconstant with respect to distance.

NON-UNIFORM FLOW

Flow in which depth or direction changes withrespect to distance. For example, in flow around abend of a pipe the direction changes withdistance, or in flow with changing cross-section thedepth changes with distance.

CRITICAL FLOW

Flow in which the specific energy head is aminimum for a given discharge. Under thiscondition, the Froude number wilt be equal to unity(one) and surface disturbances will not travelupstream.

SUB-CRITICAL FLOW

Flow in which the Froude number is less than unity.For a given crosssection of flow, there is a fixedspecific energy associated with the discharge. Thespecific energy is composed of two parts, thekinetic energy of the water and the potentialenergy of its depth. For a particular value of thespecific energy, two alternate depths of flow arepossible, one which is greater than the criticaldepth and one which is less.

In sub-critical flow the depth is greater than thecritical depth. The potential energy is arger thanthat for the alternative depth and the kinetìcenergy s less, consequently the velocity of flow isslower.

SUPER-CRITICAL FLOW

Flow in which the Froude number is greater thanunity. In super-critical flow the depth is tess thanthe critical depth, The potential energy is less thanthat for the alternative depth and the kineticenergy is greater. Consequently the velocity of flowis greater.

55

FLOW PATH (gen)

Represents a trace of the route along which a fluidmoves as it passes between any two given points ofdifferent elevation. In a soir conservation context itgenerally refers to the route along which runoff movesas it passes from a given point within a catchment orat the catchment boundary to another given pointdownstream or at the catchment outlet,

The flow path of a large natural catchment typicallyincludes the sheet f/ow from the cat chment boundaryto its initial channelisation in a drainage depression,then along a drainage line into a creek and finally infoa river. The mouth of the river is considered the end ofthe flow path. Soil conservation works are used to alterthe natural flow path, especially at the sheet flow stageand/or prior to the watercourse stage, to decrease thepotential for soil erosion.

FLOWLINE (gen)

A well defined route down which water naturallyconcentrates and flows. t is a general terni includingdrainage depression, gu//y, drainage line, creek andriver.

FLUME (eng, str)

A hydrautic structure incorporating an inlet, chute andoutlet, to convey water to a lower level without causingerosìon. It may be constructed of rock, timber, concreteor other relatively permanent material; or it may beformed from local soil material and appropriatelystabilised with vegetation.

Flumes are usually used at the head or side of a gullywhere no alternative natural disposal method or site isavailable. They are also used in association withequipment that measures flow rate or sedimentdischarge. by providing a suitable support for theequipment and concentrating the flows.

Structure of a constructed concrete flume.

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FLUME (Continued)

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Cutoffwall

Formed concrete flume.

56

Formless concrete flume.

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Verandah flume designed

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'4'LVegetated flume, fenced to ensure maintenance of vigorous grass cove,.

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7,'t, J:ttjith a low angle chute to spill runoff well clear of the gully head.

A gui/y wa/i showing fluting.

FLUTING (gen)

A process of lateral gully erosion whereby a series otvertically elongated grooves, called flutes, is created bynIl erosion of gully sides, particularly ¡n dispersible soils,The nilling is caused by runoff flowing down the gullyside- walls which eventually get cut back leaving aseries of narrow buttresses between the flutes. Thesemay become isolated trom the walls to form narrowtapered pinnacles in the gully. These pinnacleseventually collapse due to a combination of furthererosion, slumping and undermining.

FLUX (gen)

The rate of movement of material over a surfaceunconfined by flow boundaries. lt is commonlyexpressed in terms of weight per unit width per unittime.

FOLIAR COVER (ram)

The proportion ot the ground surface covered, over agiven area, by the aerial parts of plants, expressed asa percentage. Cf. COVER.

FOOTSLOPE (11m)

A moderate to very gently sloping landform al the lowerend of a slope, resulting from aggradation or erosionby sheet flow, earth!low or creep.

58

FOREDUNE (csd)

See DUNE,

FORESHORE (gen)

That part of the catchment of a waler storage whichdrains directly into the storage itself without firstentering the watercourse or its tributaries,

FORESIGHT (sur)

The last sight taken before moving the level and alsothe final sight taken during a ievet/ing operation. Seealso BACKSIGHT, INTERMEDIATE SIGHT.

FORMLESS CHUTE SPILLWAY (eng)See SPILLWAY.

FORMLINE SURVEY (sur)

A topographic survey where approximate contour linesare determined using a level or other surveyinginstrument. The survey inlormation can be recorded ona plan or aerial photograph al suitable plotting scale,

FORWARD LAP (rms)

See OVERLAP.

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TWL

STORAGE //

ALLOWANCE FOR:

SE TTLEMENT

WAVE ACTION

SURCHARGE//Dia gramrnatic representation of freeboard in a gullycontrol slructure,

FORWARDING (for)

The carrying of logs fully supported off the ground byvehicles, from t he point of felling to the log dumps. Cf.SN 16G ING

FREEBOARD (str)

The vertical distance between the top waler level andthe crest of a bank, dam or similar structure. Freeboardis provided for in designing such structures, to preventovertopping due to surcharge or wave action. n anearth structure, freeboard should include an allowancefor settlement.

FRICTION HEAD (erg)

The energy tosI due to friction when water flowsthrough a conduit. Depends on the roughness of thesurface over which the, water passes.

FRONTAL DUNE (csd)

See DUNE.

FRONTAL ZONE (csd)

The row of loredunes facing the ocean or other largebody of water. See atso DUNE.

FROST-HEAVE (alp)

The uplifting of a surface by the internal action of frost.Occurs when sub-zero temperatures cause water in thesoil to freeze and form ice crystals. In doing so itexpands, causing upward movement of the soil.

59

INLET SPILLWAY OUTLET

FROUDE NUMBER (eng)A dimensionless parameter expressing the ratiobetween the inertia and the gravitational forces in atiquid.

FV2

g.d

where: F = Froude NumberV = velocity (m/s)g = acceleration due to gravity = 9.8 (rn/s2)d = depth (m)

The Froude number is used to characterise conditionsin flowing water in terms of ils velocity and depth. Forexample, in an hydraulic jump, the state of flow beforeand after the jump is described in terms of the FroudeNumber, so that the height of the jump can becalculated.

FULL (csd)

Syn. BEACH RIDGE.

FURROW (gen)

A narrow longitudinal channel or trench made by aplough or grader. See also CONTOUR FURROW.

G.C.S. (Str)

Syn. GULLY CONTROL STRUCTURE.

GABION (eng)

A rectangutar wire mesh cage filled with rock, brick orsimilar material. The components are usually assembledon site, securely tied together. and used in theconstruction of retaining walls and anti-erosionstructures. See also RENO MATTRESS.

GANGUE MINERALS (mm)

The non-metalliferous or commercially non-valuableminerals contained in an orebody. These normallybecome concentrated in waste dumps following theextraction of the required mineral from the orebody.

GAP ABSORPTION SPREADER BANK (str)See BANK.

GAP SPREADER BANK (str)

See BANK.

GELIFLUCTION (gen)

See CREEP.

GEOLOGIC EROSION (gen)

See EROSION.

Outlet protection constructed of gabions.Those in front of the pipe function as energy dissipators.

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I. .--- -t- .."

60

GEOMORPHOLOGY (gen)

The branch of both physiography and geotogy thatdeals with the form of the earth, the generalconfiguration of its surface, and the changes that takeplace in the evolution of Iandforms.

GILGAI (11m, sol)

Surface micro-relief associated with some clayey soils,consisting of hummocks and/or hollows of varying size,shape and frequency. This phenomenon is a continuingtong-term process due to the shrinking and swelling ofdeep subsoils with changes in moisture content. lt isusually associated with the occurrence of expansivesoils.

Normal gilgai are irregularly spaced and have sub-circular depressions with vertical intervals usually lessthan 300 mm and horizontal intervals usually 3-10 m,They are associated with flat or very gently slopingterrain. Gilgai that deviate significantly from this patterninclude the following main types:

CRABROLE GILGAI

Small mounds and depressions separated by amore or less continuous shelf and the horizontalinterval extends from 3-20 rn.

LINEAR GILGAI

Long narrow parallel elongate mounds and broaderelongate depressions more or less at rightanglesto the contour, usually in sloping terrain. Verticalinterval is usually less than 300 mm and horizontalintervat usually 5-8 m,

LATTICE GILGAI

Discontinuous elongate mounds and/or elongatedepressions more or less at rightangtes to the

61

contour. Usually in sloping terrain, commonlybetween mear gilgai on lower slopes and plains.

MELONHOLE GILGAI

Irregularly distributed large depressions, usuallygreater than 3 m in diameter, sub-circular orirregular and varying from closely spaced in anetwork of elongate mounds to isolateddepressions set in an undulating shelf withoccasional small mounds, Vertical interval is usuallygreater than 300 mm and horizontal interval usually6-50 m.

GLEVING (sol)

The grey or greenish-grey colouration of soils oftenproduced under conditions of poor drainage, which giverise to chemical reduction of iron and other elements.It typically occurs in the clayey lower B horizons of soilssituated in low topographic positions where the watertable remains high for much of the year. See also SOILCOLOUR.

GOAF (mm)

ThaI part of an underground coal mine from which thecoal has been extracted. It may be more or less filledup, by back-filling, but it still remains a generallyunstable area often leading to fa/i-in,

GOOD AGRICULTURAL LAND (lev)

Land which because of its soil, climate, topography andlocation is highly suitable for a form of regularagricultural production, lt may have limitations toproduction requiring significant inputs and/orrestrictions to achieve and maintain long termproductivity, soil fertility and soil stability. See alsoPRIME AGRICULTURAL LAND, UNIQUEAGRICULTURAL LAND.

Melonho/e giigai

GOOD AGRICULTURAL SOIL (lev)

A soil which is highly suitable for a form of intensiveagricultural production but may have physical orchemical limitations which restrict the range of optionaluses available. Significant inputs may be required toachieve and maintain long term productivity, fertility andstability. See also PRIME AGRICULTURAL SOIL,UNIQUE AGRICULTURAL SOIL.

GRADATIONAL SOIL (sol)A soil in which there is a gradual change ¡n soi/ texturebetween the A and B horizons (e.g. loam over clay loamover light clay). The soil is dominated by the mineralfraction and shows more clayey texture grades onpassing down the so/um of such an order that thetexture of each successive horizon changes graduallyto that of the one below, Horizon boundaries are usuallygradual or diffuse. The texture difference betweenconsecutive horizons is less than 1 soil texture groups,white the range of texture throughout the solumexceeds the equivalent span ot one texture group. Seealso PRIMARY PROFILE FORM, SOIL PROFILE,DUPLEX SOIL, UNIFORM SOIL.

GRADE (gen)

The degree of slope of a constructed or excavatedsurface such as a road or batter. May also be appliedto the longitudinal fall of a channel such as in adiversion bank, drain or watercourse, May be expressedas a ratio or percentage.

GRADE BANK (str)

See BANK.

GRADE STABILISATION STRUCTURE(GRADIENT REDUCTION STRUCTURE) (str)

A structure used to stabilise the grade of a gully orwatercourse. The structure allows for the gradualaccumulation of sediment which results in a lesseningof the channel grade above it. This produces adecrease in 110w velocities thereby reducing erosion.Use of a number of such structures, it necessary, alongthe length of a gully, thus assists its long termstabilisation.

In designing such a system, each segment should allowfor a final grade that ensures the stability of thestructure above it. The overall faIt of the gully shouldremain the same but the erosive power of the water islessened because of the 'stepping' effect achieved,

Because flow velocities increase as water passes overeach structure, appropriate measures are required toprevent under and side-cutting, Such measures wouldinclude cut- off walls, wing walls and energy dissipators.

GRADED BANK (sfr)

See BANK.

GRADIENT REDUCTION STRUCTURE (str)

Syn. GRADE STABILISATtON STRUCTURE,

GRADING (gen)

Shaping and/or smoothing an earth, gravel or othersurface by means of a grader or similar implement.

GRADING (sol)

Refers to the distribution of particle sizes in a soit. Awell-graded soit consists of particles that are distributed

A grade stabilisation structure in a large gully,constructed of galvanised iron,

-r'

62

over a wide range in size or diameter. Such a soil's density or bearing properties can normally be easilyincreased by compaction. A poorly-graded soil consistsmainly of par tides nearly the same size, or is deficientin particles of a certain size, Because of this, the soil'sdensity can be increased only slightly by compaction.An assessment of the grading of a soil can be madeby particle size ana/ysis and is important to determinethe behaviour of a given soil when used in soilconservation earthworks,

GRASSED WATERWAY (str)

See WATERWAY.

GRAVEL (sol)

A mixture of coarse mineral particles larger than 2 mmbut less than 75 mm in equivalent diameter.

GRAVEL ENVELOPE (eng, uit)

Gravel, sometimes mixed with sand, placed around asub- surface drain to facilitate the entry of water into itbut to prevent the entry of all but the finest particles.

GRAVEL OUTLET (eng, urb)

Gravel placed to function as a filter at the outlet of abank or other structure which ponds sediment-ladenrunoff. The outlet may sometimes incorporate a core ofhay bales to assist sediment entrapment.

GRAVITATIONAL CREEP (gen)

See CREEP.

GRAZING CAPACITY (ram, agi-)

The maximum stocking rate possible which grazing landcan support in the long term without deterioration, Cf,CARRYING CAPACITY,

GREAT SOIL GROUP (sol)

A soil classification category in which soils are classifiedaccording lo their mode of formation as reflected inmajor morphological characteristics and profile form.

The grouping depends on an appraisal andinterpretation of features such as the colour, texture,structure and consistence of soil material, the varioushorizons in the soil profile and the nature of theboundary between horizons. A widely usedclassification of Australian soils, major developments ofwhich have been set out in 'A Manual of AustralianSoils' (Stephens, CG. 1962) and 'A Handbook ofAustralian Soils' (Stace H.C.T. et al. 1968).

GREEN MANURE CROP (agr)

A crop grown primarily to provide a source of organicmatter to the soil. lt is normally incorporated into thesurface soil by mechanical means, thereby, uponbreakdown, providing a source of organic nutrients forsubsequent field crops or existing row crops, such asvines or orchard trees. Green manure crops are typicallyteguminous, for example, lupins, vetches or peas, andare generally incorporated when flowering or, on lightsoils, before they have utilised excessive amounts ofsoil moisture.

GRID REFERENCE (lev)

A code for the identification of a point or location on amap or plan. Co-ordinates are stated on the edge ofmap sheets and the reference is always defined byquoting the easting value first followed by the northingvatue.

GRID SURVEY (lev, sur)

A survey which establishes spot elevations in a regularpattern (generally square) over an area in such amanner that detailed information (e.g. contours) can beportrayed at an appropriate scale.

The term may also be used to describe such surveyscarried out for the collection of land resource data, forexample, soil and vegetation type surveys.

GROUND COVER (agi)

A vegetative layer of grasses and/or other lowgrowingplants or plant residues providing protection to the soilagainst erosive agents. A good ground cover is anessential part of the majority of soil conservationprograms. Generally a percentage ground cover of 75per cent or more is needed to give adequate protectionagainst soil erosion. See also COVER.

GROUND TRUTH (rms)

The measurements or observations collected byequipment or personnel in the field for the purpose ofverifying an interpretation made From remotely senseddata. Results of analysis of such data are dependenton the field information since it provides a comparisonof accuracy between the images and the actual on-siteconditions. See also AERIAL PHOTOGRAPHINTERPRETATION.

63

GROUNDWATER (gen)

Subsurface water contained in a saturated zone of thesoil and/or a geologic stratum, lt is at a pressure equalto or greater than atmospheric pressure and willtherefore flow out into a well or at the earth's surface.See also WATER TABLE.

GROYNE (eng, csd)

A wall usually built perpendicular to the shoreline, totrap material moved by littoral dritt and/or to retarderosion of the shoreline. Similar structures are also usedto protect river banks from erosion. Groynes arecommonly constructed of large rocks, concrete, piles orother relatively permanent materials,

GULLY (gen)

An open incised erosion channel in the landscapegenerally greater than 30 cm deep. Gullies arecharacterised by moderately to very gently inclinedfloors and precipitous walls. They form by a complexof processes dominated by concentrated surface waterflow and hence are frequently found in drainage lines,Major flows only occur in gullies during and/orimmediately after periods of heavy rainfall.

Gullies vary widely in shape, depending on soil type,landform and the hydrological regime of the catchment,They may be wide in relation to depth or vice-versa, andmay be of "U" or 'V" cross-section.

See also GULLY EROSION, GULLY HEAD, RILL.

The presence of this gufly means that the land cannot beused to its full potential.

-

GULLY CONTROL STRUCTURE (GCS) (str)

A constructed wall or other barrier of earth, concreteor masonry, incorporating a stable outlet, which entrapsrunoff in a gully or drainage line as part of a scheme ofgully erosion control. lt can also act as a sediment trap,diversion bank or gully crossing.

The primary purpose of such a structure is to controlthe flow of runoff into or along a gully, thereby reducingerosion. Appropriately sited, the structure may alsoprovide for drowning of the gully head, thus restrictingheadward erosion. The inclusion of a stable outletassists safe disposal of surplus runoff so that the gullybelow the strucfure, if not filled in, can stabilisenaturally.

The siting of a GCS is important in a scheme of erosioncontrol. lt may depend on: the availability of suitableconstruction material; the achievement of a highsforage/ excavation ratio; the need to control erosionin the drainage line; the location of fencing and thepossible role of the structure as a watering point forstock; and/or the need to dispose of or divert runofffrom other soil conservation structures.

The design of such a structure s dependent on: itslocation; the size of the catchment above it and theassociated land use: availability of a suitable site for thespillway and disposal of overflow; the nature of the siteselected and the construction materials available there;and its relationship to other soil conservation structures,

The construction of a GCS involves on-siteconsideration of: the nature of the site chosen; thenature and moisture content of soil materials availableif used in construction; the conditions occurring at thetime of construction; and the equipment available inrelation to the size of structure required. Importantfactors in the construction of an effective earthen GCSinclude: compaction of the material in the wall at or nearoptimum moisture content; keying of the wall by wayof a core trench in suitable material, particularly whenbuitt across a gully; topsoiling and seeding of the finalwall and surrounding areas above top water level: andadequate spillway installation.

GULLY EROSION (gen)

See EROSION.

GULLY FILLING (sfr)

Placing material, by mechanical means, in a gully toraise its floor, and subsequently shaping it to a uniformcross- section and stabilising it to minimise the potentialfor further erosion. The aim of gully filling is to revertthe area lost through channel incision back to its originalproductive capability.

The till may include soil and rock materials, usuallyexcavated from within the immediate vicinity of thegully, but should exclude material that will rot, rust orcreate voids that form a nucleus for funnel erosion orlead to subsidence. The surface layer of fill should betopsoil to ensure a suitable medium for plant growth.

GULLY HEAD (gen)

The upstream end of a gully where runoff from thecatchment above falls to the gully floor. lt is theexposed part of the gully upon which erosive forces,

64

including water flow, splash and seepage, act to causethe gully to extend upstream by headward erosion.

See also GULLY, OVERFALL.

GULLY HEAD SILL (str)

A short bank, with a sill at each end, used above gullyheads to reduce the energy of inflow.

GULLY PROFILOMETER (gen)

See PROFILOMETER.

GULLY RE-ENTRY (gen)

Provision made for runoff, diverted from a gully head ina scheme of erosion control, to be brought back intothe gully by way of a flume or drop structure, at a pointlower down the flowline, without creating a furthererosion hazard,

GULLY SHAPING (str)

Physical reorientation of the sides ot a gully, bymechanical means, to create a uniform cross-sectionthat will cater for expected flows! without substantiallyraising the level of the gully floor. Gully shaping includestopsoiling of exposed or created surfaces and theirrevegetalion to minimise the potential for future erosion.

GULLY TRIMMING (str)

The removal of the upper edge of a gully side, bymechanical means, with the aim being to decrease thepotential for lateral erosion by creating a stable gradientalong the gully side, Gully trimming should includetopsoiling of the exposed surfaces and theirrevegetation. Material removed is generally incorporatedin the reshaped gully side, decreasing its gradient andthus, aiding gully stabilisation.

Gully trimming is not intended to raise or alter the floorof a gully and it is typically undertaken on deep gullieshaving stable floors.

GYPSUM (sol)

A naturally-occurring soft crystalline mineral which is thehydrated form of calcium sulphate, having the formulaCaSO42H2O. Deposits occur mainly in arid inland areasof Australia. Contains approximately 23 per cent calciumand t8 per cent sulphur.

This mineral is also a by-product ot the manufacture ofphosphoric acid. Such by-product gypsum, also calledDUMP GYPSUM, is more variable in quality, particularlywith respect to moisture content.

Gypsum is normally used as a soil ameliorant toimprove soil structure and reduce crusting inhardsetting clayey soils. The applied calcium increasessoil aggregation, which results in improved waterinfiltration, seed germination and root growth. Typicalrates used are up to 5 tonnes/hectare, with heavierrates being required on highly sodic soils.

Gypsum is also a useful source of nutrient calcium andsulphur, and can also be used for clearing muddy waterin dams.

N.B.lt is suggested that any unknown gypsum betested for flocculaling potential before use.

I DU I

HARDPAN (sol)

Syn. PAN.

HARDSETTING (sol)

The condition of a dry surface soil when a compadt,hard and apparently apedal condition prevails. Becauseof this characteristic such soils tend to give rise to highrates of runoff compared with better structured soifs.Clods formed by the tillage of hardsetting soils usuallyretain the con dition until completely broken down byfurther tillage operations.

Soil on which surface sealing develops may or may notbe hardselting - a surface seal is not a criterion for thehardsetting condition. The majority of soils throughoutthe wetdry climatic zones of Australia set hard in thedry season. Soils which do not set hard are pedal inthe dry, as well as in the moisi state (clay loams, clays).or are single-grained (sands). Cl. SELFMULCHING.

HARROWING (agr)

A procedure involving the pulling of a light fined or disc-type implement over the land surface. In an arablesituation it involves surface soil tiltage to break up andredistribute soil aggregates to achieve a moresatisfactory seedbed, and in some instances lo controlweed growth. In a pasture situation it may be used forweed control, manure or plant residue spreading and/or surface soil aeration.

In a stubble refont ion system. harrowing may be usedo level heaps of stubble and soil ridges, and to kill

young weeds.

60320-15204-5

65

HAY BALE BARRIER (gen, urb)

F-lay bales placed in the path of sediment-laden runoffto filter out sediment as the runoff passes through them.For example, hay bales could be placed lengthwise, insingle or double rows, around a construction site,forming a perimeter bank, to contain sediment within it.Each bale should be securely anchored and embeddedinto the soil to a depth of 10 cm.

HEAD (eng)

The height of water above any plane of reference. Itdeter mines the hydraulic head between the watersurface and the plane of reference, which may causethe water to flow lo the lower level.

HEAD WALL (eng)

A watertight barrier al the entrance to a hydraulic structure. Its primary purpose is to prevent seepage fromunder mining the structure.

HEADWARD EROSION (gen)

See EROSION,

HEIGHT DIFFERENCE (sur)

The ',artical relationship between points on the earth'ssur face, which may be related to specific referenceplanes, such as sea level. In surveying, height differenceis determined by reduction of levelling observations ortrigo nometric levelling.

A hardsetting surface soil. Note its compact andapparently apedal condition.

HEIGHT EXAGGERATION (rms)

See DISTORTION.

HERBICIDE (WEEDICIDE) (aqr)

A chemical substance used for killing plants, usuallyweeds. Such substances are typically concentrated andhave to be diluteo with waler prior to spraying on tothe soil, the growing crop or an area infested withweeds.

Herbicides act in a variety ol ways and are commonlyused to control weeds in a conservation ti/la ge program.Their use is controlled by legislation which requireseach herbicide to be registered for general or specificusage, details of which are set out on its container.

The following main types are in use:

SELECTIVE HERBICIDE

A herbicide used to kill some plants but not others.It is usually applied to a growing crop in order tokill weeds without adversely affecting the crop.Selectivity depends on the different growth habit,phy siology or growth stage of the target weedscompared with that of the crop. Ant. NON-SELECTIVE HERBtCIDE.

NON-SELECTIVE HERBICIDE

A herbicide used to kilt all plant species in the areabeing treated. Ant. SELECTIVE HERBICIDE.

CONTACT HERBICIDE (DESSICANT HERBICtDE)

A herbicide which only affects those parts of plantswith which it is in contact. Such herbicides can beeither selective or non-selective in action,depending on the rate of absorption of thechemical and/or the growth habit of plantssprayed. Ant. TRANSLOCATED HERBICIDE.

TRANSLOCATED HERBICIDE

A herbicide which is applied to the exposed aerialparts of plants (teaves and stems) and is thenabsorbed and transferred vìa the plants' vascularsystem to roots and underground parts. They lendto have slower and more widespread effects thancontact herbicides, which may include thedestruction of chlorophyll. pre vention of rootgrowth, interference with growth buds and themovement of nutrients within the plant. They canbe selective or non-selective in action, dependingon the physiology of the plants sprayed. Ant,CONTACT HERBICIDE.

KNOCKDOWN HERBICIDE

A herbicide typically applied to plant foliage andwhich is only active for a short duration. Such herbicides may be contact or translocated in theirmode of action.

RESIDUAL HERBICIDE

A herbicide which is applied to the soil where itper sists and from which it is taken up bygerminating seedtings and established weeds. Theperiod of acti vity is determined by the rate ofapplication, the soil type and the susceptibility ofthe plants being controlled, but typically is much

66

longer than that of a knockdown herbicidé. Theaction of a residual her bicide may be selective ornon-selective.

PRE-EMERGENT HERBICIDE

A herbicide which is applied lo the soil surfaceafter the crop has been sown, but before itemerges. Such herbicides are mainly setectiveresidual or non- selective contact in action, but afew non-selective translocated herbicides are alsoavailable. Selective residuat herbicides areincorporated by rain or, on rare occasions, by veryshallow cultivation.

PRE-SOWING HERBICIDE

A herbicide which is applied to kill growing or germinating weeds prior to sowing of the crop. Suchher bicides mainly include transtocated andcontact non-selective types or selective residualtypes which require rain or mechanicalincorporation into the soil.

Pro-sowing herbicides are often inctuded with thepre- emergent group in the literature.

POST-EMERGENT HERBICIDE

A herbicide apptied after the crop has emerged.Such herbicides are of the contact or translocatedtypes which are setective in action.

HIGH WALL (mm)

A steeply sloping rock face from which material is beingexcavated in an open-cut mine. See also LOW WALL.

HILLCREST (tim)

A very gently inclined to steep, smoothly convex crest,standing above a hi//slope, usually representing the topof the interi/uve between drainage lines, Hillcrest soilsare typically shallow, and they are eroded mainly bysheet flow.

HILLOCK (tim)

A smatt hill incorporating a narrow crest and itsadjoining slopes. The crest tength is less than the widthof the adjoining slopes. Cf. RIDGE.

HILLSLOPE (11m)

A gently inclined to precipitous tandform usuallycomprising sidesfopes and footslopes.

HIND DUNE (csd)

See DUNE.

HOBBY FARM (gen)

A type of land devetoprnent, irrespective of altotmentsize, involving some form of agricultural enterprisewhich is secondary to the owners main line of business.Activities vary according to factors such as income, sizeof holding, knowledge of agricultural systems and thesuitability of the holding for various agriculturalenterprises. In a soil conservation context, judiciousmanagement strategies should be adopted toadequately provide for soil erosion control.

HORIZON (sol)

A general term used to describe individual ayers withina soil. See also SOIL HORIZON.

HORIZONTAL INTERVAL (str)

The horizontal distance from one soil conservationstructure to another. For practical purposes whenapplied to banks no distinction is made between truehorizontal distance and the actual distance along theground, as banks are not normally used on steep slopeswhere the difference would be signifi cant.

See also BANK SPACING.

HOSE LEVEL (sur)

See LEVEL,

HUE (sol) See SOIL COLOUR.

HUMUS (gen)

The more or tess stable traction of soil organic matterremaining after plant and animal residues havedecomposed. See also O HORIZON.

HYDRAULIC CONDUCTIVITY (sol)

The flow of water through soil per unit ot energygradient. For practical purposes it may be taken as thesteady-state percolation rate of a soil when in filtrationand infernal drainage are equal, measured as depth perunit time.

HYDRAULIC EFFICIENCY (hyd, Str)

Characterises the economic design and performance ofa chan nel for carrying maximum flows with minimumcross-sectional area and tow maintenance requirements.consistent with low erosion hazard. The most efficientchannels are (hose having a semi-circular cross-section.However, in practical terms for the construction ofvegetated channels, a trape zoidal shape most closelyapproximates that ot a semi-circle in terms of hydraulicefficiency.

HYDRAULIC HEAD (eng)

The energy, either kinetic or potential, possessed byeach unit weight of a liquid expressed as the verticalheight through which a unit weight would have to fallto release the average energy possessed. See alsoHEAD.

HYDRAULIC JUMP (STANDING WAVE) (eng)

An abrupt rise occurring in the surface of a liquid whena high velocity flow discharges into a zone of lowervèlocity. lt occurs in open channel flow and isaccompanied by violent turbulence. May also bedefined in terms of the sudden change from super-critical tlow to sub-critical tlow.

HYDRAULIC MEAN DEPTH (hyd)

Syn. HYDRAULIC RADIUS.

67

HYDRAULIC RADIUS (HYDRAULIC MEANDEPTH) (hyd)

The ratio of the cross-sectional area 'A of a liquidflowing in a channel, to the wetted perimeter P' of thatchannel.

Symbol R = (metres).

See also MANNING'S FORMULA.

HYDROGRAPH (hyd)

Graphical representation of flow rate with respect totime, The area under the resulting curve represents thetotal amount of runoff from the rainfall event in question.The most common form of hydrograph is produced bya stage recorder.

Equivatent data can be cotlected by digital equipmentand later transformed into a graphical form if required.Analysis of the data obtained by either method can beused to determine a range of hydrologicalcharacteristics such as peak discharge, maximumstream height and total volume ot discharge.Knowledge of these characteristics is essential to thedesign of effective soil conservation works.

HYDROLOGIC CYCLE (hyd)

The continuous interchange of water between land, seaor other water surface and the atmosphere. lt hasneither beginning nor end, as water evaporates and islifted, carried and temporarily stored in the atmosphereuntil it finally precipitates. The precipitated water maybe inter cepted or transpired by plants, may run off overthe land surface or may infiltrate into the soil, Much ofthe inter cepted water and runoff is returned to theatmosphere by evaporation. The infiltrated water maybe temporarily stored as soil moisture andevapotranspired; percolate to deeper zones to bestored as groundwater which may be used by plants;flow out as springs; or seep into tlowtines and onceagain evaporate into the atmosphere. (Refer: Gray, DM.Handbook on the Principles of Hydrology. CanadianNational Committee for the International HydrologicalDecade, 1970.)

HYDROLOGY (gen)

The study of water and water movement in relation toland and soit. In the soil conservation context it isconcerned particularly with surface runoff and its effectsin causing soit erosion.

HYDROMULCHER (gen)

Syn. HYDROSEEDER.

HYDROMULCHING (gen)

A procedure whereby a mixture of seed and fertiliserand/or mulching material is applied in a water slurry toexposed soil surfaces for revegetation purposes. Themulching material is applied at heavier rates than inhydroseeding in order to provide a layer of mulch toprotect the soil sur face and create a suitable micro-environment for germinating seeds. A coloured dye is

interceptionj I Ra/nfall ILoss"

- tnterieption4t) toragel

IIInfiltraon4

Percolationj " pression- InterfioStore' Storage

.iPercolation

Water Table

HYDROMULCHING (Continued)

usually mixed into the slurry in order to observe arealcoverage as lhe operation proceeds.

Where heavy mulch applications are necessary, suchas on a rocky surface, an initial application of seed andferfitiser (hydroseeding) followed by an application ofmulch may be required to ensure success.

Hydromulching is a fast and efficient method ofstabilising disturbed areas immediately afterconstruction operations are complete. lt is particularlyapplicable on areas where a harsh growing environmentoccurs or where a low level of growth medium ispresent. Little prior treatment of the exposed surfacesis required except tor runoff control, which is necessaryto prevent the removal of material by surface flows. Seealso HYDROSEEDER.

Transpirationfc ; Soil

-'Evaporation/

68

Ground WaterFlaw

0'e ,Evaporohon Evaporation

StreamChannel

...,,.,. ,. . -s-..¶:''-t A.

Ocean

The hydrologic cycle.

HYDROPHOBIC SOILS (sol)

Syn. WATER-REPELLENT SOILS.

HYDROSEEDER (HYDROMULCHER) (gen)

A machine used to facilitate hydroseeding orhydromuiching on sites remote from it. This is achievedby spraying the seed/fertiliser/mulch slurry directly onto the exposed sur face through a pivoted nozzte, Themachine is most f re quently used for batter stabilisation,and the treatment of inaccessible sites or areas whichcannot be sown using con ventional agriculturalmachinery.

A hydroseeder spraying a road batter,

r-"t

Cloud

HYDROSEEDING (gen)

A procedure whereby a mixture of seed, fertiliser andmulching material as a carrier is applied in a waler slurryto exposed soil surfaces for revegetation purposes.Common materials used as carrying agents are woodand paper pulp. A cotoured dye is usually mixed intothe slurry in order to observe areal coverage as theoperation proceeds.

F-lydroseeding is a fast and efficient method ofstabilising disturbed areas immediately afterconstruction operations are complete. lt is particularlyapplicable where an ade quate level of growth medium,such as respread topsoil, is present. Where such amedium is not present, hydromulching is preferred. Inboth cases little prior treatment of the exposed surfacesis required except for runoff control, which is necessaryto prevent the removal of material by surface flows, Seealso HYDROSEEDER,

o

ILLITE (sol)

Clay material comprising a group of aluminositicatemica minerals of indefinite chemical composition with a2J crystal lattice structure, lt's properties are generallyintermediate between those of kao/inite andm ont mo ri/Ion ire,

ILLUVIATION (sol)

The process of deposition of soil material in the lowerhorizons of a soil as a result of its removal from upperhorizons through eluviation. Materials deposited mayinclude clay, organic matter and iron and aluminiumoxides.

IMAGE (rms)

The recorded representation ot an object produced byoptical, electro-optical, optical-mechanical or electronicmeans. lt is a term that is typically used when theetectrornagnetic radiation emitted or reflected from ascene is not directly recorded on film as is the case witha photograph.

IMAGE ENHANCEMENT (rrns)

The manipulation of a subset of the availableinformation content of a photograph or other image tofacilitate sub sequent interpretation. The process isutitised to sift out a lot of extraneous information notrelevant to the project. For example, during filmprocessing it may be exposed for longer than normalto enhance a particular grey or colour shade.

IMAGING SYSTEM (rms)

See REMOTE SENSING SYSTEM.

69

IMPACT BLOCK (eng)

A solid block ot concrete, or similar permanent materialwhich is located in the path of flowing water to functionas an energy dissipator.

IMPERVIOUS (sol)

Describes a soil through which water, air, or rootspenetrate slowly or not at all, No soil is absolutelyimpervious to water and air all the time,

IMPROVED PASTURE (agi)

See PASTURE,

IN SITU (gen)

A term meaning 'in place'. Normally applied to rocks,fossils and soils which are situated in the place wherethey were originally tormed or deposited. When usedto describe soils, it usually refers to those formeddirectly from and on bedrock, As with other latin words,the term should be printed in italics thus ' in situ,

INCIPIENT DUNE (csd)

See DUNE.

INCISED DRAINAGE CHANNEL (If m)

A channel in the land surface having distinct bed andbanks and which carries perennial or ephemeral waterflows. Normally used in the context of mappinglandform where a distinction between types of flowlinesis not required.

INCLINED PIPE SPILLWAY (eng, str)See SPILLWAY,

INCREASER (ram)

A term used to describe a plant species, theabundance of which in a particular soil-vegetationassociation shows a positive correlation with grazingpressure. Ant, DECREASER, See also INDICATORSPECIES.

INDICATOR SPECIES (gen)

A term used to describe a plant species which ischarac teristic of particular tandforrns or edaphicenvironments,

INDICATOR SPECIES (ram)

A term used to describe a plant species, theoccurrence or abundance of which can be used toindicate levels of range land condition for a particutarsoil-vegetation association, See also DECREASER,DESIRABLE, INCREASER. INTERMEDIATE, INVADER.UNDESIRABLE,

INDURATED (sol)

Rendered hard. Refers to the hardening of sedimentsinto rock or soil layers into pans by heat and/orpressure and/or cementation,

INFALL (for, gen)

See CROSSFALL DRAINAGE.

INFILTRABILITY (soi)

A general term used to describe the capacity of the soilto lake in water at its surface, depending largely onsurface texture and structure. See also INFILTRATION.

INFILTRATION (sol)

The downward movement of water into the soil. lt islargely governed by the structural condition of the soil.the nature of the soit surface including presence ofvegetation, and the antecedent moisture content of thesoil. See also RUNOFF COEFFICIENT.

INFILTRATION BASIN (eng, urb)

An excavation in highly permeable soils to temporarilystore runoff directed into it. The stored water drains byinfiltrating into the soil, thereby reducing runoff from theadjacent site. Such basins are normally excavated ator very close to the source of runoff, and are typicallyused on individual residential, commercial or industrialallotments.

INFILTRATION RATE (sol)

The rate at which water moves downward into the soilat any given time. lt is measured as volume flux per unitof sur face area, n un,ts of mm/h.

Runoff occurs when the rainfall (ate exceeds the infiltration rate for a given soil condition. The saturated (or'steady-state') infiltration rate is the rate which occurswhen the soil is saturated and infiltration and drainageare equal. See also HYDRAULIC CONDUCTIVITY.

INFILTROMETER (sol)

An apparatus for measuring infiltration,

INLET (eng, str)

The entrance ot any structure through which water mayflow. It may be a simple grate at the entrance to a pipe,a complete entrance structure such as in a drop inletcu/vert, or merely the entry point at which water flowsinto a channel.

INOCULATION (agr)

The introduction of a pure or mixed culture of micro-organisms into the soil. This is usually achieved bymixing the inoculant with the seed at sowing time orby coating the seed with it prior to sowing.

The aim of this procedure is to enhance the germinationand/or growth of plants. It is typically used to improvelegume stands by introducing the appropriate rhizobia,which are nitrogen-fixing bacteria associated withlegumes.

INSTABILITY HAZARD (gen)

The susceptibility of the land surface to displacementby mass movement. Usually related to the occurrenceot unstable soils and landtorms. For example a highinstability hazard would exist in a slip-prone area.

70

INSTRUMENT HEIGHT (sur)

Generally the difference in height between thetelescope axis of the instrument and its plumbedground mark. It can, however, be relative (vertically) toan adjacent reference mark.

INTEGRATED LOGGING (for)

See LOGGING.

INTEGRATED MAPPING UNIT (lev)

A map unit relating to a number of individual /andresource attributes in a composite form such thatparticular features of those individual attributes are notnecessarily immediately identified but can still bederived. The use of integrated mapping units facilitatesevaluation of resource data by relating individualattributes lo each other or in various combinationswhilst still enabling individual attn bute maps to bederived. Using an integrated mapping unit system forcollecting data is less time-consuming than mappingeach individual resource separatety. Cf. SINGLEATTRIBUTE MAPPING UNIT.

INTERCEPTION LOSS (hyd)

Describes that portion of rainfall which is caught byvege talion but subsequently evaporates. See alsoRUNOFF COEFFICIENT. Cf. INTERCEPTION STORAGE.

INTERCEPTION STORAGE (hyd)

Describes that portion of rainfall which is caught andstored on vegetation. In forests interception can amountto tO to 15 mm white in crops it may be only 0.5 to imm. The rate of interception is initially high but theavailable capacity is rapidly tilled so its ability to reducerunoff rates within a given catchment is relatively small.See also RUNOFF COEFFICIENT. Cf. INTERCEPTIONLOSS.

INTERCEPTOR BANK (str)

See BANK.

INTERCEPTOR DRAIN (eng)

See DRAIN.

INTERFLOW (hyd)

Shallow seepage flow, usually occurring within duplexsoils.

INTERFLUVE (If m)

The area of land between two adjacent bw/ines.

INTERMEDIATE (ram)

A term used to describe a perennial or annual plant,the abundance of which in a particular soil-vegetationasso ciation changes with increasing grazing pressure,initially by increasing its abundance but subsequentlydecreasing under heavy grazing. See also INDICATORSPECIES.

INTERMEDIATE CROP (agr)

See COVER CROP.

INTERMEDIATE SIGHT (sur)

The sight taken alter a backsight has been observedand before a foresight is taken. Intermediate sights arenot taken to change points. It a point being observedis an important one, the observation should be bookedas a fore sight so that the observation is included inthe mathemati cat check of the levelling operation.

INTERNAL DRAINAGE (PROFILEDRAINAGE) (sol)

The rate ol downward movement of water through thesoil governed by both soit and site characteristics. lt isassessed in terms of soit water status and the lengthof lime horizons remain wet (soit hotus exudes wat..,rwhen squeezed). It can be difficult to assess in the fieldand cannot be based solely on soit profite morphology.Vegetation and topography may be useful guides. Soilper mea hi/it y, ground water level and seepage are alsoimpor tant. The presence of mottling oflen, but notalways, reflects poor drainage.

Categories are as follows: Very poorly drained: Freewater remains at or near the surface for most of theyear. Soils are usually strongly p/eyed, Typically a levelor depressed site and/or a ctayey soil.

Poorly drained: Att soit horizons remain wet for severalmonths each year. Soils are usually gleyed. stronglymottled and/or have orange or rusty linings of rootchannels.

Imperfectly drained: Some soit horizons remain wet forperiods of several weeks. Subsoils are often mottledand may have orange or rusty linings of root channels.

Moderately welt drained:Some soil horizons may remainwet for a week after waler addition. Soils are oftenwhole coloured but may be mottled at depth and ofmedium to ctayey texture.

Welt drained: No horizon remains wet tor more than afew hours after water addition. Soils are usually ofmedium texture and not mottled.

Rapidly drained: No horizon remains wet except shortlyafter water addition. Soils are usually of course tex ture,or shallow, or both, and are not mottled. Cf. SITEDRAINAGE.

INVADER (ram)

A term used to describe a plant capable of establishingon new sites and subsequently dominating those areason which it was formerly scarce or absent, The invasionusually occurs as a result ot some change in landmanagement such as grazing pressure, cropping or fire.See also tNDICATOR SPECIES.

INVERT (eng)

The lowest portion of the internal surface of a channelor pipe. Where trick/e flows occur in earth channels, theinvert may have to be lined with concrete or similarmaterial to prevent erosion.

71

A concrete-lined invert carrying trickle flows in an urbansubdivision.

IRRIGATION SALTING (gen)

See SALTING,

ISOHYET (gen)

A tine on a map joining centres which receive equalamounts of rainfall.

ISOVEL (hyd)

A line representing points of equal velocity. Isovels areused to graphically demonstrate the distribution of f?owvelocities in channels.

Pinning jute mesh to hold it in place along a waterway.

dJ

JUTE MESH (agr)

A coarsely woven material of jute yarn which is biodegradable. Normally used in conjunction with anionicbitumen emulsion, il provides a useful technique oferosion control for disturbed areas where there is animmediate need to handle channelised flows. Thetreatment provides protection during establishment ofa permanent plant cover.

AppUcations include catch drains above batters, labtedrains or any channel situation where vegetativestabilisa tion is required. lt may also be used to assistin the revegetation of batters,

The site should be caretutly prepared, then sown andfer titi sed prior to pinning the jute mesh firmly to theground surface. A ayer of mulch may also be appliedbefore pinning. The treated site should not be traversedby vehicles.

72

KAOLINITE (sol)

Clay material comprising a group ot aluminosilicaleminerals with a li crystal lattice structure. They aregenerally stable clays with low shrink-swell potentialand tow cation exchange capacity. See also ILLITE,MO NTM OR IL LON ITE

KEY (str)

The zone at the base of an earth embankment whichprovides a bond between the embankment and thesurface on which it is constructed. Usually achieved bydeep ripping the surface prìor to placement of the firstlayers of embankment material. lt is of considerableimportance in the construc lion of soil conservationearthworks such as banks and gully control structures.

KEY BANK (str)

See BANK.

KEY LINE (agr)

The base line in a strip cropping plan, parallel to whichthe strips are laid out, lt is essentially a line of best fitwhich allows the strips to be put in as close as possibleto the contour,

KNOCKDOWN HERBICIDE (agi)

See HERBICIDE.

EL

LACUSTRINE FLAT (If m)

The large flat area exposed in a dry lake bed, typicallycharacterised by the presence of accumulated lakesediments,

LAGOON (Ifni)

A natural closed depression tilled with water that is typically salty or brackish, bounded al least in part by formsaggraded or built up by waves or reef buildingorganisms.

LAKE (Ifni)

A natural closed depression facilitating the collection ofrunoff and its storage as still water.

LAND (gen, lev)

The surface of the earth's outer crust not covered bybodies of water. The term land is also used in acomprehensive, integrating sense to encompass thephysical environment within a profile from theatmosphere above the earth's sur face down to somemetres below the surface. Land therefore includesclimate, landform, soifs, hydrology and vegetation, tothe extent that these influence potential for land use.

LAND APPRAISAL (1ev)

The survey, classification and evaluation of landresource data to assess and predict the performanceor response of land when used for specified purposesunder given manage ment. lt provides informationnecessary for decisìons on the use and managementof land, and socioeconomic factors form part of theappraisal.

The aim of land appraisal is to provide planners andland use decision makers with comprehensive dataupon which to make inlormed and use policies and toimplement these in an efficient and effective manner. ltis also a most useful approach to resolving problemsbetween alternate and conflicting land uses andchanging land use patterns; enabling betterunderstanding and appreciation of the effects of landuse on the environment; and providing a mechanism forpublic participation in the land use planning process.

73

LAND CAPABILITY (lev)

The ability of land to accept a type and intensity of usepermanently, or for specified periods under specificmanage ment, without permanent damage. lt is anexpression of the effect of biophysical land resources,including climate, on the ability of land to sustain usewithout damage under various uses, such as cropproduction requiring regular tillage, grazing, woodland,or wildlife. Land capability involves consideration of;

the various land resource attributes;

* the production to be obtained from the land;

the activities or inputs required to achieve thatproduction;

the risks of damage lo the land, on-site or off-site,resulting from those activities; and

* the inter-relations of the above.

Land capability is included in land suitability and in ilsmost highly developed forms may approach the latter.

If the land is used beyond its capability it ultimatelyloses its productive capacity. Therefore, land capabilityforms an essential basis for land use planning.

See also RURAL CAPABILITY, URBAN CAPABILITY,RECREATIONAL CAPABILITY.

LAND CAPABILITY CLASSIFICATION (lev)The systematic arrangement of land into variouscategories according to their capability for particularland uses and the treatment required to sustain thoseuses without land degradation.

In a soil conservation context, land capability classification is based on a balance between usage andconservation measures which allow the most intensiveuse of the land without soil erosion and with apermanently sustained level of usage. It relates to thedegree of hazards and limita tions in managing the land,and thus the classification is primarily concerned withthe risk of erosion.

See also RURAL CAPABILITY CLASSIFICATION,URBAN CAPABILITY CLASSIFICATION.

LAND CLASSIFICATION (lev)

The systematic arrangement of land into variouscategories based on selected properties of the land orits potential tor some particular purpose. Landclassification varies essentially from the geneticapproach, where land is sub divided into natural regionson the basis of environmental factors, to the parametricapproach where land is subdivided by mapping keyattributes, such as slope and terrain com ponent, inquantitative terms.

LAND DEGRADATION (gen)

The decline in quality of natural land resources,commonly caused through improper use of the land byhumans.

Land degradation encompasses soil degradation andthe deterioration of natural landscapes and vegetation.It includes the adverse effects of overgrazing, excessive

LAND DEGRADATION (Continued)

ti//age, overc/earing, erosion, sediment deposition,extractive industries, urbanisation, disposal of industrialwastes, road consiruction, decline of piani communitiesand the effects of noxious plants and animals.

LAND IMPRINTER (ram, eng)

A heavy roller with a criss-cross pattern which impartsa series or indentations to the soil surface to assistretention of rainfall on rangeland. The pattern of ridgesand furrows thus formed also help to restrict wind andwater erosion.

Land Im printer

LAND INFORMATION SYSTEM (gen)

A mapping and land information data base designed forinteractive use by land managers. Such a system is frequently computerised,

74

LAND LOCATION (gen)

Refers to the position of feature(s) or area(s) on theearth's surface. Land location may be described by:

its geographic position, i.e. latitude/longitude.

* scaling off available medium scale topographicmaps (scales of 1:25 000 to 1:100 000) in eithergeographic or map projection co-ordinates, AMO(Australian Map Grid). See also GRIDREFERENCE,

* reference to land title system maps, e.g. parish,county maps.

* reference to Portion/Deposited Plan numbersdetailed on parish maps.

* plans ot survey of portions/deposited plans.* reference to Government Gazette Notices

describing areas ot land set aside for specificpurposes.

LAND MANAGEMENT (gen)

The application to land of cultural, structural, vegetativeor any other types of measures, either sìngty or in combinafion, in order to achieve a desired tand use. In asoil conservation context and management includesprovi&on for the control and/or prevention of soiterosion.

Different land management practices have produced thiscontrast.

LAND RECLAMATION (gen)

Making land capable of more intensive use by changingils general character, as by drainage of excessively wetland, or recovery of submerged land from seas lakes,and rivers. Large-scale reclamation projects usuatly arecarried out through collective effort. Simpleimprovements, such as clearing of stumps or stonesfrom land, should not be referred to as land reclamation.

LAND RESOURCE (lev)

The total amount of land available for the supply ofnatural products from which living organisms, includinghumans, can draw, lo provide their requìrements for life.

The land resource may be subdivided into individualbasic constituent land resources - land resourceat tributes - which include physical, chemical andbiological elements. The physical attributes which areof particular relevance to soil conservation are climate.geology, soils, landlorm. vegetation and hydrology.

Most of the physical land resources are limited andexhaustible and thus, the use to which they are putmust be carefully planned lo realise their optimumpotential. Because they are fixed in their location andextent they must, in general, be developed at theirlocation. This often leads to conflicts in land usepotential and high lights the need for land appraisal.

LAND RESOURCE ATTRIBUTE (lev)

An individual land resource constituent that includesphysi cal, chemical and biological elements. Forexample, soil is a land resource attribute, made up ofnumerous individual elements such as sand, clay andorganic matter.

LAND RESOURCE EVALUATION (lev)

The determination of the extent of one ol more landresource attributes, the assessment of the potential landuses to which the resources could or should be put,and the effect upon the land if the resources are usedfor particular pur poses. Il is an integral part of landappraisal.

In a soil conservation context, land resource evaluationrelates to the assessment of the possible uses of land,with respect to the prevention and control of soilerosion.

LAND RESOURCE STUDY (lev)

The systematic analysis of an area of land to assessthe land's potentìal for development under particularland uses. lt incorporates both land resource survey andland resource evaluation bui differs trom land appraisalin that socio- economic factors are not considered,However a land resource study would form part of thedata base for a land appraisal.

LAND RESOURCE SURVEY (lev)

The systematic examination, description, classificationand mapping of one or more land resource attributeswithin a given area, The primary objective of landresource survey is to provide an inventory of data aboutthe particular attribute/s. Such surveys may becategorised according to the kind and intensity of field

75

examination as in soil sur vey or reconnaissance soilsurvey. Land resource survey is an integral part of landappraisal.

LAND SUITABILITY (lev)

The potential uses of the land based upon theconsideration ot physical, technical and socio-economicconditions pre vailing. Full suitability evaluation involvesa multi disciplinary approach fo land evaluation andincludes a basic inventory of land resource data; anunderstanding of the ecological requirements of theland use contemplated; basic data on the economicsof land use, land improvement, new technologies,marketing and transport, and a knowledge of theattitudes and goals of people affected by the pro posedchanges.

LAND SYSTEM (lev)

An area, or group of areas, commonly delineated on amap, throughout which there is a recurring pattern oftopography, soils and vegetation. See also LAND UNIT.

LAND UNIT (lev)

An area of common landiorrn, and frequently withcommon geology, soils and vegetation types, occurringrepeatedly at similar points in the landscape over adefined region. It is a constituent part of a land system.

LAND USE (lev)

The purpose for which and is used. The termencompasses the entire spectrum from generaliseddescriptions such as rural land use to specificconditions such as improved pasture production.

LAND USE PLANNING (lev)

The conscious pursuit of goals, relating to the purposefor which land may be used, by means of theformulation and implementation of strategies, policiesand programs based on scientific and technical studies,

LAND USE SURVEY (lev)

The systematic examination, description, classificationand mapping of the existing land uses within a definedarea. Although other land resource attributes and/orother ele ments of the land may be mapped during thesurvey, its prin cipal function is to describe, classify andmap the uses to which the land is currently put.

LANDFORM (lfm, lev)

Any one of the various features that make up thesurface of the earth.

The detail with which landform is described dependson the purpose for which ii is being classified orevaluated. For example, in land capability classification,the degree of slope and the morphological type arecommonly the only land form attributes recorded. Theseattributes provide the essential landform data necessaryto evaluate capability.

Detailed description of landform is discussed bySpeight in McDonald et al (1984). The basic unit chosento describe, classify and map landform is the 'landform

LANDFORM (Continued)

individual'. Depending on the map scate fixed for thesurvey, the 'land form element' modet or the 'landformpattern' model may be utilised. tn general. large scatesurveys (1:5000, 1:10000) may describe elements, whitethose of smatter scales (1:50000, 1:100000) woutddescribe patterns.

The andform etement modet is suitabte for Iandformindivi duats that are within a toposequence. Suchelements may be described by the attributes of stope,morphotogicat type, dimensions, mode ofgeomorphotogical activity and geomorpho togicat agent,

The tandform pattern model is appticabte for tandtormindi viduals that inctude the whote toposequence. Suchpatterns may be described by the attributes of relief,modat slope, stream channel occurrence, mode andstatus of geomorphotogi cat activity, geomorphotogicatagent and component tandform etements. An exampleof a tandform pattern is undulating tow hitts, with itscomponent tandform etements inctuding crest, hillslope,tower stope and drainage depression,

LANDHOLDER (gen)

Any individuat, group of individuats or organisationwhich owns, occupies or manages land for anypurpose.

LANDSCAPE (lev)

That part of the and's surface, more or tess extensive,being viewed or under study, that retates to alt aspectsof its physical appearance, inctuding various vegetationasso ciations and andforms. Undertying geology andsoils, and tand use, may inftuence the character of atandscape.

LANDSLIDE (SLIDE) (gen)

A general term used to encompass the types of massmovement where the material is displaced downstopeand atong distinct surfaces of separation. The termencompasses a wide variety of materials but relatesspecifically to s/ope failures that involve the 'stiding' ofthe moving material over the ground surface.

As wett as classification of tandstides based on theirconstituent materials, subdivision is commonly relatedto whether the material in motion is greatly deformedor not, and to whether the slide is rotational ortranslational. In rotational slides, the movement is dueto forces that cause a turning movement about a pointabove the centre of gravity of the unit and the surfaceof separation is concave upward. Translational slidesinvolve movements predominantly along more or lessplanar surfaces and are typically controlled by surfacesof weakness, such as faults and bedding planes,variations in shear strength between layers of material,or by the contact between bedrock and overlyingmaterial.

Examples of this form of landslide classification are:

BLOCK GLIDE

Describes a slide where the material in motion isnot greatly deformed and moves downslope alonga more or less planar surface of weakness.

76

SLUMP

Describes a slide where the material in motion isnot greatly deformed but has backward rotation ona more or less horizontal axis, that is, displacementalong a concave surface of separation,

Landslides that 'slide' for only retalively shortdistances and that are composed predominantly ofdebris and/or earth materials are, in practicalterms, the most relevant to soil conservation. Suchlandslides are termed lands lips and in manyinstances conventional soil conser vationmeasures, such as tree planting, can be appliedto effect their control.

LANDSLIP (SLIP) (gen)

A general term used to encompass those landslidesthat are composed predominantly of soil and underlyingweathered material, are initiated by finite shear failurealong one or more distinct slip laces and movedownslope for only relati vely short distances. In manyinstances conventional soil conservation measures.such as tree planting, can be applied to effect theircontrol,

Classification of landslips follows similar principles tothose for landslides and include:

SOIL SLIP

A shallow landslip where surface soil is displaceddue to a marked change in shear strength betweenit and the subsoil. Generally soil slips revegetatenaturally with lime, but may become a seriousproblem on Ihm soils overlying bedrock.

ROTATIONAL SLIP

A Iandslip where the material is not greatlydeformed and the surface of separation is concaveupward as in a slump.

LASER LEVELLING (sur)

See LEVELLING,

LATTICE GILGAI (Ifm, sol)See GILGAI.

LEACHATE (soI, mm)

Liquid containing dissolved minerals and salts as aresult of leaching. Under natural conditions, reters toseepage water containing dissolved minerals and salts.

In a mining context, the minerals and salts are dissolvedas water seeps through an ore body or waste material.In some waste treatment processes, chemicals areadded to promote leaching.

In a soil context, the leachate may be formed naturallyby water seeping through the soil, or artificially in thelaboratory in certain soil testing procedures.

In a landfill context, the leachate may result from waterpassing through waste material such as at a garbagedisposal site,

Overclearing on this steep slope has led to landslipproblems.

LEACHING (sol, mm)

The removal in solution of the more soluble mineralsand salts by water seeping through a soil, rock. orebody or waste material. See also LEACHATE.

LEVEE (11m)

A long linear rise bordering a watercourse, comprisingpart of the floodplain formed by deposition of sedimentfrom overbank flow during floods. Relief is low and theouter slope very gentle.

LEVEE (sfr)

A constructed embankment designed to preventflooding of selected areas. lt is usually built along thebanks ol a watercourse to prevent inundation ofadjacent land, or around a facility to prevent access offlood waler lo il.

LEVEL (sur)

An instrument that is used to establish a horizontal lineof sight. Optical levels, which are mounted on a tripodor other support, use a bubble system to establish theline ot sight. The bubble is contained in a vial of liquidattached to the instrument. Four types of level arecommonly used:

AUTOMATIC LEVEL

A level in which the line of sight is automaticallyset to the horizontal, by a compensator, provided

77

t..

the instrument is set in an approximately horizontalposi lion. This is usually done by reference to acircular bubble system.

DUMPY LEVEL (RIGID LEVEL)

A level in which the telescope cannot be tilted. Theangle between the telescope and the level'svertical axis is fixed at 90 degrees.

HOSE LEVEL

A cheap and simple water-filled apparatus todetermine relative ground levels. Comprises twotransparent, vertical and graduated tubesconnected by a hose. Variations in height of thewater columns indicate relative ground levels.

TILTING LEVEL

A level in which the telescope can be tilted tromthe horizontal. The angle between the telescopeand ver tical axis is not fixed and can be adjustedby a tilting screw,

Compact hand held levels are used forapproximating angles of elevation or depressionand/or percentage slopes. These include theABNEY LEVEL, consisting of a telescope and asemi-circular graduated arc with a tubular bubbleattached, and the optical CLINOMETER in whicha circular graduated scale is centrally pivoted in aftuid encasement. See also THEODOLITE.

LEVEL BANK (sir)See BANK.

LEVEL SILL SPILLWAY (Str! eng)

See SPILLWAY.

LEVEL SPREADER (Str)

A shallow level channel excavated al the outlet of adiver sion channel. The level section disperses outflowand so reduces its erosive effect below the outlet,which should be in a stable undisturbed area.

LEVELLING (sur)

The process of determining the difference in heightbetween points. Three methods in common use are:

DIFFERENTIAL LEVELLING (SPIRIT LEVELLING)

Involves determining height differences betweentwo or more points using a level and staff.

TRIGONOMETRIC LEVELLING (TRIG LEVELLING)

Involves measurement of vertical angles anddistances to calculate height differences. Verticalangles are measured using a theodolite, whiledistances are measured by E.O.M., tape or stadiasurvey.

LASER LEVELLING

Involves the use of a rotating laser beam which isdetected by a sensor to determine heightdifferences. The beam may be set horizontally orat a particular grade. The latter enables suchoperations as land shaping to be undertaken at apredetermined slope.

LIME (sol)

A naturally occurring calcareous material used toraise the pi-f of acid soils and/or supply nutrientcalcium for plant growth. The term normally refersto ground limestone (CaCO3) but may also includeprocessed forms such as hydrated lime (Ca(OH)2)or burnt lime (CaO). The processed forms are alsoeffective for treating dispersible soils.

The effectiveness of lime application depends onits fine ness and subsequent incorporation into thetop few cen timetres of soil. The finer grades oflime are more effective,

LIME REQUIREMENT TEST (sol)

A laboratory test used to determine the amount of limerequired to raise the pH of a soil to a pre-determinedlevel, normally in the range of 6.0-6.5.

LIMING (gen)

The application of lime to the soil.

LINE TRANSECT (ram, agr)

A line across the land surface along which samples aretaken, plants are noted and/or quantitativemeasurements of vegetation are recorded, Cf. BELTTRANSECT, POINT TRANSECT,

LINEAR GILGAI (Ifni, sol)

See GILGAI.

78

LINEAR SCALE (lev) See MAP SCALE.

LINEAR SHRINKAGE (sol)

The decrease in one dimension of a soil sample whenit is oven dried, at 105°C tor 24 hours, from the moisturecontent at its liquid limit, expressed as a percentageof the original dimension, (Reference: AS.1289.C4.1-1977).

II is used as a measure of the shrink-swell potential ofa soil. See also EXPANSIVE SOIL.

LIQUID LIMIT (sol)

See ATTERBERG LIMITS.

LISTER (eng)

A type of plough used to throw up ridges and/orexcavate furrows useful in erosion control, Variousconfigurations have application in wind and/or watererosion control work, particularly in semi-arid areas.

LITHOSOL (SKELETAL SOIL) (sol)

A shallow soil showing minimal profile development anddominated by the presence of weathering rock andtragments therefrom, Such soils are typically found onsteep slopes, exposed hillcrests and rocky rangeswhere natural erosion exceeds the formation of new soilmaterial.

LITTER (sol)

The uppermost layer of organic malerial in a soil,consisting of freshly fallen or slightly decomposedorganic materials which have accumulated at theground surface.

LITTORAL (Um)

A term applied to deposits of soil materials arrangedor transported by tidal water.

LITTORAL DRIFT (csd)

The movement of sedimentary material in the littoralzone under the influence of waves and currents.

LITTORAL ZONE (csd)

Generally, the zone related to the shoreline of a sea orlake, Strictly, the zone bounded by high and low tidelevels.

LOAM (sol)

A medium-textured soil of approximate composition 10to 25% clay, 25 to 50% silt, and less than 50% sand.Such a soil is typically well-graded. See also SOILTEXTURE, GRADING.

LOG DUMP (LOG LANDING) (for)

An area where forest products are assembled prior toloading them on to a truck for transport to processingplants or markets.

LOG LANDING (for)

Syn. LOG DUMP.

LOGGING (for)

'The felling, trimming and removal of tree trunks from aforest, typically tor commerciai timber production. lt maybe SELECTIVE LOGGING, where specific trees only areremoved, or INTEGRATED LOGGING where allmerchantable timber is removed.

LOPPING (for)

The removal from a free of foliage which does notcomprise the trunk or primary branches. In the case ofa tree having a multiple trunk habit, such as mailee,lopping excludes such trunks from being cut down. Cf.TOPPING.

LOW DENSITY RESIDENTIALDEVELOPMENT (urb)

A level ol urban development which provides for theconstruction ot roads, drainage and services to caterfor subdivision allotments typically between 0.5 and 2hectares. In most new subdivisions of this type,especially those adjoining established urban centres,water supply is usually provided but sewerage may ormay not be available. See also RESIDENTIALDEVELOPMENT, STRATEGIC DEVELOPMENT,

LOW-WALL (mm)

A sloping face in an open-cuf mine, located at the rearor backfill side of the cut. See also HIGH WALL.

LUNETTE (lfm)

A crescent-shaped dune al the margin of a playa orlake. The sediments comprising the lunelte are typicallyfine- grained and originate from the floor of the playaor lake during dry periods, Lunettes are formed by windand wave action.

LYSIMETER (sol, hyd)

A device to measure the quantity or rate of walermovement through or from a block of soil, usuallyundslurbed and in sif u, or to collect such percolatedwater for quality analysis.

MAAR (1(m)

A level floored, commonly waterfilled closed depressionwith a nearly circular steep rim, excavated byvolcanism.

MACHINE LENGTH (eng)

The longitudinal distance between the Iront and rearranks ol lines on a tillage implement.

MAIN SCARP (lfm)

See SCARP.

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MAJOR ELEMENT (agr)

See PLANT NUTRIENT.

MANNING'S FORMULA (hyd)

A formula used to predict the velocity of uniform waterflow in an open channel or pipe.

V= R2h /2

where V = mean velocity of flow (metres/second)R = hydraulic radius (metres)S = channel slope (metres/metre)n= Manning's roughness coefficient of thechannel lining.

lt is particularly uselul in soil conservation design workin calculating specifications for banks and waferways.

MAP SCALE (lev)

The relation, expressed as a ratio, between a unit oflength on a map and the actual length it represents onthe land surface. A map scale of 1:2 000 000 is a smallscale; whilst a map scale ot 1:2000 is a large scale. Thesmaller the map scale the larger the area of landsurface represented, For example, one squarecentimetre on a 1:2 000 000 scale map represents 400square kilometres whereas a similar unit on a 1:2000scale map represents 400 square metres,

Scale on a map is preferably represented by a LINEARSCALE, whereby a line is subdivided to representappropriate units, such as kilometres or metres, Thisscale has the advantage ol varying with the rest ot themap if the map is copied at an enlarged or reducedscale, or if atmospheric conditions cause the paper toexpand or contract.

MAP UNIT (lev)

A delineated area on a map representing parts of thelandscape having elements that vary within more or lessnarrow limits, depending on the intensity and objectivesof the survey. See also INTEGRATED MAPPING UNIT,SINGLE ATTRIBUTE MAPPING UNIT.

MARGINAL CROPPING LAND (lev)Land which, due to its climatic, geographic ortopographic location, and/or the nature of its soils,cannot be used for the frequent growing of cropswithout stringent land management controls to protectit from degradaf ion, In semi-arid areas there is alsoconcern that cropping of such land, irrespective of theeffects of tillage, may cause depletion of reserves ofnative vegetation. These reserves are essential (orfuture regeneration.

MARGINAL LAND (lev)

Land which, due to its climatic, geographic ortopographic location, and/or the nature of its soils,cannot be used for a form of regular agricultural orpastorat use without stringent land managementcontrols to protect it from degradation, Marginal landmay be found in different climatic zones and the factorsrendering the land marginal will vary from zone to zone.

MARKER RIP (Str)

A line across the and surface, formed by a tinedimplement, to indicate the intended tine for theconstruction of a soit conservation bank or simitarstructure.

MASONRY (eng, sir)

Describes a structure built with stone, concrete, brickor simUar material. Such structures have a sotidframework providing an erosion-resistant surface. Smallholes or gaps may be incorporated to cater forseepage.

Masonry structures are typically used where there is ahigh risk of failure associated with vegetative methodsof soit erosion control,

MASS MOVEMENT (gen)

A generat term encompassing erosion processes inwhich gravity is the primary torce acting to distodge andtransport land surface materiats. lt is a function of thegravitational stress acting on the land surface and theresistance of the materiats to dislodgement. When thegravitationat stress exceeds this resistance, massmovement occurs, The occurrence of mass movement

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depends upon the interaction of various factorsincluding landform, lithology, soil type, rainfall intensityand duration, drainage characteristics, vegetal cover,and human intervention,

There are various ways to classify mass movementincluding age, cause and degree of disruption of thedisplaced mass, but the preferred classification isbased on the type of material - bedrock, debris andearth and the type ot movement - latI, topØle, tateralspread, flow and slide.

N.B.For further description of this classificationsystem refer Varnes, D.J. Slope Movement Typesand Processes. In Landstides: Analysis andControl, Transportation Research Board, NationalAcademy of Sciences, Washington D.C., U.S.A.,Special Report 176, Chapter 2, 1978.

The main categories of mass movement relevant to soilconservation are earf h/lows, landslides and landslips.

See also SUBSIDENCE. AVALANCHE, CREEP.

Serious damage as a result o! mass movement.

MASSIVE (sol)

Refers to that condition of a soit ayer in which the tayerappears as a coherent, or solid, mass which is largelydevoid of peds. and is more than 6 mm thick. Cf. SELFMULCHING.

MATRIX (sol)

Finer-grained traction, typically a cementing agentwithin a soit or rock in which larger particles areembedded.

MAXIMUM PERMISSIBLE VELOCITY (hyd)

The highest average velocity at which water may flowin a channel without causing erosion. For soilconservation purposes vegetated channels aie incommon use, and the maximum permissible velocity isdependent upon the type, condition and density ofvegetation, the erodibility of the soil, and channel slope.Uniformity of vegetative cover is important, as thestability of the most sparsely vegetated section controlsthe stability of the whole channel. See alsoPERMISSIBLE VELOCITY.

MEANDERING (gen)

The natural winding ot channels, which results from acomplex geomorphological process involvingstreambank erosion and alluvial deposition.

Meandering of a river.

¿' .:. . .'

60320-15204-6

81

MEASURING TAPE (sur)

A device ranging in length from 3 to 100 metres, havinguniformly spaced graduations which can vary from 1

metre down to 1 millimetre. used to determinedistances. Measuring tapes may be made of fibreglassor steel, with or without a special coating to minimiserust, and are contained in specially made winders or arewound on canvas or leather reels.

MECHANICAL ANALYSIS (sol)Syn. PARTICLE SIZE ANALYSIS.

MECHANICAL STABILITY (sol)

The ability of a dry soil to maintain its structure underthe influence of mechanical agents. such as tillage orabrasion from windborne materials. It relates to soilcohcrence and is characterised in the laboratory byrepeated dry sieving on a rotary sieve, CI.STRUCTURAL STABILITY.

MELONHOLE GILGAI (lt m)

See GILGAI.

MESOPHYTE (ram)

Plant requiring regular, moderate amounts of waler. Cf.XEROPHYTE.

MICRORELIEF (Ifni)

Minor variation in the configuration of the land surfacesuch as is caused by the presence of gil gai. rabbitholes, ploughing and scalding.

t'-:'' 'Cv'-p' r ..........

I .. C-. -. . ---dt..--

MINIMUM TILLAGE (agr)

A general term describing a conservation tilla ge systemin which lhe crap s grown with the fewest possibletillage operations. Herbicides and/or grazing may beused for fallow weed control. Cf. REDUCED TJLLAGE.

MINOR ELEMENT (agr)

See PLANT NUTRIENT.

MINOR SCARP (lfm)

See SCARP.

MIRROR STEREOSCOPE (rms)

See STEREOSCOPE.

MITRE DRAIN (eng)

See DRAIN.

MOLE DRAIN (eng)

See DRAIN.

MONITORING SITE (gen)

An area of land having defined boundaries within whichlong- term changes in environmental conditions, suchas soils, vegetation and/or land use, can be studied.The site may be left undisturbed to examine naturalchanges or may be specifically managed to examinethe effects ot particular treatments. Monitoringtechniques include transect inventory, site photography,aerial photography, and remote sensing.

MONOCULTURE (agr)

A cropping system where only one type of crop isgrown.

MONTMORILLONITE (sol)

Clay material comprising a group of atuminosilicateminerals with a 2:1 expanding crystal lattice structure,They are reactive clays generally with high shrink/swellpotential and high cation exchange capacity. See alsoILLITE, KAOLINITE.

MOTTLING (sol)

The presence of more than one soil colour in the samesoil horizon, not including different nodule colours. Thesub- dominant colours normally occur as scatteredblobs or blotches, which have detinabte differences inhue, value or chroma from the dominant colour. Mottlingis often indicative ot stow internal drainage, but mayalso be a result of parent material weathering.

MOUND (ltm, str)

An artiticial elevation of earth, proportionaHy similar inlength and width, typically constructed as a temporarystorage of soil materials or permanently constructed forlandscaping purposes during the rehabilitation ofdisturbed terrain.

Small mounds are sometimes used for erosion controlin horticultural crops.

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MOUNTED HARROW (eng)

An assembly of very light spring steel lingers attachedto a rear trame member of a titlage implement to furtherrefine surface soil conditions, Normally comprises threeto five ránks of fingers which may be adjusted for angleand downward pressure. See also TINED HARROW,HARROWING.

A mounted harrow.

MUDFLOW (gen)

See EART-HFLOW.

MULCH (agr)

A natural or artificial layer of plant residue or othermaterial or the soit surface, which provides protectionagainst erosion and aids plant establishment mainly byrestricting moisture loss. lt may also increase infiltrationand minimise temperature fluctuations.

Mulches most commonly used in soil conservation are:

Bitumen: Applied as an even ayer. Slow breakinganionic bitumen emulsion is used as a mulch followingthe broadcasting of seed and fer tiliser, lt is also usedto secure other mulches, such as straw, to the exposedsurface.

Mesh/Netting: Although these materials are principallyused to secure other types ot mulch, they themselvescan be applied directly as a mulch, particularly thosewith a fine weave,

Straw/Hay: Provides a protective mulch it at least 3-5cm deep, but preferably should be 6-10 cm deep,spread evenly over the surface.

Wood Pulp/Paper Pulp: Typically used in conjunctionwith hydromulching and hydroseeding.

MULCHING (agr)

The application or retention of a mulch. Usually refersto the application of mulch to disturbed areas as atemporary expedient to assist the establishment ot

permanent vegetative cover, or the retention of plantresidues on arabte land between cropping phases toassist in erosion control. See also STUBBLEMULCHING.

MULLOCK (mm)

Discarded rock which does not contain ore that can beeconomically extracted.

MULTIPLE CROPPING (agr)

The growing of more than one crop each year on thesame parcel of land. Cf. OPPORTUNITY CROPPING.

MULTIPLE PURPOSE SURVEY (lev)

A survey conducted with more than one definedobjective. Cf. SINGLE PURPOSE SURVEY.

MULTISPECTRAL IMAGERY (rms)

An image produced by focussing various incomingbands of radiation within the electromagnetic spectrumupon a transducer, which converts the radiation to adifferent type of signal, which is then recorded uponsome medium, The three- camera television system ofviewing (he terrain in green, red and infrared used insome satellites for remote sensing is an example ofmultispectral imagery. This multispectral approachallows recognition of terrain teatures by their differencesin reftectance. For example, the green band allowsmaximum penetration of light through water to enhancesubaqueous features, while the red band givesmaximum contrast of cultural features. See also IMAGEENHANCEMENT.

MUNSELL COLOUR SYSTEM (sol)

See SOIL COLOUR.

GJ

NAPPE (hyd)

A sheet or curtain of free-fatting water flowing from astructure such as a weir, The term is also used todescribe the path of the falling water.

NATIVE PASTURE (agi)

See PASTURE.

NATIVE VEGETATION (gen)

Indigenous pasture, bushland and/or timber speciesadapted to the prevailing environmental conditionsincluding climate, soils and natural grazing patterns.

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NATURAL EROSION (gen)

See EROSION,

NATURAL RESOURCES (gen)

The naturally-occurring components of the environmentwhich are of value to the human population. includingland, soil, water, flora, fauna, minerals and energysources. The value may be direct in that the resourcefulfils an immediate human need and can be bought orsold (e.g. fish, timber), or it may be indirect, in that itis needed to support or provide amenities important tohumans (e.g. landscape).

Natural resources may also be classified according tothe nature of their supply. In this way they arecategorised as renewable (e.g. forests), non-renewable(e.g. fossil fuels) or continuous (e.g. solar energy). In thebroadest sense, soils are a renewable resource,because their formation is an ongoing natural process.However, under current Australian conditionsparticularly. this process is so slow that for soilconservation purposes they should be regarded as non-renewable.

The value ot natural resources also involves a timecomponent in that it may depend on future availabilityor technology.

NATURAL WATERWAY (sir)

See WATERWAY.

NATURALISED PASTURE (agr)

See PASTURE.

NETTING (gen)

Coarse mesh material usually placed on top of a mu/chto prevent its displacement and thus provide protectionto the soif surface from erosion during the early stagesof revegetation. Netting can also be laid directly on thesurface as a protective measure in certaincircumstances. such as on a steep rocky batter proneto mass movement,

Common netting materials are wire, plastic, paper,cotton or other woven synthetic or fibrous materials,

The netting should be pinned firmly to the groundsurface and not traversed by vehicles.

NITROGEN FIXATION (sol)

Generally, the conversion of free nitrogen lo nitrogencombined with other elements. Specifically in soils, theassimitation of atmospheric nitrogen from the soil air bysoil organisms to produce nitrogen compounds thateventually become available to plants.

NO-TILLAGE (ZERO TILLAGE) (agi)

A m/nimum ti//age practice in which the crop is sowndirectly into a soil not tilled since the harvest of theprevious crop. Weed control is achieved by the use ofherbicides and stubble is retained for erosion control.It is typically practised in arable areas where ta/lowingis important. Cf. DIRECT DRILLING,

Hard iron and manganese nodules,

NODULE (CONCRETION) (sol)

A small segregated mass of material Ihat hasaccumulated in the soil because of the concentrationol one or more parlicular constituents, usually bychemical or biological action. Nodules vary widely insize, shape, hardness and colour, and may becomposed of iron or manganese compounds, calciumcarbonate or other malerials.

NON-CAPILLARY POROSITY (sol)See SOIL POROSITY.

NON-EROSIVE VELOCITY (hyci)Syn. PERMISSIBLE VELOCITY.

NON-PHOTOGRAPHIC SENSOR (mis)

See REMOTE SENSING SYSTEM.

NON-PLASTIC (soi)

Describes soil malerial which shows no plasticbehaviour, irrespeclive of its moisture content. See alsoSOIL PLASTICITY.

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NON-POINT SOURCE (gen)

A source of pollution which cannot be pinpoinled. In asoil conservation conlexl il Iypically applies Io asediment source which is spread over a wide area. Forexample, an area of cropping land coutd be a nonpointsource of sediment conlributing Io Ihe blocking of aroad culveR. Ant. POINT SOURCE,

NON-SELECTIVE HERBICIDE (agi)

See HERBICIDE.

NON-UNIFORM FLOW (hyd)

See FLOW.

0, 01, 02 HORIZON (sol)See SOIL PROFILE.

OCCASIONAL CULTIVATION (agr)

The infrequent growing of crops requiring filage, on thesame parcel of land. Cf. REGULAR CULTIVATION,CONTINUOUS CULTIVATION.

0FF-CONTOUR TOLERANCE (agi)A strip cropping term for the amount the key line, orlines parallel to it, deviates from the true contour. It isexpressed as the slope of the key line, which iscalcutaled when this line crosses two contours,Generally a tolerance ot 0,3 per cent is acceptable onland slopes between i and 2 per cent, provided thelength ot the cross slope is not excessive.

OPEN UNLINED DRAIN (eng)

See DRAIN.

OPEN-CUT MINE (mm)

A mining operation where the extraction of the ore iscarried out (rom the ground surface, working

An open-eut coal mining operaf ion.

85

downwards removing overburden and spoil until therequired seam ot ore is reached, Removal is by surface-based machinery and vehicles. Rehabilitation of thearea after such a mining operation may involveconsiderable filling and extensive reshaping ot the landsurlace as well as topsoiling, revegetation and theimplementation of a range of soil conservationmeasures.

OPPORTUNITY CROPPING (agi)

A flexible cropping procedure whereby advantage istaken of unexpected favourable seasonal conditions,particularly those relating Io soil moisture, to grow morethan one crop per year on the same piece of land. Itmay also apply to growing a crop in localities and/or atlimes of the year when regular crop production is notpossible, to take advantage of special market situations.CL MULTIPLE CROPPING.

OPTICAL SQUARE (sur)

A hand held instrument which facilitates the setting outof rightangles in the field.

ORE (mm)

Rock or other geologic material trom which minerals areextracted. The economics of mineral extraction aredetermined by the relationship between the costs ofmining and concentrating the minerals, and their currentmarket valua

OREBODY (mm)

Generally a solid and fairly continuous mass of ore,which may include low-grade and waste as well as payore, but is differentiated by form or character fromadjoining country rock.

ORGANIC (gen)

Describes substances or materials derived from animalsor plants. See atso SOIL ORGANIC MATTER.

ORGANIC SOIL (sol)

A soil in which soil organic matter dominates the profile.The surface 30 cm should contain 20 per cent or moreorganic matter it the clay content of the mineral soil is15 per cent or lower, or 30 per cent or more organicmatter if the clay content of the mineral soil is higherthan 15 per cent, See also PRIMARY PROFILE FORM.

ORTHOGONAL PROJECTION (rms)

See ORTHOPHOTO,

ORTHOPHOTO (rms, lev)

A rectified, true to scale aerial photograph from whichall distortions such as those due to terrain elevationdifferences and camera tilt, have been removed.

Vertical aerial photographs have a CENTRALPERSPECTIVE such that ground objects closer to thecamera appear larger (e.g. details appearing on amountain top will be at a larger scale than those in thevalley below). This results trom the aerial camera"seeing' the ground from a single point. As aconsequence, images will be displaced by varyingamounts from their equivalent map position and,therefore, distances, areas and shapes will be distorted.

An orthophoto has an ORTHOGONAL PROJECTIONwhich, within the limits of the printed sheet, implies thatthe land surface represented may be treated as ahorizontal plane and the various features at differentelevations appear as though projected verticallydownwards.

The central perspective view is transformed into theequivalent orthogonal projection by the use ofsophisticated stereoplotters and rectificationinstruments,

ORTHOPHOTOMAP (rms, lev)

An orthophoto which has been produced in map formatwith Australian Map Grid co-ordinates. Cadastral and!or contour information may be added. When the tatteris added. an orthophotomap combines the wealth ofresource information contained in an aerial photographtogether with the contour information required fortopographical assessment and measurement. Cf.PHOTOMAP.

OUT OF PIT EMPLACEMENT (miii)

A stockpile of overburden material away from theexcavation of an open-cut or st rip-mine. The material isoften used to fill the final void, for landscaping purposesduring rehabilitation, or is left at the site ofemplacement, landscaped and stabilised.

86

OUTCROP (sal)

The exposure at the surface of rock that is inferred lobe continuous with underlying bedrock.

OUTFALL (for, gen)

See CROSSFALL DRAINAGE.

OUTLET (gen)

The point at which water dtscharges trom a river, creekor other flowtìne; lake, tidal basin or drainagedepression; or pipe, channel, dam or other hydrologicstructure.

OUTLET CHANNEL (str)

A natural or constructed channet used primarily to carrywater away from hydrologic structures such as banksand dams.

OUTROW (STRIPROW) (for)

A corridor of trees felled in plantations in order to allowtravel, processing, snigging or forwarding functions.

OVERALL TINE SPACING (eng)

The tateral distance between tine centres across atillage implement, rather than along a rank. Thisdistance is usually uniform across the implement. Cf.TINE LATERAL SPACING.

OVERBURDEN (mm)

Soil and rock material which must be excavated toexpose an orebody or coal seam in preparation foropen'cut mining.

OVERCLEARING (agr, for)

The removal ot trees and shrubs, particularly from steepareas, to an extent which makes the land susceptibleto appreciable soil erosion.

The presence of permanent tree cover on many steeplands ensures their stability. However, removal ot thetrees increases erosion hazard due mainly to the slopeand the typical shallowness and erodibitity of soils onsuch and, and can also cause soil salting. It may alsoleave insufficient shade and shelter for livestock. In aridand semi- arid areas the removal of trees and shrubsincreases the risk of wind erosion,

OVERFALL (gen)

An abrupt vertical drop n the bed of a flowtine. For soitconservation purposes it usually applies to the rim of agully head over which runoff faits, lt also applies tovertical or near vertical drops in the gully floor turtherdownstream, which may be associated with rockoutcrops.

OVERGRAZING (agr)

Continued grazing of pasture or rangeland at a levelwhtch permanently and adversely affects its plantcomponents. This leads to a reduced capacity toproduce forage, deterioration in pasture or rangecondition and increased erosion hazard. Cf.OVERSTOCKING.

An over fall at a mino, gully head.

OVERLAND FLOW (gen)

Syn. SHEET FLOW.

OVERLAP (rms)

The amount by which one aerial photograph includesthe same area as covered by another, expressed as apercentage. SIDE LAP refers to the overlap of adjacentruns, typically adjacent parallel flight paths. FORWARDLAP refers to the overlap between successive photosin the same line of flight. Standard specifications(National Mapping Council of Australia) provide that sidelap shall be at least 30 per cent plus or minus 10 percent, and torward lap shall be at least 50 per cent plusor minus S per cent.

OVERSHOT SPILLWAV (eng)

See SPILLWAY,

OVERSTOCKING (agr)

The placement of a number of grazing animals on agiven area of pasture or rangeland that will adverselyaffect its plant components by the end of the grazingperiod. The effect may only be temporary, and in thisrespect the term differs from overgrazing. However,continued overstocking will lead to overgrazing.

Ox-BOW (If m)

A long curved closed depression, usually swampy orwater- fitted, tormed by plugging of the ends of a bendin a stream channel with alluvium. The bend thusbecomes separated from the main channel.

87

p

PALEOSOL (so!)

Syn. BURIED SOIL.

PAN (HARDPAN) (sot)

A hardened, compacted and/or cemented horizon, orpart thereof, in the soil profile. Such pans frequentlyreduce soil permeability and root penetration and thusmay give rise to plant growth and drainage problems.Deep ripping or chisel ploughing is used to overcomesuch problems.

The hardness is caused by mechanical compaction orcementation ot soit particles with organic matter or withmaterials such as silica, sesquioxides. or calciumcarbonate. The hardness does not change appreciablywith changes in moisture content, and pieces of thehard layer are not subject to slaking.

See also CLAYPAN. PLOUGH-PAN.

PAN EVAPORATION (gen)

The depth of evaporation from a free water surfacedetermined by use ot an evaporimeter and expressedin millimetres. The figure is used to estimateevapotranspiration in field areas and for water balancestudies,

PANTOGRAPH (lev)

An instrument used for enlarging or reducing drawingsor maps. lt consists of four arms, in the form of apara!lelogram. The arms are pivoted and adjusted sothat the shape and size of the para!lelogram may bevaried. This enables a similarity of movement betweenthe tracing arm and the marking pen, facilitating theenlargement or reduction.

PARABOLIC DUNE (cad)

See DUNE.

PARALLAX (rrns)

The apparent displacement in the position of an object,with respect to a trame of reference, caused by a shiftin the position ol observation.

The camera operator, looking through the viewfinder ofan aerial camera as the aircraft moves forward, seesimages of objects move across his field of view. Anexposure records the positions of ground features atthe instant the shutter is open. The change in positionof those same images from one photo to the nextcaused by the forward movement of the aircratt iscalled STEREOSCOPIC PARALLAX, more commontyreferred to simply as parallax.

The closer the terrain point is to the camera, the greaterwill be its parallax in relation to points further away fromthe camera. lt is because of parallax that an artificialthree-dimensional model of the terrain can be observedwhen viewing the common overlap of aerialphotographs.

See also STEREOMETER BAR.

PARALLAX BAR (rms)

Syn. STEREOMETER BAR.

PARALLEL STRIP CROPPING (agr)See STRIP CROPPING.

PARAMETRIC CLASSIFICATION (lev)A method of land classification which ranks landaccording to the different characteristics which aresignificant for the specific land use under study. Forexample, different categories of urban capabilitydepend on the characteristics ot soils, landform anddrainage patterns,

PARENT MATERIAL (sol)

The geologic material from which a soif profile devetops.lt may be bedrock or unconsolidated materials includingalluvium, cotluvium, aeolian deposits or other sediments.

PARTICLE SIZE ANALYSIS (MECHANICALANALYSIS) (sol)

The laboratory determination of the amounts of thedifferent separates in a soit sample such as clay, sitt,fine sand, coarse sand and gravel. The amounts arenormally expressed as percentages by weight of drysoil and are determined by dispersion, sedimentation,sievJng, micrometry or combinations of thesetechniques,

88

PASSIVE RECREATION (urb)

A level of land development which caters for walkingtracks. parkland and the like, where minor shaping,clearing and possible revegetation may be desirable toprovide for a particular use, but no extensivedisturbance is permitted, Cl, ACTIVE RECREATION.See also RECREATIONAL CAPABILITYCLASSIFICATION.

PASTORAL (gen, ram)

Describes land use practice whereby sheep, cattle and!or other domestic animals are grazed over extensiveareas, typically rangeland.

PASTURE (agr)

Grasses, legumes and/or other herbage used orsuitable for the grazing of animals. The term alsoinctudes the land covered by such herbage and usedor suitabte for grazing. ANNUAL/PERENNIAL PASTUREconsists largely of annual/perennial grasses and/orlegumes respectively. Four pasture types are commonlyrecognised:

NATtVE PASTURE

Consists of indigenous species which are welladapted to the prevailing environmental conditionsincluding climatic factors, soit nutrient status andnatural grazing patterns. Their biomass, nutritionalvalue and palatability are often less than that ofimproved pastures, but they have advantages inlong term persistence under drought conditions ifmanaged adequately, and often prefer conditionsof low soil fertility.

IMPROVED PASTURE

Consists of introduced species not indigenous tothe area being considered, Many of the legumepasture species, such as the white clovers, havebeen introduced into Australia, PastureImprovement increases grazing productivity perunit area but requires careful management, suchas fertiliser application and weed control, tomaintain sustained production,

SEMIIMPRO VED PASTURE

Pasture where improved species have beenencouraged to invade native pasture by suchpractices as broadcast seeding and fertiliserapplication,

NATURALISED PASTURE

Pasture where a balance between improved andnative species has been reached, It results fromthe spread of improved species by natural seedand vegetative distribution or the deterioration ofimproved pastures by the invasion of nativespecies.

PASTURE FURROW (sir)

Syn. CONTOUR FURROW.

PASTURE RENOVATION (age)

The upgrading of a pasture by sod seeding ormechanical lreatmenl using such implements as anaerator or pasture harrows. Such treatments increasewater intiltration and improve soil aeration.

PASTURE TOPPING (agr)

The application of herbicides to pasture ta improve thecomposition of the established sward by suppressinggrowth and reducing seed set of undesirable species.

PATTERN (PHOTOPATTERN) (mis)

The regularity and characteristic arrangement of tonesor textures on an aerial photograph, The pattern on theground caused by certain land uses is used in theiridentification, such as the regular spaced pattern oforchards. Certain geomorphic features may alsoproduce a unique pattern in the photograph. Forexample, terracetting results in a linear pattern acrossthe slope, parallel Io Ihe contour,

PEAK DISCHARGE (hyd)

The maximum discharge resulting from a set ofhydrological conditions. (Symbol: O, Units: m3/s). Seealso DESIGN PEAK DISCHARGE, RATIONALFORMULA.

PEAK TYPE BANK (str)

See BANK.

This soil is strongly pedal, showing a blocky ped pattern.

89

PEU (sol)

An individual, natural soil aggregate. Cf. CLOD.

PEDAL (sol)

Describes a soil in which some or all al the soil materialoccurs in the form of peds in the moist state. Stronglypedal soils have two thirds or more of their soil materialin the form of peds, and weakly pedal soils have lessthan one third of their soil material in the form of peds.Cf. APEDAL,

PEDIMENT (Ifni)

A land surface worn down by erosion to a nearly flat orbroadly undulating plain, typically with numerous rapidlymigrating and very shallow stream channels. Pedimentsare eroded, and locally aggraded, by frequenlly activestream flow or sheet flow, with sub-ordinate winderosion. Cf. PEDIPLAIN, PENEPLAIN.

PEDIPLAIN (Ifni)

A land surface worn down by erosion lo a nearly flat orbroadly undulating plain with no stream channels. Byextension the term is also used for the plateau formedby the uplifting of such a surface. Cf. PEDIMENT,PE NE PLAIN

PEDOLOGY (sol)

The study of soils, particularly their formation.morphology, distribulion and classification.

-I

f

PENEPLAIN (If m)

A land surface worn down by erosion to a nearly flat orbroadly undulaling plain with sparse slowty migratingalluvial stream channels. Cf. PEDIMENT, PEDIPLAIN.

PENETRABILITY (sol)

The ease with which a probe can be pushed into thesoil. May be expressed in units of distance, speed.torce! or work depending on the type of penetrometerused.

PENETROMETER (sol)

An instrument used to measure resistance topenetration in soil. Such measurements are importantin relation to soil density studies or the location of pans.

PERCHED WATER TABLE (gen)

See WATER TABLE.

PERCOLATION (sol)

The downward movement of water through soil,contributing lo internal drainage. See also SOILPERMEABILITY.

PERENNIAL PASTURE (agr)

See PASTURE

PERENNIAL PLANT (agr)

A plant whose lite cycle extends for more than twoyears and continues to live trom year to year. Someperennials, such as grasses and herbs, have above-ground parts which die down in lhe autumn, leaving anunderground structure, such as a bulb or rhizome, tooverwinter and produce new growth in the spring.Woody perennials, such as shrubs and trees, havepermanent woody stems from which the plant makesnew growth each year. Cf. ANNUAL PLANT, BIENNIALPLANT.

PERI-LJRBAN (urb)

Syn. PURRAN.

PERIMETER BANK (urb)

A temporary barrier of compacted soil or hay baleslocated along the boundary of a construction site tocontrol the movement of runoff and sedimenl from thesite, See also HAY BALE BARRIER.

PERMANENT CLEARING (agr, for)

The removal and non-replacement of trees and shrubsto tacilitate an alternative term ot land use, such aspasture or cereal cropping.

PERMANENT SEEDING (agr)

The establishment of perennial vegetation intended teremain on an area for many years. See also SEEDING,TEMPORARY SEEDING.

90

PERMANENT WILTING POINT (sol)

A laboratory measure ol the amount of water held in asoìl.al the point when foliage wilts and does not recoverwhen placed in a humid atmosphere. Expressed as apercentage of the oven dry weight of the soil.

In the held existing foliage withers and dies as a resultof moisture stress. However, in the long term, plantsmay recover if more water becomes available, due tothe production of new shoots. See also FIELDCAPACITY, AVAtLABLE SOIL WATER, SOIL WATERPOTENTIAL,

PERMEABILITY (sol)

Syn. SOIL PERMEABILITY.

PERMISSIBLE VELOCITY (NON-EROSIVEVELOCITY) (hyd)

A velocity at which water may tlow safely in a channelwithout causing erosion. See also MAXIMUMPERMISSIBLE VELOCITY.

PERSPECTIVE DISTORTION (rms)

See DISTORTION.

pH (soI)

A measure of the acidity or alkalinity of a soil. A pH ot7.0 denotes neutrality, higher values indicate alkalinity.and lower values indicate acidity. Strictly it representsthe negative logarithm ot the hydrogen ionconcentration in a specified soil/water suspension on ascale ot 014. Soil pH levels generally tall between 5.5and 8.0 with most plants growing best in this range.See also ACID SOIL.

Soil pH is commonly measured in the field by acolorimetric method using Ratipach's indicator,. In thelaboratory a number ot methods may be used,depending on need. These are commonly based onmore accurate electrical techniques generally using

or 1.5 mixtures ot soil with waterer 001M CaCl2solution. The CaCI, method gives pH valuesapproximately 0.5 units lower than the waler method.In reports quoting pH levels, the method otmeasurement should he noted, * Reference: Raupach,M. and Tucker, BM. (1959) The Field Determination otSoil Reaction J. Aust, Inst. Ag. Sci. 25 129-133.

PHOTO SCALE (rms)

A ratio between corresponding aerial photograph andground distances measured in the same units, Moredetailed intormalion can he recorded at larger scales(cg. 1:5000) per unit area than at smaller scales (e.g.1:50 000). Thus the sampling intensity el the groundarea is reduced with decreasing scales,

Two methods are available tor the determination otvertical photo scale, The first involves the comparisonof any measured photo distance, which should be aslong as possible, with ils corresponding grounddistance, viz,:

moasuicri phoin distance lnm) ahPtiotoscaio= -

cortcsperiuincj 9co,,nd d'stanco fmni) AB

The second method involves the comparison of thecamera local length with the height of the cameraabove the ground, viz.:

Photoscale= camera tocal length (mm)

camera height abovemean ground N-hsea level (mml elevation (mm)

The above methods only provide an approximate scale,principally because of distortions within the photograph.Precise dimensions can only be obtained with the aidof precision instruments used in photogrammetry.

PHOTOGRAMMETRY (rms)

The science or art of obtaining reliable measurementsby means of photography. (Reference: Whitrnore, G.D.and Thompson, MM. Introduction to Photogrammetry.In Manual of Photogrammetry, Volume 1, Chapter 1.American Society of Photogrammetry, Wisconsin,U.S.A.. 1966). lt embraces a wide range of activitiesusing photographs, including the precise measurementof various features of aerial photographs, usingspecialised precision instruments, to produce maps andplans such as orthophotomaps.

PHOTOGRAPHIC SENSOR (rms)

See REMOTE SENSING SYSTEM.

PHOTOMAP (lev)

A single aerial photograph or an uncontrolled mosaicof vertical aerial photographs which have beenenhanced by the addition of some nomenclaturetogether with an appropriate title. Photomaps show allthe detail contained within the aerial photographs butalso include their distortions which may causediscontinuities at the edge of joined photographs. Cf.ORTHOPHOTOMAP.

PHOTOPATTERN (rms)

Syn. PATTERN.

PHREATIC LINE (sfr)

The line marking the upper surface of the zone ofsaturation in a body'ol soil material. Water movementthrough an earth embankment tollows a pathwaydetermìned by this line, i.e. seepage will occur at orbelow it. Provided the water level behind theembankment is maintained, the line of seepageeventually reaches a steadystate determined by thedensity and permeability ot the material. See alsoEARTHWORK TUNNELLING.

PHYSICAL FERTILITY (sol)

See SOIL FERTILITY.

PHYSIOGRAPHY (If m)

A broad term used to refer to the general shape of theland surface.

91

PIEZOMETER (sol)

A narrow tube, open at each end, inserted down a holein the ground to the depth of the water table, whichenables measurement of its elevation or hydraulic head

PILLAR (mm)

A solid block of coal or ore left to support the roof ofan underground mine, See also BORD AND PILLAR,

PIOSPHERE (ram)

A zone of grazing pressure centred on a stock wateringpoint in an arid area. Within the zone there is aninteraction between the reliance of stock upon thewatering point and their capacity to graze radially forfood. This interaction is registered by the vegetationpattern such that there is a radial change in vegetationwith distance from the watering point.

PIPE SPILLWAY (eng)

See SPILLWAY.

PIPING (eng, str)

Syn. EARTHWORK TUNNELLING.

PIPING FAILURE (eng, Str)

The failure of an earthwork due to piping. The 'pipewhich forms eventually allows water to flow freelythrough the wall and may ultimately cause its completecollapse.

PIT (Ifm, str, mm)

A closed depression excavated by human activity. Itmay be relatively large as associated with gravel or coalextraction, or small as associated with soil profileexamination. The term is also used synonymously withthe noun "mine". See also DISTURBED TERRAIN,

PITTING (ram)

The making of shallow pits or depressions in the soil,of suitable capacity and distribution, to retain waterfrom rainfall on rangeland. It is used as a reclamationmeasure on eroded rangeland, the pits retaining waterand thus encouraging growth of protective vegetation.Pitting is normally carried out using a disc typeimplement. However, specially designed tinedimplements may also be used, in which case theprocedure is known as TINE PITTING.

PIVOT LINE (agr)

A line joining turning points on a strip cropping plan. Itrepresents the projection along which each stripchanges direction due to changes in topography.

The angles either side of a pivot line, made by itsintersection with the key lines, must be equal otherwisethe strip widths either side will be unequal. The totalangle of a bend in the strips must not be too small, toallow for turning machinery. Recommended minimumangle is 1300, but this is negotiable provided thelandholder understands the problems.

/

PLAIN (Um)

A general term encompassing large, very gently inclinedor level landtorms ot unspecified geomorphologicalorigin.

PLANIMETER (lev)

An instrument used to measure areas on a map. Itsmain advantagelies in its ability to measure irregularshapes such as tor catchment areas. Planimetersconsist of a graduated measuring wheel pivoted on atracer arm. The area is determined by the number ofrevolutions of the measuring wheel in relation to themap scale.

PLANIMETRIC MAP (lev)

A map showing physical features and cultural detail inplan view only, omitting the dimension of retativeheights.

PLANT AVAILABLE WATER CAPACITY(sol)

See AVAILABLE WATERHOLDlNG CAPACITY.

PLANT GROWTH INDEX (agr)

A numerical representation of the probability of plantgrowth being restricted in a given area by the principallimiting factors ot soil moisture, temperature and light.Indices are derived for these factors such that eachindex has a numerical value ranging from zero,completely limiting, to unity, non-limiting. They arecalculated from water balance data, and temperature/light/pasture production data. The most limiting of thethree indices is taken as the plant growth index,

The plant growth index is used to indicate lengths ofgrowing seasons, periods when ground cover maydeteriorate, and suitable tillage and sowing times.

PLANT NUTRIENT (agi)

Any etement essential to the growth of plants or whichcan be beneficially utilised by them. Such nutrients aresupplied from the soil or from application of fertiliserand include:

Major elements: Nitrogen, phosphorus, potassium.Minor elements: Calcium, magnesium, sulfur,Trace elements: Iron, copper, zinc, manganese, boron,

molybdenum, chlorine, (sodium).

PLANTING (agi)

The ptacement of seedlings in the soil to allow for theirsubsequent growth. Cl. SEEDING.

PLASTIC (sol)

Describes soit material which is in a condition thatattows it to undergo permanent deformation withoutappreciable volume change or elastic rebound, andwithout rupture. The importance of this property in a soilconservation context relates to the soil's behaviourwhen used in earthworks or when cultivated. Thisbehaviour is characterised according to the system ofAtterberg Limits. See also SOIL PLASTICtTY.

93

PLASTIC LIMIT (sol)

See ATTERBERG LIMITS.

PLASTICITY INDEX (sol)

See ATTERBERG LIMITS.

PLATEAU (If m)

A tevel to rolling tandforrn of plains, rises or low hillsstanding above a cliff or escarpment which extendsaround a large part of the plateau's perimeter. Plateauxare commonly associated with flat-lying strata or lavaflows.

PLAYA (Ifm)

A shattow closed depression flooded intermittently andat other times displaying a surface of salt or mud.

PLOUGH-PAN (sol)

A pan made up of a layer of soi? compacted byrepeated tillage at a constant depth over many years.

PLOUGHING (agi)

A primary tilla ge operation which is performed to loosenand shatter soil with partial or complete soit inversion.The operation also incorporates organic residues intothe soil.

PLU VIOGRAPH (hyd)

See PLU VIOMETER.

PLUVIOMETER (hyd)

An instrument for measuring rainfall which incorporatesa continuous record in the form of a pen trace on agraduated time chart which is known as thePLIJVIOGRAPH, The total amount of rainfall and itsintensity at any time can be measured.

PNEUMATIC PRESSWHEEL (eng)

See PRESSWHEEL.

POCKET STEREOSCOPE (rms) SeeSTEREOSCOPE.

POINT BAR (Um)

A deposit of unconsolidated sediment on the inner bankof a stream channel meander. lt forms because thevelocity of flow in the channel is tower against the innerbank.

POINT QUADRAT (ram)

See OUADRAT.

POINT SOURCE (gen)

A source of pollution which can be pinpointed. tn a soilconservation context it typically applies to a source ofsediment which can be limited to one precise location,For example, an activety eroding gully head could be apoint source of sediment contributing to the blockingof an adjacent road culvert. Ant. NON-POINT SOURCE.

POINT TRANSECT (ram, agr)

A series of individual siles where spot samples or otherquantitative measurements of vegetation are recorded,The point transect typically follows a line along whichpoints are identified by use of a wheelpoinf or a systemof step- pointing. Cf. BELT TRANSECT, LINETRANSECT.

PONOAGE BANK (str)

See BANK.

PORE SPACE (sol)

The fraction of the bulk volume or total space withinsoils that is not occupied by solid particles. See alsoBULK DENSITY, SOIL POROSITY.

PORTAL (mm)

The constructed surface entrance to a tunnel, drive ordrift.

PORTAL CUT (mm)

Syn. BOX CUT.

POST-EMERGENT HERBICIDE (agr)

See HERBICIDE.

PRE-EMERGENT HERBICIDE (agi)

See HERBICIDE.

PRE-SOWING HERBICIDE (agi)

See HERBICIDE.

PRESSWHEEL (eng)

One of a set of wheels, attached to the rear of a drill,which passes along a row after it has been sown andfirms the soil around and/or over the seed. Singlewheels and twin inclined wheels are used which mayhave a metal or rubber tyre. The lyre may have aconvex or concave outer profile.

A pesswheel unit.

94

ZERO PRESSURE PRESS WHEELS have a rubber tyrewith no internal air pressure and raised ribs around thecircumference of the lyre are used to concentrate thesoil-firming effect of the wheel. In contrast, PNEUMATICPRESSWHEELS have a tyre with internal air pressurewhich firms the soil. Narrow section hollow steel wheelsare common on imported machines and are often called"packer wheels",

Convex zero pressure presswheel.

Concave zero pressure presswheet.Pneumatic ribbed presswheel.

7

Twin inclined presswheels.

Steel packer wheel.

PRESSWHEEL DRILL (eng)

See DRILL.

PRESSWHEEL PLANTER UNIT (eng)See DRILL.

PRIMARY BASIN (urb)

A sediment basin installed immediately upstream of adetention basin, or a system of detention basins, toentrap and thus remove the majority of sediment fromflows before they enter the detention basin system.

PRIMARY COVER (agr)

Short term quick-growing plants used in vegetativestabilisation while tonger lasting vegetation is beingestablished, See also SECONDARY COVER.

PRIMARY DUNE (csd)

See DUNE.

95

PRIMARY MINERALS (mm)

Syn. PRIMARY ORE.

PRIMARY ORE (PRIMARY MINERALS) (mm)

Ore or minerals which retain their original form andcomposition and have not been subject to chemicalchange. Cl. SECONDARY ORE.

PRIMARY PARTICLES (sol)

The individual mineral particles of which a soit is madeup, such as sand, sift and ctay particles, in their non-aggregated state.

PRIMARY PROFILE FORM (sol)

The first division of the Factual Key soil classificationsystem. Four primary profile forms are recognised -organic soils, uniform soils, gradational soils andduplex soils.

PRIMARY SPECIES (csd)

See STABIL;SÌNG SPECIES.

PRIMARY SPILLWAY (str)See SPILLWAY.

PRIMARY TILLAGE (agr)See TILLAGE.

PRIME AGRICULTURAL LAND (lev)

Land which because of its soil, climate, topography andlocation is suitable for a wide range of agricultural uses,It is invariably associated with prime agricultural soilsand high inputs are not necessary to ensuremaintenance of long term productivity, soil fertility andsoil stability. See also GOOD AGRICULTURAL LAND,UNIQUE AGRICULTURAL LAND.

PRIME AGRICULTURAL SOIL (lev)

A soil which has no significant physicat or chemicallimitations for agricultural use, and where high inputsare not necessary to ensure maintenance of long termproductivity, fertility and stability. See also GOODAGRICULTURAL SOtL, UNIQUE AGRICULTURAL SOIL.

PRINCIPAL POINT (rms)

The centre of a vertical aerial photograph. If may bedetermined by the intersection of diagonals fromcollimating marks in the corners, or the intersection oflines joining horizontal and vertical 'V' nicks on theedges of most commercially available aerialphotographs.

PRINCIPAL PROFILE FORM (sol)

The end point ot the Factual Key soil classificationsystem. A principal profite form code, such as Ug5.16,Gn2.23 or Dy3.41, describes the soil pro/ile to such anextent that it will be possible to make a reasonablyconcise statement concerning the soils belonging to it.

PRINCIPAL PROFILE FORM (Continued)

An EXTENDED PRINCIPAL PROFILE FORM may includeadditional information describing the surface soil inmore detail and/or material below the solurn. Forexample, see Northcole (1979) p. 121-122.

PRINCIPAL SPILLWAY (str)

See SPILLWAY.

PRIOR STREAM (Ifm)

The remnants of a former stream channel. Typically along, generally sinuous ow ridge built up from materialsoriginally deposited by channelised flow along the lineof the former slrearnbed. It can also include buriedchannets under alluvium which may still contain flowingwater.

PROFILE DRAINAGE (sol)

Syn. INTERNAL DRAINAGE.

PROFILOMETER (gen)

An instrument used for assessing surface microrelief.Usually consists of a portable framework with a seriesel adjustable pins which drop onto the land surfacewhen the instrument is placed on the ground. Theupper ends of the pins then depict the surface profilewhich can be photographed or numerically recorded. Aseries of such records, usually from different culturaltreatments, gives a measure of the roughness of thesurface which is valuable in soil management studies,

A GULLY PROFILOMETER is a similar instrumentadapted for characterising gully cross-sections.

A profilometer on a cultivated soil surface.

96

A gully pro uilometer being used.

PSEUDOSCALD (gen)

A natural surlace with a scald-like appearance. Theoriginal surface soil is present but the scald appearanceresults from a thin ayer of clayey material which crackson drying and reseals on wetting.

PSEUDOSCOPIC STEREO IMAGE (ims)

A three-dimensional impression of the land's surfacewhich is the reverse of that actually existing. Forexample, ridges may occur as valleys and vice versa,This effect is produced when the positions of a stereo-pair of aerial photographs are interchanged, thus whatwould normally be the right-hand photograph is placedon the left-hand side and vice versa tor the left-handphotograph.

PUDDLING (sol)

The act of destroying soil structure by compaction ortitfage of the soil at high moisture content, therebyreducing its porosity, permeability and aggregation.Stock often damage soil structure in this way when theyare tell on wet or waterlogged pasture.

QUADRAT (agi)

A plot of and selected al random tor the observationor measurement of plants within it. lt is used as asampling technique for the study of the plant populationof an area. Such a plot is usually selected by therandom throwing of a rigid trame, which is usuallysquare.

Quadrats may also be points. Such POINT OUADRATSare observed at regular ntervats along a line transect.

I 13

RAINDROP EROSION (gen)

See EROSION.

RAINDROP SPLASH (gen)

The result of the violent break up and dispersion ofraindrops when they hit the ground surtace If thesurface is not protected soil particles may be dislodgedand spattered a considerable distance, due to theenergy of the raindrops impact. See also SPLASHEROSION.

Raindrop splash on bare soi!.

60320-15204_7

97

't , 1*

4 L'-

RAINFALL INTENSITY (san)

The rate of rainfall for any given time interval, usuallyexpressed in millimetres per hour (mm/h), See alsoDESIGN RAINFALL INTENSITY.

RAINFALL SIMULATOR (gen)

A piece of equipment used in erosion studies forsimulating rainfall. Such a unit usually has its own watersupply and power source and is therefore portable.Provision is made for water to be sprayed onto a plotof soil through appropriate nozzles and at such apressure that a range ot rainfall intensities, terminalvelocities and drop sizes can be simulated. n this waythe relations between rainfall, infiltration, runoff, soilstructure, soil loss, surface roughness or cover levelscan be studied without the need for natural rainfallevents,

For small plots a single nozzle and a rotating disc withan adjustable orifice is typically used to obtain realisticraintalls and Ihe unit is called a rotating disc simutator,For long plots an oscillating spray line is typically usedto obtain realistic rainfalls in a semi-permanent set-upend the unit is called a RAINIJLATOR.

RAINULATOR (gen)

See RAINFALL SIMULATOR.

RANCE (ram)

Syn. RANGELAND.

a-

RANGE TREND (ram)

Changes in ran geland condition with time, usuallyreferring to medium or long term.

RANGELAND (RANGE) (ram)

Land used for extensive grazing of sheep, cattte orother domestic stock. Rangetand vegetation is typicaltynative or naturatised pasture, and the country in generatis often considered to receive insufficient rainfatt tosupport the economic production of crops on a regutarbasis.

RANGELAND CONDITION (ram)

Describes the current condition of rangetand in retationto the potential condition of the particular area for theattainment ot the defined tand use.

RANK (eng)

A row of tines on a tittage implement. Generally thenumber of ranks is the same as the number of ateratbars in the implement frame.

RANK SPACING (eng)

The longitudinal distance between ranks on a tillageimplement. lt is generatty the same as the spacing ofthe lateral bars in the imptement frame.

98

- - r r'.

'-C.,i'._ ,-----.,, . , . trr ._. -.r, a;.'f -t -. - ..4»'- 1;-r 4ftL-"..

A rainfall simulator ready for operation on a stubble plot.

-a--

RATING CURVE (DISCHARGE CURVE) (eng)

A graphic representation of the discharge of, or flowthrough, a structure or channel section as a function ofwater stage or depth of flow. A tabutar presentation ofthe same data is known as a rating table,

RATIONAL FORMULA (hyd)

A formula for estimating peak discharge of runoff fromthe calchment above a specific point, viz:

CIA

360

where O is peak discharge (m3/s)C is runoff coefficientlis the rainfall intensity (mm/h) for the selectedreturn period (yrs) with storm duration equal tothe time of concentration for the catchment(mins).A is the catchment area (ha)

The rational formula is based on the followingassumptions:

The rainfall is of uniform intensity over the wholecatchmenl for the duralion of the design storm.

* The rainfall duration is equal to the catchmenl'stime ol concentration.

The return period of the peak discharge is equallo that of the rainfall intensity.

As presented the tormula can be used for catchmentsup to 100 hectares. For catchments arger than 100hectares and up to 1200 hectares a correction factor isapplied, to account for the likely breakdown of theabove assumptions in larger catchments which resultsin the overestimation of peak discharge. For catchmentslarger than 1200 hectares the rational formula is notreliable and rainfall-runoff computer models may berequired for design purposes.

REAFFORESTATION (for)

The re-establishment of a foresf on land from which aprevious forest has recently been cleared or destroyed.Cf. AFFORESTATION,

RECHARGE AREA (gen)

An area where water is absorbed to be added to ageologic zone of saturation or aquifer.

RECONNAISSANCE (lev)

A level of survey which involves only a preliminaryinvestigation, providing a guide for the end user.Surveys of this nature are designed to highlightproblems and recommend further investigation it andwhere necessary.

RECREATIONAL CAPABILITY (lev)

The abitity of an area of land to sustain the mostintensive recreational use without the occurrence ofappreciable soil erosion and sedimentation. Over-use ofan area may subsequently require extensive sitemodification and in extreme cases a complete loss ofa recreational facility may occur. See also LANDCAPABIUTY.

RECREATIONAL CAPABILITYCLASSIFICATION (lev)

A method of land classilicaf ion which ranks landaccording to various intensities of recreational usewhich are compatible with conservation of the soilresources of that land. lt is designed to provideplanners with information on the stability of a site! andto identify suitable alternative areas for development,when formulating management strategies.

A key tactor in the classification is the assessment ofvisitor numbers to the recreational site. Such numbersfluctuate widely between and during seasons. Intensiveuse of an area at weekends or over a summer seasoncan cause the gradual deterioration of vegetative cover,loss of topsoil, and the eventual death of establishedtrees. The main factors considered in recreationalcapability classification are the stability of an area foractive or passive recreation, and the intensity to whichthe proposed amenity is to be utilised. This intensitymay range from uses with a heavy impact on theground surface such as playing fields to passive usessuch as viewing the landscape.

Five classes have been used by the Soil ConservationService of New South Wales to classify recreationalcapability:

99

Class A

Land suitable for active recreation with highintensity use.

This class represents the most suitable land forintensive recreational activities, including thosewith a heavy surface impact such as sportingfields, Specific soil erosion control measures foreach site may be required to maintain stability.

Class B

Land suitable for active recreation with moderateintensity use.

The erosion hazard is moderate, limiting the landto intermittent heavy pressures from such activitiesas horse riding or picnicking, Specific soil erosioncontrol measures for each site may be required tomaintain stability.

Class C

Land suitable for passive recreation with lowintensity use.

Includes land with a high erosion hazard and issuitable tor such activities as walking traits andorienteering. Activity areas should be adequatelyidentified and signposted. Vehicular traffic shouldbe controlled and restricted to well formed roadsand surfaced parking bays.

Class D

Land suitable for passive recreation withundeveloped access.

Minimum disturbance will provide the mosteffective erosion control and uses should berestricted to such activities as bushwalkìng andexploring. These activities have a low impact ifdefined trails are not provided. Vehicular accessshould be prohibited or restricted to well formedroads with adequate runoff and erosion controlmeasures.

Class E

Land suitable for passive recreation with controlledaccess.

Similar management to that of Class D butactivities need to be strictly controlled to facilitatesoil erosion control. Where considerable touristpotential exists, special provisions for erosioncontrol may include 'lookout points' at safe orstable locations, and construcled walkways intocritical areas. Erosion control measures will becostly but are essential to prevent the loss of theamenity.

See also LAND CAPABILITY CLASSIFICATION.

RECURRENCE INTERVAL (hyd)

Syn. RETURN PERIOD.

REDUCED LEVEL (sur)

The vertical distance of a point above the particulardatum adopted.

REDUCED TILLAGE (agr)

A general term describing a conservation ti//age systemn which the crop is grown with fewer tillage operationsthan would be the case for conventional ti//age.Herbicides and/or grazing may be used for fallow weedcontroL Cf. MINIMUM TIL.LAGE.

REEF FLAT (lfm)

A level area of and initially built up to low tide level bymarine organisms and subsequentJy aggraded bymarine sediment deposition.

REGENERATION (gen)

The re-establishment of depleted vegetation by naturalseIt seeding and regrowth. lt s commonly associatedwith stands ot native timber that have been logged orpartially cleared, burnt or depleted in some way, thatare being encouraged to return to their naturalcondition. In a soil conservation context, it is associatedwith erosion control, especially in low rainfall pastoralareas where native pastures are encouraged to re-establish by such practices as excluding stock andvermin.

REGOLITH (sol)

The layer or mantle of loose, noncohesiveor cohesiverock material, of whatever origin, that nearly everywhereforms the surtace of the land and rests on bedrock. ltcomprises rock waste of all sorts: votcanic ash: glacialdrift: alluvium: wind-blown deposits: accumulations ofvegetation, such as peat: and soil.

loo

REGULAR CULTIVATION (agr)

The frequent growing of crops requiring tillage, on thesame parcel of land, The proportion of time under tillagephases shall not be less than half the length of timeunder other phases. Cf, CONTINUOUS CULTIVATION,OCCASIONAL CULTIVATION.

REHABILITATION (gen)

The treatment of degraded or disturbed land to achievean agreed level of capability and stability, preferably atleast equal to that which existed prior to degradationor disturbance. Stich rehabilitation may involve, thereshaping of the land surface, spreading availabletopsoil, construction of soil conservation works,revegetation, and the establishment of land usepractices which will ensure continued stability andproductivity.

REMOTE SENSING (rms)

The collecting of information about an object orphenomenon by the use ot sensing devices not inphysical or intimate contact with the subject underinvestigation. The distance of separation might be asclose as a few millimetres or as far as 800 kilometresor more, as in the case of satellites. The devices rangelrom cameras to various scanners and radiometers.(Reference: Rib, MT. and Liang, T. Recognition andIdentification, In Landslides : Analysis and Control,

Rehabilitation work under way on an open-cut coal mine,

Transportation Research Board, National Academy ofSciences, Washington D.C., U.S.A., Special Report 176,Chapter 3, 1978).

The term is commonly used to refer to the collection ofinformation about the earth by aerial photography,airborne radar and satellite.

Most remote sensing devices collect information fromIhe electromagnetic spectrum, From longer lo shorterwave fenglhs, it includes all those techniques Ihat arenormally used in remote sensing systems; gamma rays,x-rays, ultraviolet, visibte light, infrared, microwaves andradiowaves, The most common phenomenon observedwilh remote sensing is the reflection of eleclromagnelicenergy as exemplified by normal aerial photographywhich utilises the reflection of visible light from theterrain.

The interpretation and evaluation of remote sensedmages is based on spectral variation (comparingindividual spectral signatures), spalial variation(comparing variations over a large area), and temporalvarialion (comparing variations over lime).

REMOTE SENSING SYSTEM (rms)

A technique, including methods and equipment, usedfor remote sensing. Two basic lypes of sensors arerecognised:

PHOTOGRAPHIC SENSOR

Involves the production of a permanent magewhen incoming radiation from the object beingsensed is focussed directly upon the recordingmedium. The most lamiliar and widely used sensoris the photographic camera and film, which isgenerally sensitive to wave lengths between 0.36and 0,72 micromelres (effectively the visiblespectrum).

NON-PHOTOGRAPHIC SENSOR

Involves the production of a permanent image byfocussing the incoming radiation upon a transducerwhich converts the radiation to a different type ofsignal, which is lhen recorded upon some medium,such as photographic film. Thus they require atransducer whereas photographic systems do not.Non-photographic sensor systems are often termedIMAGING SYSTEMS but this is not so in all casessince the information need not necessarily bestored as an image but can be kept, for example.on magnetic tape. Non-photographic sensorsoperate in different portions of the electromagneticspectrum, lrom the ultraviolel (0.28 m) to themicrowave (200 mm). They record either reflectedor emitted radiation, Sensors which recordreflected radiation can only operate during daylighlconditions, whilst those which record emittedradiation can operate during the day or night.

RENO MATTRESS (ROCK MATTRESS) (eng)

A mattress-shaped container made of wire mesh, fittedwith rip-rap and used to protect earth surtaces from theerosive action of waler, Il is similar to a gabion but usedwhere a gabion would be unnecessarily deep, such asin lining r!verbanks,

101

RESIDENTIAL DEVELOPMENT (urb)

A level of urban development which provides for theconstruction of roads, drainage and services to caterfor subdivision allotments for housing, typically between400 and 5000 square metres, In older subdivisions waterand sewerage facilities may or may not be available, butin most new residential developments, catering forpermaneril residence in established urban centres, suchfacilities are normally provided. See also LOW DENSITYRESIDENTIAL DEVELOPMENT, STRATEGICDEVELOPMENT,

RESIDUAL FLOW DRAIN (gen)

See DRAIN.

RESIDUAL HERBICIDE (agr)

See HERBICIDE,

RESIDUAL SITE (Ifm)

An area where the in situ processes of weathering.leaching and new mineral formation are dominant,Lateral surface movement is minimal either because oflevel landform, such as a plateau, or where soil materialis of such a nature as to resist lateral movement despitea considerable slope.

RESTORATION (gen)

Rehabilitation of degraded or disturbed land so that, notonly are the former capability and stability re-established, but also the form and usage of the landare returned to a stale closely resembling that betoredegradation or disturbance,

This form of rehabilitation is typically very expensive,and may be virtually impossible where serious soit -

removal has occurred, unless soil is imported from othersources,

RETAINING WALL (gen, urb, eng)

A harrier, usually of uniform thickness and constructedof masonry materials, designed and installed lo holdback unconsolidated rock and/or soil, Its aim is tocounter the gravitational force of the material il iswitholding and prevent mass movement, Small holes orgaps may be incorporated in the wall to cater forseepage.

RETARDANCE FACTOR (hyd)

Syn. ROUGHNESS COEFFICIENT.

RETARDATION STRUCTURE (eng, urb)

Syn. DETENTION STRUCTURE,

RETARDING BASIN (eng, urb)

Syn. DETENTION BASIN.

RETARDING MEASURE (gen)

Any measure designed to delay storm runoff andthereby reduce peak discharge. Such measures may¡nc lude grassed drains, constricted pipe outlets anddetention structures.

RETENTION STORAGE (eng, urb)

The amount of water which can be permanently storedby a retention structure.

RETENTION STRUCTURE (eng, urb)

A structure incorporating both temporary andpermanent water storage components. Runoff in excessof the permanent storage is temporarily held andallowed to drain from the structure at a controlled rateduring and after the runoff event, n order.to reducepeak discharge downstream. The permanent storagemay be used for such purposes as irrigation and/orrecreation. Cf. DETENTION STRUCTURE.

RETURN PERIOD (RECURRENCEINTERVAL) (STORM FREQUENCY) (hyd)

The average period in years between the occurrenceof a storm of specified magnitude and an equal orgreater storm.

lt is an average figure, not an interval. For example, astorm with a return period of five (5) years does notoccur regularly every five years but would probablyoccur ten (10) times in fifty (50) years. See also DESIGNRETURN PERIOD.

Return periods may also be calculated tor floods, andin such cases the term FLOOD FREOUENCY can beused.

REVEGETATION (agr)

The re-establishment of plants on an area of groundthat is depleted or devoid of vegetation, in order toprovide protection against erosive agents. lt is anintegral part of erosion control and prevention on a widevariety of disturbed, eroded and/or degraded tands.

REVERSE-BANK SEEPAGE INTERCEPTORDRAIN (str, eng)

See DRAINS

REVETMENT (eng)

A protective layer of rip-rap or other erosion-resistantmaterial, either permanent or temporary, placed alongthe edge of a stream channel or shoreline, or against abatter, to stabilise the bank and protect it from theerosive action of water.

RHIZOME (agr)

An underground stem, bearing buds and scale-likeleaves, which serves tor both vegetative propagationand survival in a perennial plant. Paspalum is a commongrass species having rhizomes. Cf. STOLON.

102

RIDGE (11m)

A hilt formation incorporating a narrow crest andadjoining slopes. The crest length is greater than thewidth of the adjoining slopes. Cl. HILLOCK.

RIDGE TYPE BANK (str)

See BANK.

RIGID LEVEL (sur)

See LEVEL.

RILL (gen)

A small channel, cut by concentrated runoff, throughwhich water flows during and immediately after rain,Pills typically form as a result of the action ot heavyrainfall on exposed soil surfaces such as recently tilledland or constructed batters. They may be up to 30 cmin depth but would be largely obliterated by tillageoperations. This distinguishes them from gullies. Seealso PILL EROStON.

RILL EROSION (gen)

See EROSION.

RING TANK (gen)

See TANK.

RINGBARKING (gen)

A method of killing trees by encircling each tree with acut deep enough to ensure removal of the cambiumlayer beneath the bark. Ringbarking is often used as alow-cost long-term way of clearing timbered land forgrazing purposes. Its aim is to atlow the gradual spreadof grasses into the ringbarked area as the tree canopydisappears, in the hope that there is a consequentincrease in stock carrying capacity.

RIPARIAN (gen)

Belonging to a river bank. Typically used to describethe rights of access to a river via its banks. Riparianvegetation is that which occurs trom normal river levelto the edge of the floodplain.

RIP-RAP (eng)

Loose rock or stone used to protect earth surfacesagainst erosion by flowing water or wave action, as ina revetrnent.

RIPPER (eng)

A heavy duty tillage imptement consisting of one ormore heavy duty tines which penetrate deepty.loosening and shattering the soil without inversion.Depth of working normally exceeds 200 mm.

A mounted rippei

RIPPING (agr)

The tillage of soil or other material by tined implementwithout inversion, for the purpose of loosening it and-ar improving waler movement and root penetration.Ripping carried out to loosen the soil below normallillage depth is known as DEEP RIPPING (SUBSOILING).See also CONTOUR RIPPING.

RIPPLE DRIFT (gen)

The wavy pattern left on sandy soils after saltaUon hastaken place for some time. See also WIND EROSION.

RISER (eng)

A vertical length of pipe used in a hydraulic structurespecifically to control the level of waler in the structure.Typically used as the inlet of a pipe spi/!way.

RIVER (gen)

See WATERCOURSE.

ROADSIDE BATTER (str, eng)

A batter on the side of a road formed by excavation ordeposition of material durìng road construction.

ROADSIDE EROSION (gen)

Soil erosion associated with the presence of a roadacross a landscape. Such erosion may be directlycaused by the road, or may be existing erosionaggravated by the location, nature or construction ofthe road.

Roadside erosion is usually a result of one or more ofthe following factors:

Lack of provision for safe disposal of water fromthe road surface.

Lack of adequate drainage under the road,particularly where the road crosses a drainage line.

103

Concentration of runoff water along the sides ofthe road, from the road itself and/or from theadjacent catchment.

* Lack of stabilisation of the road shoulders, tab/edrains, mitre drains, batters or other adjacentareas.

ROCK MATTRESS (eng)

Syn. RENO MATTRESS.

ROCK PLATFORM (If rn, Csd)

A level area of rock forming part ot the seashore thatis exposed at low tide. lt results principally from theaction of waves undercutting precipitous shore lines,thus producing the typical coastal rock platform/cliffassociation. The wave action is enhanced by thecontinuous wetting and drying with the tides which aidsthe weathering process.

ROD WEEDER (eng)

A light secondary ti//age implement used for weedcontrol whose main component is a horizontallymounted rod which rotates slowly under the soil surtacein an opposite direction to the direction of travel. Therod is typically of a square or round cross-section 25mm in diameter. lt may be driven by a ground wheel,by tractor power take-oft or hydraulic motor, and rodsurface speed should be about 10% greater than themachine's forward speed. A DEAD ROD is a self-rotating rod mounted behind other tillage implements.

A rod weeder.

ROLLOVER BANK (sfr)

See BANK.

ROOTSTOCK (agr)

An underground plant stem used for vegetativepropagation. See also RHIZOME,

ROTAMETER (lev)

An instrument used for measuring the length of anirregufar line, such as a road or watercourse, on a map.It consists of a small wheel at the foot of the instrumentwhich is guided along the line, and a dial with a rotatinghand that indicates the distance travelled on a

ROTAMETER (Continued)

graduated scate. The measured distance can then beconverted to the corresponding distance on the groundby reference to the map scale. Complete revolutions ofthe rotating hand are registered on a small integratedrecessed diat,

ROTARY SIEVE (gen)

An apparatus used for separating dry soit into itsvarious constituent fractions. lt consists of a rotatingnest of concentric cylindricat sieves of variousdiameters. Rotations are generaily stow, typicaffy 7

ROTATIONAL GRAZING (agr)

The successve grazing of pastures on a sequentialbasis as a means of optimising management of bothstock and pasture. Such a system often invotves shortperiods of heavy grazing fotlowed by periods of rest forherbage recovery in the same season, This aflows forcontrot of weeds, stock parasites, pasture cover, swardheight, stage of growth and composition. lt atsoprovides opportunities for pasture fertilisation andrenovation as necessary, and generat pasturemanagement in retation to stock numbers, teedavaitabitity and rainfatf occurrence,

ROTATIONAL SLIP (gen)

See LANDSLtP.

ROUGHNESS COEFFICIENT (RETARDANCEFACTOR) (hyd)

A measure of the retardance to ftow in a channel. Themore retardance the higher the roughness coefficient.t is computed to assist in the prediction of ftowvetocitres for design purposes using Manning's Formulaand has the symbot 'n'.

Factors which affect retardance inctude:

- physicat roughness of the materiat forming thechannel, e.g. presence of surface irregutarities inmin9 materials increases n.

vegetation, e.g. height, density, type.

cross'section, e.g. abrupt changes in sectionatong the channel increase n, as does anincrease in depth of flow.

channel atignment, e.g. severe meandering withcurves having relatively small radii increase n.

erosion and sedimentation, e.g. active erosionincreases n.

obstructions. e.g. number, type, size.

The vatue of 'n' in a naturat or constructed vegetatedchannef varies with the season and from year to yearand hence is not a fixed value. Thus, att the abovefactors shoutd be evaluated with respect to the kind ofchannel, the degree of maintenance, the seasonatrequirements and the season of the year when thedesign storm normatty occurs, as a basis for setectingthe vatue of the roughness coefficient.

104

ROUGHNESS ELEMENT (gen)

An object which interrupts wind ftow over a surface.

RUBBLE DRAIN (eng)

See DRAtN,

RUNNER OPENER (eng)

See SOIL OPENER.

RUNOFF (gen)

That portion of precipitation not immediatety absorbedinto or detained upon the soit and which thus becomessurface ftow. Runoff is the major agent of water erosionparticularly on fitted soils, The amount of runoff dependson rainfall intensity and duration, land stope, surfaceroughness, vegetative cover and surface soit conditionsincluding moisture content, (Symbol: R, Units: mm).

RUNOFF COEFFICIENT (hyd)

The C factor in the rational formula, which equats theratio of the rate of runoff to the rate of rainfatt, tindicates the proportion of the raintatt rate that isactuatty contributing to the runoff rate and as such thecoefficient is atways tess than 1.0.

The runoff coefficient depends on rainfall infensif y,topography, depression storage, infiltration, interception/oss and interception storage. For its estimation,numericat vatues are attocated lo various runoff-producing characteristics retated to these factors. thesum of which gives the runoff coefficient. Thisassessment is subjective and represents one of themain probtems in the application of the rational formulafor catcutating runoff rates.

N.B. A stricter definition of the runoff coefficientis that, for a specific runoff event, it is the ratio ofthe peak rate of runoff to the mean rainfall intensityof the storm causing the runoff, when both rainfalland runoff are expressed in the same units. Forpracticat soit conservation purposes, the twodefinitions are taken as being the same,

RUNOFF PLOTS (gen)

Smatt uniform parcets ot tand from which runoff and soilloss can be measured under natural or artificial rainfall.Typically a series ot plots is established, with suitablereplication, and each plot is treated so that runoff andsoit loss can be measured under different landmanagement practices.

RUNON (gen)

Surface water flowing onto an area as a result of runoffoccurring higher up the slope. Often used in an urbancontext as a contributing factor to increased erosionhazard, Also used in semi-arid areas to refer to surfacewater which is diverted from sloping country onto flatterland to achieve increased production from such land.See also WATERSPREADING,

RURAL CAPABILITY ('ev)

The ability of an area of and to sustain permanentagricultural or pastoral production, at its most intensivelevel, consistent with protection from soil erosion andwithout permanent damage. Land which is usedbeyond its rural capability will deteriorate rapidty,resulting in loss of production and a permanent loss ofsoil resources. See also LAND CAPABILITY.

RURAL CAPABILITY CLASSIFICATION(lev)

A method of (and c/assification which ranks landaccording to various intensities of rural use which arecompatible with conservation of the soil resources ofthat land.

The classification does noi necessarily reflect theexisting land uses, rather it indicates the potential ofthe land for such uses as crop production, pastureimprovement and grazing. In assessing this potential.the classification takes into account climate, physicalcharacteristics of the soil and landform to determine themost intensive rural use which is compatible withconservation management and sustained production.

The dominant emphasis in rural capability ctassificationis placed on soit breakdown which is essentially relatedto the potential use of the land in terms of tillagepractices. The classification system used by the SoilConservation Service of New South Wales is based onfour categories related lo tillage practices. (N.B. OtherStates systems may vary somewhat.)

The tirst represents land suitable for regu/arcu/tivaf ion. The land must be capable ofsustaining at least two successive seasonal orannual tillage phases for crop production inwhich the tilled layer is inverted or shatteredwithout producing either a significant increase insoil erosion susceptibility or a significantdeterioration in soil structure. The proportion oftime under tillage phases shall not be less thanhalf the length ottime under other land uses. ltincludes land where the soils are: sufficientlydeep with a structure and texture which will notreadily break down under tillage: free ofexcessive salts: relatively free ot large stones soas not to restrìct the use of tarm machìnery: andwhich have efficient drainage but sufficientmoisture holding capacity to suit therequirements of the crop to be grown.

The second category includes tand suitable foroccasiona/ cu/fivaf ion, which is capabte of theinfrequent growing of crops utilising tillagepractices involving a series of soil workings. lt island suitable tor grazing that can be occasionaltytilled for pasture establishment or renewal, butbecause of site factors such as soil type, slope.topographic location or drainage is not suited toregular cultivation.

The third category represents grazing landunsuited to tillage operations and includesexcessively steep or stony land, areas with higherosion potential and/or soils which limitproductivity due to their depth or physica1fertility.

105

The final category includes land unsuitable forthe cropping or grazing enterprises mentionedabove because of the land's physical limitationsto conventional rural production, which result inan extreme erosion hazard if general landclearing occurs.

These four categories, defining potential intensity ofrural use, are further subdivided depending on the soitconservation measures required to sustain permanentproduction. The following eight classes are defined:

Land suitable for regular cultivation.

Class I

No special soil conservation measures required.

Class II

Simple soil conservation measures required suchas adequate crop rotation. May include strategicearthworks.

dlass III

Intensive soil conservation measures required, suchas graded or diversion banks and waterways.together with mana gement practices as in Class

Land suitable for grazing and occasionalcultivation.

Class IV

Simple soil conservation measures required suchas stock control and application of fertiliser. Mayinclude strategic earthworks.

Class V

Intensive soil conservation measures required, suchas level or diversion banks and contour ripping,together with management practices as in ClassIV.

Land suitable for grazing only.

Class VI Judicious soil conservation managementmeasures required to ensure an adequate groundcover is maintained. Such measures may includelimitation of stock, broadcast seeding and fertiliserapplication, prevention of fire and destruction ofvermin. May include strategic earthworks.

Land unsuitable for general rural production.

Class VII

Land best protected by green timber because oferosion hazard, steepness, shallowness orinfertility. General clearing of timber is notrecommended but strategic logging or very limitedgrazing may be practised under strict control formanagement purposes such as fire control.

Class VIII

Land unsuitable for agricultural or pastoral uses.Should not be cleared, grazed or logged butulilised for activities compatible with thepreservation of the natural vegetation such aswildlife reluges and scenic areas.

See also SOIL CONSERVATION FARM PLAN, LANDCAPABILITY CLASSIFICATION.

RURAL RESIDENTIAL DEVELOPMENT(uit)A level of urban development which provides for theconstruction of roads, drainage and services to caterfor subdivision attotments typically between 2 and 10hectares. Water and sewerage supply may or may notbe provided. Such development generally caters forpermanent residence in rural areas close to urbancentres, including hobby farms or rura/ retreats.

RURAL RETREAT (gen)

A type of land development involving the retention orestablishment of as much native vegetation as possibleand the exclusion of agricultural practices includingtillage and/or grazing. Controlled clearing may benecessary on each lot to provide a house site, areasonable view and for fire control.

RURBAN (PEAl-URBAN) (urb)

A general term used to describe land on the peripheryof established urban centres. The land is characterisedby an assortment of land use activities, including marketgardening and hobby tarms, which are typicallyinfluenced by the adjacent settled areas. Rurban tandis often considered in the context of having potentialfor future urban expansion.

S.T.P.P. (sol)

Syn. SODIUM TRIPOLYPHOSPI-IATE.

SACRIFICE ZONE (ram)

The centrat portion of a piosphere in which thevegetation inevitably becomes degraded or the soilseroded due to high pressures of grazing and trampling.

SALINE SOIL (sol)

A soil which contains sufficient sotuble salts toadversely affect plant growth and/or land use. Generallya level of electrical conductivity of a saturation extractin excess of 4 mS/cm at 25°C is regarded as a suitablecriterion to define such a soil. See also SOIL SALINITY.

SALINISATION (gen)Syn. SALTING.

SALTATION (gen)

Particle movement in water or wind where particles skipor bounce along a stream bed or land surface.

The preferred usage relates to the bouncing movementof partictes of soil or sand grains across the landsurface when being moved by wind. Partictes between

106

0.1 and 0.5 mm are commonly moved in this way andusually bounce no higher than 50 cm. When they returnto the surface the moving particles impinge on othermaterial, which may detach more particles therebyperpetuating the process. See also WIND EROSION.

SALTING (SALINISATION) (gen)

The accumulation of free salts in part of a landscapeto an extent which causes degradation of vegetationand/or soils. Typically caused by hydrological changesas a result of human use of land, particularly in areasof marine geology. Two broad types of salting arerecognised:

DRYI.AND SALTING

Salting associated with non-irrigated land. It iscommonly caused by the clearing of hillslopeswhich allows an increase in rainfall intake and arise in water table level. Subsequently, seepage isincreased enabling dissolved salts to flow laterallyunderground and surface as salty water lowerdown the slope. The salt becomes concentratedin out-flow patches typically resulting in death ofnormal vegetation and the creation of bare areaswhich become an erosion hazard. Salt crystals canoften be observed on lhese patches.

Rec/amation measures may include diversion ofextraneous runoff, sowing of appropriate salt-tolerant species with minimum soil disturbance,mulching with straw or hay, heavy fertilisation andexclusion of stock. In some situations deep ripping,incorporation of gypsum, catchmenl tree plantingand/or artificial drainage may also be appropriate.

In level semi-arid areas or dunefields, salineseepage at the toe of dunes may occur afterclearing, along with salting of the lower swales,Naturally saline areas also occur in certainundulating arid areas, and occasional very largerains flush salt from these, adversely affectingvegetation downslope.

IRRIGATION SALTING

Salting associated with irrigated land. It is causedby the irrigation of crops using river water and/orgroundwater which may be already mildly saline.A cycle can build up, under continued irrigation,whereby the salinity of both soils and watersources increases. This is due to a complexinteraction of irrigation practice, crop needs,leaching requirements and the nature of soils,landform, geology and climate of the area.

Salting of irrigated land can follow the raising ofsaline water tables lo within capillary reach of plantroots, due to movement of excess water to thewater table.

Control measures include careful regulation ofirrigation in relation to crop needs, crop selection,drainage and soil amelioration as well as improvedcatchment management to reduce base levels ofriver salinity. See also SALINE SOIL, SOILSALINITY.

Extensive dry/and salting o! a grazing paddock.

SAND (gen, csd)

A fairly uniform deposit ol granular breakdown materiallargely derived lrom sUiceous 'rocks and composedmainly of quartz grains. In some soils calcareousfragments of sand size are included.

SAND (sol)

A soil separate consisting of partictes between 0.02 and2.0 mm in equivalent diameter. Fine sand is defined asparticles between 0.02 and 0.2 mm, and coarse sandas those between 0.2 and 2.0 mm.

SAND BLAST (agr)

The damage to plants caused by abrasion fromparticles moved by wind action.

SAND DRIFT (gen)

Sand moved by wind action, either by surface creep orsaltation and subsequently deposited.

SAND FLOW (gen)

See EARTHFLOW,

SAND PLAIN (If m)

An extensive, sandy, level to gently undulating landformwith little topographic relief and without streamchannels. Sand plains were possibly formed by sheet

107

- C._-c-'itt

- -: - -- -.- >__r.- C-

"---. ,C-' ---

-. .

-a,

¿-1- f,

e,

or stream flow, but are now relict and modified by windaction, They are usually found in arid or semi-aridregions, exhibit low inherent fertility and carry scrub orheath type native vegetation, They may also occurbehind coastal sand dunes.

SAPLING (for)

A young free less than 100 mm in diameter chSt-high.

SATURATION EXTRACT (soi)

A solution derived by saturating a soil sample withwater under standard conditions for a period longenough ta dissolve the soluble constituents present.The solution is subsequently extracted by fittration orcentrifuged, and used in chemical analysis ormeasurement related to the soluble constituents and/or other ions present.

SAW LOG (for)

A fog that is suitable for the production of timber orother products by sawing.

-

SCALD (gen)

A bare area produced by the removal of the surface soilby wind and/or water erosion. The result is exposureof the more clayey subsoil which is, or becomes,relatively impermeable to water. A typical erosion formon duplex soils in arid or semi-arid regions. Scalds vary

SCALD (Continued)in size from a few square metres to hundreds ofhectares, and are very difficult to revegetate due to thelack of topsoit. tow permeabiHty, and often satinesurface. The term is atso used for a bare surface areacaused by salting.

SCALDING (gen)

The process involved in the formation of sca/ds.

SCARIFIER (eng)

A filage implement used for both primary andsecondary ti//age at depths up lo 150 mm. Medium dutytines are fitted at an overall tine spacing ranging from150 fo 250 mm. The usual tine cross-section is suchthat the longitudinal dimension is greater than Ihe lateraldimension. Breakout torce is usually in the range of 0.6to 1.4 kN.

SCARIFY (agr, gen)

To abrade, scratch, or modify the surface, such as toscratch the impervious seed coal of hard seed or fobreak the surface of the soil with a scarifier.

A sca filie!.

SCARP (If m)

A vertical ornear vertical peripheral surface created bythe displacement of overlying material typically by massmovement,

108

Lf'

-s ;- ..

_____--t- - - -.,-. c.

'

- - ___-s

-t

Scalded country in western New South Wa/es.

In a broad sense, the term encompasses variousprecipitous faces, including those of cliffs andescarpments, but it is usually applied to descriptions oflandslides. The MAN SCARP is the exposed surfaceof separation remaining on the undisturbed ground atthe periphery of Ihe landslide. Main scarps may alsooccur on some flow-related mass movements.

MINOR SCARPS are produced by displacements withinthe landslide's moving mass and this distinguishesthem from flow-related movements,

SCOURING (gen)

A lerm commonly used to mean localised erosion of abank or channel which typically occurs due to excessiveslope, turbulence or flow velocity. Can also be appliedto focalised del/ation due to wind erosion.

SCREE (lfm)

Steep slope covered with loose fragments of rock, Seealso ESCARPMENT. Cf. TALUS.

SCROLL (Ifm)

A long curved very low ridge, built up by channelisedflow and efl retid by channel migration.

SEASONAL CRACKING (sol)

A phenomenon in expansive soils which, during a dryperiod, develop cracks as wide or wider than 6 mm andwhich penelrale at least 0.3 m into the soil material.

SECONDARY COVER (agr)

Long term or permanent cover used in vegetativestabilisation. lt can be established at Ihe same time asor aller a primary cover.

SECONDARY DUNE (csd)

See DUNE.

SECONDARY MINERALS (mm)

Syn. SECONDARY ORE.

SECONDARY ORE (SECONDARYMINERALS) (mm)

Ore or minerals resulting from the chemical alteralionof primary ore. For example, weathering and oxidationchanges original sulphides to sulphates, carbonates andoxides.

SECONDARY SPECIES (csd)

See STABILISINC SPECIES.

SECONDARY SPILLWAY (sfr)

See SPILLWAY.

SECONDARY TILLAGE (agr)

See TILLAGE,

SEDIMENT (gen)

Material ol varying size, both mineral and organic, thatis being, or has been, moved lrom its site of origin bythe action of wind, water, gravity, or ice, and comes torest on the earth's surface either above or below sealevel, See also BEDLOAD, SUSPENDED SEDIMENT.

SEDIMENT BASIN (gen)

The pondage of a large sediment trap, formed by theconstruction of a barrier or dam, built at a suitablelocation on a flowtìne to entrap gravel, sand, silt or othersedimentary material carried by runoff.

SEDIMENT CONCENTRATION (hyd)

The instantaneous measurement of the quantity ofsediment carried in a unit volume of water, If bedloadis not sampled then the suspended sedimentconcentration can be determined. The preferred symbolis Cs, with units of kgfm3.

r

"4-

t-e

1?'' ;---c-

109

SEDIMENT DISCHARGE (hyd)

The quantity of sediment, measured in dry weight perunit time, transported through a channel cross-section.lt is obtained by multiplying the sediment concentrationby the stream discharge.

SEDIMENT LOAD (gen)

The sediment carried in ftowing water, includingsediment in suspension and bedload.

SEDIMENT TRAP (SILT TRAP) (gen)

A structure, usually relatively small, designedspecifically to collect sedimentary material in a drainageline. Such a structure may be built in a gully aboveanother larger structure to prevent it becoming fittedwith sediment, and has the additional advantages ofreducing flow velocity and minin-iisìng channel scouring.lt may also be fabricated as a box-like device inassociation with a culvert or other similar structure,Sediment traps should be regularly cleaned out tomaintain their efficiency. Cf, SEDtMENT BASIN,

SEDIMENT YIELD (gen)

The total amount of sediment produced by a catchmentand delivered by flowing water to a point underevaluation, usually the catchment outlet. lt may beexpressed in terms of a single rainfall event or in termsof a specified period of time,

SEDIMENTATION (SILTATION) (gen)

Deposition of sediment. The typical use of the termwould infer deposition by water, tn a soil conservationcontext, sedimentation is an end point in the erosionprocess, with transported soil material being deposited

Sedimentation of a town water supply dam,

SEDIMENTATION (Continued)

in locations such as in a channel, along a fence lineon an area of low slope, or in a gully, creek, riversediment trap or dam.

N.B. Technically the term siltation refers to thedeposition of silt particles, but il is more commonlyused lo refer to the deposition of sediment.

SEEDBED (agr)

The layer ol soil which, when suitably prepared,receives sown seeds and provides for their subsequentgermination and growth.

SEEDER (eng)

Syn. DRILL.

SEEDING (agi)

Any process whereby seeds are transmitted to asuitable growth medium which will provide for theirgermination and subsequent growth. lt may occurnaturally or be carried out as in sowing. See alsoBROADCAST SEEDING, TEMPORARY SEEDING,PERMANENT SEEDING, DIRECT SEEDING, BANDSEEDING, Cf. PLANTING,

SEEPAGE (gen)

The process by which water percolates downwardsand/or laterally through the soil, often emerging atground level lower down a slope. The term is frequentlyused in relation to the percolation of water through aconstructed earth wall, See also SITE DRAINAGE,EARTHWORK TUNNELUNG.

SEEPAGE INTERCEPTOR DRAIN (str, eng)See DRAIN.

SELECTIVE HERBICIDE (agr)

See HERBICIDE.

SELECTIVE LOGGING (for)

See LOGGING.

SELF-MULCHING (sol)

The condition of a weIlaggregated soil in which thesurface layer forms a shallow mulch of soil aggregateswhen dry. Aggregation is maintained largely as aresponse of the clay minerals present to the naturalprocesses ot wetling and drying. Such soils typicallyhave moderate lo high clay contents and markedshrink-swell potential. Any tendency lo crust and sealunder the impact of rain is counteracted by shrinkageand cracking, thus producing a mulch effect as the soildries out. Tillage when wet may appear to destroy thesurface mulch which, however, will reform upon drying.Cf. HARDSETTING, MASSIyE.

110

SEMI-ARID (l'arn)

Refers to climates or regions which lack sufficientrainfall for regular crop production. Usually defined asa climale with annual average rainfall greater than 250mm (10 inches) but less than 375 mm (15 inches). Innorthern Australia regular crop production may becomeunreliable where annual average rainfall is less than 700mm (28 inches), mainly due to high evaporation rates.See also ARID.

SEMI-IMPROVED PASTURE (agi)

See PASTURE.

SENSOR (rms)

Any device which gáthers energy, typically electro-magnetic radiation, and presents it in a form suitablefor obtaining information about the environment, Passivesensors such as thermal infrared and microwave, utiliseelectro-magnetic radiation produced by the surface orobject being sensed. Active sensors such as radarsupply their own energy source,

SETBACK (csd)

A nominal boundary designed to delineate a coastalbuffer zone.

SEULEMENT (str)

The loss in height and volume of a newly formed earthstructure through the process of consolidation, Theamount of settlement depends on how well thestructure is compacted during construction, and on soiltype. See also FREEBOARD.

SHADOW (rms)

The reflected image of a ground object imprinted on anaerial photograph. Shape and shadow are closelyassociated in terms of aiding identification, i.e. shapeof the shadow, such as in the identification of coniferousspecies.

SHANK (eng)

Syn. TINE.

SHAPE (rrns)

Refers to the ground outline of an image on an aerialphotograph, Such land features as roads and railwaylines have special characteristics. Houses, commercialpremises and recreation areas all have characteristicshapes which will be recorded on the aerial photograph.

SHAPING (sfr)

Physical reorientation of land surface materials bymechanical means to produce a pre-conceivedlandtorm, See also GULLY SHAPING.

SHEAR FAILURE (eng, sol)

A breakdown of the ability of soil material to maintaìnits aggregated structure such that one body of soilmaterial is caused to move past, or in relation to, the

adjacent materials. It ¡s a principal factor in the initiationof landslides and landslips. Shear failure is triggeredby:

* Factors that contribute to increased shear stressincluding: removal of lateral support (e.g. erosion bywaler and ice, previous mass movement, huñianactivity by cut and till operations); surcharge (e.g.weight of precipitation, seepage pressures,construction ot till, weight of buildings): transitorystresses (e.g. earthquakes, vibrations from blasting):removal of underlying support (e.g. undercutting byflowing water or waves, weathering, tunnel erosion):and lateral pressure (e.g. freezing water in cracks).

Factors that contribute to low or reduced shearstrength including: initial state of the material givingit inherent low strength through its composition (e.g.sedimentary clays and shales), texture (e.g.unconsolidated material) and gross structure andslope geometry (e.g. faults, bedding planes, inclinedstrata): changes due to weathering (e.g. physicaldisintegration of granular rocks, removal of matrixmaterial): and changes in intergranutar forces due towater content and pressure in pores and fractures.

Factors that contribute to both increased shearstrength and reduced shear strength such as theaddition of water,

SHEAR STRENGTH (sol, eng)

The internal resistance of a soil to shear along a plane.The resistance is caused by inter-granular friction andcohesion.

SHEAR STRESS (soL eng)

The torce per unit area acting along a given plane andtending to cause shear (allure within a soil mass. Alllandslides invotve shear failure of land surface materialsunder shear stress.

SHEET EROSION (gen)

See EROSION.

SHEET FLOW (OVERLAND FLOW) (gen)

Water flowing in a thin layer over the land surface. In asoil conservation context it is usually storm runoff andmay lead to sheet erosion.

SHELTERBELT (gen)

An area of living trees and/or shrubs established andmaintained for the protection of grazing animals fromadverse climatic conditions. Shetterbelts may also serveas windbreaks.

SHRINK-SWELL POTENTIAL (sol)

The capacity of soil material to change volume withchanges in moisture content, frequently measured bya laboratory assessment of the soil's linear shrinkage.Relates lo the soil's content of montmorillonite.typeclays. High shrink- swell potential in soils, such as

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cracking clays, can give rise to problems in earthfoundations and soil conservation structures. Categoriesused are:

Linear Shrinkage0- 12%

12- 17%17 -22%> 22%

In an urban context shrink-swell potential is particularlyrelevant in consideration of building and roadfoundations. lt is non-critical when linear shrinkagevalues are low, marginai when medium, critical whenhigh, and very critical when very high. Where marginalor higher values are recognised, structural engineeringexpertise is required to ensure the construction ofstable foundations. See also EXPANSIVE SOIL.

SHRUB (gen)

A perennial plant having one or more woody mainstems, frequently branching near ground level. Cf,TREE.

SIDESLOPE (Ifm)

That section of a hillslope which comprises the middleand upper slopes where soil processes are usuallyfransporlational. A sideslope generally lies between ahillcrest and a toofslope, supplying depositional materialfor the latter.

SIGNATURE (rms)

Any characteristic or series ot characteristics by whicha material may be recognised. For example, signaturesin photographs relate Io colour reflectance,

SILL (str)

A horizontal section at the outlet of a soil conservationor hydrologic structure which spreads water flowingfrom the structure, hence preventing it fromconcentrating and forming gullies. When not associatedwith a specific structure. they are often calledCONTOUR SILLS, having a similar function Io a contourditch.

When constructing earthen sills adjacent downslopevegetation should be retained for erosion protection. ltis desirable lo prevent stock trampling these areas, as'the maintenance of the horizontal edge of the sill is vitalto ils proper function.

SILT (sol)

A soil separate consisting of particles belwen 0.002 and0.02 mm in equivalent diameter. See alsoSEDIMENTATION.

SILT TRAP (str)

Syn. SEDIMENT TRAP.

SILTATION (gen)

Syn. SEDIMENTATION.

Shrink-Swell PotentialLowMediumHighVery High

A properly constructed sill in operation. Note that eventhough the discharge rate is low the flow is distributedevenly over the full width of the sill.

SILVICULTURE (for)

The establishment, development, care and reproductionot stands of trees with the aim ot continuous productionot timber.

SINGLE ATTRIBUTE MAPPING UNIT (lev)

A map unit relating to an individual land resourceattribute which is separately identified in the mapping,display and analysis phases ot a land resource survey.Examples include the mapping of Iandform, vegetation.soils, or soit erosion as separate units. Cf. INTEGRATEDMAPPING UNIT.

SINGLE PURPOSE SURVEY (lev)

A survey conducted with only one defined objective. Cf.MULTIPLE PURPOSE SURVEY,

SINK-HOLE (Ifm)

A steep-sided closed depression, often in a timestoneregion, through which water may enter the ground andpass into an underground watercourse. The hole isformed by solution and erosion of soluble material and/or the roof collapse of an underground cavern.

SITE DRAINAGE (gen)

Thenatural interception and removal of excess surfacewater from land. Cf. INTERNAL DRAINAGE. See alsoDRAINAGE.

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a-'r

SKELETAL SOIL (sol)

Syn. LITHOSOL.

SLAKING (sol)

The partial breakdown of soil aggregates in water dueto the swelling of clay and the exputsion of air from porespaces. It does not include the effects of soildispersion. It s a component, along with soil dispersionand soil detachment, of the process whereby soitstructure is broken down in the field. This breakdownresults from the action of raindrop impact, raindropsplash, runoff and seepage, and contributes to soilerosion and the failure of earth structures.

SLASHER (eng)

A machine used to reduce the size of standing ptantmaterial. Such material may comprise trash from a priorcrop or fallow, or a stand of vegetation which needscutting down for a specific management purpose. Theblades of the machine rotate in a horizontal plane andare driven by the tractor power take-off. Wide machinesmay have several rotors, and double sets of blades aresometimes used to achieve finer cutting. The blades ofa FLAIL SLASHER rotate in a vertical plane. It has amore aggressive cutting action and higher powerrequirement than a slasher.

SLIDE (gen)

Syn. LANDSLIDE.

A slasher. Note blades in horizontal plane.

A flail slasher, where blades are in a vertical plane.

SLIMES (mm)

Finely crushed tailings, pumped in suspension from arefining or concentrating plant and usually deposited insettling ponds or dumped into abandoned open-cutmines. The term refers specifically lo lailings frommelalliferous mines. Slimes usually contain chemicalsadded during the concentrating process, and hence thedumps or settling ponds are difficult to revegetate aspart of an eventual rehabilitation program. Cf. SLURRY.

SLIP (gen)

Syn. LANDSLIP.

SLIP CIRCLE (gen)

A slip face having a characteristic uphill curvature,principally associated with rotationa/ slips.

SLIP FACE (gen)

A surface of separation associated with a landslip, Sliplaces commonly consist of planes where abruptchanges occur in texture, structure or hardness withinthe soil material. Such slip laces are typically parallelto the ground surface. Slip faces may also occur inrelatively homogeneous material when the loading of aunit of soil exceeds the shear strength of the in-placematerial giving rise to a rotational slip. These slip facesare typically concave.

60320-15204-8

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SLIP-PRONE (gen)

Susceptible to landslip.

Slip-prone areas are often recognisable by features ofprior landstips, such as slip scars or the lateraldisplacement of fence posts. Where these features aredifficult to recognise, data on soil mineralogy, sitedrainage and slope- soil morphology can assist in

identifying slip'prone areas. Such data is used todetermine the presence of potentiat slip faces, soilstrength and other factors influencing the potential forlandslìp.

SLOPE (gen)

An incline, upward or downward, from the horizontal.Its angle is measured in degrees or as the ratio of thedifference in elevation to the horizontal distancebetween two points, expressed as a percentage.

In land resource surveys, slope is measured at thedirection of greatest declivity. This allows theidentification of the most limiting slope. Sincemeasurement of individual slopes is impractical withbroad scale surveys, slope intervals are utitised. Suchintervals are selected on the basis of practicability andexperience in land resource data evaluation for landcapability classification. In a soil conservation context,slope intervals are chosen on the basis of anassessment of the inter-relationships between slope andsoil erosion hazard for specific types of land use. Seealso CROSS SLOPE.

SLOPE (Ifni)

A tandform which is neither a crest nor a depressionand that has an inclination greater than about one percent, See also FLAT.

SLOPE FAILURE (gen)

A general term referring to the occurrence of massmovement on hillstopes.

SLOW-BREAKING BITUMEN EMULSION(gen)

See BITUMEN EMULSION,

SLUMP (gen)

See LANDSLIDE

SLUMPING (gen)

The collapse and fall of an overhang of soil or rockmaterial, resulting from undercutting.

SLURRY (mm)

Fine sized (<2 mm) rock, clay and carbonaceousmaterials discarded after the final washing andscreening of coal. It is usually pumped in suspensionto settling ponds or dumped into abandoned open-cutmines, to be eventually revegetated as part of a minerehabilitation program. The term may also refer to finereject from other washing operations such as in opalmining or sand and gravel extraction. Cl. SLIMES.

SNIG TRACK (for)

A track atong which logs are putied during sngging.Cf. TIMBER EXTRACTION TRACK.

SNIGGING (for)

The putting of logs, either wholly or partty supported onthe ground, from the point otte/fing to the log dump.Wheeted or tracked vehicles are the most common formof traction. CI. FORWARDING.

SOAK (gen)

A site where subsurf ace seepage water emerges atground levet.

SOD (TURF) (agr)

A piece of earth containing plants with matted roots.Frequentty used for the revegetation of criticat areaswhere a stable vegetative sward is required for erosioncontrot. Grasses such as kikuyu and couch, which havestolons, are particutarty suited to this method ofrevegetation.

SOD CULTURE (agr)

Conservation farming practice associated withhorticutturat and viticultural tand uses involving theestablishment and maintenance of permanent pasturesbetween rows of trees/vines.

Sod laid in position fo stabilise a newly constructedflume.

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SOD SEEDING (agr)

The sowing of seed, with or without fertiliser, directlyinto pasture. When pastures and weeds are killed byherbicides at or prior to sowing the term SPRAYSEEDING may be used See also CONSERVATIONTILLAGF.

SODDING (TURFING) (agr)

A method of revegetation whereby pieces of earthcontaining plants with matted roots are placed togetherover an area to quickly establish a stable vegetativeeover for erosion control. These sods may be held inplace with netting until established, particularly in criticalareas.

SODIC SOIL (sol)

A soit containing sufficient exchangeabte sodium toadversely affect soil stability, plant growth and/or landuse. Such soils would typicatty contain a horizon inwhich the ESP or amount of exchangeable sodiumexpressed as a percentage of cation exchange capacitywould be 6 or more. The soils would be dispersible andmay be improved by the addition of gypsum. Stronglysodic soils are considered to be those with an ESP of15 per cent or more. See also SOIL DISPERSIBILITY,

SODIUM TRIPOLYPHOSPHATE (STPP) (sol)

A manufactured chemical of the general formulaNa5P3O06H2O, used for the dispersion of aggregatedsoils. This may be in the laboratory for particle sizeanalysis, or for sealing leaking waterholding structuresbuilt in or from aggregated soils.

SOIL (eng)

Syn. REGOLITH.

SOIL (gen)

The natural dynamic system of unconsolidated mineraland organic material at the earths surface, It has beendeveloped by physical, chemical and biologicalprocesses including the weathering of rock and thedecay of vegetation. Soil materials include organicmalter, clay, silt, sand and gravel mixed in such a wayas lo provide the natural medium for the growth of landplanls.

Soil comprises organised profiles of layers more or lessparallel to the earths surface and formed by theinteraction ot parent material, climate, organisms andtopography over generally long periods of time. lt differsmarkedly from its parent material in morphology,properties and characterìstics.

SOIL ABRASION (gen)

The process by which moving soil particles erode thesoil surface thus providing more particles which maysubsequently move.

SOIL AERATION (sol)

The process by which air in the soit is replenished byair trom the almosphere. In a well-aerated soil the soilair is similar in composition to the atmosphere abovethe soil. Poorly aerated soils usually contain a muchhigher percentage of carbon dioxide and acorrespondingly lower percentage of oxygen. The rateof aeration depends largely on the volume andcontinuity of pores in the soil.

SOIL AGGREGATE (sol)

A untt of soil structure consisting of primary soilparticles held together by cohesive forces or bysecondary soil materials such as iron oxides, silica ororganic matter. Aggregates may be natural, such aspeds, or formed by tillage, such as crumbs and clods,

SOIL AMELIORANT (SOIL CONDITIONER)(sol)

A substance used to improve the chemicat or physicalqualities of the soil. For example, the addition of limeto the soil to increase pH to the desired level foroptimum plant growth, or the addition of gypsum toimprove soit structure,

SOIL AMENDMENT (sol)

The alteration ol the properties of a soil by the additionof substances such as time, gypsum and sawdust, forthe purpose of making the soil more suitable for plantgrowth. See also SOIL AMELIORANT,

SOIL ASSOCIATION (sol, lev)

A soil mapping unit in which two or more soi/ taxonomieunits occur together in a characteristic pattern, such asa foposequence, The units are combined because thescale ol the map, or the purpose for which it is beingmade, does not require delineation of individual soils.

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The soil association may be named according to theunits present, the dominant unit, or be given ageographic name based on a locatity where the soitassociation is well developed.

SOIL CLASS (sol)

The common taxonomie unit for a group of soils thatare characterised by a particular set of morphologicalfeatures or surface features that are related to soilmanagement. lt is commonly used in the mapping ofsoils for specific purposes and represents a group ofsoils that respond similarly to a set of managementpractices,

White no specific taxonomic units can be attributed toa soil class, as their definition depends on the purposeof the soil mapping, soil class often coincides with soi/series, soi/ phase or an extended principal profile form.

SOIL CLASSIFICATION (sol)

The systematic arrangement of soils into groups orcategories on the basis of similarities and differencesin their characteristics. Soils can be grouped accordingto their genesis (taxonomic classification), theirmorphology (morphological classification), theirsuitability for different uses (interpretative classification)or according to specific properties.

The purposes of soil classification are as follows:

* Generally, as a means of grouping soils into usefulcategories so that statements about one particularsoit are likely to apply to other soils in the samegroup.

With experience, the identification and categorisinginvolved may lead to the inference of other soilproperties (apart from those used in theclassification).

* A formal system of classification encourages thescientific and logical study of soils,

* The standardisation and objectivity involved aredesirable for communication purposes, See alsoFACTUAL KEY, GREAT SOIL GROUP, SOIL SURVEY,

SOIL COHERENCE (sol)

The degree to which soil material is hetd together atdifferent moisture levels. If two-thirds or more of the soilmaterial, whether composed of peds or not, remainunited at the given moisture level then the soil isdescribed as coherent.

SOIL COLOUR (sol)

The colour of soit material as determined by comparisonwith a standard Munsell soil colour chart (Munsell ColorCompany, 1975) or its equivalent. The colourdesignation thus determined specifies the relativedegrees of the three variables of colour ' HUE, VALUEand CHROMA. Hue represents the spectral colour, forsoils normally in terms of red and yellow. Valuerepresents the lightness or darkness of colouration, andchroma its intensity. For example, 5YR 4/6 has a hueof SYR, a value of 4 and a chroma of 6. Equivalentdescriptive colour names can be used if desired, usingthose listed in the Munsell chart.

SOIL COLOUR (Continued)During soil survey, soil colour is determined on a freshlybroken aggregate of both dry and moist soil material,to ensure complete documentation of colour. Since asoils colour may vary, depending on soil moistureconlent, the moist soil colour provides a base forcomparison with other soil samples.

A whole-coloured soil is one in which less than 10 percent of the soil mass is affected by mottling. Its colourwould be specified as a single colour, whereas mottledsoils would be described in terms of the dominantmatrix colour and the subdominant colour of themottles.

Soil colour is particularly important in the identificationof bleaching and gleying in a soil profile.

SOIL COMPLEX (sol)

A soil mapping unit in which two or more soil taxonomicunits occur together in an undefined or complexpattern. The soils are intimately mixed and it ¡sundesirable or impractical to delineate them at the scaleof the map. The soil complex may be named accordingto the units present, the dominant unit or be given ageographic name based on a locality where the soilcomplex is well developed.

SOIL COMPRESSIBILITY (sol)

The capacity of a soil to decrease in volume onapplication of loading. Such decrease is equal to thedecrease in the volume of the soils pores. Changes involume of the particles themselves are considered tobe negligible.

Soil compressibility is commonly measured by anoedometer, in which the soil sample is laterally confinedin a rigid metal ring but is compressed vertically bymechanical or hydraulic means. The changes inthickness with increasing and decreasing incrementalloadìng over various time periods are plotted andthence used to compute a stiffness modulus (E) whichis the expression of the soils compressibility(meganewtons per square metre or MN/m2).

SOIL CONDITIONER (sol)

Syn. SOIL AMELIORANT.

SOIL CONSERVATION (gen)

The prevention, mitigation or control of soil erosion anddegradation through the application to land of cultural,vegetative, structural and land management measures,either singly or in combination, which enable stabilityand productivity to be maintained tor future generations.

SOIL CONSERVATION FARM PLAN (lev)Plan of a rural property showing the land's ruralcapability and proposed soil conservation structuresand land management measures. The plan alsoincorporates a report describing in more detailmeasures required on each class of land. Soilconservation structures proposed might include areasof banks, gully control structures and waterways. Landmanagement measures might include recommendationson pasture improvement, rabbit control, fencing andaccess track layout.

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The main purpose of the plan is to ctassify each areaof the farm to show the most productive type of use towhich it is suited, the type and degree of soil erosionhazard and the type of management and protectionneeded for continued production and prevention orcontrol of soil erosion, Its implementation should bringthe rural property up to its productive potential basedon existing technology. See also AURAL CAPABILITYCLASSIFICATION.

SOIL CONSISTENCE (sol)

The resistance of soit material to deformation or rupture.Terms used for describing consistence of soil materialsat various soil moisture contents and degrees ofcementation are: wet - nonsticky, slightly sticky, sticky,very sticky, non-plastic, loose, very friable, friable, firm.very firm, and extremely firm. Dry - loose, soft, slightlyhard, hard, very hard, and extremely hard. Cementation- weakly cemented, strongly cemented and indurated,

SOIL CREEP (gen)

See CREEP.

SOIL CRUSTING (sol)

Syn. SURFACE SEALING.

SOIL DEGRADATION (sol)

Decline in soil quality commonly caused through itsimproper use by humans. Soil degradation includesphysical, chemical and/or bìological deterioration.Examples are toss of organic matter, decline in soilfertility, decline in structural condition, erosion, adversechanges in salinity, acidity or alkalinity, and the effectsof toxic chemicals, pollutants or excessive flooding.

SOIL DETACHABILITY (sol)

The susceptibility of a soil to the removal oftransportable fragments by an erosive agent, such asrainfall, running water or wind. Depends largely on soiltexture and structure, and is an important componentof soil erodibitity.

SOIL DISPERSIBILITY (sot)

The characteristic of soils relating to their structuralbreakdown in water, into individual particles. Usuallyassociated with high levels of exchangeable sodium onthe clay traction, and tow levels of soluble salts in thesoil. These factors cause clay particles to separate inwater. As clay is one of the chief agents holding soilmaterials together. this leads to collapse of the soilstructure and consequent instability.

Oualitative categories of soit dispersibility are high,moderate and low which generally retate to classes t,2 and 38 respectively of Emerson's Aggregate Test.See also DISPERSIBLE SOIL, DEFLOCCULATION,SODIC SOIL, SLAKING.

SOIL DISPERSION (sol)

The process whereby soil aggregates break down andseparate into their constituent particles (clay, silt, sand)in water, due to detlocculat ion. The process is differentfrom but often associated with, slaking. See alsoDtSPERSIBLE SOIL, SOIL DISPERSIBILITY.

Soil degradation as a result of loss of topsoil.

SOIL ERODIBILITY (sol)

The susceptibility of a soil to the detachment andtransportation of soil particles by erosive agents. lt is acomposite expression of those soil properties that affectthe behaviour of a soit and is a function of themechanical, chemical and physical characteristics of thesoil, lt is independent of the other factors influencing

117

soil &osion such as topography, land use, rainfallintensity and plant cover, but may be changed bymanagement.

The qualitative categories ot soil erodibitity used arelow, moderate, high. very high and extreme. The mosthighly erodthle soils are those that are most easilydetached and transported by erosive forces, High soildispersibility is a good indicator of high soil erodibility.

In the Universal Soil Loss Equation soil erodibility isrepresented by the "K" factor which is defined as therate of soil loss per erosion index unit as measured on

SOIL ERODIBILITY (Continued)

a unit ptot. Such a ptot is 72.6 ft. tong with a uniformlengthwise slope of 9 per cent, in continuous fallow,titled up and down the slope. The "k" value can alsobe estimated from a knowledge of soit properties,through the use ot a nomograph. (Reference:Wischmeier and Smith, 1978).

Cf. EROSION HAZARD.

SOIL EROSION (gen)

See EROSION.

SOIL FABRIC (sol)

Describes the appearance of the soil material using ax10 hand lens. Differences in fabric are associated withthe presence or absence of peds. and the lustre! or lackthereof, of the ped surfaces, and the presence, size andarrangemenf of pores (voids) in the soil mass.Descriptive terms used are Earthy, Sandy, Rough-pedand Smooth-ped. Reference: Northcote (1979).

SOIL FAMILY (sol)

A unit of soil classification and soil mappingintermediate between soil series and Great Soil Group,consisting of or describing groups of similar soil series,Soil properties used to define a soil family include depthof solum, differences in structure, occurrence of mottlingor sodium contents. The use of the term is notwidespread in Australia,

SOIL FERTILITY (sol)

The capacity of the soil to provide adequate suppliesof nutrients in proper balance for the growth ofspecified plants, when other growth factors, such aslight, moisture and temperature are favourable. Themore general concept of soil fertility can be divided intothree components:

* CHEMICAL FERTILITY refers specifically to the supplyof plant nutrients in the soil.

* PHYSICAL FERTILITY refers specifically to soilstructure conditions which provide for aeration, watersupply and root penetration.

BIOLOGICAL FERTILITY refers specifically to thepopulation of micro-organisms in the soil, and itsactivity in recycling organic matter.

SOIL HORIZON (sol)

A layer of soil material within the soil pro/ile with distinctcharacteristics and properties which are produced bysoil-forming processes, and which are different fromthose of the layers below and/or above. Generally,horizons are more or less parallel to the land surface,except that tongues of material from one horizon maypenetrate neighbouring horizons,

The boundary between soil horizons defines the natureot the change from one horizon to another, lt isspecified by the width of the transition zone and theshape as expressed in vertical section. Width ofboundary may be expressed as:

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Sharp = boundary is less than 2cm wide* Clear = boundary is 2 to 5 cm wide

Gradual = boundary is 5 to 10cm wide* Diffuse = boundary is more than 10cm wide

Shape of boundary may be expressed as:

Even = boundary is almost a plane surface* Wavy = boundary waves up and down and the

pockets so formed are relatively wider than theirdepths

* Irregular = boundary waves up and down and thepockets so formed are relatively deeper than theirwidths

* Broken = boundary is discontinuous,

SOIL LANDSCAPE (sol, lev)

An area of land that has recognisable and specifiabletopography and soils, that is capable of beingpresented on maps and of being described by concisestatements,

Thus a soil landscape has a characteristic landform withone or more soil taxonomic units occurring in a definedway. It is often associated with the physiographicfeatures of the landscape and is similar to a soilassociation but in a soil landscape the landform patternis specifically described. The soil landscape may benamed according to the soil taxonomic units present,the dominant unit, or be given a geographic namebased on a locality where it is well developed.

SOIL LOSS (gen)

The amount of soil material removed from a given areadue to an erosion event, including mineral particles,organic matter and nutrients. Expressed in units ofweight per unit area, the term typically applies to lossessustained by paddock-sized areas ( 100 ha) and ismeasured as the amount of sediment eaving such anarea as a result of the event.

This approach however, does not account tor soil whichmoves only within the area, or that which moves on tothe area from outside it, For practical purposes thesetwo discrepancies work in opposition and, dependingon local circumstances, their net effect on the actual soilloss may be smatl.

The difficulty of measurement of all soil movement to,from and within an area normally precludes moreaccurate and/or meaningful assessment of soIl losses.In practice, the smaller the area under consideration,the closer measured soil loss comes to the actual soilerosion occurring.

See also SOIL LOSS PREDICTION, SOIL LOSSTOLERANCE.

SOIL LOSS EQUATION (gen)

A mathematical relationship between soil loss and thevarious factors affecting it, used for soil loss prediction.The most widely used soil loss equation is theUNIVERSAL SOIL LOSS EOUATION (USLE) which is anerosion model developed in the United States anddesigned to predict the long term average soil lossesin runoff trom specific field areas under specifiedcropping and management systems.

The USLE is:

A RxKxLxSxCxPwhere:

A is the computed soil toss per unit area per yearR is the rainfall/runoff factor K is the soit erodibility

tactorL is the slope length factorS is the slope steepness tactorC is the cover/management tactorP is the conservation practice factor.

Numerical values for each of the six factors have beenderived from research data and analyses for mostconditions in the United States. These are available ina series ot charts and tables,

The major purpose of the USLE is to supply specificand reliable guides for selecting adequate erosioncontrol practices. The procedure is also useful forcomputing the upland erosion phase of sediment yieldas a step in predicting rates of sedimentation ofreservoirs or streams, but the USLE factors are moredifficult to evaluate tor large mixed calchments. Theequation is not recommended for prediction of specificsoil loss events. (Reference: Wischmeier and Smith(1978).

An equation of similar form has also been developedto predict soil losses due to wind erosion, on cropland.This equation is:

E = f (I, K, C, L, V) where:

E is the erosion per unit arealis the soil erodibility tactorK is the soil roughness (actorC is the climatic factor (including wind and soil

moisture)L is the length along the fieldV is the vegetative cover tactor.

The equation was also developed in the United Statesand has not been widely used in Australia.

(Reference: Woodruff, NP, and Siddoway, F.H. (1965)Soil Sci. Soc. Am. Proc. 29 602'S).

SOIL LOSS PREDICTION (gen)

The estimation of future soil losses for a given set ofsoil, climate! topography and land use conditions. Thetechnique is usually used to predict ong term averagesoil losses br specified conditions. See also SOIL LOSSEQUATION.

SOIL LOSS TOLERANCE (gen)

The maximum rate of annual soil erosion that may occurand still permit a high level of crop productivity to beobtained economically and indefinitely. Such a rate isarbitrarily determined taking into account soil depth,physical properties and other characteristics affectingroot development, gully prevention, on-site sedimentproblems, seeding losses, and soil organic matterreduction and plant nutrient losses.

When soil loss prediction procedures give a predictedlevel of soil loss, any cropping and managementcombination for which the level is less than thetolerance rate may be expected to provide satisfactory

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erosion control. From the alternatives indicated by theseprocedures, the one best suited to a particular tarmmay then be selected.

lt should be noted that in many parts of Australia soilformation rates are generally considered to be close tozero, and therefore the soit loss tolerance iscorrespondingly low.

SOIL MOISTURE CHARACTERISTIC (sol)

The graphical relationship between soil water contentand soil wafer pot enlia! for a given soil. lt may varywidely, depending on the texture, structure and poresize distribution of the soil. The relationship is used toindicate the ease or difficulty ot removing water fromthe soil at different soil water contents and cantherefore be important in relation to soil structure andplant growth studies.

SOIL OPENER (eng)

A tiltage assembly used to slice through soil and createan opening tor the placement of seed and/or fertiliserduring the operation of sowing. A number of suchassemblies form the essential functional components ofa drill. Three types are in common use:

DISC OPENER

A soil opener consisting oI one, two or three discsarranged so that a small furrow is opened up forplacement of seed and/or fertiliser. The boot isusually an integral part of such an opener.

A triple disc opener.

A funnel opener.

SOIL OPENER (Continued)

A tine opener, also showing sowing tube and boot.

RUNNER OPENER

A soil opener consisting of a (fl/age tool of narrowcross-section which forms a narrow groove in thesoil. Normally used for shallow seed placement intoa prepared seedbed.

TINE OPENER

A soil opener consisting of a Une, a boot and atillage tool.

SOIL ORGANIC MATTER (sol)That fraction of the soil including plant and animalresidues at various stages of decomposition, cells andtissues of soil organisms, and substances synthesisedby them. lt is of vital importance as it contributes to thecation exchange and field capacities of the soil andprovides a major source of plant nutrients andsubstances which assist in soil structure maintenance.

SOIL PACKER (eng)

An implement used to form a seedbed by crushing soilclods. lt may also assist erosion control by anchoringplant residue. Packers usually consist of one or twogangs of heavy rollers made up of many individualsegments ora spiral.

A spiral soit packer.

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SOIL PERMEABILITY (sol)

The characteristic of a soil, soil horizon or soil materialwhich governs the rate at which water moves throughit. lt is a composite expression of soil properties anddepends largely on soil texture, soil structure, thepresence of compacted or dense soil horizons, and thesize and distribution of pores in the soil. The rate varieswidely in the field, from more than 3 000 mm/day inpoorly graded sands and gravels, to less than 0.01 mm/day for some heavy plastic clays. The qualitativecategories of permeability for general use are:

Slowly permeable less than 10 mm per dayModerately permeable - 10 mm to 1000 mm per dayHighly permeable more than 1000 mm per day.

When applied to a soil protile, the rate of watertransmission is controlled by the least permeable layerin the soil. Cf. INTERNAL DRAtNAGE.

SOIL PHASE (sol, lev)

A subdivision of a soil taxonomic unit based oncharacteristics that affect the use and management ofthe soil, but do not change the classification of the soil,Such characteristics include slope, erosion, depth,stoniness and rockiness, drainage, depositionat layers,gilgai or scalding.

SOIL PLASTICITY (sol)

The degree to which a soil is plastic. A highly plasticsoil has plastic properties over a wide range of moisturecontents. A subplastic soil has properties suggestingthat less clay is present than is actually the case. Suchsoil materials may be identified by determining two soiltextures. The initial texture obtained by a 1-2 minuteworking of the soil sample will appear to be of a lessclayey grade than the texture obtained after a 10minute working. A non plastic soil has properties whichdo not allow plastic behaviour, whatever the moisturecontent. See also AUERBERG LIMITS, SOIL TEXTURE.

SOIL POROSITY (sol)

The degree to which the soil mass is permeated withpores or cavilies Porosity can be generalty expressedas a percentage of the whole volume of a soil horizonthat is unoccupied by solid particles. In addition, thenumber, sizes, shapes, and distribution of the voids areimportant. Generally, the pore space of surface soil isless than one- half of the soil mass by volume, but insome soils it is more than half. The part of the porespace that consists of small pores that hotd waler bycapillary action is called CAPILLARY POROSITY, Thepart that consists of larger pores that do not hold waterby capillary action is called NON-CAPILLARYPOROSITY, See also BULK DENSITY.

SOIL PROFILE (sol)

A vertical cross-sectional exposure of a soil, extendingdownwards from the soil surface to the parent materialor, for practical purposes, to a depth of one metrewhere the parent material cannot be differentiated, lt isgenerally composed of three major layers designatedA, B and C horizons. The A and B horizons are layersthat have been modified by weathering and soildevelopment and comprise the so/um. The C horizon

is weathering parent material which has not, as yet,been significantly attered by biological soit formingprocesses. A surface organic (0) horizon and/or a subSsotum (D) horizon may atso occur.

The boundaries between successive soil horizons arespecified by their width and shape.

O HORIZON:

A surface layer of plant materials in varying stagesof decomposition not significantly mixed with themineral soil. Often not present or only poorlydeveloped in Australian soils except in someforests. When highly developed it can be dividedinto two parts:

O, HORIZON is the surface layer of undecomposed plant materials.

02 HORIZON is the layer beneath the O, which ispartly decomposed.

A HORIZON:

This is the original top layer of mineral soil. lt canbe divided into two parts:

A, HORtZON

is the surface soil and generally referred to astopsoil. Relative to other horizons it has a highcontent of organic matter, a dark colour andmaximum biological activity. This is the most usefulpart ot the soil for revegetation and plant growth.lt is typically from 5 to 30 cm thick.

A2 HORIZON is a layer of soil of similar texture tothe A horizon, but is paler in colour, poorer instructure, and less fertile. A white or greycolouration, known as bleaching, is often causedby impeded soil drainage and/or eluviation. The A2horizon is typically from 5 to 70 cm thick, but doesnot always occur.

B HORIZON:The layer of soil below the A hoyizon.It is usually finer in texture (i.e. more clayey),denser, and stronger in colour. In most cases it isa poor medium for plant growth. Thickness rangesfrom 10 cm to over 2 metres. lt can be divided intotwo parts:

B HORIZONis a transitional horizon domi nated byproperties characteristic of the underlying B2horizon. B2 HORIZONis a horizon of maximumdevelop ment due to concentration of sili cate clayand/or iron, and/or aluminium and/or translocatedorganic material. Structure and/or consistence isunlike that of the A and C horizons and colour istypically stronger.

C HORIZON: Layers below the B horizon whichmay be weathered, consolidated or unconsolidatedparent material little affected by biological soil-forming processes. The C horizon is recognised byits lack or pedological development, and by thepresence of remnants of geologic organisation. Itsthickness is very variable,

60320-15204-91

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D HORIZON: Layers below the solum which are notC horizon, and are not related to the solum incharacter or pedologic organisation.

R HORIZON:Hard rock that is continuous,

SOIL REACTION TREND (sol)

The change in pH with depth in a soil profile, fromsurface soil to deep subsoil. Four such trends havebeen defined: strongly acid, acid, neutral and alkaline.

(Reference: Northcote, K.H. (1979)). See also pH.

SOIL RESOURCE (sol, lev)

The total extent of soil within a given area available asa natural medium for plant growth. It is limited andexhaustible, and thus, its management must aim toavoid degradation to ensure its potential productivecapability is maintained or improved.

SOIL SALINITY (sol)

The characteristic of soils relating to their content ofwater-soluble salts. Such salts predominantly involvesodium chloride, but sulphates, carbonates andmagnesium salts occur in some soils,

High salinity adversely affects the growth of plants, andtherefore increases erosion hazard. Soit salinity isnormally characterised by measuring the electricalconductivity of a soil/water saturation extract and isexpressed in millisiemens per centimetre at 25°C (mS/cm). See also SALINE SOIL, SALTING.

SOIL SERIES (sol, lev)

A unit of soil classification and soil mapping comprisingor describing soils which are alike in all major profilecharacteristics, Each soil series is developed from aparticular parent material, or group of parent materials,under similar environmental conditions, t approximatesto the extended principal profile torm, The name givento a soil series is geographic in nature, and indicates alocality where the soil series is well developed.

SOIL SLIP (gen)

See LANDSLIP.

SOIL SOLUTION (sol)

The water in a soil containing ions dissociated from thesurfaces of soil particles, and other soluble substances,See also SATURATION EXTRACT,

SOIL STABILISER (sol)

A substance or material used to improve soil stability,strength or bearing capacity. In a soil conservationcontext the primary purpose of a soil stabiliser is toreduce erosion potential. For example the addition ofproprietary chemicals to achieve soil flocculation, or theincorporation of organic materials such as hay or strawinto newly topsoiled areas,

SOIL STRUCTURE (sol)

The combination or spatial arrangement of primary soilparticles (clay, siltt, sand, gravel) into aggregates suchas peds or clods and their stabitity to deformation.Structure may be described in terms of the grade classand form of the soit aggregates, as follows:

Grade ' expresses the degree and strength of soitaggregation determined on moist soil. Thegrades range from structureless, if there isno observable aggregation, to strong,where more than twothirds of the soil isaggregated.

Class - expresses the main size range of theaggregates.

Form- expresses the shape of the individualaggregates as crumb, granular, sub-angularblocky, angular blocky, prismatic, columnaror platy.

Soil structure is an important property with respect tothe stability, porosity and infiltration characteristics ofthe soil. Well-structured soils tend to be more resistantto erosion due to their ability to absorb rainfall morefreely and over longer periods, and because of theresistance of their aggregates to detachment andtransport by raindrop splash and/or overland flow. Theyalso have good soil/water/air relationships for thegrowth ot plants. Poorly-structured soils have unstableaggregates and low infiltration rates. They tend to breakdown quickly under heavy rainfall which leads to soildetachment and erosion. Under certain conditionssurface sealing occurs and this gives rise to rapid andexcessive runoff.

SOIL SURVEY (sol, lev)

The systematic examination, description, classificationand mapping of soils, with the aim ot categorising soildistribution within a defined area. In practice, most soilsurveys also include statements on the geology,topography, climate and vegetation of the areaconcerned. They may be carried out for general use, inwhich case a wide range of soil properties is examined,or for a particular purpose such as crop irrigation orurban planning, in which case only a limited number ofsoil properties may be relevant. Soil survey involves thefollowing steps;

1, deciding which properties of the soit areimportant for the particular purpose;

selecting categories for each property relevantto the particular purpose;

classifying soils into map units so that soilvariation within units is less than that betweenunits;

locating and plotting the boundaries of theseunits on maps; and

preparing maps and reports for publication.

SOIL TAXONOMIC UNIT (sol, lev)

A general term for a grouping of soils based onsimilarities of the soils within the group, and differencescompared with other groups. Note that the generaltaxonomic units such as great soil group and principal

122

profile form need to be distinguished from the soilsurvey taxonomic units such as soil series and soilassociation,

SOIL TEXTURE (sol)

The coarseness or fineness of soil material as it affectsthe behaviour of a moist ball of soil when pressedbetween the thumb and forefinger. lt is generally relatedto the proportion of soil particles of differing sizes (sand,silt, ¿lay and gravel) in a soil, but is also influenced byorganic matter content, clay type, and degree ofstructural development of the soil.

Six main soil texture groups are recognised;

Approx. claycontent

Sands <5%Coarse

Sandy Loams - 10-15%

Loams 20-25%Medium

Clay Loams 30%

Light Clays 35-40%Fine

Heavy Clays > 45%

For field identification of these main groups, take asmall handful of soil and knead with water until ahomogeneous soit ball or bolus is obtained. Largepieces of grit and organic material should be discarded.Small clay peds should be crushed and worked in withthe rest of the soil. The feel, behaviour and resistanceof the soil to manipulation during this process isimportant. The bolus should be kept moist so that it justfaits to stick to the fingers. The six main texture groupsshould be apparent as follows;

Sands

have very little or no coherence and can not berolled into a stable ball. Individual sand grainsadhere to the fingers.

Sandy Loams

have some coherence and can be rolled into astable ball, but not a thread Sand grains can befelt during manipulation.

Loams

can be rolled into a thick thread, but this will breakup before it is 3-4 mm thick. The soil ball is easyto manipu late and has a smooth spongy feel wìthno obvious sandiness.

4, Clay Loams

can be easily rolled to a thread 3-4 mm thick, butit will have a number ol fractures along its length.Soil becoming plastic, capable of being mouldedinto a stable shape.

5. Light Clays

can be rolled lo a thread 3-4 mm thick withoutfracture. Plastic behaviour evident, smooth feelwith some resistance to rolling out,

Texture Group

6. Heavy Clays

can be rolled to a thread 3-4 mm thick and formedinto a ring in the palm of the hand without fracture.Smooth and very plastic, with moderate-strongresistance to rolling out.

In a soil conservation context, soil texture is veryimportant as it not only has a major influence on theerodibilily of soils but also on their performance whenused in water storage structures. In particular it largelydetermines soil permeability.

See also GRADING, PARTICLE SIZE ANALYSIS.

SOIL TEXTURE GRADE (sol)

A minor category of soil texture as set out in the tableunder soil texture group.

SOIL TEXTURE GROUP (sol)

A major category of soil texture as set out in thelollowing table:

Texture Groups Texture Grades

Sands sand; loamy sand; clayey sand;* Sandy Loams sandy loam; fine sandy loam;

light sandy clay loam;Loams loam; loam, fine sandy; silt loam;

sandy clay loam;Clay Loams clay loam; silty clay loam; fine

sandy clay loam;* Light Clays sandy clay; silty clay; light clay;

light medium clay;Medium-Heavy medium clay; heavy clay.Clays

SOIL TYPE (sol, lev)

A general term used to describe a group of soils thatcan be managed similarly and which exhibit similarmorphological features. lt is largely a layman's term andnow has no formal soil taxonomic meaning.

SOIL VARIANT (sol, lev)

A soil having a morphology which is distinct from thesurrounding soils but comprises such a limitedgeographic area that the delineation of a new map unitor the naming of a new soil taxonomic unit, is notjustified.

SOIL WATER (sal)

Water contained in, or in transit by drainage through thesoil.

SOIL WATER POTENTIAL (sol)

In general terms, the amount of work (or suction) whichmust be applied to remove water from soil, For moredetailed explanation see Beckmann et al (1976).

The waler content at a suction of -15 bars is taken toapproximate the permanent wilting point, and the watercontent at a suction of -0.1 bar is taken to approximatefield capacity.

123

SOLIFLUCTION (sol)

See CREEP.

SOLUM (sol)

The upper part of a soil profile above the parentmaterial, in which current processes of soil formation areactive, The solum consists of either the A and Bhorizons or the A horizon alone when no B horizon ispresent. The living roots and other plant and animal lifecharacteristic of the soil are largely confined to thesolum.

SOLUTION (sol)

That part of natural weathering processes wherebysubstances in rocks and soil are dissolved ingroundwater. Such water usually contains some carbondioxide and organic compounds from plant breakdownwhich make it mildly acid, thereby enhancing its abilityto dissolve rock materials.

SORTING (gen)

Separation of particle sizes by an erosive fluid,according to their equivalent spherical diameters, as aresult oI changes in flow velocity.

SOWING (agr)

The process of placing seeds in a suitable mediumwhich will provide for their germination and subsequentgrowth. Usually refers to the farm practice wherebycrop seeds are sown into prepared soil, using amachine called a drill or seeder at a set depth, rate andspacing.

In a soil conservation context the operation of sowingis critical to many revegetation programs. See alsoSEEDBED, DRILLING, SEEDING.

SOWING TUBE (eng)

A flexible tube for conveying seed and/or fertiliser fromeach metering mechanism on a drill to its respectiveboot and soil opener.

SPECIFIC ENERGY HEAD (eng)

See TOTAL ENERGY HEAD.

SPELLING (ram)

Temporary removal of stock from a grazing area tofacilitatè regrowth of vegetation and stabilisation of soilsurfaces. The length of time involved may be as shortas 6-8 weeks to permit a pasture species to sel seed,or one or two growing seasons to allow developmentof plant cover to fully stabilise an area.

SPILLWAY (str, eng)

An open or enclosed channel, or a combination of both,used to convey excess water from a dam or similarstorage, gully control structure or detention structure.

Location, design and construction of an adequatespillway is essential to prevent overtopping andpossible structure failure, and provide for safe waterdisposal without causing soil erosion. Each spillway has

SPILLWAY (Continued)

an inlet, control and outlet section, The control section,which conveys the flows, is critical to the success ofthe spiliway and must cater for the discharge derivedfor the design return period.

Most small pondage structures require only onespillway. On larger structures, more than one spillwaymay be necessary. The first spillway to accept excessflows is termed the PRIMARY (PRINCIPAL) SPILLWAYand is constructed Io accept the design discharge.Flows greater than this discharge are carried by aSECONDARY (EMERGENCY) SPILLWAY,

Spiliways may be constructed Io convey waler awayfrom or around the embankment - BYWASH SPILLWAY;over the embankment - OVERSHOT 5PILLWAY; orthrough the embankment - PIPE SPILLWAY.

For soil conservation purposes the majority of pondagestructures are constructed of soil material andincorporate a bywash spillway, also referred to as aCONVENTIONAL SPILLWAY. Its control section isgenerally trapezoidal in cross section and leads to eithera diversion channel or spills directly onto the naturalground surface by way of a sill (LEVEL SILLSPILL WAY).

Where site conditions or large expected dischargesrestrict the use of conventional earth spiltways, or wherethe spillway is designed for a specific purpose, suchas in a detention structure, one or more of the followingtypes ot spillways may be required:

CHUTE SPILLWAY

A spillway having a chute for its control section.Where soil material is used for its construction,special precautions regarding stabilisation have tobe taken to prevent erosion. In most cases chutespillways are constructed of non-earth materialssuch as reinforced concrete, sand/cement bags,cement grouted rock or synthetic ultraviolet-resistant membranes.

Depending on requirements, form work may benecessary to achieve particular results. However,FORMLESS CHUTE SPILLWAYS, constructed byshaping the earth subgrade as required and thenimplacernent of the chosen lining material, providesavings in lime and cost.

Where a chute spillway incorporates a dropstructure at its inlet, it is referred to as a DROPINLET CHUTE SPILLWAY, These are commonlyused where it is necessary to control outflowvelocity by initially dropping the water to aprescribed level prior to its flow down the chute.

PIPE SPILLWAY

A spillway having a pipe for its control section. Twotypes are in common use for soil conservationstructures: INCLINED PIPE SPILL WAY - the pipepasses through the embankment with a tallthroughout its length. DROP INLET PIPESPILLWAY . the pipe passes through theembankment horizontally or near horizontally andflows enter it through a drop inlet, typically avertical box or riser, The riser must be larger thanthe horizontal pipe if the pipe is to flow full, Risers

124

can be designed to control the rate of entry ofwater into the pipe and thus, drop inlet pipespillways are typically used in conjunction withretention structures, These spillways can alsoprovide for a high rate of outflow with only a smallincrease in the depth of stored water.

DROP SPILLWAY

A spillway having a vertical drop for its controlsection. They are typically overshot spillways andconstructed of reinforced formed concrete. Anadequate energy dissipator is necessary at itsoutlet, Where the crest of the drop structure formsa direct continuum with the adjacentembankments, as in a weir, the spillway is knownas a STRAIGHT DROP SPILLWAY.

Where it is desirable to increase the crest lengthwithout increasing the outlet width a BOX INLETDROP SPILLWAY may be used. In this case arectangular masonry box forms the drop ätructureand the water enters from three sides, drops to anapron and passes through the downstream end byway of an energy dissipator. These spillwaysprovide for a high rate of outflow with only a smallincrease in the depth of stored water.

In addition to one or more of the various spiliwaysdescribed, a pondage structure may incorporate atrickle pipe to convey trickle flows through theembankment, Control of trickle flows in earth structuresis particularly important to prevent erosion along andbelow their spillways.

SPIRIT LEVELLING (sur)

Syn. DIFFERENTIAL LEVELLING.

SPLASH EROSION (gen)

See EROSION.

SPLIT BUBBLE (sur)

An accurate method of aligning a theodolite or level ona horizontal plane. Its principle lies in simultaneouslysighting both ends of a bubble, attached to theinstrument in a vial of liquid, through a prism, andbringing the ends into coincidence.

SPOIL (mm)

Soil, rock and other waste material excavated duringmining, quarrying. or other extractive operations.

SPOON DRAIN (eng)

See DRAIN.

SPORADIC BLEACHING (sol)

See BLEACHING.

SPRAY SEEDING (agr)

See SOD SEEDING.

SPREAD BAiTER DAM (gen)

See TANK,

SPRIGGING (agr)

The planting of pieces of rhizome or stolon over an areato enable a stable vegetative cover to rapidly establish.The method typically uses such grasses as couch orkikuyu which, given adequate soil moisture, can quicklyspread over an area and stabilise it.

SPUR DRAIN (sir, eng)

Syn. MITRE DRAIN.

STABILISATION (gen)

The provision of adequate measures, vegetative,structural and/or mechanical, to prevent or controlerosion,

STABILISING SPECIES (csd)

Plant species used for the stabilisation of driftingcoastal sand dunes, all capable of withstandingshoreline exposure. Three broad types are recognised:

PRIMARY SPECIES

Plant species which will colonise bare sand withoutprotection from other vegetation. These plants relyon sand drill for nutrient replenishment. Examplesare Sand Spinifex and Marram grass.

Marram grass used as a primary stabilisingspecies on a newly [aimed sand dune.

125

SECONDARY SPECIES

Plant species which will establish following thecessation of sand drift brought about by primarystabilising species. An example is Coastal Wattle.

TERTIARY SPECIES

Plant species which can only establish followingthe cessation of sand drift and under protection ofestablished vegetation. Examples are Banksia,Botttebrush and Paperbark.

STABILISING SPECIES (gen, agr)

Plant species used for the stabilisation ol areas whichhave been eroded or disturbed.

STABLE (gen)

The condition of a parcel of land or flowline whichexperiences no appreciable soil erosion orsedimentation and is thus, under current management,adequately protected from erosive agents.

The term is also used to describe a soil conservationor hydrologic structure which is functioning effectivelyand is not adversely affected by erosive agents.

STABLE OUTLET (ACCEPTABLE OUTLET)(sfr)

An outlet which is adequately protected from erosionand is stable under current conditions.

STADIA SURVEY (sur)

A surveying operation undertaken to determine theposition and reduced level of a number of points usinga staff and level or theodolif e. lt involves themeasurement of horizontal angles and distances by useof the stadia hairs in the telescope of the instrument.Vertical anles can also be measured when using atheodolite. The principal use of stadia survey is toproduce a contour map.

STAFF (sur)

A pole having a graduated scale to be observed whenheld in the vertical position, used in conjunction with alevel or theodolite to measure differences in heights.

STAFF BUBBLE (sur)

A circular bubble container which is held against a stattto ensure that it is being held vertically.

STAGE (eng)

The elevation of the free surface of stored or flowingwater relative to a fixed datum.

STAGE RECORDER (eng)

An instrument used for measuring and recording theheight of water in a channel. lt incorporates a float,rising and falling with the changes in water stage in astilling well, that is connected to a recordingmechanism. By relating water heights to rates of flow,using a rating curve, a complete hydro graph isrecorded. This can be used in conjunction with rainfalldata to study the relation between rainfall and runofffrom a catchment, and the way it is affected bylandtorm, land management, land use and soilconservation practices. The recorder should only beused in conjunction with a calibrated flume or weir.

STAND (for)

An aggregation of trees or other growth occupying aspecitic area and sufficiently uniform in composition(species), age arrangement and condition as to bedistinguishable from the forest or other growth onadjoining areas.

STANDARD DATUM (sur)See DATUM.

STANDING WAVE (eng)

Syn. HYDRAULIC JUMP.

STATIC HEAD (eng)

The hydraulic head due to the height of the static poolof water held in a weir or similar hydrologic structure,with respect to a fixed datum. lt equals the depth ofwater plus the height of the channel floor above datum.

STEADY FLOW (hyd)

See FLOW.

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STEP POINTING (ram, agr)A simple system of establishing a point transectwhereby the operator steps along a line and records orsamples vegetation at regula( intervals Each point isdefined by a mark on the operator's boot which isobserved after a regular number of steps.

STEREO-DIP COMPARATORS (rms)A set of perspex slides used in aerial photointerpretation to estimate land slopes. Photographs ofconstructed slopes ranging from 5 to 50 degrees,increasing in 5 degree intervals, are compared withslopes as seen through a stereoscope.

STEREO-PAIR (rms)Two consecutive vertical aerial photographs with somedegree of overlap. The left eye looks at the left-handphoto and the right eye at the right-hand photo suchthat the two images of the overlapping scene are fusedto give the appearance of a three-dimensional model.See also STEREOSCOPE.

STEREOMETER BAR (PARALLAX BAR)(rms)

An instrument used to determine the apparent heightof objects, or between two points, from the three-dimensional image of a stereo-pair of aerialphotographs. Parallax provides the principle upon whichthe instrument works. Any difference in ground heightwill correspond to a difference in parallax.

STEREOSCOPE (rms)An optical instrument facilitating the fusion of the twoimages of an overlapping scene in a stereo-pair toobtain the appearance of a three-dimensional model.This is achieved by the instrument enabling each eyeto be easily focussed on its respective photograph.

The stereoscope does not produce the threedimensionat model, rather it aids the ability of anindividual to perceive the stereoscopic image.Stereoscopy is an inherent trait of the individual, andsome people do not have stereoscopic vision.

Two types of stereoscopes are in common use:

POCKET STEREOSCOPEA small lens type stereoscope that gives amagnified image, is compact and very suitablo forfield use. Unfortunately it permits observation ofonly a limited part of the overlap without bendingthe overlapping print. Also, the image may have aslightly concave or dished effect towards theedges.

MIRROR STEREOSCOPE

A relatively large instrument, more suited togeneral reconnaissance of large areas. Its mainadvantage is that the eye base is widened opticallyby means of mirrors and prisms so that thecomplete overlap is seen in the field of view. Thewidened eye base gives less exaggeration to theimage and less distortion than with the lens type.Binocular attachments are often provided for amagnified view of parts ot the overlap. For viewingwith the mirror stereoscope the photographsshould not overlap as they do when viewing withthe pocket stereoscope.

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127

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A pocket stereoscope.

A mirror stereoscope.

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STEREOSCOPIC PARALLAX (ms)

See PARALLAX.

STEREOSCOPY (rms)

The perception of images in three dimensions. See alsoAERIAL PHOTOGRAPH INTEREPRETATION,PARALLAX.

STILLING BASIN (eng, str)

The pondage located at the foot of an over fall, pipe,flume, spülway or similar structure to reduce the energyof the descending stream of water and associatedturbulence, subsequently reducing outlet velocities toa non-erosive level. The basin's dimensions arecalculated according to the size of the hydrau lic jumpoccurring at the design peak discharge. See alsoENERGY DISSIPATOR.

STILLING WELL (eng)

A vertical chamber, having closed sides and bottomexcept for a small intet or inlets connected to a mainbody of water, for the attentuation of waves or surgeswhilst permitting the water level within the chamber torise and fall with the major fluctuations of the mainwater body. Used with water measuring devices andstage recorders to improve the accuracy ofmeasurement.

STOCKING RATE (ram, agr)

The actual number of animals, or animal equivalents,carried per unit area of grazing land at a specific time,See atso GRAZING CAPACITY. CARRYING CAPACITY.

STOLON (agr)

A horizontally growing stem which runs along thesurface of the ground and takes root at intervals, thusproducing new plants. This enabtes rapid vegetativepropagation and is valuable in the revegetationtechniques of sodding and sprig ging. Examples ofstoloniferous species, commonly used for soilconservation purposes are couch, kikuyu and sandspinifex. Cf. RHIZOME.

STOPE (miR)

A cavity created in the final ore extraction process inan underground mine. It involves the excavation of theore between two adjacent levels or between adjacentshafts on the same level including pillars, to obtain themaximum amount of ore from the orebody. Stopes aretherefore unstable and susceptible to collapse.

STORAGE/EXCAVATION RATIO (str)

The ratio of a dam's storage capacity to the excavatedvolume. The higher the ratio, the more economicallyefficient the storage is. implying low capital cost per unitvolume of water stored.

STORM DURATION (byd)

The timespan from the commencement to the cessationof a storm. See also DESIGN STORM DURATION.

128

STORM FREQUENCY (hyd)

Syn. RETURN PERIOD.

STRAIGHT DROP SPILLWAY (eng)

See SPILLWAY.

STRATEGIC DEVELOPMENT (urb)

A tevet of urban development such that the physicalconstraints of the land restrict subdivision to adispersed pattern. The area is generally unsuited toresidential development but closer investigation maypermit pockets of land to be identified for individualhomesites, by assessment of engineering measuresrequired to maintain stability on what would otherwisebe unsuitable land for development.

STRAW CHOPPER (eng)

A machine attached to the rear of a grain harvester thatreduces the size of straw ejected from it. Straw leavingthe harvester is chopped into small lengths and blownto the side and rear of the harvester. The chopper'spurpose is to avoid heavy windrows of straw left behindthe harvester which cause problems with subsequenttillage or sowing operations. Cf. STRAW SPREADER.

A straw chopper. Note vanes to spread the chopped straw.

STRAW MULCH (agr)

See MULCH.

A straw spreader attached to the rear of a harvester.

STRAW SPREADER (eng)

A machine attached to the rear of a grain harvester thatpropets straw and chaff to either side of the harvester.Both rotating flails and fans are used to propet thematerial. The spreaders purpose is to avoid heavywindrows of straw lef t behind the harvester whichcause problems with subsequent tittage or sowingoperations, Cf. STRAW CHOPPER.

STREAM (gen)

See WATERCOURSE.

STREAM CHANNEL (lfm)

A linear, generatty sinuous, open depression in thelandscape in various parts eroded, excavated, built upand aggraded by concentrated water flow, Comprisesstreambed and streambanks, and in certain cases barsand channel benches,

STREAMBANK (BANK) (lfm)

A lateratty extensive, moderatety inclined to precipitousslope forming the margin of a stream channel andresulting from erosion or aggradation by channelledstream flow. Streambanks are identified as left or rightlooking downstream.

STREAMBANK EROSION (gen)

See EROSION.

STREAMBED (11m)The floor of a stream channel as distinct from thestream- bank.

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129

STRIP CROPPING (agr)

The conservation farming technique of growing cropsin rotation in a systematic arrangement of strips atrightangles to the direction of water flow, lt is typicallyused on lands of low slope (< 2 per cent) to spreadrunoff and reduce its velocity in order to reduce erosion.lt can also be used on generally level country to controlwind erosion, the strips being orientated al rightangleslo the prevailing winds. Width of strips would dependon height of vegetation and soil erodibility.

Judicious use of crops with different growing seasonsand ta/lowing requirements allows sufficient plant coverto be maintained continuously over large areas torestrict both wind and waler erosion Io minimum levels.There are three main types of strip cropping:

CONTOUR STRIP CROPPING

Layoul and tillage follow the contour and only verysmall deviations of strip boundaries trom the exactcontour are peimissible.

FIELD STRIP CROPPING (PARALLEL STRIPCROPPING)

Strips of a uniform width are positioned across thegeneral slope but they may not exactly follow thecontour.

BUFFER STRIP CROPPING

Permanent pasture strips, often called CONTOURGRASS STRIPS, are utitised between contourplanted strips of crops in rotation. Their functionis to cause runoff to spread out and drop a largepart of its suspended sediment.

Strip cropping - an aerial view.

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STRIP CROPPING (Continued)

Development of a field strip cropping p/an.

Step 1. Key line identification

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Step 3. Key and pivot linesI r«°rtt

Step 5. Correction oreo location

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Correction area(becomes part of strip)

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STRIP-MINE (mm)

An opencut coal mne consisting of a number ofelongated excavations which are parallel or concentric.Overburden from one strip is used to backfill theprevious, adjacent excavation. The method isparticularly suited to excavation by dragline.

130

Step 2. Pivot line identificatione1

'3 '3 '3

Correction

Area

Step ó. Placement of strategic works

Stategic bank Low s(ope area

i

Strips continue on steeper slopebetow the bank

I

STRIP WIDTH (agr)

The width ot strips in a system of strip cropping. Theymay range in width from 20 metres to 110 metres.

Ideally, for maximum erosion control, the strips shouldbe narrow enough to atlow the backwater effect [romthe strip of growing crop to cover the cultivated strip

areaStep 4. CorrectionI I

above. However, for practical management purposes,other factors must be considered. This will usuallyproduce a basic strip width [or a property that is widerthan the optimum for erosion control.

The maximum width of strips permissible, given specificconditions for the erosion hazard of a site, is influencedby the following factors:

slope of the landsoil lype and structural stability

* rainfall intensity* management practices* type of crops being grown

slope lengthvolume of topwater

* previous erosion historyfarm machinery widthaerial spraying width.

STRIPROW (for)

Syn. OUTROW,

STRUCTURAL DEGRADATION HAZARD(sol)

The susceptibility ot a soils structure to breakdown asa resull of cultivation. Three categories are recognised:

High -applies to a soil with a structure thatreadily degrades to a massive condition followingcultivation.

- Moderate -applies to a soil with a structure thatdegrades to a massive condition after someyears of continuous cultivation.

Low -applies to a soil with a structure that resistsdegradation to a massive condition except aftermany years of continuous culti vation,

STRUCTURAL STABILITY (sol)

The ability of a soil to maintain its structure under theinfluence of tillage, rainfall, trampling or other adverseforces, which tend to disintegrate such structure,Sometimes characterised in the laboratory by variouswet and/or dry sieving techniques. See also SOILSTRUCTURE, WATER-STABLE AGGREGATION. Cf.MECHANICAL STABILITY.

STRUCTURE (sol)

Syn. SOIL STRUCTURE.

STRUCTURE (sfr)

Any man-made device or thing adapted or designed,and constructed of earth, masonry or other material, forthe purpose of soil conservation and the mitigation otsoil erosion.

STUBBLE (agi)

The straw residue that remains after a grain crop hasbeen harvested. It includes standing straw and thatdischarged by the harvester, Cf. CROP RESIDUE.

131

STUBBLE BURNING (agr)

A management practice in which the stubble from onecrop is burnt after harvest, prior to the sowing of asubsequent crop. However, removing the stubbleexposes the soil to erosive forces. Cf. STUBBLERETENTION.

STUBBLE INCORPORATION (agi)

A conservation farming practice whereby stubble isincorporated into the surface soil by tillage, therebypromoting stubble breakdown and providing someprotection to the soil from erosion. Cf. STUBBLEMULCHING,

STUBBLE MULCHING (agi)

A conservation tarming practice whereby stubble isretained on the surface of the soil, thereby protectingthe soil from erosion. Necessary tillage is undertakenusing implements such as the blade plough whichcause minimum surface disturbance and stubble burial,Cf, STUBBLE INCORPORATION.

STUBBLE RETENTION (agr)

A conservation tarming practice which involves theretention of stubble either in or on the soil, betweenharvest and the sowing of the subsequent crop. Thisis done primarily to protect the soil against erosion butalso to conserve soil moisture. See also STUBBLEMULCHING, STUBBLE INCORPORATION,

SUB-CRITICAL FLOW (hyd)See FLOW,

SUB-GRADE (eng)

Prepared ground surface on which road pavements areconstructed,

SUBSIDENCE (gen, mio)

The more or less vertically downwards displacement ofland surface material, under the influence of gravity, dueto the collapse of a sub-surface cavity, such as wherean underground mine caves in causing surface collapse.See also MASS MOVEMENT.

SUBSOIL (gen)

Sub-surface soit material comprising the B horizons ofsoils with distinct profiles. In soils with weak profiledevelopment, the subsoil can be defined as the soilbelow the topsoil.

SUBSOILING (agr)

See RIPPING.

SUCCESSIVE CROPPING (agr)

Syn. CONTINUOUS CULTIVATION,

SUPER-CRITICAL FLOW (hyd)See FLOW.

SURCHARGE (eng)

The temporary increase in the tevet of water in achannet or storage caused by rapid inflow in excess ofspittway capacity. lt may atso refer to an increase inloading on any structure, brought about by increasedwater pressure or other temporary load change. Seealso FREEBOARD.

SURFACE BARRIER RATIO (gen)

The ratio of the distance between successive surfacebarriers (Ds) to the height of the barriers (H), used inthe planning of wind erosion control. A high ratio impliespoor erosion control and a low ratio good erosioncontrol. The CRITICAL SURFACE BARRIER RATIO isthe ratio at which the arrangement of barriers justprevents the movement of erodible tractions by wind.

SURFACE CREEP (gen)

See CREEP.

SURFACE DETENTION (hyd)

The depth of water temporarily held on the land surfacewhile moving freely downslope, before being transferredto the category of infiltration, channel or depressionstorage.

SURFACE SEALING (SOIL CRUSTING) (sol)

The orientation and packing of dispersed soil particlesin the immediate surface layer of the soil, rendering itrelatively impermeable to water. Typically occurs due tothe effect of raindrop impact on bare soil and results ina reduction in infiltration. Runoff and the potential forsoil erosion are thus increased, and a crust may formon drying out.

However, surface sealing can be an important factor inreducing wind erosion, as the seat tends to resistremoval of soil particles by wind action.

SURVEYING (sur)

The collection of data by measurement of relativeheights and distances needed for determining theboundaries, size, position, shape and/or contour of land.n a soil conservation context, surveying is undertakento enable the drafting of maps and plans on which soilconservation measures are shown. See alsoLEVELLING.

SUSPENDED SEDIMENT (gen)

The sediment that is being transported by water or airwhilst held in suspension. Ct. BEDLOAD.

SUSPENSION (gen)

Particle movement in water or air where particles arekept dispersed by fluid motion in currents, byturbulence and/or by molecular motion of thesurrounding medium.

With respect to wind action, suspension involves thefiner soil particles, which are commonly detached bysa/tation, and are lifted into the air and carried away asdust, Particles thus moved are usually less than 0.1 mm

132

in diameter and constitute the silt and clay fragmentsof the soil together with decomposed organic matter.See also WIND EROSION,

SWALE (Ifni, csd)

'A linear level-floored open depresáion excavated bywind or formed by the build-up of two adjacent ridges.Typically associated with the depression between twoadjacent sand dunes,

SWAMP (If m)

A vegetated depression with a seasonal or permanentwater table at or slightly above the floor of thedepression.

SWASH ZONE (csd)

The area affected by the rush of sea-water up a beachfollowing the breaking of waves.

SWEEP (eng)

A wing-shaped tillage tool fitted to sweep ploughs. lt isdesigned for sub-surface tillage with minimum surfacedisturbance and minimum residue incorporation. Sizesrange up to 1000mm in width. Cf. BLADE.

SWEEP PLOUGH (eng)

A tillage implement fitted with sweeps for both primaryand secondary ti//age at depths up to 150 mm. Sweepsizes range up to 1000 mm in width. Sweep ploughscontrol weeds but cause little disturbance of the surfacesoil and incorporate a minimum of residue, and arethrefore widely used in conservation tillage programs.

A sweep p/ough.

SWELLING SOIL (sol)

Syn. EXPANSIVE SOIL.

SYNECOLOGY (gen)

The study of relationships between communities ofspecies and their environment. Cl, AUTECOLOGY.

TABLE DRAIN (eng)

See DRAIN,

TAIL WALL (eng)

See WING WALL.

TAILINGS (mm)

Those portions of refined and/or concentrated ore whichare regarded as being too poor to be treated further.Consist of a mixture of gangue minerals, country rockand ore which have escaped the refinement process.The term is also sometimes used for the fine materialcarried in slurry from coal washeries,

TALUS (11m)

An aècurnulatìon of rock fragments and other soilmaterials at the foot ol a cliff or steep slope, usuallyforming a moderately to steeply inclined lower slope,aggraded by gravity. Due to its mode of formation it isgenerally unstable and may be subject lo massmovement. See also ESCARPMENT, Cf. SCREE.

TANK (gen)

A waler storage, typically excavated in level or gentlysloping terrain, ìn which a large percentage of thecapacity is below ground level. A RING TANK(TURKEY'S NEST DAM) is a special case whereadditional storage is provided by encircling theexcavation with the excavated soil. This type issometimes known as a SPREAD BATTER DAM. Cf.DAM.

TANK DRAIN (sfr)

See DRAIN.

60320-15204-10

133

TEMPORARY CLEARING (agi, for)

The removal of trees and shrubs from land to allow forthe planting of commercial timber or other tree crops.

TEMPORARY CONSTRUCTION EXIT (urb)

A pad of coarse gravel located at exits fromconslruction sites to reduce the transfer of sedimentonto public roads on the wheels of motor vehicles.

TEMPORARY SEEDING (gen, agr)

The establishment of temporary vegetative cover on anarea, for the purpose of erosion control, while waitingfor further construction or other activity to take place.See also SEEDING, PERMANENT SEEDING,

TERMINAL VELOCITY (hyd)

The ftnal steady-state velocity of falling raindrops beforethey hit the soil surface,

TERRACE (11m)

A former floodplain on which erosion and aggradationby channelled and overbank stream flow is barely activeor is inactive, Deepening or enlargement of the streamchannel has lowered the level of flooding.

TERRACETTING (If m)

The characteristic pattern formed by numerous gentlyinclined steps or ledges traversing a hillslope. lt isapparently caused by the combined action of soi/ creepand the tread of animals,

Terracetting on a hill slope showing the typical pattern ofparallel ledges.

TERRAIN (lev) TEXTURE CONTRAST SOIL (sol)A tract of land having particular physical features. Whenclassifying terrain various features may be setecteddepending on the purpose of the ctassification. Forexample, if process is important the terrain may bedescribed as altuvial, colluvial or aeolian; if shape isimportant the terrain may be described as ftat, gentlystoping. undulating, hitly or mountainous.

When evaluating terrain the aim is to subdivide thefeatures such that each subdivision is essentiatlyhomogenous with respect to the properties of thecritical attributes relevant to the purpose of theevaluation. For example, the PUCE, (Pattern Unit -

Component - Evaluation) Program for Terrain Evaluationfor Engineering Purposes identifies attributes related tofeasibility or planning studies in open countryside.(Reference: Grant, K. (1975) Division of AppliedGeomechanics. 0.5.1RO., Technical Papers 15 and 19).

Under the PUCE. program a study area is divided intoterrain provinces (areas of constant geology), thenceterrain patterns (areas of recurring topography, soilassociations and natural vegetation formations) andfinally terrain units (areas ccntaining a singletopographic feature which has a characteristic soilassociation and natural vegetation formation).

Subsequently, detailed evaluation for design andconstruction purposes identifies terrain components.These are the basic units of the evaluation and each ishomogenous with respect to slope (constant rates ofchange of curvature), underlying lithology. consistentassociation of soils (such that each layer can beexpressed within one class of the USOS. and thewhole profile within one class of a subdivision of theprimary profile form), and consistent vegetationassociation.

Terrain classification and terrain evaluation do not aimto answer specific questions at specific sites; rather,each gives a probability of the occurrence of particutarsels of conditions at particular sites.

TERTIARY SPECIES (csd)

See STABILISING SPECIES.

TEXTURE (rms)

The frequency of tone change with the images on anaerial photograph. It is defined in terms ranging fromfine to coarse. For example, in a single area a featuresuch as vegetation will show greater detail - coarse -at a large scale of photography (1: 2000), whereas itwill show less detail - fine - at a small scale ofphotography (1:50000).

Texture can be used to identify changes in vegetationpattern. For example, sapling regrowth can bedifferentiated from established vegetation by texturecomparison. The established vegetation as a largeindividual unit has a coarse texture because it showsmore detail whereas the sapling regrowth being asmaller unit shows less detail and is therefore of a finetexture.

TEXTURE (sol)

See SOIL TEXTURE,

134

Syn, DUPLEX SOIL,

THEMATIC MAP (lev)

A representation and description of a particular themeor topic such as soils, vegetation or rainfall. Thematicdata are either overprinted on a line or photobase mapor digilised and expressed in terms of their coordinateand numerical descriptions.

THEMATIC MAPPER (mis)

A multispectral non-photographic sensor, with narrowband width, designed to sense specific phenomena.Often used in remote sensing of specific geologic andvegetative characteristics.

THEODOLITE (sur)

An optical instrument used to measure horizontal andvertical angles. lt is the most precise instrumentavailable for such observations and as such is usedwidely in a variety of surveying apptications. Its basiccomponents are a telescope with a defined line of sight,a system for setting the vertical axis truly vertical, andboth a horizontal and a vertical graduated circle, similarto protractors, to determine the angles. See also LEVEL.

THRESHOLD VELOCITY (sol, eng)

The wind velocity al which saltation is initiated.

THRUST BLOCK (eng)

An external anchor which secures a pipe against forcesarising from water flows within the pipe.

TIDAL FLAT (Ifm, csd)

A large level area of land in the littoral zone subject toinundation by water that is usually salty or brackish.

TILE DRAIN (eng)

See DRAIN.

TILLAGE (agr)

The mechanical preparation of the soil to facilitate thegrowth of a crop or pasture, through the principalfunctions of seedbed preparation and weed control, It

involves the rearrangement of the entire topsoilstructure. Tillage is undertaken by various types ofploughs, scarifiers, cultivators, harrows or weeders, Theuse of drills for sowing is not generally regarded astillage, although the soil is given a full cultivation whena combine drill or air seeder is used.

PRIMARY TILLAGE constitutes the initial major soilworking preceding a new crop or pasture. SECONDARYTILLAGE refers to subsequent tillage operations usedfor weed control or to refine soil conditions beforesowing. Cf. CULTIVATION.

TILLAGE DEPTH (eng, agr)

The vertical distance from the initial soil surface to thelowest point of penetration of a tillage implement duringtillage.

TILLAGE TOOL (eng)

An individual soil working element such as a point,share, sweep, couller or blade.

TILT (rais)

See AERIAL PHOTOGRAPH.

TILTH (gen)

A general term used to describe the physical conditionof a soil as related to its ease of tillage and fitness asa seedbed, A soil in good tilth will not impede seedlingemergence and root penetration.

TILTING LEVEL (sur)

See LEVEL.

TIMBER EXTRACTION TRACK (for)

A route used for transport of logs from the point oftelling to the log dump, where no part of the logs is incontact with the ground. Cf. SWIG TRACK.

TIME OF CONCENTRATION (hyd)The shortest time necessary for all points on acatchment area to contribute simultaneously to flowpast a specified point. It is equivalent to the timerequired for runoff to 110w trom the most remote part ofthe catchment to the specified point, normally thecatchment outlet.

The time of concentration is used to calculate the peakdischarge tor a catchment by using the rational formula.This formula assumes that the peak discharge will becaused by a storm of duration equal to the time ofconcentration for the catchment.

Time of concentration is determined by either of twomethods, depending on the presence or absence ofsigniticant runoff diversions within the catchment.

f the catchment flow paths remain unaltered, time ofconcentration is estimated by the modified BransbyWilliams tormula. (References: Williams, GB. (1922), TheEngineer 29 321, Logan, J.M. (1967) J. Soil Cons.N.S.W. 23 270.289).

It the catchment flow paths are significantly affected byrunoff diversions, time of concentration is estimatedusing the combined times of overland and channelisedflow. (Reference: Institution ot Engineers, Australia(1977) 'Australian Rainfall and Runoff'.)

TINE (SHANK) (eng)

That part of a tillage implement that extendsdownwards from the frame and to which the (il/agetools are attached. The tine may be a single rigidmember, or one which hinges or deflects when itsbreakout force is exceeded. This tatter facitity hasresulted in the development of shear-bolt, spring-release, hydraulic, stump-jump, coil and spring tines,

TINE ASSEMBLY (eng)

A complete tine unit comprising a fine, a f/ne releasemechanism, a clamp or fixing and a tilla ge tool,

135

TINE LATERAL SPACING (eng)

The horizontal distance between adjacent tines in arank, It may not necessarily be uniform throughout theimplement. Cf, OVERALL TINE SPACING.

TINE OPENER (eng)

See SOIL OPENER.

TINE PITTING (ram)

See PITTING,

TINE RELEASE MECHANISM (eng)

An arrangement provided to protect the tine assemblyby allowing il to move backwards and upwards uponstriking an obstruction or hard conditions. Four typesin common use are cushion spring, lock toggle,improved cushion spring and hydraulic mechanisms.'Shear pins may also be used to protect tine assemblies.

Cushion spring tine release mechanism.

Lock toggle tine release mechanism.

Improved cushion spring tine release mechanism.

Hydraulic tine release mechanism.

TINED CULTIVATOR (eng)Syn. FIELD CULTrvATOR.

TINED HARROW (eng)

A light secondai y tilla ge implement normally used ontilled soil to retine surface soil conditions for theproduction ot a seedbed. Short sprung or rigid tines areassembled on a trame at close spacings. Tined harrowscome in a variety of types such as spring-tine, peg-tooth, spike-tooth, diamond, rotary, stubbte and pastureharrows. See also HARROWING.

A fined harrow.

136

TINE RELEASE MECHANISM (Continued) TOE (Um, str)

The lowest part of a slope where it stops or levels out.In a soil conservation context, for example, it describesthe zone where the wall of a gully control structuremeets the gully floor.

TONE (rms)

Refers to the range of grey scale from black to white,observed in an aerial photograph. lt is extremelyimportant in the identification of tand use, soil type andvegetation type. Tone is also a criterion used in theinterpretation of photographs involving other forms ofremote sensing. See also TEXTURE.

TOPDRESSING (agr)

The application of soil, sand, fertiliser or other materialto established or establishing vegetation to maintain thesupply of nutrients and/or to provide an improved soilenvironment for the continued growth ot desirableplants. Cf. TOPSOILING.

TOPFEED (ram)

Syn. BROWSE.

TOPOGRAPHIC MAP (lev)

A map which indicates both the horizontal and verticalrelationship of the features represented. The mostprecise representation ot relative height is by contourand such maps are commonly known as contour maps.

TOPOGRAPHY (gen)

The shape ot the ground surface as depicted by thepresence of hills, mountains or plains. Steep topographyis characterised by steep slopes and hilly land: flattopography is characterised by flat land with minorundulations and gentle slopes.

TOPOSEQUENCE (Um)

A continuous series of landtorms encountered betweena crest and a depression. For example, a toposequencemay consist of a hittcrest, sideslope, footslope,floodplain and stream channel.

TOPOSEQUENCE (sol)

A repetitive sequence of soils encountered betweenhilfcrests and the valley floor. A catena is a special caseof a toposequence in which the parent material isuniform.

TOPPING (for)

The removal of foliage from a tree at or above the originof the lowest branch. In the case of a tree having amultiple- trunk habit,, such as maltee, topping infers theremoval of each trunk at or above the origin of thelowest branch. Cf. LOPPING.

TOPSOIL (gen)

That part of the soil profile, typically the A, horizon,containing material which is usually more fertile andbetter structured than underlying layers. When the A2

horizon also meets these criteria, it may be included.Topsoil is the most important part of the soil withrespect to the growth of crops and pastures and itsloss or degradation represents the most serious aspectof soil erosion, Its retention is particularly important inthe revegetation of exposed batters or earthworM. Seealso TOPSOILING.

TOPSOILING (gen, agi)

The application of topsoil to exposed or eroded areas,including batters and earthworks, to encourage therapid growth of vegetation over them, for the purposeof stabilisation against erosion. On disturbed sites thetopsoil may be derived from a borrow area or may bethe original topsoil, stripped and stockpiled beforedisturbance. Cf, TOPDRESSING,

TOPWATER (agr)

A strip cropping terni for sheet flow coming on to thetreated area from land above.

TOR (lfm)

A very steep to precipitous peaked rocky hillockcharacteristically denuded of soil and eroded by sheetflow. Also often refers to an isolated and highlyweathered outcrop of granite.

TOTAL CATCHMENT MANAGEMENT (gen)The management of land, water and other biophysicalresources and activities, on a catchment basis. Its aimis to ensure:

- the continuing stability and productivity of thesoils,

the maintenance of an appropriate protectiveand productive vegetative cover,

a satisfactory yield of water of high quality, and

* minimisation of adverse environmental effectsdue to development.

Such management is achieved by the co'ordination ofpolicies and activities of relevant departments,authorities, companies and individuals who haveresponsibilities for the management of land withincatchments.

TOTAL ENERGY HEAD (eng)

The sum of the elevation of a free water surface, at agiven point above datum, and the velocity head of theflow at that point, viz,:

Total Energy Head

H

H

where Hyz

V2

2g

Static Head + Velocity Head= Hs + Hv= (y + z) +

2g

= Total energy head (m)Depth of flow (m)

= Height of channel flóor abovedatum (m)

= Velocity Head (m)

137

SPECIFIC ENERGY HEAD = Depth of flow + VelocityHead

V2He = y +

TOXICITY (sol)

The characteristic of a soil relating to its content ofelements or minerals which adversely affect plantgrowth. lt is of particular concern in relation to acidsoils. Soils with pH less than 5.0 may give rise tomanganese and aluminium toxicities which reduce plantgrowth and hence ground cover. lt is also of concernin the rehabilitation of heavy metal mines, where toxiclevels of such elements as copper. zinc and lead inmine tailings create difficulties in their revegetation.

TRACE ELEMENT (agr)

See PLANT NUTRIENT.

TRACK (gen)

Syn TRAIL,

TRAIL (TRACK) (for, gen)

A road of minimal construction standards which closelyfollows the natural landform and is constructed with aminimum of culverts and earlhworks, The surface israrely gravelled and, following initial construction,receives little maintenance, Construction standardsprovide for intermittent, but reliable, loaded four-wheeldrive travel in fair weather conditions and generally atlow speeds. More extensive use, or use during wetconditions, may lead to rapid deterioration of the trail,

TRAINER BANK (str)

See BANK.

TRANSECT (gen)

A projection across the land's surface along whichsamples or measurements are recorded, Transects aretypically used in vegetation and soil surveys and theprojection is usually fixed to enable recurringmeasurements to be taken, See also BELT TRANSECT,LINE TRANSECT, POINT TRANSECT,

TRANSLOCATED HERBICIDE (agi)See HERBICIDE,

TRANSPORT CAPACITY (hyd)

The ability of runoff to carry sediment from one pointto another.

TRANSPORTATION (sol)

That part of erosion processes in which detached soilor rock material is moved from one place to another,This may be accomplished by running water, rainfall,wind, gravity, ice action, or subsurface seepage.

TRANSPORTATIONAL SITE (If m)

An area where both sub-surface in situ processes andsurface processes of lateral movement occur. This isnormal on hillslopes, but, depending on the type ofmaterials involved. lateral movement of surface materialmay occur on very gentle gradients.

TRASH (agr)

A general term tor ali vegetative material, including bothcrop and weed residues, retained on or in the soil in aconservation ti//age system.

TRASH RACK (eng)

A grill, grate or other barner placed across the niet ofa hydraulic structure to prevent oversize debris fromentering and blocking the structure.

TRASH SEEDER (eng)

See DRILL.

TRAVERSE (sur)

A procedure for measuring between various points bya series of horizontal angles and distances. See alsoSTADIA SURVEY.

TREE (for, gen)

A perennial plant having a self-supporting woody mainstem or trunk which usually devetops woody branchessome distance above the ground. Cf. SHRUB.

TREE CROWN (for)

The branches and foliage of a tree.

TREE LOT (gen)

A group of trees retained or planted for a specificpurpose such as shade, shelter, beautification or winderosion control,

TRENCH (If m, sir)

A long narrow excavation generally with uniform cross-section, excavated by human activity. See alsoDISTURBED TERRAIN,

TRICKLE FLOW (hyd)

The extended low flow which occurs in manycalchments following major runoff events, In somecatchments, depending on their hydrologiccharacteristics, such flows may be sustained bygroundwater seepage and Ihus become continuousexcepl during periods of drought. This is known asBASE FLOW and is particularly relevant in uplandenvironments during the winter months, when rainfallintensities and evapotranspiration are typically low, andthere is a marked increase in the proportion ofprecipitation contributing to groundwater seepage.

In a soil conservation context. control of trickle flows irearthen structures is most important, to prevent thekilling of vegetation and consequent erosion along andbelow their spit/ways. Control is normally achieved bythe use of trickle pipes.

138

TRICKLE PIPE (str)

A small diameter pipe inserted through the wall of aponding structure to accommodate trickle f/ows or tolower the water level in the structure at a controlledrate,

Trickle pipes may be installed with a fall throughouttheir length or with an initial rise then a fall to producea self-priming syphon. Straight trickle pipes arecommonly used to accommodate trickle flows byinstalling them lust below the nIet level of the primaryspil/way. Self-priming syphons also accommodate trickleflows but have the added advantages of eliminating theneed to- lit co/lars and providing additional flooddetention capacity.

The term trickle pipe may also be used to describe theprimary outlet of a detention or retention structure, Inthis case the pipe is specifically designed to allowdrawdown at a controlled rate, to a prescribed level,following a major storm,

A trickle pipe to carry low flows through the wall of an earthdam,

TRIG LEVELLING (sur)

Syn. TRIGONOMETRIC LEVELLING.

TRIGONOMETRIC LEVELLING (sur)

See LEVELLING.

TRIPLE DISC DRILL (eng)

See DRILL.

TRUNCATED (sol)

Describes a soil profile that has been cut down byaccelerated erosion or by mechanical means. The profitemay have lost part or all of the A horizon andsometimes the B horizon, leaving only the C horizon.Comparison of an eroded soil profile with a virgin profileof the same area, soil type, and slope conditions,indicates the degree of truncation.

TUMULUS (Ifni)

A hillock thrust up by volcanism,

TUNNEL EROSION (gen)

See EROSION.

TUNNELLING (str, gen)

See EROSION.

TUNNELLING FAILURE (sir)

The failure ol an earthwork due to tunnel erosion. Seealso EARTHWORK TUNNELLING.

TURBIDITY (gen)

The cloudy condition caused by suspended solids in aliquid. In a soil conservation context, the term reters tothe muddy condition of runoff in which sediment issuspended.

TURF (agr)

Syn. SOD.

TURFING (agr)

Syn. SODDING.

TURKEY'S NEST DAM (gen)

See TANK.

TURNING POINT (agr)

The point at which two key lines meet on a stripcropping plan, due to changes in topography. See alsoPIVOT LINE.

TWO PEG TEST (sur)

Syn. COLLIMATION TEST,

139

U.S.C.S. (sol, eng)

Syn. UNIFIED SOIL CLASSIFICATION SYSTEM.

U.S.L.E. (gen)

Syn. UNIVERSAL SOIL LOSS EQUATION.

U-DUNE (csd)

See DUNE.

UNDER-FRAME CLEARANCE (eng)

The vertical distance measured from the lowest pointon the cutting edge of any tillage tool up to theunderside of the tillage implement frame. Thismeasurement does not give a clear indication of theimplement's residue handling capacity. Cf. EFFECTIVECLEARANCE.

UNDERCUTTING (gen)

Removal of material at the base of a steep slope, clii!,over/all or sueambank by water or wind action. Thisremoval steepens the slope, or produces an overhangwhich may eventually be subject to slumping.

UNDERGROUND MINE (mm)

A mining operation where the extraction of the ore/coalis carried out from subsurface shafts and tunnelsdriven directly into the seams of ore. Removal is byspecialised machinery and vehicles designed foroperating underground. Rehabilitation rquirements aftermining are far tess than for an open-cut mine as thereis considerably less disturbance of the land surface.

UNDERLAY (mm)

A sloping, as opposed to vertical, mine shaft.

UNDERSOWING (agr)

The procedure whereby two sowings are made in theone seedhed, either at the same time, or more usuallyone after the other. The technique is typically used tosow a pasture mixture under, a cereal crop and ensuresthat. given adequate seasonal conditions, the grass ¡sfully established by the time the cereal is harvested.This gives advantages in time saving, grazingmanagement and erosion protection. Depending onconditions, the grass seed is sown at or immediatelyafter cereal sowing, or when the cereal s fullyestablished.

The concept is also used in the growing of two rowcrops which are sown and mature at different times,thus ensuring maximum plant cover and soil protectionfor the greater part of the year.

UNDESIRABLE (ram)

A term used to describe a perennial or annual ptant oflittle or no grazing value that increases or invades tothe detriment of desirables and intermediates ondegraded sites. See also INDICATOR SPECIES.

UNIFIED SOIL CLASSIFICATION SYSTEM(USOS) (sol, eng)

A soil classification system based on the identificationof soil materials according to their particle size, grading,plasticity index and liquid limit. These properties havebeen correlated with lhe engineering behaviour of soilsincluding so// compressibility and shear strength.(Reference: Casagrande. A. (1947) Froc. Am. Soc. Civ,Engrs. 73 783-810). The system is used to determinethe suilability ot soil materials for use in earthworks,oplimal conditions tor their construction, specialprecautions which may be needed, such as souameliorants, and final batter grades to be used toensure stability. See also ATTERBERG LIMITS.

UNIFORM FLOW (hyd)

See FLOW.

UNIFORM SOIL (sol)

A soil in which there is little, if any, change in so/ltexture between the A and B horizons (e.g. loam overloam, sandy clay over silty clay). The soil is dominatedby the mineral fraction and shows minimal texturedifferences throughout, such that no clearly definedtexture boundaries are to be found. The range oftexture throughout the solum is not more than theequivalent span of one soil texture group. See alsoPRIMARY PROFILE FORM, SOIL PROFILE. DUPLEXSOIL, GRADATIONAL SOIL.

UNIQUE AGRICULTURAL LAND (lev)

Land which because of its soil, climate, topography orlocation possesses special features which make it mostsuitable for specific agricultural production.

Significant inputs and/or restrictions may be requiredto maintain long term productivity and fertility. Goodgeneral agricultural potential may not be necessarilypresent. Such lands may have limited area and extentand in terms of the crop which can be produced theirsignificance often relates to the non-availability ofsuitable alternative sites, See also FRIMEAGRICULTURAL LAND, GOOD AGRICULTURAL LAND.

UNIQUE AGRICULTURAL SOIL (lev)

A soif which possesses specific features which make itmost suitable for specific agricultural production.

Significant inputs may be required to maintain long termproductivity and fertility and good agricultural potentialmay not necessarily be present. Such soils may havea limited area and extent and in terms of the crop whichcan be produced their significance often relates to thenon- availability of suitable alternative sites. See alsoFRIME AGRICULTURAL SOIL, GOOD AGRICULTURALSOIL.

UNIT PLANTER (eng)

See DRILL.

UNIVERSAL SOIL LOSS EQUATION (USLE)(gen)

See SOIL LOSS EOUATION.

140

UNSTEADY FLOW (hyd)

See FLOW.

URBAN CAPABILITY (lev)

The ability of an area of land to support a particularintensity of urban development without the occurrenceof serious soil erosion and sedimentation during theconstruction phase, and possible instability anddrainage problems n the long term. See atso LANDCAPABILITY,

URBAN CAPABILITY CLASSIFICATION(lev)

A method of land c/assilication which ranks landaccording to various intensities of urban use on thebasis of the physical constraints applying to it. Theclassification does not consider development costs,social implications, aesthetics or other factors relatingto ecology and the environment, It is based on physicalcriteria alone and thus the classification of various areasas suitable for a particular type of urban developmentis an assessment of the capability of those areas tosustain a particular level of disturbance.

It is not a recommendation that such a form ofdevelopment be adopted but rather it forms the basisonto which other town planning consideratìons may beimposed to derive a development plan.

Urban capability classification is not a substitute, forspecific engineering and design investigations whichmay be required to more accurately define constraintsin the location and design of roads, individual buitdingsor recreational facilities. Nor does it imply the capacityof a site to support multi-storey units or other majorstructures. Before structural works of such magnitudeare undertaken, a detailed analysis of engineeringcharacteristics of the soil, such as bearing capacity andshear strength, may be necessary on a specificdevelopment site.

The Soil Conservation Service of New South Walesdefines five primary classes of urban capability: ClassA -Areas with little or no physical limitations to urbandevelopment. Class B -Areas with minor to moderatephysical limitations to urban development. Theselimitations may influence design and impose certainmanagement requirements on development to ensurea stable land surface is maintained both during andafter development. Class C -Areas with moderatelimitations to urban development. These limitations canbe overcome by careful design and by adoption of sitemanagement techniques to ensure the maintenance ofa stable land surface, Class D 'Areas with severephysical limitations to urban development which will bedifficult to overcome, requiring detailed site investigationand engineering design. Class E -Areas where no formof urban development is recommended because of verysevere physical lìmitations to such development that arevery difficult to overcome.

Within these primary classes a number of sub-classesare defined by letter subscript to indicate the physicallimitations which restrict development. The combinationof several subscripts indicates a number of limitationswhich interact to restrict development. The dominantconstraint is indicated first, Subscripts and thelimitations to which they apply include:

Soil Limitations

C very high permeabilityd shallow soil

e erodibilityg low wet strengthI satinity

p ow permeabilityx extraclalion/disposalsite

Other Limitationsf flooding

m mass movementr rock outcrop

s slopet topographic feature(e.g. rock fall, runon etc.)

w seasonal waterlogging

See also LAND CAPABILITY CLASSIFICATION.

cgI

VALLEY FLAT (11m)

A small gently inclined to level area of land typicallyenclosed by hillslopes. lt may or may not contain astream channel,

VALUABLE AGRICULTURAL LAND (gen)A general term used to encompass both prime andgood agricultura! land.

VALUE (sol)

See SOIL COLOUR.

VEGETATION (agr)

Plants in general or the sum total of plant life in an area.The role of vegetation in a soil conservation context isa vital one. Whether it be comprised of grasses, shrubsor trees, vegetation protects the soil from wind and/orwater erosion by one or a combination of the following:

Providing a canopy to protect the soil from raindropimpact.

* Providing a near-ground retardance to runoff flow,

Binding the soil together by root proliferation.

Reducing the velocity of wind near the ground.

* Providing organic matter to improve soil slructure.

Providing plant litter to protect the soil.

VELOCITY (hyd)

Rate of movement of water flowing past a point in aspecific direction.

Symbol: V, Unit: m/s.

141

VELOCITY HEAD (eng)

The hydraulic head due to the velocity of moving waler,obtained by dividing the square of the velocity by twicethe acceleration ol gravity, viz.:

V2Hv=

Kv Velocity Read (m)Velocity of flow (m/s)Acceleration due Io gravity (9.8 m/s2)

VELOCITY HEAD ROD (hyd, eng)

A metal rod, specially designed and calibrated, used forthe instantaneous measurement of the hydraulic headand mean velocity of waler flow in a channel. Amodified velocity head rod, mounted in the channel, canalso be used to record the maximum head and flowvelocity at a remote location, A special water-solubledye painted on the rod gives an indication of themaximum water level, and the levels indicated on theupstream and downstream edges of the rod are usedto compute maximum velocity.

VERTICAL INTERVAL (Str)

The vertical distance from one soil conservationstructure to another. Commonly applied to the verticaldistance between banks and used in design and layoutwork as it is somewhat independent of slope for a givenlandscape/soil situation.

The term also describes the vertical distance betweencontour lines on a map.

VIRGIN SOIL (sol)

A soil that has not been significantly disturbed from itsnatural environment.

WASKAWAY (gen)

A small localised gully or till resulting from some site-specific change in soil, vegetation or hydrauliccircumstances, usually caused by human activity.

WASTE ROCK (mm)

Country rock and low-grade ore which is excavated atthe same time as the orebody but is discarded prior tomilling and refining.

WATER BALANCE (agr, sol)

An estimated state of equilibrium within the soilmoisture regime based on rainfall, evapotranspiralion,runoff, drainage and soil moisture storage.

Soit moisture is assumed to severely limit plant growthin months when rainfall, together with an antecedentmoisture content up to a maximum of 100 mm, is lessthan 40 per cent of pan evaporation. At other times soilmoisture is regarded as being adequate for plantgrowth. When the assumed field capacity of the soil isreached any further rainfall is regarded as being lost asrunoff. (Reference: Fleck, B.C. (1971) J. Soil Cons,N.S.W. 27 135-144.)

The water balance provides information as to suitabletitlage and sowing times, condition of ground cover andalso whether other activities are restricted by wet or drysoil conditions, lt atso gives useful informationconcerning periods of major catchment flow and trichleflows, However, being based on monthly averages,short periods of intense rainfall are omitted. This rainfallis important in initiating soil erosion and providing runofffor stock watering purposes,

WATER DISPOSAL AREA (ABSORPTIONAREA) (gen)

An area onto which runoff is discharged in order todisperse it without causing soil erosion. Such an areausually has a stable cover of vegetation, and is of suchslope and tandform that discharged runoff does notconcentrate sufficiently to create an erosion hazard,May also be called a WATER SPREADING AREA.

WATER EROSION (gen)

See EROSION,

WATER SPREADING AREA (gen)

Syn. WATER DISPOSAL AREA.

WATER TABLE (gen)

The upper surface of unconfined groundwater belowwhich the pores of rock or soil are saturated. APERCHED WATER TABLE is the surface of a local zoneof saturation held above the main body of groundwaterby an impermeable layer, usually clay, and separatedfrom it by an unsaturated zone.

WATER-HOLDING CAPACITY (sol)

Syn. FIELD CAPACITY.

142

WATER-REPELLENT SOILS(HYDROPHOBIC SOILS) (sol)

Sous which resist wetting when dry. Drops of water donot spread spontaneously over their surface and intopores. The degree of water repellence may be severewhere water drops remain on a flattened surface forsome minutes. In other cases drops appear to beabsorbed readily, but quantitative measurements showthat the height of capillary rise is diminished.

This characteristic is mainly a feature of some sandysoils (topsoils) and is generally attributed to organiccoatings on the sand grains which resist water entryinto the soil.

WATER-STABLE AGGREGATION (sol)

An indication of the resistance of soi/ aggregates tobreakdown by water. This is normally measured by thedegree to which different size fractions of aggregatesare broken up by agitation in water using a wet-sievingprocedure.

The degree ot water-stable aggregation is used as ageneral indicator of soit erodibility. However, theprocedure is not widety accepted because of problemsof standardisation and the paucity of clear evidencerelating it objectively to a soil's susceptibility to erosion.

WATERCOURSE (gen)

A channel, having defined bed and banks, down whichsurface water flows on a permanent or semi-permanentbasis or at least, under natural conditions, for asubstantial time after periods of heavy rainfall within itscatchment. lt is a general term including:

RIVER

A watercourse that conveys relatively large flows.Under average coastal and tabletand climaticconditions rivers typically have continuous flows.

CREEK (STREAM)

A smatter watercourse than a river which usuallyforms the link between a drainage line and a riverin a natural catchment //ow path.

WATERING POINT (ram, agr, gen)

A site at which stock obtain drinking water, fromunderground supplies via a bore or well, or fromnaturally occurring surface supplies. See alsoPIOSPHERE. SACRIFICE ZONE.

WATERLOGGED (sol)

The condition of a soit which is saturated with waterand in which most or alt of the soil air has beenreplaced. The condition, which is detrimental to mostplant growth, may be caused by excessive rainfall,irrigation or seepage, and is exacurbated by inadequatesite and/or internal drainage.

WATERPONDING (ram)

A technique involving the ponding ot shallow sheets ofrunoff, using an appropriatety designed system of towabsorption banks or furrows, primarily on land affected

t-, --aHeclamation o! scalded land by waterponding.

by scalds. This is done lo achieve a change in soilproperlies which wilt allow the eslabtishmenl andpersislence of a vegetative cover. Both erosion controland land reclamalion are involved in this practice, whichis commonly used in semi-arid areas where scalds area problem.

WATERSHED (gen)

The dividing ridge between two catchments.

WATERSPREADING (ram)

A technique whereby surface runoff is collected andspread over areas of land to improve natural vegetalivecover and/or lo allow pasture or crop production, whilstreducing the risk of erosion.

The technique is commonly used in semi-arid areas inorder to take advantage of the large volumes of runoffemanating from hard ridges or other high runoff-yieldingcatchments after relatively small amounts of rain. Suchwater, normally concentrated in flowlines which wouldbe subject to erosion when cultivated, can be spreadover large areas, reducing its erosive power and makingit available for crop or pasture growth. See alsoWATERSPREADING BANK.

WATERSPREADING BANK (str)See BANK.

143

WATERWAY (str)

A stable longitudinally-sloping water disposal area ofsufficient capacity, used to discharge surplus runoff andto allow it to flow to a lower level without causingerosion. The runoff would normally be concentrated bythe landscape above or by soil conservation banks and/or gully control structures which feed into the waterway.The waterway is selected/designed lo link up to thenatural drainage system of the area.

Waterways may he natural or constructed. NATURALWATERWAYS are those where runoff naturally flows orcan be made to do so without constructed retainingbanks or channel excavation/shaping. CONSTRUCTEDWATERWAYS are those requiring constructed retainingbank(s) and/or channel excavation/shaping to containrunoff. Three types are commonly recognised:

A stable natural depression confined by constructedbanks fo increase its capacity.

A strip of evenly sloping land confined by waterwaybanks running up and down the slope and allowingfor entry of runoff from graded banks on either sideand/or at the lop as necessary. A trapezoidal channelis thus formed, the floor of which is the naturaf landsurface, which may have natural vegetation or mayrequire fo be sown. Such a waterway may notnecessarily follow the natural flowline but may bebetter located to suit the paddock layout, for exarnptealong a fence line.

A llowline subject to parabolic gully shaping and notbanked, being sown with native or introducedspecies.

WATERWAY (Continued)

The first two types of constructed waterway (above)require banks that define their width and capacity. If thewaterway cross-section is level and/or a goodgroundcover of vegetation is present the waterwaybanks shoutd be constructed by excavation fromoutside the waterway area. This external constructionmay atso be used where topsoil depth is shallow andwhere revegetabon problems are expected. Theadvantages of externat construction are that thewaterway is ready for immediate use, its constructionis tess costty and the undisturbed naturat vegetationoften provides the best groundcover in a waterway. Thedisadvantage is that there is a danger that excavatedareas, which run directly down slope, may erode. tnaddition the waterway has no capacity betow.groundtevet. Consequently, channels of any banks feeding intothe waterway must be correctty graded into it, toprevent ponding or overtopping.

Alternatively, the waterway banks can be buitt byexcavating from within the waterway area. Thesewaterways must be revegetated after construction toprovide adequate ground cover to ensure surfacestabitity. The advantages of internat construction arethat the dLrection of runoff flow is not restricted todirectty downslope; waterways can more reasonabtyfollow existing fence tines or tead to speciat outtetpoints, provided such deviation dóes not requireexcessive cut and fill: and water is carried betowground tevel so that grading bank channels into thewaterway is easier. However, there witt be a detay

t

s

144

before the waterway can be used whitst vegetation isre-es tab t is h in g

Construction costs are atso higher, particutarty withwide waterways because of the need to conserve andrespread topsoit over the excavated area.

For att types of waterway, proper maintenance is equattyas important as the original design and construction.

GRASSED WATERWAYS must be managed to maintaina dense and vigorous cover about 15 cm high. This canbe achieved by regutar topdressing with fertitiser, goodgrazing management and/or mowing and bating. Awaterway used for grazing shoutd onty be stocked bya targe number of animats for short periods. Vegetationshoutd not be mown or stashed too ctose to the groundand plants, particutarty annuats, shoutd be attowed tomature and set seed.

Waterway banks can be damaged by vermin such asfoxes and rabbits, stock, soit setttement, tunnet erosion,soil cracking and ritt erosion. Regutar inspections shoutdbe made to find these probtems and the damageshoutd be repaired immediatety. Sedimentation ofwaterways can also occur, reducing their capacity anddiverting ftows. Sediment should be removed whenrunoff rains are teast likety to occur. Topsoit andvegetation should be retained and respread afterdesitting; and the treated area seeded and fertitised.

Graded banks leading runoff into a waterway to protectarable /and from erosion. Note waterway stubs to the /efto! the waterway.

n

-L.- -5HQçr I

WATERWAY BANK (Str)

See BANK.

WATERWAY STUB (str)

A constructed entry built as part of a waterway bank.lt is typically a short lateral bank which directs waterinto the waterway. The stub may eventually beextended, when the waterway is stable, forming agraded bank as part of a system of soil erosion control.

WAVE UPRUSH (csd)

The rush of sea-water up onto the beach following thebreaking of a wave. See also SWASH ZONE.

WEATHERING (sol)

The physical and chemical disintegration, alteration anddecomposition of rocks and minerals at or near theearth's surface by atmospheric and biological agents.

WEEDICIDE (agr)

Syn. HERBICIDE,

WEIR (eng, hyd)

A structure or wall built across a flowline to raise thewater level to allow diversion or measurement ofdischarge rate. Diversion may be by pumping or otheroff take From the pool formed by the weir. A measuringweir is designed specially for the operation ofmeasuring instruments. A weir is an overflow structuredesigned to allow flows to pass directly over it once thepool is Full.

A V-notch sharp-crested we!,.

T»- -r-t

145

Weirs may be either sharp-crested or broad-crested. Asharp-crested weir causes the nappe to immediatelyspring clear of the edge, leaving the flow sustantiallyfree from viscous effects, Broad-crested weirs are longenough, in the direction of flow, to permit parallel flowacross the weir before the nappe leaves the structure.

A weir is said to be in a state of free discharge whenthe upstream water level is not affected by thedownstream water level, that is, the nappe is notdischarging underwater. When the nappe is dischargingunderwater, and the upstream water level is affectedby the downstream level, the weir is said to besubmerged or drowned.

WEIR COEFFICIENT (hyd)

See WER FLOW EQUATION.

WEIR FLOW EQUATION (hyd)

A mathematical formula for determining weir discharge,viz,:

O CLH3/2

= discharge (m3/s)= weir length, perpendicular to flow (m)= measured head (m)= weir coefficient

The WEIR COEFFICIENT is an adjustment factor tomake allowance for different crest types. Higher valuesof C allow tor weirs with smooth upstream aprons suchas wood- float finished concrete, while lower valuesallow for weirs with rough upstream aprons such ascoment-grouted rock.

where OLHC

-'I-". -

- a-'-"--w-- -OIÇ.Z.-za- -k's-aç

!9 ':c; 1.. -ts A3y2S-

WET SAND FLOW (gen)

See EARTHFLOW.

WETTED PERIMETER (hyd)

The length ot the boundary wetted by flow in a channelor pipe at a specified section, measured along a planeat right angles to direction of flow. Used in calculatingthe hydraulic radius for Manning 's formula.

WHEELPOINT (ram)

A device tor laying down a point transect, consisting ofa rimless spoked wheel and handle. Points are locatedby contact with the ground by specified spokes.

WIND EROSION (gen)

See EROSION.

WIND FETCH (gen)

The distance along which the wind has an uninterruptedflow.

WIND RIDGING (gen)

A system of small ridges formed, on or near the contourat regular intervals across the land! to restrict theeffects ot wind erosion. The aim is to torm a low barrier,by deep ripping or furrowing, to intercept soil particlesmoving by the process ot saltation. On flat land theridges woutd be formed at right'angles to the directionof the prevailing wind. The system is sometimes usedas an emergency procedure on land which, due lounusual climatic, soil or vegetation conditions, isparticularly susceptible to wind erosion.

Wind ridging on sandy soils. Note windblown sand trappedin the foie ground.

146

WINDBREAK (gen)

A barrier ol living trees and/or shrubs or other materialswhich reduces the velocity of the wind near the soilsurface, thus protecting the soil from wind erosion, Seealso SHELTERBELT.

WINDBREAK PERMEABILITY (gen)

The 'openness' ot a windbreak which allows wind lopass through it, Cf. WINDBREAK POROSITY.

WINDBREAK POROSITY (gen)

The percentage of a windbreak occupied by voids. Cl.WINDBREAK PERMEABILITY.

WINDOWPANE CLEARING (ram)

A land management technique of ctearing adjacentuniform size blocks, usually not exceeding 120 hectares,such that each block is surrounded by unclearedcountry generally not less than loo metres in width, Thegrid pattern so produced minimises wind erosion duringthe cropping phase.

Windowpane clearing is principally used n semi-aridareas particularly on light-textured soils. lt also providesfor the retention of native vegetation which ensures areadily available seed source tor the re-establishmentot a protective vegetative cover tot lowing the croppingphase.

WINDROW (gen)

A longitudinal accumulation of straw, timber, soil orother material, stacked or piledup by mechanicalmeans.

In generai agriculture. windrows are typically associatedwith hay crops, whereby, alter cutting, the hay iswindrowed to allow more uniform drying prior to baiting.

During land clearing, felled trees and other debris areoften windrowed to facilitate burning or inter-windrowplanting.

Earth windrows are typically created due to spillage' atthe edge of a bulldozer blade during earthmovingoperations. They may build up along the edges of trailsduring their construction and maintenance. This mayprove useful in directing runoff to a stable outlet inwhich case it is called a windrow drain. However, inother circumstances it may prevent runoff leaving thetrail, causing erosion. Blading is thus necessary toremove the windrows and facititate cross fall drainage.

WINDROW DRAIN

See DRAIN.

WINDTHROW (for)

A tree which has fatten as a result of natural forces.

W!NG WALL (eng)

An extension to a head wall or other end support.designed to prevent seepage from undermining ahydrologic structure, control turbulence at its side and/or retain adiacent soit material. In the case of culverts,flumes or similar structures, wing walls also confine anddirect flows of water.

At the outlet of these types of structures, the wing wattsare often referred to as TAIL WALLS Tait watts mustbe set at a horizontal angle of not tess than 45 degreesto the direction of outflow to avoid problems caused byturbulence.

The term s also used to refer to a bank constructedon the outside of a tank, fo impound large flows. A pipethen facilitates water entry into the tank. The wingwattalso allows settlement of sediment prior to inflow.

WINZE (mm)

An excavation or shaft sunk downwards from a levelpassageway in an underground mine.

147

XEROMORPHIC (ram)

Describes vegetation adapted to dry climatic conditionsand able to withstand prolonged droughts.

XEROPHYTE (ram)

A xeromorphic plant. Cf. MESOPHYTE.

V

YIELD (hyd)

The amount of runoff that is produced or expected tobe produced from a catchment. lt may be expressedon a unit area or unit time basis.

ZERO PRESSURE PRESSWHEEL (eng)

See PRESS WHEEL,

ZERO TILLAGE (agr)

Syn. NO-TILLAGE.

ZONED EMBANKMENT (eng, Str)

The earth watt of a dam built with different types ofmaterials comprising different parts of the wall. lt isused when materials with particular useful propertiesare in short supply. For example when ctayey materialis scarce, the available supply is used as a central corein the watt to prevent it from leaking.

BY AUTHORITYD. WEST. GOVERNMENT PRINTER. NEW SOUTH WALES-19&6