F4

August 1993

Delft Universityof Technology

255

Intraductian to bed bank shareproteetionEngineering the interface of soil and water

G.J. Schiereck

Faculty of Civil EngineeringHydraulic and GeotechnicalEngineering DivisionHydraulic EngineeringGroup

/4

SHORE PROTECTIQN_,B/,INTRODUCTION TOBED

Engineering the interface of sou and water

September 1993GJ.Schiereck

f4 September 1993 650255 ±f1.17.50

VOORWOORD

Ter herhaling van en in aanvulling op het op college gezegde het volgende:

De kern van het verhaal wordt gevormd door de hoofdstukken 6 tlm 12.Problemen die op het tentamen aan de orde gesteld worden gaan altijd overzaken uit die hoofdstukken. De hoofdstukken 2 tot en met 5 zijn nodig omzinnig te kunnen praten over de belastingen die uitgeoefend worden. Zebevatten veel herhalingen van stof uit de eerdere jaren; nieuw zijnwaar·schijnlijkenkele dingen over turbulentie in hoofdstuk 2 en de tur­bulente stroming door poreuze media in hoofdstuk 5. Een paar zaken overonregelmatige golven worden aangesneden in hoofdstuk 3 omdat niet iedereenhet vak windgolven doet en het dan zo vreemd is om in hoofdstuk 10 ineensover ~p of ~M te praten.

Hoewel de hoofstukvolgorde op enige logika berust, wil dat niet zeggen datdie volgorde ook de meest plezierige is bij een eerste lezing. Daarvoor zoubijv. aangehouden kunnen worden:Inleiding 1, Stroming 2,6,9, Golven 3,4,7,10, Filters engrondmechanische aspekten - 5,7,8,11, Praktijktoepassingen 12,13,14

Formules zijn nodig om ontwerpberekeningen te maken. Niemand kent dieallemaal uit het hoofd en dat is maar goed ook, dus dat wordt ook niet ophet tentamen gevraagd. Wel is het nodig om zo'n formule met verstand tekunnen hanteren en te weten wat er ongeveer in zo'n formule zit en waarom.In de veelheid van empirische relaties, geldt dat vooral voor paragrafenals 6.3, 9.1, 10.1, 10.2.1, 11.1, 11.3.2 en 11.3.3.

CONTENTS

CHAPTER/Paragraph page

CONTENTS

REFERENCES v

SYMBOLS x

DICTIONARY xiii

1. INTRODUCnON1.1 General1.2 Relevant phenomena

1.11.4

2. WADS part I - Flow2.1 Introduetion2.2 Basic equations2.3 Boundary shear stress2.4 Flow around bodies2.5 Turbulent jets and wakes

2.5.1 General2.5.2 Mixing layers2.5.3 Free jets2.5.4 Plane wall jets2.5.5 3-Dimensional wall jets

2.6 Summary and examples2.6.1 Vertical constriction and expansion2.6.2 Horizontal constriction and expansion

2.12.22.62.8

2.102.102.112.122.142.152.162.162.18

3. WADS part n-Waves3.1 General3.2 Wind waves

3.2.1 Wave height distribution3.2.2 Wave spectra

3.3 Boundary shear stress3.4 Waves on slopes

3.4.1 Standing waves3.4.2 Breaking waves3.4.3 Run-up and run-down3.4.4 Wave impacts

3.13.43.53.63.83.93.93.103.143.16

4. WADS part m- Ships4.1 General4.2 Primary waves4.3 Secundary waves4.4 Propeller races

4.14.34.7

4.10

5. LOADS part IV - Porous flow5.1 Genera!

5.1.1 Steady flow5.2 Laminar flow

5.2.1 Steady flow5.2.2 Non-steady flow

5.3 Turbulent flow5.3.1 Steady flow5.3.2 Non-steady flow

5.15.25.45.45.75.85.85.9

6. EROSION part I - Flow6.1 Genera!6.2 Scour by jets6.3 Time-dependent scour

6.3.1 Process description6.3.2.The factor ex6.3.3 Influence of bottom proteetion6.3.4 The slope f36.3.5 Non-stationaryflow6.3.6 Non-stationarystructure6.3.7 Equilibrium depth

6.4 Scour around bodies6.4.1 Scour around bridge piers6.4.2 Scour around abutments6.4.3 Scour behind groynes6.4.4 Scour in constrictions

6.5 Discussion on scour

6.16.36.56.56.86.106.116.126.126.136.146.146.166.176.176.18

7. EROSION part n-Remainder7.1 Erosion by waves

7.1.1 Slopes7.1.2 Bottom scour

7.2 Erosion by ships7.3 Erosion by porous flow

7.3.1 Piping7.4 Erosion by gravity

7.4.1 Slides7.4.2 Flow-slides

7.17.17.27.37.47.47.67.67.7

8. LOAD REDUCTION8.1 Flow reduction8.2 Wave reduction

8.2.1 Dams8.2.2 Pile sereens8.2.3 Floating brea1cwaters8.2.4 Reed

8.3 Ship's loads reduction8.4 Porous flow reduction

8.4.1 Flow reduction8.4.2 Pressure reduction

8.18.28.28.38.48.58.58.68.68.7

ii

9. srABILITY part I - Flow9.1 Loose material

9.1.1 Uniform flow - horizontal bed9.1.2 Strength reduction9.1.3 Load increase9.1.4 Reduced strength and increased load

9.2 Coherent material9.2.1 Placed elements9.2.2 Gabions9.2.3 Cohesive soils9.2.4 Vegetation

9.19.19.69.89.129.149.149.149.159.15

10. srABILITY part n -Waves10.1 Loose material

10.1.1 Horizontal bed10.1.2 Slopes10.1.3 Berms and toes10.1.4 Low crests10.1.5 Heads10.1.6 Ship's waves

10.2 Coherent material10.2.1 Placed blocks10.2.2 Impervious layers10.2.3 Vegetation

10.110.110.210.710.710.810.810.910.910.1410.15

H. srABILITY part m - Porous now11.1 Granular filters

11.1.1 Introduetion11.1.2 Geometrie criteria11.1.3 Hydraulic criteria11.1.4 Applicationof results

11.2 Geotextiles11.2.1 Introduetion11.2.2 Sandtightness11.2.3 Permeability

11.3 Stability of slopes11.3.1 Macro stability11.3.2 Micro stability11.3.3 Impervious layers

11.111.111.311.411.711.811.811.9

11.1011.1211.1211.1511.16

iii

12. PROTECTIONS12.1 Shore protections

12.1.1 Shape of protections12.1.2 Revetment choice12.1.3 Transitions12.1.4 Toes12.1.5 Groynes12.1.6 Breakwaters

12.2 Bank protections12.2.1 Bank proteetion types12.2.2 Limits of proteetion12.2.3 Groynes12.2.4 Falling aprons

12.3 Bed protections12.3.1 Outlet structures12.3.2 Bridge piers12.3.3 Seawalls

12.112.212.312.412.612.712.812.912.912.1012.1112.1212.1312.1412.1612.16

13. CONSTRUCTION ANDMAINTENANCE13.1 General

l3.1.1 Quality assurance13.2 Construction

l3.2.1 Waterbome - Loose material13.2.2 Waterbome - Coherent materiall3.2.3 Land based - Loose material13.2.4 Land based - Coherent material13.2.5 Construction costs

13.3 Maintenance13.3.1 General13.3.2 Theory13.3.3 Practice

13.113.2l3.313.313.613.713.813.913.1013.1013.1113.13

14. DESIGN14.1 Design process

14.1.1 Introduetion14.1.2 Influencing factors14.1.3 Design phases

14.2 Conceptual design14.2.1 Generation of alternatives14.2.2 Selection of alternatives

14.3 Structural design14.3.1 Failure14.3.2 Safety

14.114.114.314.514.714.714.814.914.914.13

Annex A: MATERIALS

Annex B: ENVIRONMENTAL ASPECTS

iv

Akkerman1985

Akkerman1986

Ariëns1993

AshidalBayazit1973

Battjes1974

Bear1972

REFERENCESHydraulic designcriteria for rockfillclosure of tidal gaps - Vertical closuremethod,Delft Hydraulics Laboratory report M1741 part IV

Hydraulic design criteria for rockfill closure of tidal gaps - Horizontal closuremethod, Delft Hydraulics Laboratory report S 861

Relatie tussen ontgrondingen en steenstabiliteit van de toplaag (in Duteh), MScthesis, Delft University of Technology

Initiation of motion and roughness of flows in steep channels, Papers IAHR­congress Istanbul, page 475-484

Computation of set-up, longshore currents, run-up and overtopping due to wind­generated waves, DissertationDelft University of Technology

Dynamics of fluids in porous media, American Elsevier

BezuyenIBurger Taludbekledingenvan gezette steen, samenvattingvan!Klein Breteler onderzoeksresultaten 1980-1988M17951H195 deel XXIV (in Duteh)1990 RWS-DienstWeg- en Waterbouwkunde

Blom1991

Blom1993

Booij1986

Bouter1991

Turbulent flow over a sill, IAHR-congressMadrid

On the shallowwater equationsfor turbulent flow over sillsDelft University of Technology, 1993

Turbulentie in de waterloopkunde(in Duteh), lecture notes b82, Delft Universityof Technology

Wave dampingby reed- An investigationin environmentfriendly bank protections,PIANC bulletin, no 75

BreuserslRaudkivi Scouring, Balkema1991

BruunlGunbak1977

CIRIA1990

CURICIRIA1991

CURrrAW1992

Stability of sloping structures in relation to ~ = tanatv'HILCoastal Engineering 1, page 287-322

Use of vegetation in civil engineering, CoppinlRichards editorsCIRIAlButterworths

Manual on the use of rock in coastal and shoreline engineering,CUR Report 154/CIRIASpecial Publication 83, Balkema

Handboek voor dimensioneringvan gezette taludbekledingen(in Duteh),Rapport 155, Centrum Uitvoering research/TechnischeAdviescommissievoor deWaterkeringen

v

Cohen de Lara1955

Coefficient de perte de charge en milieu poreux basé sur l'équilibrehydrodynamique d'un massif (in French), La Houille Blanche No 2, page 167-176

Delft Hydraulics Stroombestendigheid los materiaal in wervel straat (in Dutch)1960 report M 598 - VI

Fredsee/Deigaard Mechanics of coastal sediment transport, Advanced series in Ocean Engineering,1992 Volume 3, World Scientific

van Gent1992

Formulae to describe porous flow, Report no 92-2, DUT Civil Engineering

de Graauw/vdMeulen Design criteria for granular filters, Delft Hydraulics publication 287IvdDoes de Bye1983

GroenlDorrestein Zeegolven (in Dutch), Koninklijk Nederlands Meteorologisch Instituut1976

GrunelKohlhase Wave trans mission through vertical slotted wall, Proceedings 14th International1974 Conference on Coastal Engineering, Vol lIl, page 1906-1923

Hedar1986

Hewlett1985

Hoffmans1992

Hoffmans1993a

Hoffmans1993b

Hudson1953

IzbashlKhaldre1970

lansen1979

Jonsson1966

Armor layer stability of rubble-mound breakwaters, ASCE Joumal of Waterway,port, coastal and ocean engineering, Vol 112, No 3, page 343-350

Reinforcement of steep grassed waterways, CIRIA

Two-dimensional mathematical modelling of local-scour holes, DissertationDelft University of Technology

A study concerning the influence of the relative turbulence intensity on local scourholes, Report W-DWW-93-251, Rijkswaterstaat, Road and Hydraulic EngineeringDivision

A hydraulic and morphological criterion for upstream slopes in local scour holes,Report W-DWW-93-255, Rijkswaterstaat, Road and Hydraulic EngineeringDivision

Wave forces on breakwaters, Proceedings-Separate ASCE, No 113, page 653-685

Hydraulics of river channel closure, Butterworth

Principles of river engineering, The non-tidal alluvial river, Pitman

Wave boundary layers and friction factors, Coastal Engineering Conference,Chapter 10, page 127-148

vi

JorissenNrijling Local scour downstream hydraulic constructions, IAHR-congress Ottawa1989

JorissenIKonter1991

van der Knaap1986

Kuijper1992

LeMéhauté1957/1958

LeMéhauté1976

van Mierlolde Ruijter1988

van der Linden1985

van der Meer1989

Prediction of time developmentof local scour, New Orleans _

Design criteria for geotextiles beyond the sandtightness requirement,Delft Hydraulics, publication 358

Onderhoud in de waterbouw (in Dutch), Master thesis, Delft University ofTechnology, Civil Engineering

Permeabilité des digues en enrochements aux ondes de gravité périodiques (inFrench), La Houille Blanche, dec. 1957- june 1958

Hydrodynamicsand waterwaves, Springer

Turbulence measurements above dunes, Report Q789, Volume 1 and 2, DelftHydraulics Laboratory

Golfdempende constructies (in Dutch), Master thesis, Delft University ofTechnology, Civil Engineering

Rock slopes and gravel beachesunder wave attack, Dissertation, Delft Universityof Technology

van der Meer Wave transmission at low-crested structures, Conference on Coastal Structures,Id'Angremond 1991 Telford

OumeracilPartenscky Wave-inducedpore pressure in rubble mound breakwaters, Int. Conf. on1990 Coastal Engineering, Delft

Paintal1971

Pilarczyk1990

Concept of critica! shear stress in loose boundary open channels, Joumal ofhydraulic research, 9-1, page 91-113

Coastal protection, Proceedings of short course on coastal protection, DUT,Balkema

Pilarczyklden Boer Stability and profile developmentof coarse materials and their application in1983 coastal engineering, Delft Hydraulics, publication 293

Rajaratnam1976

Turbulent jets, Elsevier

RajaratnamlBerry Erosion by circular turbulent wall jets, Joumal of Hydraulic Research 15(3)1977

Rajaratnam1981

Erosion by plane turbulentjets, Joumal of Hydraulic Research 19(4),page 339-358

vii

Rajaratnam Erosion by plane wall jets with minimum tail water, ASCE Joumal of Hydraulic/McDougall,1983 Engineering 109(7)

RWS1985

RWS1987a

RWS1987b

RWS1990

RWS1991

RWS1992

RWSIDHL1988

RWSIDHL1986

RWSIDHL1985

Schlichting1968

Sleath1978

Sorensen1973

SPM1984

van der Veer1979

Veldhuijzen v.Zanten, 1986

Tbe use of asphalt in hydraulic engineering, Rijkswaterstaat communicationsno 37

Kwaliteit en kosten van rijksvaarwegen (in Duteh), Rijkswaterstaat, Dienst Weg­en Waterbouwkunde, Delft

Tbe closure of tidal basins, Delft University Press

Waterbouw, Rekenregels voor waterbouwkundig ontwerpen (in Duteh), BouwdienstRijkswaterstaat

Handboek uitvoering bodemverdedigingsconstructies van losgestorte granulairematerialen (in Duteh), Bouwdienst Rijkswaterstaat

Transportmodel voor filters, Eindrapportage filteronderzoek (in Duteh),Rijkswaterstaat Dienst Weg- en Waterbouwkunde/Grondmechanica DelftlDelftHydraulics

Aantasting van dwarsprofielen in vaarwegen (in Duteh), Report M1115 XIX

Sekundaire scheepsgolven en hun effect op de stabiliteit van taludbekledingen (inDuteh), Report M1115 VI

Schroefstralen en de stabiliteit van bodem en oevers onder invloed van destroomsnelheden in de schroefstraal (in Duteh), Report M1115 vnBoundary layer theory, McGraw-Hill(First German edition 1951)

Measurements of bed load in oscillatory flow, ASCE Joumal of the waterway portcoastal and ocean division, Vol 104, NoWW4, page 291-307

Water waves produced by ships, ASCE Journal ofWaterways, harbors and coastalengineering division

Shore proteetion Manual, US Army Coastal Engineering Center

Grondwaterbeweging onder oeverconstructies (in Duteh), in:Kust- en oeverwerkenin praktijk en theorie

Geotextiles and geomembranes in civil engineering, Balkerna

viii

Vellinga1986

Ven te Chow1959

van Vledder1990

de Vries1992

van der Weide1989

Xie Shi-Leng1981

Beach and dune eros ion during storm surges, Dissertation, Delft University ofTechnology

Open-Channel hydraulics, McGraw-HiII

Literature survey to wave impacts on dike slopes, Delft Hydraulics,Report H976

River Engineering, Lecture notes flû, Delft University of Technology

General introduetion and hydraulic aspects, Short course on design of coastalstructures, AIT Bangkok

Scouring patterns in front of vertical breakwaters and tbeir intluences on tbestability of the foundationsof the breakwaters, Delft University of Technology

ix

SYMBOLS

11 Symbol I1Meaning I Dimension

a Wave amplitude (=H/2) m30 Amplitude of horizontal wave motion at bottom mA Area of cross-section m2

Ac Area of cross-section of navigation channel m2

As Area of midship section of ship m2

b Width of shear Iayer, plane jet or canal mbo Width of outflow nozzle in plane jet mB Width of square nozzle of jet or ship mc 1. Wave celerity mis

2. Coefficient in piping formulaC Coefficient of Chezy mo.slsCo Drag coefficientCF Friction coefficientCL Lift coefficientCR Velocity decay coeff. in rough wall jetsd Diameter of grain (= d"so, m

unless otherwise stated)D Diameter of cylinder or outflow nozzle or m

ship's propeller or height of dam or sillg Acceleration of gravity m/s2h Waterdepth mho Original waterdepth before scouring mh, Scouring depth mh.m Maximum depth in scouring hole mh.m... Asymptotic or equilibrium max. scouring depth mH Wave height mHs Significant wave height mHl Incident wave height mHR Retlected wave height mHT Transmitted wave height mI Slopek 1. in waves: Wave number (=21r1L) lIm

2. in porous tlow: Permeability misks Equivalent sand roughness mKo Coefficient in Hudson's formulaKR Wave retlection coefficientKT Wave transmission coefficientL Wave length m10 Wave length in deep water m~ Entrance length of ship's bow mt, Ship's length mm, Area of wave spectrum mM Momentum kg/s?n Porosity (volume of voids/total volume)N Number of waves in vdMeer's formulap 1. Pressure N/m2

x

2. Coefficient in parabolic beach profile m°.22P Power WQ Discharge m3/sr 1. Relative turbulence

2. Radial distance from center of jet mR Hydraulic radius mRu Wave run-up mRo Wave run-down ms Distance from ship's sailing line mS Sediment transport mJsSd Damage level in vdMeer's formulat Time sT Wave period or averaging period in turbulence sTM Meao wave period sTp Wave period with maximumwave energy sTs Significantwave period su Velocity in x-direction mislIc Critical velocity misUt Filter velocity misu, Shear velocity (=V TIp) mIsUo Outtlow velocity in jets; verticaly averaged velocity misu", Maximumvelocity misü Average velocity (in time) misu' Turbulent velocity f1uctuation mis1\ Amplitudeof wave'velocity at bottom misUR Return current along ship misv Velocity in y-direction misVL Limit speed of ship misVs Ship's speed misw Velocity in z-direction misW Weight kg.m/s? =Nx Distance along horizontaI axis m

parallel to main flow directiony Distance along horizontaI axis m

perpendicular to main flow directionz Distance along vertical axis mZR Waterlevel depression in primoship wave m

1. Slope angle degrees2. Coefficient in scour formula3. Coefficient in piping formula

{3 Slope of scour hole degrees'YI> Breaker depth ratio (Bib)Ö Boundary layer thickness m~ Relative density (Ps - Pw)1Pwe Turbulent (eddy) viscosity m2/sfa Eddy diffusivity of sediment m2/s11 Dimensionless distance in jetsl1t Waterlevel in waves mr Bow-geometry coefficient in ship's waves

xi

K. von Karman constant »0.4À Leakage height mA Leakage length mP- l. Dynamic viscosity kg/m.s

2. Discharge coefficientu Kinematic viscosity m2/s~ Breaker parameterPs Density of sediment kg/m'Pw Density of water kg/m'(] Standard deviationT Shear stress N/m2 = PaTc Critical shear stress N/m2 = Pa70 Wall shear stress N/m2 = Pa<P 1. Angle of repose degrees

2. Potential in porous flow m1/1 Stream function m2/sw Angular frequency in waves (21l"ff) 1/s

THE GREEK ALPHABET

Lower case Capita! Name Lower case Capital Name

ex A Alpha JI N NuIJ B Beta ~ Z Xil' r Gamma 0 0 Omicron/) .:1 Delta 11" II PiE E Epsilon P P Rhor Z Zeta (] E Sigma1'/ H Eta 7 T Tau8 e Theta u Y UpsilonL J Jota <P ~ PhiK. K Kappa X X ChiÀ A Lambda 1/1 'Ir PsiP- M Mu w o Omega

SPECIAL SIGNS

ex Proportional to

xii

DICTIONARY

abutmentantinodeapron

landhoofdbuik (van trilling)stortebed, bodembescherming (lett. beschermlap,voorschoot)beschermen, pantserenterugstroming (in golfoploop )oever(zand)bankbodemboegdichtslibbensamenhangendcohesiefin elkaar stortenbotsenbetonvernauwingbouw, uitvoering, constructiekemkruinduiker(sluis)interferentie piekrommel, afvalterugstromen (in golfoploop )slepen, trekken ,stromingsweerstandneer, wervelevenwichtzinkstukzettingsvloeiinggrindkribromp (van schip)niet poreus, ondoorlatendondoordringbaar, ondoorlatendtreffen, botsenbegin van bewegingbuigengrensvlak, overgangstraaluitlogenlekverwekingimpulsknoop (van trilling)tuit(uitstroom )openingpijler, pierplaveien, zetten

armouringbackwashbankbarbedbowcloggingcoherentcohesivecollapsecollideconcreteconstrictionconstructioncorecrestculvertcuspdebrisdownrushdrageddyequilibriumfascine mattressflow slidegravelgroynehuilimpermeabieimperviousimpingeincipient motioninflectioninterfacejetleachleakageliquefactionmomentumnodenozzleorificepierpitch

xiii

plungepropeller raceprotrudequicksandquarryrectifierrevetmentripraprubblerun-downrun-upsaturatedscourseepagesegregationsettlementshallowshear stresssheet pilesillslagsslidespillsplit-bargespur-dikesternsurfsurgetailwaterthresholdtuguprushvoidsvortexwakewater-borne

duikenschroefstraaluitstekendrijfzandsteengroevegelijkrichteroeverbescherming, bekledingbreuksteen, stortsteenpuin, stortsteen(golf)terugloop(golf)oploopverzadigdontgronding, uitschuringkwelontmengingzettingondiepschuifspanningdamwanddrempelslakkenafschuivingmorsensplijtbakkrib, schermhek, achterstevenbrandingdeinenbenedenwaterdrempelsleepbootomhoog stromen in golfoploopporieënwervelzog (van schip)vanaf het water (lett. door het water gedragen)

xiv

1

GENERAL

The interface of land and water bas always played an important role in buman development.Settlements and economie activities are often located at coasts, river-banks or deltas. Harbours,waterways, dikes, dunes and beaches, structures for water-control and water-resources managementetc. are examplesof bydraulicengineering on a macro-scale. In these lectures, the interface is studiedon a micro-scale. The occurringphenomena are important in all branches of hydraulic engineering.

In a natural situation, the interfacemoves freelywith the forces of erosion and sedimentation.Actually, there is nothing wrong with erosion,until some interest is threatened. Erosion issomewhat like weed: as long as it is in nobodiesway, no action is neededor evenwanted. Theresbould always be a balance between the effortsof proteetion against erosion and the damagethat would occur otherwise (see Figure 1.1).Moreover, it sbould be realised that once a Figure 1.1 Erosion and threatlocation is protected along a coast or riverbankthat is eroded on a large scale, the protectedpart can induce extra erosion and in the end the whole coast or bank has to be protected. So, lookbefore you leap, should be the motto.

In many cases however, a proteetion is necessary: bottom proteetion bebind outlet-structures oraround objects, revetmentsin rivers and canals, dike protection, coastaIdefenceworks etc. Figure 1.2gives some examples.

Figure 1.2 Examples of proteetion

1.1

A bare, erodable interface on one side and an interface that is protected with building materials likeconcrete, asphalt or rock on the other side, are two extremes. Nature itself offers a lot of possibilitiesin between, with vegetation as a major proteetion material. Mangrove trees along coasts and estuariesand reed along river banks are just two examples of a natural and low-cost protection. An importantcause of eros ion can be the removal of this vegetation, disturbing an equilibrium that has existed formany ages. So, a first measure in fighting erosion, will be the conservation of vegetation at theinterface.

These lecture notes deal primarily withsituations where the loads exceed the presentstrength and there is someone who wants tochange that. In that case there are twopossibilities to go from an unstable to a stabiesituation, see Figure 1.3:

A Reduce the load, e.g. build a wave reductorin front of the considered location

B Increase the strength, e.g. build arevetmentat the location

For both strategies it is necessary to have agood understanding of the relevant phenomenaand the interaction between load and strength.Therefore, there is ample attention for thebackground of the phenomena in the comingsections.

:r:l­C)ZW0:::I­(f) B

UNSTABLE

LOADFigure 1.3 Load vs strength

At first, we will start to review some basic knowledge of hydraulic engineering in chapter 2 through5 to get insight in the loads and forces acting on the interface. One can study these subjects on variousscientific levels. Here the choice is made for a level that goes "one degree deeper" than the empiricaldesign relations presented in the following chapters. This is considered necessary and appropriate tomake asensibie use of the empirical relations. Although it can be boring to have to go through allthis tough stuff before getting to the real thing, it is thought to be rewarding in the end.Chapter 6 and 7 deal with the effect of the various loads on an unprotected interface, while chapter8 gives some possible methods to reduce the loads. In chapter 9 through 11, the stability ofprotections is discussed. In chapter 12, possible construct ion types are presented, while theconstruction and maintenance aspects are reviewed in chapter 13. Finally, chapter 14 comes to thepoint of designing.

This division was chosen on purpose, with the idea in mind that a designer should have a thoroughknowledge of the processes that occur at the interface of land and water in his head, before thinkingof solutions. The same approach leads to chapters about erosion and load reduction before discussingstability; one should have an idea of possible eros ion before one can have an idea of the necessaryprotection. The chapter on design is the last one: only after gaining knowledge about the phenomena,the possible proteetion types and the peculiarities of construction, talking about design is fruitful.

The story of protecting the interface of land and water is told three times in these notes: once in thetext, once in the formulae and last, but certainly not least, in the figures. Although not really a comic­book, the reader is advised to study them carefully, because, often they teil the story in the mostaccessible and comprehensive way.

1.2

Although protections of the interface of land and water are being made for more than 1000 years (atleast in the Netherlands), that does not mean that there is nothing new. On the contrary, like inarchitecture there are always new materials, creating new possibilities and changing demands fromsociety, creating new challenges.Relatively new materials, like geo-textiles, give newopportunitiesto meet the contradictingdemandsin the design as showed in Figure 1.13. There is not yet one ideal material combining the rightstrength, flexibility and permeability but there are a lot more possibilities. The same goes forconstructionmethods: new equipmentmakes application feasible of hitherto impossible structures.Major contributions to the design practice in the last decades, have been made possible by newresearch facilities, like (large scale) wind wave flumes, (turbulent) flow measurementdevices etc.In general there is a tendency to use a more scientific approach in the research and design ofhydraulic structures. Much knowledgeis fragmented and it wouldbe a step forward to get an overallpicture. Moreover most knowledgeis of an empiricalnature, leadingto sometimesdubious relations.Dimensional homogenity is not always present while the use of the same variabie in twodimensionlessparameters can lead to spurious correlations, see de Vries,1992. One of the challengesof the coming years is the combinationof the use of more scientificmethodswith experiencewhichwill always remain an important factor in hydraulic engineering.

An everlasting pressure on the designer is to create cheap solutions. "Cheap" has to be consideredin a broad sense: low investment can mean high maintenance 'costs and vice versa. The optimalsolution should be found. An important cost factor in western countries is the construction;mechanisation replaces more and more the old labour-intensive handwerk, while in developingcountries material and equipment is very expensive and labour relatively cheap. This cao lead to acompletely different design.

An important development in hydraulic engineering is the increasing relevanee of environmentalaspects. It was already mentionedthat vegetationcao act as proteetion in manycases and in situationswhere vegetation is present, it should be preserved as much as possible. There are several examplesin the world where problemswith erosiononly startedafter the natural vegetationwas removed (oftento use plants or wood of trees or to make mooring facilities for ships). In the Netherlands, more andmore use is made of vegetation as proteetion where possible. This bas to do with the importanceofthe interface of soil and water in the ecosystem as a whoie. It is of crucial importance for a lot ofspecies of plants and animals. Not only the base of the food-chain, like worms and insects, livesthere; river banks for example are vital for many kinds of fish, looking for quiet places with lowvelocity to lay eggs. Mammals, like deer, have difficulties in climbing out of the water at artificialriver banks. Other mammals, like the readers of these notes have their demands when it comes toattractivenessof the landscapeetc. In the designof a proteetionwork, one shouldbe aware of the factthat the interfaceof land and water is an essentialpart of the eco-system.More in general, especiallyin densily populated areas, there is a growing pressure on the use ofthe interfacewith manydifferentinterests. This leads to a growing awareness of the multi-functionalityof a shore, a bank or a dike.These (usually conflicting) interests, have to be incorporated into the design.

Environmental aspects and new materials come together in the use of waste material in hydraulicengineering. Here again there are conflicting interests. On the one hand there is the need to get ridof a lot of waste material like slags from furnaces, which form a cheap building material. On theother hand there is the danger of leaching, causing contaminationof the water-system.Annex B gives more information.

1.3

RELEVANT PHENOMENA

Water Type Rivers Lakes &tua- Seas CanalsPhenomenon (Units) ries

Discharges

waterlevel fluctuations (m) 1-10 1-10 0,1-1 - 0-1

flow velocity (mis) 1-2 0,1 0,1-1 - 0,1-1

(velocity in in- andoutlet sluices betweenwaters: 1 - 5 mIs)

Tides

waterlevel fluctuation (m) - - 1-10 1-4 -flow velocity (mis) - - 1-4 1-2 -Wind

waterlevel fluctuation (m) 0,1 0,1-1 1-5 1-5 0,1

wave height (m) 0,1-0,5 0,1-1 0,5-1 1-5 0,1-0,5

Ships

primary wave height (m) 0,2-0,5 0,1-0,2 0,1-0,2 0-0,1 0,2-0,75

secundary wave height (m) 0,2- 0,1-0,75 0,1-1 0,1-1 0,2-10,75

Interfaces between land and water come in all sizes and circumstances.The table gives an idea of theloading phenomena and the order of magnitudeof extemalloads that can be expected. The interfacestability will be treated in these lecture notes for the phenomena on the vertical axis and the watersystems on the horizontal axis. Not by treating them separately, but by treating them elementary,based on the physical processes. This is more exceptionalthan it seems, becausemost textbooks dealwith either shore proteetion or river training works or shipping canals etc. This is mainly becausemuch of the knowledge of these proteetion works is based on experience and experience is oftengained in one of the mentioned fields and not in all of them. This is a pity because many of thephenomena involved are similar: ship waves and wind waves have different sources, but act verymuch the same. The same holds for flow in a river, through a tidal closure or in an outlet sluice,when it comes to proteet the bed or bank. Therefore, an attempt is made to fmd the core of all theserelated problems. One thing all these protections have in common, is that their function is towithstand the energy loss of moving water.

Water in motion contains energy: currents, wind waves, ship movement, groundwater-flow etc.,which can be available to transport material. The energy comes from extemal sourees like wind, shipsor the sun (evaporation, leading to preeipitation in high areas, giving potential energy). Eventuallyit ends as heat by means of viscous friction. Just to get an idea of the amount of energy present inmoving water, the following comparison is made.

1.4

To lift a mass of 1000 kg with a speed of 1 mis, a power ofm.g. v (mass * acceleration of gravity * velo city) = 10 kWis needed (force x velocity). The equivalence of this powerdelivered by moving water can be caIculated from the energyloss in various cases. The expression "energy toss" isactually not correct. It is an energy transfer, from kineticenergy via turbulence to heat. In the foIIowing examples, theequations from basic hydraulics are considered weIl known. Figure 1.4 "Power lifting"

1. For an outflow of Q m3/s w th a head difference of MI m, the loss is:

äP = pgQäH (1.1)

Q and MI are related via:

Q = u.A = ~';2gäH.A (1.2)

For A = 1 m2 and p. = 1 we find MI = 0,37 m. So, a hole of 1 m2 anda modest head difference deliver 10 kW to lift 1000 kg with 1 mis.

2. For a uniform flow in a river with Q m3/s and a slope I, the loss is:

äP = pgQl (per m in flow direction) (1.3)

where Q and I are related via:

Q = A.C/hl (1.4)

For a slope of 104, Q = 10000 m3/s, h = 5 m , C = 50 vmls and awidth of about 1800 m, give an energy loss 10 kW. These are highvalues but the loss is per m length, while the first example gave a totaIloss. This aIso shows that alocal outflow gives a more concentratedattack than a flow with a gentle slope.

3. The energy loss caused by e.g. a bridge pier, is given by:

äP = FD.u (1.5)

(the water exerts a drag force Fo on the body and, reversely, the bodyexerts a same force on the water). The force and the flow velocity arerelated via:

(1.6)

VELOCITY HEAD

--t<---~tIJ. Hr ------

Q~

Figure I.S Energy lossin outflow

, VELOCITY HEAO

~"­

~I --. Q

~

Figure 1.6 Energy lossin river

D++

U FD h~ I'~

Figure 1.7 Energy lossin flow behindobstruction

For a pier with a diameter of 1 m in 10 m waterdepth and Co = 1, this gives a velocity u = 1.25mis to get an energy loss of 10 kW.

1.5