Volume 5_Irrigation and Agricultural Drainage.pdf

GOVERNMENT OF MALAYSIA DEPARTMENT OF IRRIGATION

AND DRAINAGE

Jabatan Pengairan dan Saliran Malaysia Jalan Sultan Salahuddin 50626 KUALA LUMPUR

Volume 5 Irrigation and Agricultural Drainage

Volume 5 - IRRIGATION AND AGRICULTURAL DRAINAGE

March 2009 i

Disclaimer Every effort and care has been taken in selecting methods and recommendations that are appropriate to Malaysian conditions. Notwithstanding these efforts, no warranty or guarantee, express, implied or statutory is made as to the accuracy, reliability, suitability or results of the methods or recommendations. The use of this Manual requires professional interpretation and judgment. Appropriate design procedures and assessment must be applied, to suit the particular circumstances under consideration. The government shall have no liability or responsibility to the user or any other person or entity with respect to any liability, loss or damage caused or alleged to be caused, directly or indirectly, by the adoption and use of the methods and recommendations of this Manual, including but not limited to, any interruption of service, loss of business or anticipatory profits, or consequential damages resulting from the use of this Manual.


ii March 2009

Foreword

The first edition of the Manual was published in 1960 and was actually based on the experiences and knowledge of DID engineers in planning, design, construction, operations and maintenance of large volume water management systems for irrigation, drainage, floods and river conservancy. The manual became invaluable references for both practicing as well as officers newly posted to an unfamiliar engineering environment. Over these years the role and experience of the DID has expanded beyond an agriculture-based environment to cover urbanisation needs but the principle role of being the countrys leading expert in large volume water management remains. The challenges are also wider covering issues of environment and its sustainability. Recognising this, the Department decided that it is timely for the DID Manual be reviewed and updated. Continuing the spirit of our predecessors, this Manual is not only about the fundamentals of related engineering knowledge but also based on the concept of sharing experience and knowledge of practicing engineers. This new version now includes the latest standards and practices, technologies, best engineering practices that are applicable and useful for the country. This Manual consists of eleven separate volumes covering Flood Management; River Management; Coastal Management; Hydrology and Water Resources; Irrigation and Agricultural Drainage; Geotechnical, Site Investigation and Engineering Survey; Engineering Modelling; Mechanical and Electrical Services; Dam Safety, Inspections and Monitoring; Contract Administration; and Construction Management. Within each Volume is a wide range of related topics including topics on future concerns that should put on record our care for the future generations. This DID Manual is developed through contributions from nearly 200 professionals from the Government as well as private sectors who are very experienced and experts in their respective fields. It has not been an easy exercise and the success in publishing this is the results of hard work and tenacity of all those involved. The Manual has been written to serve as a source of information and to provide guidance and reference pertaining to the latest information, knowledge and best practices for DID engineers and personnel. The Manual would enable new DID engineers and personnel to have a jump-start in carrying out their duties. This is one of the many initiatives undertaken by DID to improve its delivery system and to achieve the mission of the Department in providing an efficient and effective service. This Manual will also be useful reference for non-DID Engineers, other non-engineering professionals, Contractors, Consultants, the Academia, Developers and students involved and interested in water-related development and management. Just as it was before, this DID Manual is, in a way, a record of the history of engineering knowledge and development in the water and water resources engineering applications in Malaysia. There are just too many to name and congratulate individually, all those involved in preparing this Manual. Most of them are my fellow professionals and well-respected within the profession. I wish to record my sincere thanks and appreciation to all of them and I am confident that their contributions will be truly appreciated by the readers for many years to come.

Dato Ir. Hj. Ahmad Hussaini bin Sulaiman, Director General, Department of Irrigation and Drainage Malaysia


March 2009 iii

Acknowledgements Steering Committee: Dato Ir. Hj. Ahmad Husaini bin Sulaiman, Dato Nordin bin Hamdan, Dato Ir. K. J. Abraham, Dato Ong Siew Heng, Dato Ir. Lim Chow Hock, Ir. Lee Loke Chong, Tuan Hj. Abu Bakar bin Mohd Yusof, Ir. Zainor Rahim bin Ibrahim, En. Leong Tak Meng, En. Ziauddin bin Abdul Latiff, Pn. Hjh. Wardiah bte Abd. Muttalib, En. Wahid Anuar bin Ahmad, Tn. Hj. Zulkefli bin Hassan, Ir. Dr. Hj. Mohd. Nor bin Hj. Mohd. Desa, En. Low Koon Seng, En. Wan Marhafidz Shah bin Wan Mohd. Omar, Sr. Md Fauzi bin Md Rejab, En. Khairuddin bin Mat Yunus, Cik Khairiah bt Ahmad. Coordination Committee: Dato Nordin bin Hamdan, Dato Ir. Hj. Ahmad Fuad bin Embi, Dato Ong Siew Heng, Ir. Lee Loke Chong, Tn. Hj. Abu Bakar bin Mohd Yusof, Ir. Zainor Rahim bin Ibrahim, Ir. Cho Weng Keong, En. Leong Tak Meng, Dr. Mohamed Roseli Zainal Abidin, En. Zainal Akamar bin Harun, Pn. Norazia Ibrahim, Ir. Mohd. Zaki, En. Sazali Osman, Pn. Rosnelawati Hj. Ismail, En. Ng Kim Hoy, Ir. Lim See Tian, Sr. Mohd. Fauzi bin Rejab, Ir. Hj. Daud Mohd Lep, Tn. Hj. Muhamad Khosim Ikhsan, En. Roslan Ahmad, En. Tan Teow Soon, Tn. Hj. Ahmad Darus, En. Adnan Othman, Ir. Hapida Ghazali, En. Sukemi Hj. Sidek, Pn. Hjh. Fadzilah Abdul Samad, Pn. Hjh. Salmah Mohd. Som, Ir. Sahak Che Abdullah, Pn. Sofiah Mat, En. Mohd. Shafawi Alwi, En. Ooi Soon Lee, En. Muhammad Khairudin Khalil, Tn. Hj. Azmi Md Jafri, Ir. Nor Hisham Ghazali, En. Gunasegaran M., En. Rajaselvam G., Cik Nur Hareza Redzuan, Ir. Chia Chong Wing, Pn. Norlida Mohd. Dom, Ir. Lee Bea Leang, Dr. Hj. Md. Nasir Md. Noh, Pn. Paridah Anum Tahir, Pn. Nurazlina Mohd Zaid, PWM Associates Sdn. Bhd., Institut Penyelidikan Hidraulik Kebangsaan Malaysia (NAHRIM), RPM Engineers Sdn. Bhd., J.U.B.M. Sdn. Bhd. Working Group: Dato Ir. Mohd. Azhari Ghazalli, Tn. Hj. Abdul Halim Abdul Jalil, Ir. Loh Kim Mon, Dr. Mohammud Husain, Ir. Hj. Daud b. Mohd Lep, Tn. Hj. Mohd Yazid b. Abdullah, Ir. Hj. Zainol Abidin b. Mahmud, Tn. Hj. Jamil b. Shaari, Tn. Hj. Raja Roslan b. Raja Baharom Shah, Pn. Azizah bt. Mohamad, Tn. Hj. Raja Abdul Aziz Bin Raja Ismail, Pn. Marenawati bt. Abd Malek, Tn. Hj. Hussien b. Harun, En. Kamaruddin b. Saleh, Ir. Hj. Mohd Radzuan b. Mohamad, En. Tee Sing Tiat, En. Tan Woon Yang, Tn. Hj. Ismail b. Ahmad, En. Mohamad Razali b. Jusoh, En. Tang Soo Yugh, Mazolizam b. Mohamad, En. Terrence Eddy Wong, En. Salahuddin b. Ali, En. YoulHydell b. Abdul Rahman, Ir. Mohamad Suaimi b. Ramli, Abdul Aziz b. Mohd Yusof, En. Lee Liang Wang, En. Thian Kim Tai, Kalaisaravelem, Ir. Wan Mokhtar Nawang, Prof. Dr. Mohd Amin Mohd Soom, Dr. Abdullah Al Mamun, Dr. Md. Rowshon Kamal, En. Mohamad Amir Mat, Cik Ernie Munyati Ulwi, Pn. Suriani Mamat.


iv March 2009

Registration of Amendments

Amend No

Page No

Date of Amendment Amend No

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Date of Amendment


March 2009 v

Table of Contents

Disclaimer.. i

Foreword. ii

Acknowledgements iii

Registration of Amendments .. iv

Table of Contents.. v

List of Volumes .. vi

Glossary.. vii

How to Use the Manual............. xliv

List of Symbols xlix

List of Abbreviations. lx

SI and English Units and Conversion Factor lxv

Part A Introduction and Administration

Chapter 1 Malaysian Perspective

Chapter 2 Administration

Chapter 3 System and Technology

Part B Planning

Chapter 4 Planning Process

Chapter 5 Water Demand Estimation

Chapter 6 Hydraulic Fundamentals

Chapter 7 Computer Applications

Part C Irrigation Design

Chapter 8 Water Intake Facilities

Chapter 9 Irrigation Conveyance

Chapter 10 Surface Irrigation

Chapter 11 Microirrigation

Chapter 12 Sprinkler Irrigation

Part D Drainage Design

Chapter 13 Surface Drainage

Chapter 14 Subsurface Drainage

Chapter 15 Drainage Water Control and Treatment

Part E Farm Infrastructure

Chapter 16 Hydraulic Structures

Chapter 17 Roads and Bridges


vi March 2009

List of Volumes Volume 1 FLOOD MANAGEMENT Volume 2 RIVER MANAGEMENT Volume 3 COASTAL MANAGEMENT Volume 4 HYDROLOGY AND WATER RESOURCES Volume 5 IRRIGATION AND AGRICULTURAL DRAINAGE Volume 6 GEOTECHNICAL MANUAL, SITE INVESTIGATION AND ENGINEERING SURVEY Volume 7 ENGINEERING MODELLING Volume 8 MECHANICAL AND ELECTRICAL SERVICES Volume 9 DAM SAFETY, INSPECTIONS AND MONITORING Volume 10 CONTRACT ADMINISTRATION Volume 11 CONSTRUCTION MANAGEMENT


March 2009 vii

Glossary

Term Description

AADT Average annual daily traffic (AADT) is the total volume of vehicle traffic in both directions of a highway or road for a year divided by 365 days. AADT is a useful and simple measurement of design standard and road category. AADT is also used in pavement design and also useful in road network management tool.

Absorption A process by which substances in gaseous, or solid form dissolve or mix with other substances.

Acid Soil Soil that is free of lime with a pH of more than 7.

Adsorption Adherence of gas molecules, ions or molecules to solid surfaces.

Advance time Time required for a given surface irrigation stream of water to move from the upper end of a field to the lower end. Time required for a given surface irrigation stream to move from one point in the field to another.

Aeration A process where a substance becomes permeated with air or another gas. The term is usually applied to aqueous liquids being brought into close contact with air by spraying, bubbling or agitating.

Aesthetic The aspects of water that are perceivable by the senses (such as vision, smell, etc.).

Algae Comparatively simple chlorophyll-bearing plants, most of which are aquatic and microscopic in size.

Algicide Any substance that will kill or control algae growth.

Alkaline soil Soils with a pH of below 7 (opposite of acid soils).

Alkalinity The quantitative capacity of aqueous media to react with hydroxyl ions. It can also be referred to the equivalent sum of the bases that are titratable with strong acid. Alkalinity can also be defined as the capacity factor, which represents the acid-neutralising capacity of an aqueous system.

Allowable depletion That part of soil moisture stored in the plant root zone managed for use by plants, usually expressed as equivalent depth of water in acre inches per acre, or inches.

Allowable velocity Flow velocity of water in an open channel, just below the velocity that would cause

Alluvial plain A plain bordering a river, formed by the deposition of alluvium eroded from areas of higher

Alternate set irrigation

A method of managing irrigation whereby, at every other irrigation, alternate furrows are irrigated or sprinklers are placed midway between their locations during the previous irrigation.

Ambient The natural conditions that would be expected to occur in waters not influenced by man. For stream sampling purposes, those periods of streamflow are not influenced by recent storm events.


viii March 2009

Glossary

Term Description

Annual exceedance probability (AEP)

Refers to the probability or risk of a natural event with a given size occurring or being exceeded in any given year. A 90% AEP event represents a high probability of flood occurring or being exceeded; meaning it would occur quite often and would be relatively small. On the other hand, a 1% AEP event has a low probability of occurrence or being exceeded; therefore it would be fairly rare but it would be relatively large.

Antecedent moisture condition (AMC)

A qualitative indication of the moisture content of surficial soils at the beginning of a storm event.

Anthropocentric Human derived or man-made.

Anti-seep collar A device installed around a culvert, pipe or conduit through an embankment, which lengthens the path of seepage along the exterior of the conduit.

Application efficiency (Ea)

The ratio of the average depth of irrigation water infiltrated and stored in the root zone to the average depth of irrigation water applied, expressed as a percentage. Also referred to as AE.

Application efficiency low

The ratio of the average of the lowest one-fourth of measurements of quarter (Eq) irrigation water infiltrated to the average depth of irrigation water applied, expressed as a percentage. Also called AELQ. Used as an indication for uniformity of application.

Application efficiency low half

The ratio of the average of the low one-half of measurements of irrigation (Eh) water infiltrated and stored in the root zone to the average depth of irrigation water applied, expressed as a percentage. Also called AELH. Used as an indication for uniformity of application.

Application rate Usually expressed in inches per hour.

Application rate, sprinkler

The rate at which water is applied to a given area by a sprinkler system.

Application time, set time

The amount of time that water is applied to an irrigation set.

Aquatics Plants that grow either partly or completely submerged in water.

Aquifer A water-bearing formation that provides a groundwater reservoir. It can be made up of a single, part of or group of formation/s, which contain/s sufficient permeable material capable of yielding significant quantities of water to wells and springs.

Arid climate Climate characterized by low rainfall and high evaporation potential. A region is usually considered as arid when precipitation averages less than 10 inches (250 mm) per year.

Available soil water The difference between actual water content of a soil and the water held by that soil at the permanent wilting point.

Available water capacity (AWC)

The portion of water in a soil that can be readily absorbed by plant roots of most crops, expressed in inches per inch, inches per foot, or total inches for a specific soil depth. It is the amount of water stored in the soil between field capacity (FC) and permanent wilting point (WP). It is typically adjusted for salinity (electrical conductivity) and rock fragment content. Also called available water holding capacity (AWHC).


March 2009 ix

Glossary

Term Description

Average annual precipitation

The long-term or historic (generally 30 years or more) arithmetic mean of precipitation (rain, snow, dew) received by an area.

Average daily peak use rate

Calculated or measured water used by plants in 1 day through evapotranspiration, expressed as inches per day.

Average recurrence interval (ARI)

The average elapsed time in years between floods of a given size occurring. For example a 1 year flood occurs on average once every year, therefore the ARI value would be relatively small. Contrast to that, a 100 year ARI flood (i.e. occurs on average once every one hundred years and fairly rare) would have a relatively large ARI value.

Backflow prevention device

Safety device that prevents the flow of water from the water distribution system back to the water source.

Barrel A closed conduit used to convey water under or through an embankment, which is a part of the principal spillway.

Baseflow The portion of a stream flow that is not due to storm runoff, and is supported by groundwater seepage into a channel.

Basic intake rate Rate at which water percolates into soil after infiltration has decreased to a nearly constant value.

Basin irrigation Surface irrigation by flooding areas of level land surrounded by dikes. Generally used interchangeably with level border irrigation. In some areas level borders have tailwater runoff. If used in high rainfall areas, storm runoff facilities are necessary.

Berm A shelf that breaks the continuity of a slope; a linear embankment or dike.

Best management practice (BMP)

A structure or practice designed in runoff management to prevent the discharge of one or more pollutants to the land surface thus minimising the chance of wash-off by runoff. It can also be referred to a structure or practice to temporarily store or treat runoff to reduce flooding, remove pollutants, and provide other amenities (such as recreational, fishing spots, etc.).

Bioavailable A fraction of the chemicals in the surrounding environment that can be taken up by organisms. The environment may include water, sediments, suspended particles and food items.

Biochemical oxygen demand (BOD)

The quantity of oxygen consumed during the biochemical oxidation of matter over a specified period of time (See also COD). It is measured in the dark as the decrease in the oxygen content (in terms of mm/L) of a water sample with a certain temperature over a certain period of time. The decrease in oxygen content is brought about by the bacterial breakdown of organic matter. The decomposition usually proceeds as far as after 20 days until no further change occurs. The oxygen demand is measured after 5 days (and is termed BOD5), where 70% of the final value is expected to be reached.

Bioengineering Restoration and stabilisation techniques that use plants, often from native species, to mimic the natural functions and benefits.

Biofiltration The use of a series of vegetated swales to provide filtering treatment for runoff as it is conveyed through a channel. These swales can either be grassed, contain emergent wetlands or high marsh plants.


x March 2009

Glossary

Term Description

Biofiltration swale A sloped, vegetated channel or ditch that provides both conveyance and water quality treatment to runoff runoff. It does not provide runoff quantity control but may convey runoff to BMPs, which are designed for that purpose.

Bioretention A water quality practice that utilises landscaping and soils to treat runoff runoff by collecting it in shallow depressions before filtering through a fabricated planting-soil media.

Blaney-Criddle Method

A method to calculate grass reference crop evapotranspiration (ETc) based on long-term air temperature data, estimates for humidity, wind movement and sunshine duration, and a correction to ETc downward for elevations above 1,000 meters above sea level.

Bloom An unusually large number of organisms in a unit of water, usually made up of one or more algae species.

Border irrigation Surface irrigation by flooding strips of land, rectangular in shape, usually level perpendicular to the irrigation slope, surrounded by dikes. Water is applied at a rate sufficient to move it down the strip in a uniform sheet. Border strips having no down field slope are referred to as level border systems. Border systems constructed on terraced lands are commonly referred to as benched borders.

Broad-crested weir Any of a group of thick-crested overspill weirs used for flow measurements in open channels. Some broad-crested weirs may have flow transitions, roundings, or plane surface ramps on the upstream side. Thin versions without transitions approach the behavior of sharp-crested weirs. Thick versions with transitions approach the behavior of long-throated flumes. Broad-crested weirs typically operate with very little head loss.

Bubbler irrigation Micro irrigation application of water to flood the soil surface using a small stream or fountain. The discharge rates for point-source bubbler emitters are greater than for drip or subsurface emitters, but generally less than 1 gallon per minute (225 L/h). A small basin is usually required to contain or control the water.

Buffer The zone contiguous with a sensitive area that requires continual maintenance, function, and structural stability. The critical functions of a riparian buffer (those associated with an aquatic system) include shading, input of organic debris and coarse sediments, uptake of nutrients, stabilisation of banks, interception of fine sediments, overflow during high water events, protection from disturbance by human and domestic animals and maintenance due to hydrologic or climatic effects. The critical functions of terrestrial buffers include protection of slope stability, attenuation of surface water flows from storm water runoff plus precipitation and erosion control.

Bulk density Mass of dry soil per unit volume, determined by drying to constant weight at 105 oC, usually expressed as gm/cc or lb/ft3. Rock fragments 2 mm or larger are usually excluded or corrected for after measurement.

Bypass flow Flow which eludes an inlet on grade and is carried to the next inlet downgrade in the street or channel.


March 2009 xi

Glossary

Term Description

Cablegation A semiautomatic furrow irrigation system where a gated pipe is used to deliver water to each furrow. A continuous moving plug is attached to a speed control device with a small cable. The moving plug allows flow out of newly passed gates. As the plug moves downstream, the water level drops in upstream gates thereby shutting off flows.

Capillary rise The upward movement of water from a free watertable due to adhesion of water to the tubular soil pores (capillaries) and the cohesion of water molecules.

Capillary water Water held in the capillary, or small pores of the soil, usually with soil water pressure (tension) greater than 1/3 bar. Capillary water can move in any direction.

Carryover soil moisture

Moisture stored in the soil within the root zone during the winter, at times when the crop is dormant, or before the crop is planted. This moisture is available to help meet water needs of the next crop to be grown.

Casing A tubular retaining structure installed in a well bore in order to maintain the opening of the well.

Catchbasin A chamber or well usually built at the kerb line of a street for the admission of surface water to a sewer or subdrain. At the base of the chamber or well, a sediment sump is designed to retain any grit and detritus located below the point of the overflow.

Catchment An area draining flow to a particular location or site. It may frequently include an area of tributary streams and flow paths as well as the main stream.

Cation exchange capacity (CEC)

The sum of exchangeable cations (usually Ca, Mg, K, Na, Al, H) that the soil constituent or other material can adsorb at a specific pH, usually expressed in centimoles of charge per Kg of exchanger (cmol/Kg), or milli equivalents per 100 grams of soil at neutrality (pH = 7.0), meq/100g.

CBR The California Bearing Ratio (CBR) test is an empirical test first developed in California, USA, for estimating the bearing value of sub-bases and subgrades of roads. It is a simple strength test that compares the bearing capacity of a material with that of a well-graded crushed stone (thus, a high quality crushed stone material should have a CBR @ 100%).

Check dam An earthen or gabion structure placed perpendicular across a stream to enhance aquatic habitats. This structure when used in grass swales reduces water velocities, promotes sediment deposition and enhances infiltration.

Check, check structure

Structure to control water depth in a canal, lateral, ditch, or irrigated field.

Chemical oxygen demand (COD)

A monitoring test that measures all the oxidisable matter found in a runoff sample in which a portion of these matters deplete dissolved oxygen in receiving waters.

Chemigation

Application of chemicals to crops through an irrigation system by mixing them with irrigation water.

Detritus Unconsolidated sediments composed of inorganic (i.e. dead and decaying) and organic material.


xii March 2009

Glossary

Term Description

Christiansens uniformity

A measure of the uniformity of irrigation water application. The average coefficient (CU) depth of irrigation water infiltrated minus the average absolute deviation from this depth, all divided by the average depth infiltrated. Also called coefficient of uniformity. Typically used with sprinkle irrigation systems.

Cipolletti weir A sharp-crested trapezoidal weir with sides inclining outwardly at a slope of 1 horizontal to 4 vertical.

Combination Inlets The use of both a curb opening inlet and a grade inlet.

Compensating emitter

Micro irrigation system emitters designed to discharge water at a near constant rate over a wide range of lateral line pressures.

Concentration The quantifiable amount of chemicals in the surrounding water, food or sediment.

Cone of depression A depression in the water table or potentiometric surface of a groundwater body that is in the shape of an inverted cone developed around a pumped well. It also defines the area of influence of the particular pumped well.

Confined aquifer An aquifer bounded above and below by beds that have distinctly lower permeability than that of the aquifer.

Conservation The protection, improvement and use of natural resources according to principles resulting in greater economic and social benefits.

Constructed wetland The creation of a wetland on a site, which is designed specifically to remove pollutants from runoff runoff.

Consumptive use See Evapotranspiration and Crop evapotranspiration.

Contaminated site A site where hazardous substances with concentrations above approved levels exist and through assessment it indicates the probability of immediate or long-term hazards to the human health or environment.

Continuous flushing emitter

Micro irrigation system emitters designed to continuously permit passage of large solid particles while operating at a trickle or drip flow, thus reducing filtration requirements.

Contracted weir A measuring weir that is shorter than the width of the channel and is therefore said to have side or end contractions. Sometimes called a sharpcrested weir.

Contributing watershed area

A portion of the watershed contributing to its runoff at the point of interest.

Control structure Water regulating structure, usually for open channel flow conditions.

Conventional pollutants

Contaminants other than nutrients (such as sediments, oil, and vehicle fluids).

Conveyance A mechanism for transporting water from one point to another (which includes pipes, ditches and channels).

Conveyance efficiency (Ec)

The ratio of the water delivered to the total water diverted or pumped into an open channel or pipeline at the upstream end, expressed as a percentage.


March 2009 xiii

Glossary

Term Description

Conveyance loss Loss of water from a channel or pipe during transport, including losses resulting from seepage, leakage, evaporation, and transpiration by plants growing in or near the channel.

Conveyance system It refers to drainage facilities of both natural and man-made that collect, contain and provide for the flow of surface and runoff from the highest points of the land right down to receiving waters. The natural elements of the conveyance system include swales and small drainage courses, streams, rivers, lakes and wetlands. The human-made elements of the conveyance system include gutters, ditches, pipes, channels and most retention/detention facilities.

Corrugation irrigation A surface irrigation system where small ditches, channels, or furrows are used to guide water downslope. Can be used in combination with graded border systems to provide more uniform flow down the border strip.

Critical depth The depth of flow during critical flow events.

Critical flow The flow in an open channel that is at a minimum specific energy and has a Froude Number equal to 1.0.

Crop coefficient (Kc) A factor used to modify potential evapotranspiration: (1) Ratio between crop evapotranspiration (ETc) and the reference crop (ETo) when crop is grown in large fields under optimum growing conditions, or ETc = Kc times ETo. (2) The ratio of the actual crop evapotranspiration to its potential evapotranspiration

Crop evapotranspiration (ETc)

The amount of water used by the crop in transpiration and building of plant tissue, and that evaporated from adjacent soil or intercepted by plant foliage. It is expressed as depth in inches or as volume in acre inches per acre. It can be daily, peak, design, monthly, or seasonal. Sometimes referred to as consumptive use (CU).

Crop growth stages Periods of like plant function during the growing season. Usually four or more periods are identified: InitialBetween planting or when growth begins and approximately 10 percent ground cover. Crop developmentBetween about 10 percent ground cover and 70 or 80 percent ground cover. Mid seasonFrom 70 or 80 percent ground cover to beginning of maturity. LateFrom beginning of maturity to harvest.

Crop rooting depth Crop rooting depth is typically taken as the soil depth containing 80 percent of plant roots, measured in feet or inches.

Crop water stress index (CWSI)

An index of moisture in a plant compared to a fully watered plant, measured and calculated by a CWSI instrument. Relative humidity, solar radiation, ambient air temperature, and plant canopy temperature are measured. Improperly called an infrared thermometer (plant canopy temperature is measured by infrared aerial photography).

Crop water use Calculated or measured water used by plants, expressed in inches per day. Same as ETc except it is expressed as daily use only.

Cross slope The rate of change of roadway elevation with respect to the distance perpendicular to the direction of travel. It is also known as transverse slope.

Crown The aerial expanse of a tree excluding the trunk.


xiv March 2009

Glossary

Term Description

Cumulative Brought about or the increased in strength, by successive additions at different times or in different ways.

Cumulative intake The depth of water absorbed by soil from the time of initial water application to the specified elapsed time.

Cutback irrigation The reduction of the furrow or border inflow stream after water has advanced partly or completely through the field to reduce runoff and improve uniformity of application.

Cutback stream Reducing surface irrigation inflow stream size (usually a half or a third) when a specified time period has elapsed or when water has advanced a designated distance down the furrow, corrugation, or border.

Cutthroat flume Open-channel waterflow measuring device that is part of a group of shortthroated flumes that control discharge by achieving critical flow with curving streamlines through contraction. The flume is rectangular in cross section, has two main parts resembling a Parshall Flume with the contracted throat removed or cut out (hence its name), and has a flat floor throughout. Calibrations depend on laboratory ratings.

Cycle time The length of water application periods, typically used with surge irrigation.

Darcys law An empirical law based on experimental evidence for the flow of fluids assuming the flow is laminar and inertia can be neglected. It states that the velocity of the flow through a formation is directly proportional to the hydraulic gradient.

Dead storage A permanent pool volume located below the outlet structure of a storage device. Dead storage provides water quality treatment but not water quantity treatment.

Deep percolation (DP)

Water that moves downward through the soil profile below the plant root zone and is not available for plant use. A major source of ground water pollution in some areas.

Deficit irrigation An irrigation water management alternative where the soil in the plant root zone is not refilled to field capacity in all or part of the field. Delivery box Water control structure for diverting water from a canal to a farm unit often including a measuring device. Also called delivery site, delivery facility, and turnout.

Demand irrigation delivery

Irrigation water delivery procedure where each irrigator may request irrigation water in the amount needed and at the time desired.

Depth of irrigation (1) Depth of water applied, measured in acre inches per acre. (2) Depth of soil affected by an irrigation event.

Design storm A selected rainfall event of specified amount, intensity, duration and frequency used as the basis of design.

Detention A temporary storage of storm runoff in a BMP, which is used to control the peak discharge rates by controlled release rate(s).

Detention facility A drainage facility designed to hold runoff for a short period of time and then releasing it to the surface and subsurface runoff management system.

Detention time The amount of time a volume of water is detained in a BMP.


March 2009 xv

Glossary

Term Description

Direct runoff The streamflow produced in response to a rainfall event and is equal to the total stream flow minus its baseflow.

Discharge

The volume of water that passes a given location within a given period of time (e.g. outfall; the flow of water from a well, a pump, a pipe, a drainage basin or an aquifer in m3/s).

Discharge area An area in which water is lost from the saturated zone.

Discharge structure The outlet structure of a structural BMP (such as a pond) designed to release water at a designed flow rate.

Dissolved constituent Constituents in a water sample that will pass through a 0.45 m membrane filter.

Distribution system A network of open canals or pipelines to distribute irrigation water at a specific design rate to multiple outlets on a farm or in a community.

Distribution uniformity (DU)

The measure of the uniformity of irrigation water distribution over a field. NRCS typically uses DU of low one-quarter. DU of low one-quarter is the ratio of the average of the lowest one-fourth of measurements of irrigation water infiltrated to the average depth of irrigation water infiltrated, expressed as a decimal. Each value measured represents an equal area.

Diurnal cycling Having a period of variation of one day.

Drainage area The area of a watershed within which all surface runoff drains by gravity into a stream channel or lake upstream of a given location.

Drainage inlets The receptors for surface water collected in ditches and gutters, which serve as a mechanism whereby surface water enters storm drains and this refers to all types of inlets (such as grate inlets, curb inlets, slotted inlets, etc.).

Drainage system (1) A natural system of streams and/or water bodies by which an area is drained. (2) An artificial system of land forming, surface and subsurface drains, related structures, and pumps (if any), by which excess water is removed from an area.

Drainage techniques The various physical methods that have been devised to improve the drainage of an area

Drawdown The vertical distance where the free water elevation is lowered, or the reduction of the pressure head due to the removal of free water.

Drip irrigation A micro irrigation application system wherein water is applied to the soil surface as drops or small streams through emitters. Discharge rates are generally less than 2 gallons per hour (8 L/h) for single outlet emitters and 3 gallons per hour (12 L/h) per meter for line source emitters.

Dry pond A facility that provides runoff quantity control by containing excess runoff in a detention basin and then releasing it at allowable levels.

Dry-pit stations Pump stations that use both wet and dry wells. Runoff is stored in the wet well, which is connected to the dry well by horizontal suction piping.


xvi March 2009

Glossary

Term Description

Ecology The study of the habits and modes of life-living organisms (such as plants and animals), and their relationships to each other and their environment.

The runoff pumps are located on the floor of the dry well.

Effective precipitation (Pe)

The portion of precipitation that is available to meet crop evapotranspiration. It does not include precipitation that is lost to runoff, deep percolation, or evaporation before the crop can use it.

Effective rooting depth

The depth from which roots extract water. The effective rooting depth is generally the depth from which the crop is currently capable of extracting soil water. However, it may also be expressed as the depth from which the crop can extract water when mature or the depth from which a future crop can extract soil water. Maximum effective root depth depends on the rooting capability of the plant, soil profile characteristics, and moisture levels in the soil profile.

Effluent Waste material (e.g. liquid industrial discharge or sewage) that may be discharged into the environment.

Electrical conductivity (EC)

A measure of the ability of the soil water to transfer an electrical charge. Used as an indicator for the estimation of salt concentration, measured in mmhos/cm (dS/m), at 77 oF (25 oC). ECe = Electrical conductivity of soil water extract. ECi = Electrical conductivity of irrigation water. ECaw = Electrical conductivity of applied water.

Electrical resistance blocks

A block made up of various material containing electrical contact wires that is placed in the soils at selected depths to measure soil moisture content. Electrical resistance, as affected by moisture in the block, is read with a meter.

Emergency spillway The channel of a pond-type BMP, designed to pass a storm event that exceeds the design capacity of the primary discharge structure.

Emergent plants Aquatic plants that are rooted in the sediment but whose leaves are at or above the water surface. These wetland plants often have high habitat values for wildlife and waterfowl, and can aid in pollutant uptake.

Emitter A small micro irrigation dispensing device designed to dissipate pressure and discharge a small uniform flow or trickle of water at a constant discharge. Also called a dripper or trickler.

Energy dissipater Any means by which the total energy of flowing water is reduced. In runoff design, they are usually mechanisms that reduce velocity prior to, or at, discharge from an outfall in order to prevent erosion. They include rock splash pads, drop manholes, concrete stilling basins or baffles, and check dams.

Energy gradient A plotted line relating total energy elevations along an open channel or energy grade line conduit, typically a pressure pipeline. (See Hydraulic grade line).

Enhancement To raise ecological value, desirability or attractiveness of an environment associated with the surface water.

Entropic Abundant in nutrients and having high rates of productivity frequently resulting in oxygen depletion below the surface layer of a waterbody.


March 2009 xvii

Glossary

Term Description

Environmental control

Controlling air temperature and humidity or soil moisture conditions to minimize effects of low and high air temperatures on crop quality and quantity.

Environmental values Particular values or uses of the environment that are conducive to public benefit, welfare, safety or health and that require protection from the effects of pollution, waste discharges and deposits. Several environmental values may be designated for a specific waterbody.

Ephemeral stream A stream which does not flow continuously or flows only for short period of time.

Erosion The wearing of the land surface by water or wind and the subsequent detachment and transportation of soil particles.

Erosion and sediment control

Temporary or permanent measures taken to reduce erosion, control siltation and sedimentation, ensuring that sediment-laden water does not leave a site.

Erosive velocities Velocities of water that are high enough to wear away land surface. Exposed soil will generally erode faster than stabilised soils. Erosive velocities will vary according to the soil type, slope, structural or vegetative stabilisation used to protect the soil.

Eutrophication Enrichment of water with nutrients, primarily phosphorus, causing abundant aquatic plant growth (mainly algae blooms).

Evaporation The physical process by which a liquid is transformed to the gaseous state, which in irrigation generally is restricted to the change of water from liquid to vapor. Occurs from plant leaf surface, ground surface, water surface, and sprinkler spray.

Evaporation The physical process by which a liquid (such as water) in a stream, lake or moist soil is transformed into a gaseous state. It may be expressed as the total (or the mean) rate in units of mass (or volume) per unit area or as an equivalent depth of water for the period concerned.

Evaporation pan (1) A standard U.S. Weather Bureau Class A pan (48-inch diameter by 10-inch deep) used to estimate the reference crop evapotranspiration rate. Water levels are measured daily in the pan to determine the amount of evaporation. (2) A pan or container placed at or about crop canopy height containing water. Water evaporated from the device is measured and adjusted by a coefficient to represent estimated crop water use during the period.

Evapotranspiration (ET)

The total water vapour loss from an area by evaporation and transpiration from plants over a given time period. It includes the evaporation of water from soils, dew and intercepted precipitation, as well as transpiration from plants. Sometimes called consumptive use (CU).

Event mean concentration (EMC)

The average concentration of an pollutant measured during a storm runoff event. The EMC is calculated by flow-weighing each pollutant sample measured during a storm event.

Excess rainfall An amount of rainfall greater than what the soil can absorb, resulting in runoff.


xviii March 2009

Glossary

Term Description

Exchange capacity The total ionic charge of the absorption complex active in the adsorption of ions. See Cation Exchange Capacity (CEC).

Exchangeable cation A positively charged ion held on or near the surface of a solid particle by a negative surface charge of a colloid and which may be replaced by other positively charged ions in the soil solution.

Exchangeable sodium ratio

The fraction of cation exchange capacity of a soil occupied by sodium ions, percentage (ESP) expressed as a percentage. Exchangeable sodium (meq/100 gram soil) divided by CEC (meq/100 gram soil) times 100. It is unreliable in soil containing soluble sodium silicate minerals or large amounts of sodium chloride.

Exfiltration The downward movement of runoff through the bottom of an infiltration BMP into the soil layer.

Extended detention A runoff management BMP that provides for the gradual release of a volume of water over a time interval designed to increase settling of pollutants and protect downstream channels from frequent flooding.

Faecal coliform bacteria

Minute living organisms associated with human or animal faeces that are used as an indirect indicator of the presence of other disease-causing bacteria.

FDT Field density test (FDT) is performed to confirm that the fill has been compacted to a density that meets or exceeds a specified level. If this level has not been reached, further compaction or other adjustments such as grain size, change of source of materials, compaction, (static, dynamic, vibrating) etc will be required in the field. If the compaction criterion has been reached or exceeded, the fill is acceptable and engineering performance characteristics such as strength and compressibility are ensured.

Feel and appearance method

A method to estimate soil moisture by observing and feeling a soil sample with the hand and fingers. With experience, this method can be accurate.

Field application duration

The elapsed time from the beginning of water application to the first (irrigation period) irrigation set to the time at which water application is terminated on the last irrigation set of a field.

Field capacity The amount of water retained by a soil after it has been saturated and has drained freely by gravity. Can be expressed as inches, inches per inch, bars suction, or percent of total available water.

Field slope, grade The terms field slope and grade are interchangeable. Surface irrigation designers typically refer to elevation differences in the direction of water movement as the irrigation grade. Cross slope refers to the land grade perpendicular to the direction of irrigation.

Filtration media The sand, soil or other organic material in a filtration device used to provide a permeable surface for pollutant and sediment removal.

Final infiltration rate See Basic intake rate.

Float valve A valve, actuated by a float that automatically controls the flow of water.


March 2009 xix

Glossary

Term Description

Flood Relatively high streamflow which overtops the natural or artificial banks in any part of a stream or river.

Flood irrigation, wild flooding

A surface irrigation system where water is applied to the soil surface without flow controls, such as furrows, borders (including dikes), or corrugations.

Flood routing Determining the rise and fall of floodwater as it progresses downstream.

Flood standard (or designated flood)

The flood selected for planning purposes. The choice should be based on an understanding of flood behaviour and the associated flood risk. It should also take into account social, economic and ecological considerations.

Flood storages Parts of the floodplain that are important for the temporary storage of floodwaters during the passage of a flood.

Floodplain The low land adjacent to a waterbody, which is subjected to flooding.

Floodways Areas where a significant volume of water flows during floods. They are often aligned with obvious naturally defined channels. Floodways are areas, which even if only partially blocked would cause a significant redistribution of flood flow that may in turn adversely affect other areas. They are often, but not necessarily the areas of deeper flow or the areas where higher velocities occur.

Flow divider An engineered, hydraulic structure designed to divert a percentage of canal or drainage flow to a field or BMP located out of the primary channel.

Flume (1) Open conduit for conveying water across obstructions. (2) An entire canal or lateral elevated above natural ground, or an aqueduct. (3) A specially calibrated structure for measuring open channel flows.

Flushing emitter A micro irrigation application device designed to have a flushing flow of water to clear the discharge opening each time the system is turned on.

Foot valve (1) A check valve used on the bottom of the suction pipe to retain the water in the pump when it is not in operation. (2) A valve used to prevent backflow.

Forebay An extra storage area provided near an inlet of a pond BMP to trap incoming sediment before it accumulates in a pond BMP.

Foreshore The land between a water body and the dominant ridge line facing the water body.

Free drainage Movement of water by gravitational forces through and below the plant root zone. This water is unavailable for plant use except while passing through the soil. (See Deep percolation.)

Freeboard The space from the top of an embankment to the highest water elevation expected for the largest design storm stored. This space is required as a safety margin in a pond or basin.

Frost protection Applying irrigation water to affect air temperature, humidity, and dew point to protect plant tissue from freezing. The primary source of heat (called heat of fusion) occurs when water turns to ice, thus protecting sensitive plant tissue. Wind machines and heating devices are also used.


xx March 2009

Glossary

Term Description

Full irrigation Management of water applications to fully replace water used by plants over an entire field.

Fungicide Chemical pesticide that kills fungi or prevents them from causing diseases on plants.

Furrow (1) A trench or channel in the soil made by a tillage tool. (2) Small channel for conveying irrigation water downslope across the field. Sometimes referred to as a rill or corrugation.

Furrow dike Small earth dike formed in a furrow to prevent water translocation. Typically used with LEPA and LPIC systems. Also used in nonirrigated fields to capture and infiltrate precipitation. Sometimes called reservoir tillage.

Furrow irrigation A surface irrigation system where water is supplied to small channels or furrows to guide water downslope and prevent cross flow. Called rill or corrugation irrigation in some areas.

Furrow stream The streamflow in a furrow, corrugation, or rill.

Gate A device used to control the flow of water to, from, or in a pipeline or open channel. It may be opened and closed by screw or slide action either manually or by electric, hydraulic, or pneumatic actuators. In open channels, gates slide on rails and are used to control drainage or irrigation water.

Gated pipe Portable pipe that has small gates installed at regular intervals along one side for distributing irrigation water to corrugations, furrows, or borders.

Grade The slope of a land surface, road or channel bottom.

Grass channel An open vegetated channel used to convey runoff and to provide treatment by filtering pollutants and sediments.

Grate inlets Parallel and/or transverse bars arranged to form an inlet structure.

Gravel pack An artificially-graded filter placed immediately around a well screen so as to increase the local permeability, to prevent soil particles from entering the well, and to allow a somewhat larger slot size in the well screen

Gravimetric (oven dry) method

A method of measuring total soil water content by sampling, weighing, and drying in a oven at 105oC. Percent water, usually on a dry weight basis, is calculated.

Gravitational water Soil water that moves into, through, or out of the soil under the influence of gravity.

Gross irrigation Water actually applied, which may or may not be total irrigation water requirement; i.e., leaving storage in the soil for anticipated rainfall, harvest.

Gross irrigation requirement (Fg)

The total irrigation requirement including net crop requirement plus any losses incurred in distributing and applying water and in operating the system. It is generally expressed as depth of water in acre inches per acre or inches


March 2009 xxi

Glossary

Term Description

Gross irrigation system capacity

Ability of an irrigation system to deliver the net required rate and volume of water necessary to meet crop water needs plus any losses during the application process. Crop water needs can include soil moisture storage for later plant use, leaching of toxic elements from the soil, air temperature modification, crop quality, and other plant needs.

Gross pollutant trap A device used to intercept gross pollutants being transported in runoff.

Gross pollutants Runoff laden debris typically larger than 3 mm (includes litter and organic matter).

Groundwater Water in land beneath the soil surface, under conditions where the pressure in the water is greater than or equal to atmospheric pressure, and where all the voids are filled with water

Groundwater mound A round, mound-shaped surface in a water table or other potentiometric surface that builds up as a result of the downward percolation of water.

Groundwater table The free surface of the underground water that is frequently subjected to conditions such as fluctuating atmospheric pressure with the season, withdrawal rates and restoration rates. Therefore, the groundwater table is seldom static.

Growing season The period, often the frost-free period, during which the climate is such that crops can be produced.

Gypsum block An electrical resistance block in which the material used to absorb water is gypsum. It is used to measure soil water content in non-saline soils.

Habitat The kind of locality in which animal breeds or plants normally grow. It is also the geographic distribution or native home of plant or animals.

Head ditch Ditch across the upper end of a field used for distributing water in surface irrigation.

Head gate Water control structure at the entrance to a conduit or canal.

Herbicide A chemical substance designed to kill or inhibit the growth of plants, especially weeds. Types include: ContactA herbicide designed to kill foliage on contact. Non-selectiveA herbicide that destroys or prevents all plant growth. Post-emergenceA herbicide designed to be applied after a crop is above the ground. Pre-emergenceA herbicide designed to be applied before the crop emerges through the soil surface. SelectiveA herbicide that targets specific plants.

Humid climates Climate characterized by high rainfall and low evaporation potential. A region generally is considered as humid when precipitation averages more than 40 inches (1,000 mm) per year.

Humus Rich black or brown material formed from decayed organic matter.

Hybrid Cross between two different species.

Hydrant An outlet, usually portable, used for connecting surface irrigation pipe to an alfalfa valve outlet.


xxii March 2009

Glossary

Term Description

Hydraulic conductivity

The ability of a soil to transmit water flow through it by a unit hydraulic gradient. It is the coefficient k in Darcys Law. Darcys Law is used to express flux density (volume of water flowing through a unit cross-sectional area per unit of time). It is usually expressed in length per time (velocity) units, i.e., cm/s, ft/d. In Darcys Law, where V = ki, k is established for a gradient of one. Sometimes called permeability.

Hydraulic conductivity

For isotropic porous medium and homogenous fluids. The term refers to the volume of water at the existing kinematic viscosity that will move in unit time under a unit hydraulic gradient through a unit area measured at right angle to the direction of flow. Replaces the term coefficient of permeability.

Hydraulic grade line (HGL)

A plotted line relating operational energy elevations along an open channel or closed conduit. With open channel (non-pressure) flow, the HGL is at the water surface. The HGL is the elevation water would rise in an open stand at a given location along a pressure pipeline. (See Energy grade line).

Hydraulic grade line (HGL)

A line coinciding with the level of flowing water in an open channel. In a closed conduit flowing under pressure, the HGL is the level to which water would rise in a vertical tube at any point along the pipe. It is equal to the energy gradeline elevation minus the velocity head, V2/2g.

Hydraulic gradient Slope of the water or potentiometric surface. The change in static head per unit of distance in a given direction. If not specified, the direction generally is understood to be the maximum rate of decrease in head.

Hydraulic head The height above a datum plane (such as sea level) of the column of water that can be supported by the hydraulic pressure at a given point in a groundwater system. For a well, the hydraulic head is equal to the distance between the water level in the well and the datum plane.

Hydraulic jump A flow discontinuity, which occurs at an abrupt transition from subcritical to supercritical flow.

Hydraulic radius This is the ratio of cross sectional area of the flow to the wetted perimeter. For a circular pipe flowing full, the hydraulic radius is one-fourth of the diameter. For a wide rectangular channel, the hydraulic radius is approximately equal to the flow depth.

Hydraulic ram Device that uses the energy of flowing water to lift a portion of the flow to a higher elevation or greater pressure.

Hydraulics The study of water flow; in particular the evaluation of flow parameters such as stage and velocity in a river or stream.

Hydrogeology The science that deals with subsurface waters and related geologic aspects of surface waters. Also used in the more restricted sense of groundwater geology.

Hydrograph A graph showing stage, flow, velocity, or other characteristics of water with respect to time. A stream hydrograph commonly shows rate of flow; a groundwater hydrograph shows the water level or head.


March 2009 xxiii

Glossary

Term Description

Hydrologic abstractions

Losses of rainfall that do not contribute to direct runoff. These losses include water retained in surface depressions, water intercepted by vegetation, evaporation and infiltration.

Hydrologic budget (Balance)

An account of the inflow to, outflow from and storage in a hydrologic unit such as a drainage basin, aquifer, soil zone, lake, or reservoir. It is also expressed as the relationship between evaporation, precipitation, runoff and the change in water storage by the hydrologic equation.

Hydrologic equation The equation that balances the hydrologic budget.

Hydrology The study of the rainfall and runoff process and relates to the derivation of hydrographs for given floods, draughts and other water resources aspects.

Hydroperiod A seasonal occurrence of flooding and/or soil saturation. It encompasses depth, frequency, duration and seasonal pattern of inundation.

Hydroplanning Separation of the vehicle tire from the roadway surface due to a film of water on the roadway surface.

Impermeable A condition where a material is incapable of transmitting significant quantities of water under pressure differences.

Impervious surface A hard surface area, which either prevents or retards the entry of water into the soil mantle under natural conditions, and/or causes water to run off the surface in greater quantities or at an increased rate of flow compared to the present flow under natural conditions; prior to development. Common impervious areas include (but are not limited to) rooftops, walkways, patios, driveways, parking lots, storage areas, concrete or asphalt paving, gravel roads, packed earthen materials and oiled macadam.

Imperviousness The percentage of impervious cover within a defined area.

Impoundment The body of water retained by a berm, dam or dike.

Indigenous Native to; belonging naturally to a particular area, country etc. (endemic).

Infiltration The downward movement of water from the soil surface at ground level into the underlying subsoil. Water infiltrates into the soil profile and percolates through it. The infiltration capacity is expressed in terms of mm/hr. Infiltration depends heavily on the vegetative cover of the soil surface, while permeability depends on the soil texture and compaction.

Infiltration basin A facility that provides runoff quantity control by containing excess runoff in a detention facility, then percolating that runoff into the surrounding soil.

Infiltration capacity The maximum or limiting infiltration rate.

Infiltration rate The rate at which a soil under specified conditions absorbs falling rain, melting snow, or surface water expressed in depth of water per unit time (centimetres per second, inches per hour).


xxiv March 2009

Glossary

Term Description

Infiltration, infiltration rate

The downward flow of water into the soil at the air-soil interface. Water enters the soil through pores, cracks, wormholes, decayed-root holes, and cavities introduced by tillage. The rate at which water enters soil is called intake rate or infiltration rate.

Infiltrometer A device for determining the intake rate of soil. Water infiltrated by the soil in the test section (typically 10 meters) is replaced with water from a reservoir to keep the flow rate constant. The rate of water infiltrated versus time is observed and plotted. Accumulated infiltration versus time is also plotted. An equation (typically for a curvilinear line) then represents the intake characteristics for that particular soil condition.

Initial intake Depth of water absorbed by a soil during the period of rapid or comparatively rapid intake following initial application. Expressed in inches per hour.

Inlet A form of connection between the surface of a ground and a drain or sewer for the admission of surface and runoff runoff.

Instantaneous application rate

The maximum rate, usually localized, that a sprinkler application device applies water to the soil, expressed in inches per hour. Instantaneous application rates of over 30 inches per hour have been measured near the ends of low pressure center pivot irrigation laterals.

Intake family A grouping of intake characteristics into families based on field infiltrometer tests on many soils. Used to analyze and design border and furrow irrigation systems.

Intake family curve A set of accumulated intake versus time curves grouped into families intake characteristic curve having similar border or furrow intake characteristics. Intake family curves are unitless and do not represent the average infiltration rate. The infiltration process in borders differs from that in furrows, thus each irrigation system has a different set of intake family curves.

Intake rate The rate at which irrigation water enters the soil at the surface. Expressed as inches per hour. (See infiltration.)

Interception That part of precipitation or sprinkler irrigation system applied water caught on the vegetation and prevented from reaching the soil surface.

Invasive exotic plants Non-native plants having the capacity to compete and proliferate in introduced environments.

Invert The lowest point on the inside of a culvert or pipe.

Inverted siphon A closed conduit with end sections above the middle section; used for crossing under a depression, under a highway or other obstruction. Sometimes called sag pipe.

Irrecoverable water loss

Water loss that becomes unavailable for reuse through evaporation, phreatophyte transpiration, or ground-water recharge that is not economically recoverable.

Irrigable area Area capable of being irrigated, principally based on availability of water, suitable soils, and topography of land.

Irrigating stream (1) Flow for irrigation of a particular tract of land. (2) Flow of water distributed at a single irrigation. Sometimes called irrigating head, normally expressed as a rate or volume.


March 2009 xxv

Glossary

Term Description

Irrigation Applying water to the land for growing crops, reclaiming soils, temperature modification, improving crop quality, or other such uses.

Irrigation check (1) Small dike or dam used in the furrow or alongside an irrigation border to make the water spread evenly across the border. (2) A plastic or canvas tarp dam placed in a field ditch to raise the water level in the ditch for diversion onto a field.

Irrigation company A semi-public, private group, or commercial enterprise set up to deliver irrigation water.

Irrigation district, company

A cooperative, self-governing semipublic organization set up as a subdivision of a state or local government to deliver irrigation water.

Irrigation efficiency The ratio of the average depth of irrigation water beneficially used to the average depth applied, expressed as a percentage. Beneficial uses include satisfying the soil water deficit, leaching requirement for salinity control, and meeting other plant needs. Generally used to express overall field or farm efficiency, or seasonal irrigation efficiency.

Irrigation frequency, interval

The time, generally in days, between irrigation events. Usually considered the maximum allowable time between irrigations during the peak ET period.

Irrigation method One of four irrigation methods used to apply irrigation water: surface, sprinkle, micro, and subirrigation. One or more irrigation systems can be used to apply water by each irrigation method.

Irrigation scheduling Determining when to irrigate and how much water to apply, based upon measurements or estimates of soil moisture or crop water used by the plant.

Irrigation set The area irrigated at one time within a field.

Irrigation set time The amount of time required to apply a specific amount of water during irrigation period one irrigation to a given area, typically refilling the plant root zone to field capacity minus expected rainfall.

Irrigation slope Elevation difference along the direction of irrigation expressed as, a percentage. Sometimes called irrigation grade.

Irrigation system Physical components (pumps, pipelines, valves, nozzles, ditches, gates, siphon tubes, turnout structures) and management used to apply irrigation water by an irrigation method. All properly designed and managed irrigation systems have the potential to uniformly apply water across a field.

Irrigation water management

Managing water resources (precipitation, applied irrigation water, (IWM) humidity) to optimize water use by the plant. Soil and plant resources must also be considered.

Irrigation water requirement

The calculated amount of water needed to replace soil water used by the crop (soil water deficit), for leaching undesirable elements through and below the plant root zone, plus other needs; after considerations are made for effective precipitation.


xxvi March 2009

Glossary

Term Description

Julian day, day of year

Sequential numbering of days starting January 1 as day one and continuing until the end of the year, as day 365 (leap year day 366).

Kinematic wave A method of mathematical analysis of unsteady open channel flow in which the dynamic terms are omitted because they are small and assumed to be negligible.

Land levelling, land grading

Shaping the surface of the soil to planned elevations and grades. precision land levelling

Laser controlled levelling

Land levelling or grading in which a stationary laser transmitter and a laser or grading receiving unit mounted on each earthmoving machine are used for automated grade control.

Laterite Laterite is the suitable material for earth roads. Laterite covered road surface can be classified as all weathered roads, as it can be used in all seasons of the year. It is a mixture of soil particles, gravels, and other hard particles. The soil strength of four days socked CBR is generally varies from 4.0 to 62.1, the average is 17.738 with a standard deviation of 17.845 (as seen in Jalan Pintas Rawang, Kuala Lumpur). A proper borrow pit with higher CBR value can be selected for laterite road.

Leaching The loss of nutrients from the existing ground (i.e. when rain dissolve the nutrients and are carried away). There are possibilities that chemical fertilisers leached from the ground are able to pollute streams and other water sources.

Leaching fraction The ratio of the depth of subsurface drainage water (deep percolation) to the depth of infiltrated irrigation water. (See Leaching requirement.)

Leaching requirement

(1) The amount of irrigation water required to pass through the plant root zone to reduce the salt concentration in the soil for reclamation purposes. (2) The fraction of water from irrigation or rainfall required to pass through the soil to prevent salt accumulation in the plant root zone and sustain production. (See Leaching fraction.)

Length of run The distance down the furrow, corrugation, or border to the planned end of irrigation, typically the edge of the field.

Level Spreader A device used to spread out runoff runoff uniformly over the ground surface as sheet flows (not through channels). The purpose of level spreaders is to prevent concentrated and erosive flows from occurring, thus enhancing infiltration.

Limited irrigation Management of irrigation applications to apply less water than needed to satisfy the soil water deficit in the entire root zone. Sometimes called deficit or stress irrigation.

Line-source emitter Water is discharged from closely spaced perforations, emitters, or a porous wall along a micro irrigation lateral.

Low energy precision A water, soil, and plant management regime where precision down-in-crop application (LEPA) applications of water are made on the soil surface at the point of use. Application devices are located in the crop canopy on drop tubes mounted on low pressure center pivot and linear move sprinkler irrigation systems. Generally limited to circular plantings on less than 1 percent slopes and no translocation of applied water. Furrow dikes, good soil condition, and crop residue are usually required to control water translocation.


March 2009 xxvii

Glossary

Term Description

Long throated flume Open-channel flow measuring devices of various cross-sections, having three to five main sections. Their operation is based on critical flow occurring in a contracted throat, with parallel walls and level floor, that is long enough to produce nearly parallel flow streamlines. This allows accurate calibration by computational methods. The name usually refers to devices with contractions from the channel sides or from both the sides and bottom. Flumes with bottom-only contractions are traditionally referred to as a type of broad-crested weir, but are hydraulically the same as longthroated flumes.

Long-path emitter Employs a long capillary sized tube or channel to dissipate pressure and discharge water in discrete droplets or seeps.

Low pressure in canopy (LPIC)

A low pressure in-canopy system that may or may not include a complete water, soil, and plant management regime as required in LEPA. Application devices are located in the crop canopy with drop tubes mounted on low pressure center pivot and linear move sprinkler irrigation systems. Limited water translocation within the field and some minor nonuniformity of water application usually exists.

Lowflow channel An incised or paved channel from the inlet to the outlet in a dry basin, which is designed to carry low runoff flows and/or baseflow directly to the outlet without detention.

Lysimeter An isolated block of soil, usually undisturbed and in situ, for measuring the quantity, quality, or rate of water movement through or from the soil. Management allowed The planned soil moisture deficit at the time of irrigation. It can be depletion (MAD) expressed as the percentage of available soil water capacity or as the depth of water that has been depleted from the root zone. Sometimes called allowable soil depletion.

Macrophyte A member of the macroscopic plant life, especially of a waterbody.

Major storm A precipitation event that is higher than the typical largest rainfall for a year.

Management plan A document including, as appropriate, both written and diagrammatic information describing how a particular area of land is to be used and managed to achieve defined objectives. It may also include description and discussion of various issues, problems, special features and values of the area, the specific management measures which are to apply and the means and timing by which the plan will be implemented.

Manufacturers coefficient

A measure of the variability of discharge of a random sample (of a given of variation make, model, and size) of micro irrigation emitters, pressure regulators and sprinkler nozzles, as produced by the manufacturer and before any field operation or aging has taken place. It is equal to the ratio of the standard deviation of the discharge to the mean discharge of the emitters.

Mathematical (Computer) models

The mathematical representation of physical processes (e.g. rainfall and runoff, or mobilisation and transport of pollutants by runoff). These models usually run on computers due to the complexity of the mathematical relationships.


xxviii March 2009

Glossary

Term Description

Matric potential Matric potential is a dynamic soil property and will be near zero for a saturated soil. Matric potential results from capillary and adsorption forces. This potential was formerly called capillary potential or capillary water.

Maximum application rate

The maximum discharge, in inches per hour, at which sprinklers can apply water without causing significant translocation.

MDD and OMC Maximum dry density (MDD) and Optimum moisture content (OMC) are good references for earthwork operations. The optimum moisture content is the water content at which the highest dry density was achieved with a specified amount of compaction. The water within a soil aids in the lubrication of the particles to enable closer packing and helps fill the air voids. Compaction is the reduction of air voids, whereas consolidation is the reduction of total voids (mostly driving out water from the pore spaces). Adding water to a dry soil helps to pack the solids closer together but at some point, by adding more water, the voids within the soil matrix with water, and not solids, thus reducing the dry density of the soil. The compaction study of a soil typically forms a bell shaped graph, with the peak indicating the OMC and MDD.

Mean depth The average depth described as the cross-sectional area of the inundated channel divided by its surface width.

Micro irrigation The frequent application of small quantities of water as drops, tiny streams, or miniature spray through emitters or applicators placed along a water delivery line. The micro irrigation method encompasses a number of systems or concepts, such as bubbler, drip, trickle, line source, mist, or spray.

Microclimate Atmospheric conditions within or near a crop canopy.

Mixed-flow pump A centrifugal pump in which the pressure is developed partly by centrifugal force and partly by the lifting action of the impellers in the water.

Moisture deficit The difference between actual soil moisture and soil moisture held in the soil moisture depletion soil at the field capacity.

Moisture stake See Tensiometer.

Mulch Organic material spread on soil to aid moisture retention and prevent weed growth. It also provides nutrients and helps to open soil texture.

Multi-outlet emitter Supplies water to two or more points through small diameter auxiliary tubing.

Multi-stage pump A pump having more than one impeller mounted on a single shaft.

Nappe Sheet or curtain of unsubmerged water flowing from a structure, such as a weir or dam.

Naturalise The establishment of plants in a manner as though they are of wild species.


March 2009 xxix

Glossary

Term Description

Net irrigation The actual amount of applied irrigation water stored in the soil for plant use or moved through the soil for leaching salts. Also includes water applied for crop quality and temperature modification; i.e., frost control, cooling plant foliage and fruit. Application losses, such as evaporation, runoff, and deep percolation, are not included. Generally measured in inches of water depth applied.

Net irrigation water requirement

The depth of water, exclusive of effective precipitation, stored soil moisture, or ground water, that is required for meeting crop evapotranspiration for crop production and other related uses. Such uses may include water required for leaching, frost protection, cooling, and chemigation.

Net positive suction head

The head that causes liquid to flow through the suction piping and enter (NPSH) the eye of the pump impeller. Required NPSH is a function of the pump design and varies with the capacity and speed of the pump. It must be supplied by the manufacturer. Available NPSH is a function of the system in which the pump operates and represents the energy level in the water over vapor pressure at the pump inlet. The available NPSH must equal or exceed the required NPSH or cavitation occurs.

Neutron gauge, neutron probe

A nondestructive method, used primarily by researchers, to measure in situ neutron scattering device soil moisture. High speed neutrons are emitted from the radioactive source. Electronic count of the returning slow speed neutrons (or reflected), primarily affected by hydrogen atoms in the soil, is calibrated to represent total soil-water content. When properly calibrated and used, the neutron moisture gauge is probably the most accurate and repeatable method to measure soil moisture. The equipment is expensive, data collection is time consuming, training and licensing for personnel using the gauge and for storage are required.

Nonpoint source (NPS) pollution

Pollution caused by sediment, nutrients, organic and toxic substances originating from land-use activities and/or from the atmosphere, which are carried to surface waterbodies by runoff. NPS pollution occurs when the rate at which these materials entering waterbodies exceeds natural levels.

Non-saline sodic soil A soil containing soluble salts that provide an electrical conductivity of the saturation extract (ECe) less than 4.0 mmhos/cm and an exchangeable sodium percentage (ESP) greater than 15. Commonly called black alkali or slick spots.

Nutrient A substance necessary for the growth of organisms.

Nutrient management Managing the application rate and timing of fertilizers to optimize crop use and reduce potential pollution of ground and surface water.

Observation well A test well installed in an infiltration BMP to monitor draining times and sediment accumulation after installation.

Off-line A runoff management system designed to manage a storm event by diverting a percentage of runoff events from a stream or storm drainage system.

Off-line BMP A BMP system that is located outside of the stream channel or drainage path. A flow splitter is used to divert runoff from the channel and into the BMP for treatment.

Off-site Any area lying upstream of the site that drains onto the site and any area lying downstream of the site.


xxx March 2009

Glossary

Term Description

On-line A runoff management system designed to manage runoff in its original stream or drainage channel.

Operational spills Planned or emergency spills made along or at the end of an open ditch (lateral) in a community irrigation water delivery system. Planned spills include the discharge of administrative or carry through water carried in laterals, to allow turnouts to be opened and closed without precision management of lateral flow rates. Emergency spill structures include overflow structures to discharge precipitation runoff water that has entered an irrigation water delivery system, and relief gates to discharge irrigation water in case of ditch or structure failure. Typically planned and emergency spill structures discharge water into a natural watercourse or protected channel.

Opportunity time The time that water inundates the soil surface with opportunity to infiltrate.

Organism Any living animal or plant; anything capable of carrying on life processes.

Orifice An opening with closed perimeter usually sharp-edged and of regular form in a plate, wall, or partition through which water may flow. Generally used for the purpose of measurement or flow control.

Orifice emitter A micro irrigation system application device employing a series of orifices to dissipate pressure.

Outfall The point or structure of a conduit discharging to a waterbody.

Outlet Point of water disposal of a stream, river, lake, tidewater or artificial drain.

Overflow rate Detention basin release rate divided by the surface area of the basin. It can be thought of as an average flow rate through the basin.

Overhead irrigation See Sprinkler irrigation.

Overtopping To flow over the limits of a containment or conveyance element.

Oxidation The combination of oxygen with a substance, or the removal of hydrogen from it, or more generally, any reaction in which an atom loses electrons.

Oxygenation The process of adding dissolved oxygen to a solution.

Pan coefficient A factor to relate actual evapotranspiration of a crop to the rate water evaporates from a free water surface in a shallow pan. The coefficient usually changes by crop growth stage.

Parameter A measurable (or quantifiable) characteristic (or feature).

Parshall flume Open-channel water flow measuring devices which are a part of a group of short-throated flumes that control discharge by achieving critical flow with curving streamlines in a contracted throat section. The sidewallls of the throat section are parallel, but the floor slopes downward in the direction of flow then rises again in a diverging side wall section. Calibrations are based on laboratory ratings. The flume is used for measuring water flow rates with very small total head loss (also see venturi flume). Ten critical edges and surfaces must be met for construction of an accurate Parshall flume.

Pathogen An organism capable of eliciting disease symptoms in another.


March 2009 xxxi

Glossary

Term Description

Peak discharge The maximum flow for a given hydrologic event at a specified location.

Peak period ET The average daily evapotranspiration rate for a crop during the peak water use period. Sometimes commonly called peak period CU (consumptive use).

Peak use rate The maximum rate at which a crop uses water, measured in inches (acre inches per acre) per unit time; i.e., inches per month, inches per week, inches per day.

Penman-Monteith Method

A (radiation and advection) method used to estimate reference crop evapotranspiration (ETo) using current climatic data including air temperature, relative humidity, wind speed, and solar radiation.

Percolation Movement of the water through the soil profile. The percolation rate is governed by the permeability or hydraulic conductivity of the soil. Both terms are used to describe the ease with which soil transmits water.

Percolation The movement under hydrostatic pressure of water through the interstices of rock or soil, except for the movement through large openings such as caves.

Percolation rate The rate expressed as either velocity or volume per unit of time at which water percolates through a porous medium.

Perennial Plant that grow for more than two years.

Permanent wilting point (PWP)

The moisture percentage, on a dry weight basis, at which plants can no longer obtain sufficient moisture from the soil to satisfy water requirements. Plants will not fully recover when water is added to the crop root zone once permanent wilting point has been experienced. Classically, 15 atmosphere (15 bars) or 1.5 mPa, soil moisture tension is used to estimate PWP.

Permeability (1) Qualitatively, the ease with which gases, liquids, or plant roots penetrate or pass through a layer of soil (2) Quantitatively, the specific soil property designating the rate at which gases and liquids can flow through the soil or porous media. The degree of permeability depends upon the size and shape of the openings and the extent of the interconnections of the material.

Pervious Allowing for the passage of water.

Pest management Management to control undesirable plants, animals, fungi, or bacteria that are troublesome, annoying, or degrading to crop quantity and quality.

Pesticide A substance or mixture of substances used to eliminate unwanted species of plants or animals. Includes insecticides, herbicides, and fungicides.

pH Value taken to represent the acidity or alkalinity of an aqueous solution. It is defined as the negative logarithm of the hydrogen ion acidity of the solution.

Phreatophyte transpiration

Transpiration from water loving vegetation along streams and water bodies, generally considered a loss for irrigation purposes. Phreatophyte vegetation may be a highly valuable food source and habitat for fish and wildlife.

Point source A distinct, identifiable source of pollutants.


xxxii March 2009

Glossary

Term Description

Pollinate To apply pollen to the stigma or receptive surface of the female organ (of plants).

Porous pavement An alternative to conventional pavement whereby runoff is diverted through a porous asphalt layer or manufactured pavement grid into an underground stone reservoir. Thus, the stored runoff gradually infiltrates into the subsoil.

Post-development peak runoff

Maximum instantaneous rate of flow during a storm after a land conversion or development is completed.

Potential evapotranspiration

The maximum evapotranspiration that will occur when water is not (ETo) limiting. In some methods of computing evapotranspiration, it is measured as evaporation of water from a free surface. When used as reference crop evapotranspiration, it is for either well watered short grass or alfalfa. Care should be used in determining which factors are used. Preferred term is reference evapotranspiration.

Practicable The availability and capability of performing a certain task or tasks after taking into the consideration of costs, existing technology and logistics in light of the overall project purposes.

Present value The current worth of a regular series of payments over a defined period (e.g. annual maintenance costs over an 80 year period).

Documents

Volume 5_Irrigation and Agricultural Drainage.pdf