tr
Performanceof RiverFlood Embankments
R Bettess C E Reeve
Report SR 384 April 1995
E"R Wattingford
Addressand RegisleredOlfice: HR WallingfiordLtd. Houbery Park,Wallingford, O R.fistorEd in Endmd No 2562099. HR Wdlingiord b a wtrclv m€d {bdda.y of HR Walhgbrd Grap Ltd. tr Contract The repoil describeswork commissionedby the Ministry of Agriculture, Fisheriesand Foodto investigatelhe Performanceof Flood Embankments. The nominatedofficer was Mr J Goudie and the HR WallingfordProiect Directorwas Dr W R White. The HR job numberfor ihe projectwas QPS00 13/E The work was canied out by membersof the RiversGroup. Preparedby KKM n_ [1.r"r t+P*1 l,ta-15 Approvedby ...... 1...... ' v Dare....afsff.' @ Ministryof Agriculture,Fisheries and Food,1995 SR 384 200/Y95 tr Summary Performanceof RiverFlood Embankments R Bettess C E Reeve ReportSR 384 April 1995 Embankmentsare often used to protect land on flood plains from river flooding. When a flood eventpasses down a river,a high head of water is containedby the embankment,preventing the floodwater from inundatingthe floodplain. A surueyof the hydraulicperformance of flood embankmentsin the United Kingdomis described. Floodplains are commonlybuift up of highlypermeable river sand and gravel deposits,over lain by a low permeabilityoverburden of silt and clay alluvium. There is a potenlialfor groundwaterflow to take place within a flood plain aquifer,beneath the embankment.This can leadto sudaceponding due to exfihrationof groundwaterwithin the protectedarea. A descriptionof the groundwaterflow system is given. A methodfor making an approximate assessmentof the degree of groundwaterresponse to a given river hydrographin a particularflood plain is described. Remedialmeasures are discussedbriefly. The pore water pressureswithin flood embankmentsfluctuate as a resultof variationsin both river and groundwaterlevels. These fluctuationsin pore water pressurecan resuhin stabilityproblems and potentiallyembankment failure. The methodsavailable for the study of embankmentstability are described. Floodembankments are designedfor a particularflood returnperiod. For floodsgreater than the design flood, there is thedanger that the waterwill flow over the embankment.This can resultin floodingof the land behindthe embankmentand in some circumstancesit can be sufficientlysevere as to cause the embankmentto fail. The extent of this problem in the UK is assessedand methodsavailable for its studyare described. SR 384 1d0/Y95 tr Contents Title page Contract Summary Contents lntroduction Survey of hydraulic performance of f lood embankments 3 The groundwater system 4 3.1 GeneralDescription 4 3.2 Typesof Aquifer 4 4 Seepagebeneath flood embankments 4.1 ApproximateAssessment of groundwaterresponse to a flood event . 6 4.2 RemedialMeasures 7 Stabilityof flood embankments. . 5.1 Fundamental factors affecting the stability of embankments. .. 7 5.1.1 Soilcharacteristics 7 5.1.2 Effectivestress 8 5.1.3 Soilstrength 8 5.1.4 Pore water pressureand groundwater . . . . . I 5.2 Stabilityanalysis of embankments 9 5.2.1 Factorof safety I 5.2.2 Methodsof stabilityanalysis 10 5.2.3 Procedurefor stability analysis 14 5.3 Computer software for stability analysis of embankments. .. 14 5.3.1 STABLE 14 5.3.2 CRISP(CRltical State Prognm) . . . 15 5.3.3 Softwaretesting 16 5.4 Comparisonof limit equilibriumand stress-strain methodsof embankmentstability 16 5.5 lmpactof changesin porepressure on embankment stability 17 5.5.1 Embankmentgeometry 17 5.5.2 Soilcharacteristics 17 5.5.3 Pore water pressures. . 17 5.5.4 Programmeof analyses 17 5.5.5 Result 17 6 Flow over Embankments . . 18 6.1 Descriptionof problem 18 6.2 CIRIAwork on useof grass . 19 SR 384 190/v95 tr Contents continued 6.2.1 Hydraulicroughness of grassedsurtaces 19 6.2.2 Protection from hydraulic action provided by grasscovered surtaces 20 6.2.3 Other forms af embankmentprotection 20 6.3 Descriptionof flow 21 6.3.1 Modular-flowdischargeequation 21 6.3.2 Flow on landwad face of embankment. . . . . 22 6.4 Acceptabledegree of ovefiopping. . 22 6.4.1 Avoiding supercritical flow on the downstreamface . . 22 6.5 Developmentof a breachin an embankment 24 6.6 Probabilisticapproach to flowover embankments and darnages 24 6.6.1 Probabilityof overtopping 25 6.6.2 Volumeof overtopping 25 6.6.3 Convertingthe volume of overtoppinginto a depth of fboding 26 6.6.4 Determinationof the damage cosfs . 26 6.7 Assessmentprocedure 27 6.7.1 Use of figures 27 6.8 Maintenance. . . 28 Concfusionsandrecommendations ...28 References ...... 31 Tables Table5.1 Soil characteristicsused in stabilityanalysis .....16 Figures Figure3.1 The groundwatersystem Figure3.2 Typesof aquifer Figure5.1 Cross-sectionof embankmentgeometry used in software testing Figure5.2 Piezometricsurfaces used in testingthe impactof pore pressureon embankmentstability Figure6.1 Frictional resistance of grass swards for various retardancecategories (after USSCS, 1954) Figure6.2 Recommendedlimiting velocities for erosionresistance of plain and reinforcedgrass against unidirectionalflow (afterHewfett et a|,1987) Figure6.3 Growthof a gap with widih b in the case of two dyke breaches Figure6.4 Maximumallowable depth of overtopping:Poor cover, shoft grass(<50mm) Figure6.5 Maximumallowable depth of overtopping:Poor cover, mediumgrass (50-250mm) S8384 t0/O/V95 tr Contents continued Figure6.6 Maximumallowable depth of ovefiopping:Poor cover, long grass(>750mm) Figure6.7 Maximumallowable depth of overtopping:Average cover, short grass(<50mm) Figure6.8 Maximumallowable depth of overtopping:Average cover, mediumgrass (50-250mm) Figure6.9 Maximumallowable depth of overtopping:Average cover, long grass(>750mm) Figure6.10 Maximumallowable depth of overiopping:Good cover, short grass(<50mm) Figure6.11 Maximumallowable depth of overtopping:Good cover, mediumgrass (50-250mm) Figure6.12 Maximumallowable depth of overtopping:Good cover, long grass(>750mm) Appendices AppendixA Returnedquestionnai res sR3&t 100lu95 tr 1 lntroduction Embankmentsare often used to protect land on flood plains from river flooding. When a flood event passesdown a river,a high head of water is containedby the embankment,preventing the floodwater from inundatingthe floodplain. Theseflood plainsare commonlybuih up of highlypermeable river sand and graveldeposits, over lain by a low permeabilityoverburden of silt and clay allwium. Thereis a potentialforgroundwater flow to takeplace within a flood plainaquifer, beneath the embankment.This can leadto surfaceponding due to exfiltrationof groundwaterwithin the protectedarea. The pore water pressureswithin flood embankmentsfluctuate as a resultof variationsin both river and groundwaterlevels. These fluctuationsin pore water pressurecan resuhin stabilityproblems and potentiallyembankment failure. The hydraulicsof the groundwatersystem associated with flood embankments should be consideredduring the design of flood embankmentschemes in orderto identifyareas at riskand to assessthe true degreeof flood protection provided. Flood embankmentsare designedfor a particularflood return period. For floodsgreater than the designflod, there is the dangerthat the waterwill overtopthe embankment.This can resultin floodingof the land behindthe embankmentand in some circumstancesit can be sufficientlysevere as to causethe embankmentto fail. 2 Surueyof hydraulic performanceof flood embankmenfs ln orderto examinethe hydraulicperformance of embankmentsin the UK a questionnairewas circulatedto the then RegionalManager responsible for flood defencein each of the NationalRivers Authority regions. They were askedto identifyproblems and examplesassociated with embankments. A copy of the questionnaireand a list of the correspondentsis includedin AppendixA. A total of 35 questionnaireswere retumedfrom 5 of the 10 NationalRiver Authorities contacted. General information was receivedfrom a further3 regions. The problemsassociated with embankmentswere : . Groundwaterseepage below or throughembankment . Flowover embankments . Sudaceerosion resulting from: - flowsover embankments - riverflood flows - wave action - operationof sluices,gates . Massfailure SR 384 .|00,1/95 tr . Landdrainage problems due to embankmentsand flap gates . Maintenance,control of vegetation Seepageduring periods of highflow was identifiedin manycases as a rnajor problem. Manyembankments are foundedon silt and peatsoils which permit seepageunder enrbankments during floods as a resultof the large applied hydraulichead. Methodsmentioned for preventingsuch seepageincluded sealingthe bankswith clay or insertionof a butylor bentonitemembrane in the embankment. Manyof the repliesreceived identified erosion endangering the stabilityof the embankmentsas a majorproblem. Erosionmay be due to the effectsof wind and waves;tides; wash from ship navigation;weathering and frost action; bunowingvermin and grazingstock; and high velocitiesduring flood flows. These effectswere exacerbatedby loss of vegetationon the banks due to differentialsummer ard winter levels in the river. Protectionmethods mentionedincluded revetments, gabions, stone batters,faggots and piles. Erosionof the inland face of the bank caused by ovedoppingwas also identifiedas a problem. This leadsto reductionin the suface wldth of the embankmentand furtherinstability. Duringa separateproject (NRA R & D project459/C06) vermin activity was cited as probablythe largestsingle cause of bank failure in the NorthWest region.Traditionalcontrol measures include removing the vermin and stepping up the holes,but this can leavea labyrinthof tideswithin the bodyof the bank. Completedisrnantling of the defenceand reconstructionmay be requiredto preventheavy seepage and subsequentbreaching. A third major problem identified by the survey was the failure of an embankmentimmediately following the recessionof a flood. This is due to the creationof a potentialshear suface when pore water pressuresremain high in the bank after water against the slope has been removed. This was identifiedas'a commonfauft in flashyrivers'. Responsesto the questionnairemade a numberof referencesto the problems causedby embankmentovertopping. The regionsthat explicitlymentioned overtoppingproblems were: Anglian, Severn-Trent, Southern, South-West and Wessex. Discussionswith NationalRivers Authority engineers suggested, however,that overtoppingof embankmentsis a generalproblem throughout the NRA, ratherthan limitedto particularregions. lt was mentionedmore frequentlyin the contextof tidal areas but whetherthis is a true reflectionof the distributionof overtoppingproblems is notclear. The surveyrevealed that settlementof embankmentmaterial may take place as a resultof frequentsaturation and then dryingand this is morecomrnonly a problemin tidal areasbut may also occurwith river embankments. Many of the problemswhich were identifiedby the surveywere subjectsof normalmaintenance procedures and very few cases of total collapsewere repoiled. Very old banksand sand constructionswere concludedto be the mostat risk of collapse. SR 384 1ry0/U95 tr It shouldbe notedthat the initialsource of a problemmay notappear to be the causeof the finalfailure.Burrowing animals rnay weaken an embankmentand promotepiping though the embankmentultirnately fails duringa flood. Thus failuresfrequently occur as a resuhof a sequenceof changesdue to a rangeof causesratherthan as a resultof a singlemechanism. There may be interactionbetween different mechanisms which together lead to failure. One of the rnaincauses of the failureof coastalembankments in 1953was iniliated by flow through the embankmentand then geo-technicalfailure associatedwith fissuresin the crest of the clay banks. A separatestudy has identifiedthe followingfailure mechanisms: Erosiondue to directwave attack Erosion(landward face) due to overtopping Erosionof crest and reductionof height Scourof seawardtoe leadingto oversteepening Under-seepagein permeablelayer leading to piping Seepageleading to slippingor slidingof landwardface Slipcombined with lateralcompression Upliftpressure leading to floating Upliftpressure leading to bursting rapiddrawdown leading to front face failure Crackingof sudacematerial leading to effectivereduction in height Densificationof core rnaterialleading to effectivereduction in height Animalburrows causing general weakening and piping Humandamage, vandalism Damageby ship collision Bank instabilityin absenceof flood Foundationinstability in absenceof flood The directionof this researchproject was aheredin the lightof the responses to the questionnairebut it was not possible,within the constraintsof the project,to addressallthe problernsthat were identified. Consideration should be givento whetherfurther research is requiredon thesetopics, particularly: (1) Surfaceerosion resulting from: . rMerflood flows . wave action . operationof sluicesand gates. (2) Massfailure (3) Land drainageproblems due to embankmentsand flap gates (4) Maintenanceand the controlofvegetation Item(4) falls outsidethe experienceof HR but the othertopics would certainly be anrenableto fuflherresearch. The responsesto the questionnairesuggest that such researchwould be economicallyjustifiable. sR 384 10v04/95 tr 3 Thegroundwater system 3.1 GeneralDescription To understandthe sourceof the groundwaterrelated problems associated with embankmentsand their solution,one mustfirst developa descriptionof the groundwatersystem. Figure3.1 showsa cross-sectionthrough the type of systemenvisaged. The groundwaterflow is initiallyin a steadycondition, usually with a net flow of waterto the dverwhich acts to drainthe floodplain (Figure 3.1a). Withthe onsetof a floodevent, the waterlevel in the riverrises, reversing the direction of groundwaterflow as the riverrecharges the aquifer (Flgure 3.1b). When the riverlevel recedes, the highgroundwater heads dissipate and the groundwater drainsback toward the river(Figure 3.1c). The speed and degreeof responseof the groundwatersystem to the river floodevent (Figure 3.1d) depends on the geo-hydraulicproperties of the flood plain;the hydraulicconductivities and storagecoefficients of the aquiferand ovetturden, and also on the geometryof the groundwatersystem; the thicknessof aquiferand overburdenand the width of the dvervalley. 3.2 Typesof Aquifer There are three basic types of aquiferthat may be considered:unconfined, confinedor semi-confinedaquifers, depending on the degreeof influenceof the alluvialoverburden. The unconfined,or phreatic,aquifer is one above whichthe overburdenis absentor has negligibleeffect. In the confinedcase, the overburdenis consideredlo be totally impermeable.These are the two extremeswhen consideringthe influenceof the overburden.The most likely situationto occur naturally,however, is that of a low, but not negligible, permeabilityoverburden which semi-confines the aquiferbut rnayalso transmit high pore waterpressures and possiblyallow seepage to the sudace. Eachcase is consideredin a littlemore detail below: (.l) Unconfinedaquifer, Figure 3.2a. The unconfinedaquifer contains a water table which reflectsthe hydraulic headelevation in the aquifer(phreatic surface). lf a volumeof wateris added to the aquiferthe watertable will rise,say from levelA to B in Figure3.2a, in accordancewith the availablepore space or specificyield of the aquifer. This storage is the differencebetween the unsaturatedand saturatedmoisture contentsof the aquifer material. For an unconsolidatedgranular soil, the avaifabfestorage may be in the region15 - 35 Y"of aqurtervolume, depending on the particlesize grading. As thereis no restrictinglayer in an unconfinedaquifer, if the hydraulichead in the aquifer rises above ground level, level C, exfiltrationand surface pondingof groundwaterwill occur. (iD Confinedaquifer, Figure 3.2b The confinedaquifer is fully saturated.The hydraulichead elevationis given by the piezometricsurface, which is abovethe top of the aquifer,level A on Figure3.2b. lf this were not the case, an unconfinedcondition would exist, level B. There can, therefore,be no storagedue to the specificyield of the sR 384 t0/04/95 tr soil. Instead,a smalldegreeof storageis availabledue to the elasticstorage of the aquifer. This $orage coefficientincorporates the slightcompressibility of waterand the stress-strainrelationship of the soil matrlx. In compadsonto specificyield, the elasticstorage is very small,typically in the region 0.01 - O.5% for unconsolidatedgranular aquifers. This meansthat groundwaterresponses willbe morepronounced for confinedthan unconfined aquifers. As no exfiltrationof water can occur through the overburden,there is no dangerof seepagewhen the piezometricsurface exceeds lhe groundsudace, levelC. Thereis, instead,a dangerof upliftpressure due to the excesshead above the top of the aquifer, becominggreater than the downwardsoil pressure,resulting in fbtation and rupturingof the overburden.This modeof soil failurecaused by high piezometricresponses to embankedriver floods was noted as being highly destructivein the Bay of Plenty,New Zealand (RaudkiviandCallander, 1976) and also in lse Bay,Japan (Naguchi, 1989). This potentialfor generatinguplift pressuresis an importantaspect when consideringthe flood protectionof urbanizedflood plains. (iii) Semi-confinedaquifer, Figure 3.2c In this casewe needto considerthe hydraulicproperties of the overburden materialas well as the aquifer,in order to take the hydraulichead in the overburdeninto account. High upliftpressures rnay evolve similarly to confinedaquifers but the excess headthis time is due to the differencein headbetween levels A and B, Figure 3.2c. Anothermode of soil failurethat may occur in this situationis that of high groundwaterheads evolvingwithin the overburden. These high pore waterpressures result in a loweringof the effectivestress and subsequent loss of soil strengthwhich can leadto subsidencearound foundations. An importantpoint to notehere is that in the aquifer,vertical gradients are very smalland so the groundwatervelocity is alwayspredominantly horizontal; vr, due to headdifference h' in Figure3.2c. The groundwaterhead changes muchfaster in the aquiferthan in the oveburden,due to the largedifference in permeabilitybetween them. This generates predominantlyvertical groundwatervelocities in the overburden;v, due to head differenceh, on Figure3.2c. Semi-confinedaquifers present more complex modelling challenges than fully unconfinedand confinedaquifers. Models of theselatter two typesof aquifers may suffice in many situations. lf soil stability calculationsare to be performed,however, the responseof groundwaterpressure in the overburden materialneeds to be assessedin as muchdetail as possible. sB 384 10/01/95 l tr 4 Seepagebeneath flood embankments 4.1 ApproximateAssessment of groundwaterresponse to a flood event In their studiesof baseflowrecessions of stream-aquifersystems, Singh and Stall(1971) introduced the dimensionlessconstant, t, to characterizeaquifers whereby t =TI/SL2 (1) where T = aquifertransmissivity S = aquiferstorage coefficient L = distancefrom riverto catchmentedge t = time of recession Thetransmisslvrty (product of hydraulicconductivity and depth of flow)and the storagecoefficient rnay be foundfrom conductingon-site pumping tests. Watkins (1988) used this equationto characterizeflood plain aquifersby substituting 1 = periodof flood cycle L = widthof flood plain Using a simple,full hydraulicconnection, river boundarycondition and neglectingthe overburden,the responseto sinusoidalflood cycles was examinedfor variousvalues of t. Whenr = 1, the responseis considerable and groundwaterproblems are likelyto occur. At t = 10, 99 % of the river flood peak is transmittedto the aquiferlocation furthest from the river. Thus ? was usedto assessthe degreeof responseto the aquifer. The parameterSL2/T can be interpretedas the aquifer response time (Nutbrownand Downing,1976). Designatingthe aquiferresponse time as r*, c- = SL2/T (2) and applying the values of r considered above, t=0.1 t*=lQ1 x=1 t*=t t=10 t.=0.1 t The aquiferresponse time, G, may, therefore,be used to characterizethe responseof a flood plain aquiferto a flood event. lf r. is of the order of ten times the flood cycle period or lnore, then groundwaterresponses will be small. lf r. is of the same order as the flood cycle periodthen groundwater responsesrnay be considerableand are liableto cause problems. lf t. is aroundone tenth of the floodcycle period or less,the aquiferwill respondfully to the flood hydrographright across the valley. Notethat an orderof magnitudeis nota largevariation when considering field measurementsof T and S. SR384 10/O/V95 tr This approachfor evaluatingseepage beneath flood embankmentsis very simple and it has the advantagethat it allows a rapid assessmentof the magnitudeof the problemwhich may be expected.Groundwater models can be usedfor site specificstudies. Theseallow a numberof additionalfactors suchas the degreeof saturation,the propertiesof the overburdenand vertical flow componentsto be taken into account. 4.2 RemedialMeasures Vertical impermeablebarriers constructed in the aquifer beneath the embankmentrnay restrict seepage but willalso affectgroundwater discharge and impedethe riverdraining the floodplain naturally. lt mayalso be possible to constructpartial barriers that impedegroundwater responses enough on the time-scaleof a flood eventwhilsl $ill allowingrelatively unimpeded steady- statedrainage. The balancebetween the designof an effectiveand ineffective scheme,however, is delicate. A rnorereliable method of controllingthe groundwaterresponses is by pumped drainage.A drainsituated at the insidetoe of the embankmentmay be used to controlgroundwater within the protectedarea. Becausethe drainwould be usedwhen anbient groundwaterand riverlevels are high,the dischargewould need to be pumped. The feasibilityof such a scheme,the rate at which pumpingwould be requiredand design details may be studied by the applicationof numericalmodels. 5 Stability of flood embankmenfs Slope instabilitycan result in rnaterialfalling, sliding or flowing down a embankment,possibly damaging structures or endangeringlife. Assessingthe stabilityof an embankmentis thereforea common@ncern for the engineeror engineeringgeologist. lt is for this reasonthat attemptshave been made over manyyears to understandthe processeswhich govem embankment stability. This has resultedin the developmentof methodsof slopestability analysis, in orderto makea quantitativeassessment of the stabilityof a particularslope. A majorproblem is the failureof an embankmentimmediately following the recessionof a flood. This is due to the creationof a potentialshear surface when pore water pressuresremain high in the bank after water againstthe embankmenthas been removed. 5.1 Fundamentalfactors affecting the stabilityof embankments 5.1.1 Soilcharacteristics The natureof the soilformingthe embankmentis an importantfactor affecting itsstability. Soilconsists of particlesof rock,or rockforming minerals, with air and waterfilling the pore spacesbetween. Rockforming minerals can be eitherrnassive (eg. quartz)or clay minerals(eg. illite),and whereasmassive mineralsgenerally form angular blocks of silt or sand,clay mineralsform much smallerflake shapedparticles. The type of mineralspresent affects the abilityof the soilto absorbwater, and thereforedetermines the physicalinteraction between soil pafticles.ln general, massiveminerals do notabsorb much water. However, clay mineralsare often sR 384 lov&vgs E electricallycharged and absorbwater readily, leading to the soil swellingand shrinkingas the soil environmentchanges. The type of mineralspresent also affectsthe permeabilityof the soil. Soils consistingof largeparticles, such as sands,contain more voids and thus have a largerpermeability lhan soils whichconsist of fine particlessuch as chys. Claymaterials commonly exhibit very lowpermeabilities. These propefiies are impoilantwhen consideringflow throughor underembankments. 5.1.2 Effectivesfress The principleof effectivestress is fundamentaltosoil mechanics.Stress may be transmittedthrough a soil by the soil skeletonand by the pore fluid. Pore fluid can exert only an overall stress, whereasthe soil skeletonis able to transmitnormal and shearstresses through the soil. lt is for this reasonthat the soilstrengthis controlledby the stressestransmitted by the soilskeleton. A high porefluid pres$Jrewill reducelhe effectivestress on the soil, as there is a reductionin the stresstransmitted through contacts between soil particles. 5.1.3 Soilstrength As mentionedpreviously, soil strengrthis essentialtyderived from the soil skeleton,ie. the contactsbetween soil particles. Friction between soil particles resuftsin a shearstrength that is controlledby the effectivestresses on the soil. lf a soil is only just supportingthe stressesimposed on it, its shear strengthis fullymobilized and plasticdeformations occur. Cohesionlesssoils such as sandsand gravels,have no shearstrength when they are unconfined,however when confinedsome shear strength is derived from the interlockingof soil particlesand the frictionbetween them. When sheared,initially the confinedsoil dilatesgiving a peak strength. lf shearing is continued,the shear strengthdrops until shearingat a constantvolume occurs.Unconfined cohesionless soils tend to contractwhen sheared, untilthe constantvolume condition or the critical stateof the soil is reached. In contrast,cohesive soils such as clays have some shear stren$h when unconfined.This is mainlydue to sub-atmosphericpore pressures,but there can be bondingbetween clay particles.For this reason,soil permeabilityand drainageare importantto the shearbehaviour of clays. The plate-likeshape of clayparticles means that they willoften align themselves with a shearplane, therefore reducing the shear strength of the plane in relation to the surroundingsoil. The reducedshear strength along the planeis termedthe residualstrengrth. Fullydrained cohesive soils behavein a similarway to cohesionlesssoils when sheared,eg. over-consolidatedclays will initiallydilate, whereas normally-consolidatedclays will contracton shearing.lf shearingis continued, then the criticalstate is reached,and eventuallya shearplane is formed. The shearstrength of the clay is then reducedto the residualvalue. Soil drainageis very importantto the soil strength in both cohesiveand cohesionlesssoils. For instance,a saturatedsoil with a constantvolume (ie. undrained)will havea constantstrengfih. lf drainageis allowedhowever, the soil strengthwill changewith different loads. sR 384 tO0#95 tr 5.1.4 Pore waterpressure and groundwater Porewater pressure has a directeffect on the effectivestresses which control the shearstren$h of soils,and thereforeon the stabilityof an embankment. When using an effective stress method of slope stability analysis, the determinationof the pore water pressuredistribution within the embankment is essential. The evaluationof the pore water pressuresmay involvefield measurementsor modellingsoil seepage,which is detailedin such texts as Cedergren(1967). Embankmentinstability can occur when pore water pressuresare out of equilibriumwith the boundaryconditions of the embankment.This maybe due to changesin the pore waterpressures as a resultof undrainedloading and unloading,or a recent change in hydraulicboundary conditions. As equilibrationof pore water pressure@curs, the stabilityof the soil changes. For instancewhere an enbankmentis constructed,the soil beneathit will graduallybecome more stable as pore waterpressures are reduced. Where a cuttingis made,the side slopeswill graduallybecome less stableas pore water pressuresare increased.The behaviourof embankmentsand cutting is complicatedby the natureof any drainage,and by the type and zoningof soil involved. Where there is rapid drawdownbehind an embankmentor dam, and the permeabilityof the soil is such that it impedesoutflow, the responseof the porewater pressures in the soil maylag behindthe drawdownof the reservoir. When the loadingof water on the embankmentis removed,there may be someresidual high pore water pressures remaining in the embankmentwhich could renderit unstable. It is clearthen that porewater pressures are very importantwhen considering the stabilityof an embankment,and vital if the stabilityis to be evaluatedin terms of effectivesoil stress. Informationon pore water pressuremay be representedas a piezometdcsurface, or as a porepressureratio rn The former,although useful in simpleregimes, cannot be usedto describecomplex pore waterdistributions. The pore-pressureratio is given by the pore water pressureat a point in the soil dividedby the vefiicaltotalstress at that point, (whichmay be calculatedroughly using the soils unit weight and the depth below groundlevel). This ratio may be averagedalong a slip surface,or for zones of differentsoil types, however,it shouldbe used with cautionwhen modellingslope stability,as averagingwill often result in large reductionsin accuracy. 5.2 Stabilityanalysis of embankments 5.2.1 Factorof safety It is usualto expressthe resultsof slopestability analyses in termsof an index of refativestability called the factorof afety (F/. This is the ratioof the actual strengthavaihble to that mobilizedie. tr _ Available shear strength sR 384 1U0{95 tr In the analysisof stabilitythe faclorof safetytraditionally has severalfunctions, 1 To take intoaccount uncertainty of shearstrength parameters due to soil variability,and the relationshipbetween the strengthmeasured in the laboratoryand the operatbnalfieldstrength. 2 To take into account uncertaintiesin the loading on the slopes (eg. surfaceloading, unit weight,pore pressures) 3 To take into accountthe unceftaintiesin the way the model represents the actualconditionsin the slope,which include, (a) the possibilitythat the criticalfailuremechanism is slightlydifferent from the one whbh has been identified,and, (b) that the modelis not conservative. 4 To ensuredeformations within lhe slopeare acceptable. The factor of safety does not allow for the possibilig of gross errors,for examplea bad choiceof failuremechanism, such as ignoringthe presenceof existingshear surfaces in a slope. A disadvantageof the Factorof safetyis that it doesnot necessarilyrepresent the probabilityof failure. The failureprobability is an importantelement of risk analysisused to comparethe costs and benefitsof alternativeschemes. A probabilisticapproach takes accountof the uncertaintyin soil parameters,in pore pressuresand, if necessary,in the soil behaviourmodel, to evaluatethe probabilitythat the slopewillfail. 5.2.2 Methodsof stabilityanalysis An exact stability analysis of embankments would involve solving simuhaneouslythe conditionsof equilibriumand compatibilitythroughout the embankment.Clearly a completeknowledge of the stress-strainbehaviour of the soil would be requiredand the calculationswould be very complicated. Forthisreason, the simplerlimit equilibrium approach is oftenused to analyse the safety of a slope, even though these methodswill not give details of deformationunder stress. Limit equilibriummethods Thereare a numberof differentmethods of stabilityanalysis, the procedures of whichare generallysimilar in concept.The embankmentand embankment materialbeing consideredare modelledtheoretically, taking accountof the loadingson the embankment.Although embankment instability may result in rock falls or mud flows, most failures start or progress by sliding along surfaceswithin the soil mass. For mostengineering purposes then, sliding modelsare cpnsidered to be sufficient,and these 'limit equilibrium methods of analysis are widely used for the analysis of slopes, ernbankrnentsand excavations. Simple sliding methods of analysis are adequate for most engineering applications.These are usedto determinethe factorof safetyfor the critical slip surface,and therefore, the embankment.The presenceof beddingphnes or other soil features in some embankmentswill result in a slip sudace approximatelyparallel to the embankmentsurface. Other embankments, 10 sR 384 t0/OV95 tr wheresoilformations are predominantlycohesive, will havennre deepseated slip surfaces,which can often be describedby the arc of a circle. When usinga limit equilibriummethod of stabilityanalysis, the first step is to assumea surfacealong which the slope is likelyto fail. The mobilizedstress alongthis surfaceis then calculatedand comparedwith the stressrequired to cause failure along the sudace,the resuh being a factor of safety for that pafiicularslip surface. Limit equilibdummethods of analysis may be broadly divided into two categories:linear methodsand non-linearmethods. Linear methodsare simplerto use, as the factorof safetycan be calculateddirectly from a linear equation. However,the assumptionsmade in these methodswill result in conservativefactors of safety. Non-linearmethods have non-linearfactor of safety equations,which must be solved using an iterative procedure. Assumptionsmust also be made in these analyses,however most methods are held to produceacceptable factors of safety. Linear methods Whereshallow forms of embankmentfailure are likelyto occur over a large cross-sectionalslope area, the infiniteslope analysis(Taylor, 1948) may be the mostappropriate method of analysis. In this case,failure is assumedto occuralong a planeslip surfacewhich is parallelto the groundsurface. Forces acting on the top and toe of the slide are considerednegligible and are ignored(ie. the slopeis infinitein lengrth).The soil propertiesand groundwater conditionsare assumedto be constantalong the slip. This methodis also describedby Skemptonand Delory(1957). Wedgeanalysis, or the graphicalwedge method may be usedwhere the slip sufface may be simplyapproximated by a few straightlines. For instance wherethe geologyof the embankmentdictates the positionof a slip sudace. The soil is dividedinto a numberof blocksor wedges. The factorof safetyis then obtainedby solvinghorizontal and vertical equilibrium equations for each block,and constructingforce polygons. Assumptions about interwedge forces must be made. The circulararc methodof analysis(Fellenius, 1936) is commonlyused io assessembankment stability. Failure of the embankmentis assumedto occur by the soil masssliding along a cylindricalslip surface,where the undrained soil strengthcan be rnobilized.The simplestmethod which assumes a circular arc slip surface,is the gu = 0 method. Herethe shearstrength of the soil is assumedto be purelycohesive, as the angleof frictionfor the undrainedsoil is ignored. This assumptionsimplifies the calculationof the maximum availableresisting moment, ie. the sumof allthe cohesivestrengths multiplied by the areasor lengthsover whichthey act, and the radiusof the slip circle. The factor of safety is then calculatedby dividingthe maximumavailable resistingmoment by the momentof disturbingforces. The undrainedshear strengithis used in this method of analysis, which implies that effective stressesand porewater pressures in the soil havenot yet reachedequilibrium. This methodis appropriatefor the analysisof problemsin the short term, immediatelyaft er construction. The ordinarymethod of slicesis an effectivestress analysis where failure is again assumedto occur by rotationof the soil mass about a cylindricalslip SR 384 1U0,v9s tr surface. The methodrequires that the variationof the normalstress around the slip sudace is determined,and in order to do this the mass of soil is dividedinto slices. lt is assumedthat the resultantof the intersliceforces on eachslice is paralleltoits base. The npmentequilibrium about the centreof the slip circle is examinedto obtainthe factor of safetyof the embankment. This is the simplestmethod of slicesto use, however,the assumptionsabout the inter-sliceforces can leadto largeunder-estirnations of the factorof safety, and so it is not often used (Nash,1987). Non-linearmethods In orderto determinethe effectivestresses around a failuresurface, the failure mass of soil is dividedinto slices.However, many of the forces actingon a slice are unknownat the beginningof lhe analysis. The numberof unknown variablesis greaterthan the nunber of equationsavailable. This meansthat assumptionsfor somevariables must be madein orderto solvethe equations for the remainder. The assumptionsmay be about the normal stress distributionover the slip sudace;the positionof the line of thrust of interslice forcesor the inclinationof intersliceforces. Mostnon-linear methods of slices assumethat the normalforce acts on the centreof the base of each slice. This is acceptableif the soil massis dividedinto a relativelylarge numberof slices. The assumptionsmade, and whetheran overall force or moment equilibriumsare considered,distinguish the differentmethods of slices. The generalor conventionalmethod of analysisexamines the overallmoment equilibriumabout an assumedcentre of rotation,or overallforce equilibrium in order to obtaintwo expressionsfor the factor of safety. The slip surface may be circular or non-circular,and an assumptionmust be made about intersliceforces. Bishop(1955) improved on the conventionalmethod of slices;which takes no account of intersliceforces, by assuming that the intersliceforces are horizontal,and resolvingall the forcesfor a slicevertically. In this method,a centrepoint for thetrial slip circle is specified,along with a pointthrough which the circle passes(eg. the toe of the slope). Momentsare taken about the centreof the circleand by examiningthe overallstability a factorof safetyfor the slip circle is obtained. A detaileddescription of Bishopssimplified or 'routine'method of slicesmay be foundin his paperof 1955,and in a number of geotechnicaltexts(eg. Bromhead (1986); Anderson & Richards(1987)). ln order to determinethe most likely slip surfacefor the slope,a numberof differentcircles are examined,the centresof whichare usuallyspecified as a rectangulargrid. Contoursof factorof safetyfor eachcircle centre point can then be drawnand the surfacewith the lowestfactor of safetyagainst sliding may be determined. In certaincircumstances when usingBishop's method, problems can arise when evaluatingthe factorof safetyat the toe of a embankment.When the soil at the toe segmenthas a high angleof frictioncompared with the soil of the rest of the slope,this may be incompatiblewith the overalllow factor of safetyfor the embankment. Janbu'smethod (Janbu et al. 1956)developed Bishop's routine method sothat it couldbe appliedto any shapeof slip surface. Althoughthe generalrules of Bishop'smethod are followed,this methoduses the force ratherthan moment 12 sR 384 1Cy04/95 tr equilibriumequation. The intersliceshear forces are assumedto be zero,but the introductionof an empiricalcorrection faclor which is applied to the convergedfactor of safety, allows for them. The sliding mass should be dividedinto narrowslbes when usingthis method. A methoddeveloped by Spencer(1967) examinesboth overall force and overall equilibrium,so that two expressionsfor the factor of safety are produced. The intersliceforces are assumedto be at a constantinclination and the inclinationis foundat whichboth expressions give the samefactor of safety. This methodrnay be appliedto non-circularslip surfaces. Morgensternand Pricedeveloped a methodof analysiswhich could be applied to both circularand non-circularslip sudaces. This methodwas specifically devisedto overcomeproblems with programmingother methodsof stability analysisfor use with computers. The methodassumes that intersliceshear forces(X) are relatedto the interslicenormalforces (9 bVthe following: X =],.I8\E where/(x) is a functionwhich varies continuously across the slip surfaceand X,is a scalefactor. The value of l, and the factorof safety(F) are computed for the assumedfunction /(r). The factorof safetyof a slip sudacehas been shownto be relativelyinsensitive to the /(x) used,not varyingby morethan about5%, for this reasonit is comrnonlyassumed that /(x) = 1. ln this methodthe sliding rnassis dividedinto a relativelysmall nurnberof verticallysided sections which are generallymuch wider than the slicesused in othersimilar methods of analysis. Withineach of thesesections, a sliceof infinitesirnalwidthis considered, and with the aboveassumption regarding the relationshipbetween Xand E,the equationsforforce and momentequilibrium are solvedsimultaneously. The analysisinvolves a complexprocess of iterationand is therefore,intended to be usedwith the aid of a computer. Methodssuch as the Morgenstemand Priceprocedure have been modified and improvedcontinually. Detailed accounts of commonlyused methodsof slopestability analysis are given in severaltextseg. Tezaghi and Peck,(1967); Bromhead,(1986); Anderson and Richards(1 987); Cedergren, (1967). The resultsof the variousslope stability analyses above are usuallyexpressed as a factor of safetyfor the particularembankment. However, the analysis may be adapted to give details such as the slope angle at which a embankmentwould fail. For circularfailure surfaces,the factor of safety is often contouredby writingil againstthe centreof each slip circle markedon a cross-sectionof the embankment. Stress - strain analysis : Finite element methods Numericaltechniquessuch as finiteelement analysis can be usedto obtainan approximatedistribution of the $resses and strainsthroughout a slope. With moderncomputers these techniquesare extremelypowerful and they are particularlyusefulfor analysing the conditions in a stableslope or embankment whenit is subjectedto changesof loadingor geometry.However their usefor analyslngslopes which are on the point of failure is less satisfactoryand in SR384 100/V95 tr generaltheir use is limited by the difficultyof modellingthe stress-strain behaviourof soil. This is a sophisticatedmethod which requires very accurateinput data if the analysisis to be useful. 5.2.3 Procedurefor stability analysis It is inporiantto understandthe theoreticalbasis of a particularmethod before applyingit in practice. A thoroughsite investigationis essentialtoestablish the soil and groundwater conditions,followed by carefulsoilte$ing. Oncethe soil and groundwaterconditions have been established,a method of analysismay be chosenwhlch is appropriateto the anticipatedmechanism of failure. ln practicethe simplestmethods are often used initiallyto give an indicationof the magnitudeof the problem.When the problemdemands more sophisticatedmethods these can then be used. lt is often usefulto ascedain the sensitivityof the resultof the analysisto small changesin the assumed parameters so that engineering decisions may be based on a full understandingof the problem. One approachis to use probabilisticmethods to give a full descriptionof the situation. 5.3 Computersoftware for stabilityanalysis of embankments 5.3.1 STABLE There is a rangeof computersoftware currently available which can be used to carryout stabilityanalyses of embankments.Though their detailsvary the approachof manyof them is similar. The programSTABLE was selectedfor use in this studyas beingtypicalof a classof software.STABLE is a program for assessingthe stabilityof circularor non-circularslip surfaces.Slip sudaces may be in a naturalslope, a cuttingor excavation,an embankment,or an earthdam. The programcan analyse'pre-existing'slip surfacesi.e. where slippagehas already occurred. The programcan accommodate soil reinforced slopes. The slope stability analysis program 'STABLE' allows the embankment geometryand othercharacteristics such as piezometricsurface, to be defined graphicallyusing a CAD (computeraided design) software package. Results of the analysiscan also be shown on the graphicaldisplay. The program calculatesthe factor of safety of the slope against sliding, and tabulates informationderived from the analysis. The program is able to apply any of four methodsof analysis based on differentassumptions as follows, - Bishop'sMethod : circularpath - Morgenstern& Price'smethod : non-circularpath - Sarma'smethod : non-circularpath - Greenwood'smethod : circularpath. 14 sR384 lO0.Y95 tr Bishop's method lf the Bishopsslip circle methodof analysisis chosen,then the redangular boundaryto the grid of circlecentres is drawndirectly on to the cross-section of the embankment.The userhas the choiceof defininga pointwhich the trial circlesintercept as eithera singlepoint (or tangent), or two points(or tangents) in whichcase a specifiednumber of interpolatedpoints are taken in between the two. The rangeof slip circleswith different centre points and radiiare then analysed,and the sudace with the lowestfactor of safety is given. lf the centreof this circlelies on the edge of the rectangulargrid, then analysis shouldbe repeatedwith anothergrid of circle centres. Morgenstern& Price's method 'STABLE', When usingthe Morgensternand Priceoption in the geometryof the slope underconsideration is definedin the same way as for the Bishops option. The slip surfaceis describedhowever, by a seriesof straightlines ratherthan by pointsdefining a circle. Sarma's method Sarma'smethod assumes a non-circularwedge-shaped slip surface,as does Morgensternand Price, but Sarma is more rigorous, not constraining subdivisionsof wedgesto verticalslices. By iterationthe programlocates the optimumslip surfaceand optimuminter-wedge inclinations. Greenwood'smethod Greenwood'smethod assumes a circularslip surface- as for Bishop'smethod - but employsa differentgoverning equation. Greenwood'smethod permits the modellingof soil reinforcementas a set of straightlines seen in section. Eachstrip has an associated'force'value. 5.3.2 CRISP (CRltical State Program) CRISP (Brittoand Gunn, 1990)is a finite elementprogram incorporating criticalstate modelsof soil behaviour. The model has been developedby membersof the CambridgeUniversity Engineering Department soil mechanics group. CRISP-9O,a PC version,can be run in INTEL80386 processor with a minimumof 2 MB RAM,a mathsco-processor, VGA colourmonitor, mouse and MS DOS3.30 or higher. The model may be used to perform an undrainedanalysis (to predict behaviourin the shortterm), a drainedanalysis (for long term behaviour),or a coupledconsolidation analysis. Two dimensionalplane strain, three dimensionaland axisymmetricsolid bodiescan be analysed. Varioussoil modelsare availablewithin the packageincluding linear elastic, anisotropicelastic and inhomogeneouselastic properties; critical state soil modelsincluding cam clay, rnodifiedcam clay and Horslevsuface; elastic perfectlyplastic models Tresca, von Mises, Mohr-Coulomband Drucker- Prager. The programhas the abilityto specifynon-zero in-situ stresses. Boundary conditionsinclude prescribed displacements, pressure loading and porewater pressures. sR 384 1U04i95 tr 5.3.3 Softwaretesting As part of the research,copies of STABLEand CRISP were obtained;a courseon CRISPwas attendedby a menrberof HR Wallingfordstaff. The softwarewas usedto studythe perforrnanceof a typicalembankment section. Embankmentgeometry The cross-sectionof the embankmentgeometry, which was analysedin this studyis givenin Figure5.1. h waschosen in orderto comparethe minimum factorof safety(F) for the differentslopes with variedsoiltypes. Soil characteristics Three soil types were used in this dudy; clay, gravel and silty clay. The respectivesoil characteristicswhich were requiredfor the stabilityanalyses, are shownin Table5.1. Table 5.1 Soil characteristics used in stability analysis SOIL ANGLEOF COHESION UNITWEIGHT FRTCT]ONo', G'(kN/m2) T clay (A) 18" 3 19 Gravel(B) 40" 0 19 Silty clay (C) 21" 2 19 Porewater pressures in the embankmentsoilwere calculated from the position of the specifiedpiezometric sudace. This line is shownon Figure5.2. Programmeof analyses For eachembankment geometry, STABLE using Bishops' method of analysis (ie.circular and non-circularslip surfaces),and CRISPwere used to assess the stabilityof the embankment.These analyses were carried out for the three soil typesdescribed above, ard for the homogeneoussoil cross-section 5.4 Comparisonof limitequilibrium and stress-strain methodsof embankmentstability Brinkgreveand Bakkercarried out analysisof embankmentsusing a finite elementformulation. The finite elementmethod was used to estirnatethe factor of safetyfor an embankmentunder the mostdangerous conditions. For the samesituation the critical slip circle accordingto Bishop'smethod was calculated. A drained analysiswas carriedout for both the finite elementapproach and the Bishop approach.Whilst the positionsof the slip circleswere somewhatdffierent for the two approachesthe safetyfactor in both Bishop'smethod and the finite elementcalculation was exactlythe same. From this analysisit might be concludedthat the finite elementmethod has no advantagein comparison with,simpler, more conventional methods. In the simplecase investigated this happensto be true but the finite elementmethod will also detectnon-circular slip surfacesand associatedfactors of safety. SR 384 ld0'V95 tr 5.5 lmpactof changesin pore pressureon embankment stability As described above, pore water pressures are very important when consideringthe stabilityof a embankment.Embankment instability can occur whenpore water pressures are out of equilibriumwith the boundaryconditions of the embankment. This may be due to a recent change in hydraulic boundaryconditions. This situatbn was investigatedusing the STABLE software. 5.5.1 Embankmentgeometry The cross-sectionof the embankmentwhich was analysedin this study is givenin Figure5.2. 5.5.2 Soilcharacteristics Two soiltypeswere usedin this study;a clay and a sihyclay. The respective soil characteristicswhich are requiredfor the stabilityanalyses, are given in Table5.1. Two soil type arrangements were tested for the embankment, ie. homogeneoussoil overthe wholecross-section. 5.5.3 Porewater pressures Porewater pressures in the ernbankmentsoil were calculated from the position of the specifiedpiezometric surface. Locaiionsof the piezometricsurface at differenttimes during the passageof a floodare presentedin Figure5.2; these were calculatedfrom the seepagemode! described in Chapter3. 5.5.4 Programmeof analyses For eachcondition STABLE, using Bishops methodsof analysis(ie. circular and non-circularslip surfaces),was used to assess the stability of the embankment. These analyses were carried out for the two soil types describedabove, for the homogeneoussoil cross-sectionand for the different locationsof the piezometricsurface. 5.5.5 Result The analysisshowed that during a flood event the factor of safety can be significantlyreduced. The factorsof safetyobtained using transient porewater pressuredistribution that can occur during a flood event were substantially lower than those under static equilibriumconditions. In some cases the reduct'ronswere up to a factorof 10 for the least stableconfigurations. The lowestfactors of safetywere obtained at the heightof the floodwhen the water levelwas at its higheston the outsideface of the embankment.The results conclusivelyindicate that in determiningthe stabilityof an embankmentit is not sufficientto considerstatic, equilibrium pore-pressures and that it is necessary to considerthe transientpore-water pressure that can developduring the progressof a flood. 17 sR 384 l0r/04/95 tr 6 Flow over Embankments This section addressessome of the problems related to flow over flood embankments. 6.1 Descriptionof problem Flood embankmentsare designedfor a particularflood return period. For floodsgreater than the designflood there is the dangerthat the waterwill flow over the embankment.On this reportwe will distinguishbetween the case, frequentlyfound in coastalsituations, where the meanwater level is belowthe crestof embanlcnentbtrt waves overtop the embankment.We will reseruefor this case the term 'oveflopping'. Wherethe mean water level exceedsthe height of the embankmentand flow takes place over the embankment continuouslythen this will be referredto as flow overthe embankment.ln the case of flow over embankmentsflow takes placedown the landwardside of the embankment.Depending on the degreeof overflowing, the slopeof the embankment,the rnaterialof the embankmentand the protectionon the downstreamslope, erosionof the embankmentrnay take place. In some circumstancesthis can be sufiicientlysevere as to causethe embanlanentto fail. lt is important,therefore, to ensurethat embankmentsshould be capable of survivingthe expecteddegree of ovedlowing. Whenflow begins to take placeover an embankmentthe flowvelocities on the crest of the embankmentare usually low. As the waler flows down the landwardface, however,it accelerateswhich can resultin very much higher velocities.The flowvelocities achieved depend upon the depthof flowand the slopeof the embankment.These velocities can be suchthat the shearstress appliedto the embanlcnentmay erodematerialfrom the embankmentface. In extremecases the flow downthe embankmentcan becomesuper'critical. Wherethe flow meetsthe base of the embankmentor, if there is a tailwater level,pail way up the embankment,a hydrauliciump can form. This can resultlocally in high shearstresses being applied to the embankmentfill and can resultin severeerosion. Where an embankmenthas a consistentheight then the flow over it is distributeduniformally along the lengthof the embankment.lf thereare local featuresor anomaliesin the heightof the embankmentor its profile,these may act to concentratethe flow in pafiicularareas. Insteadof largeareas being subjectto quitemodest shear stresses, which the embankmentcan withstand, this may result in large shear stressesconcentrated at particularlocations. This mayresult in erosionthus leadingto the failureof the embankment.Thus the detailingof the designand the maintenanceof the embankmentcan be important. Smalldegrees of overflowingmay initiaternore serious forms of failure. The water ovedlowingthe embankmentmay percolate into the soil of the embankmentand by raisingpore water pressuresinduce slip failuresin the innerslope. Altemativelythe waterpercolating into the embankmentmay trap air inclusionswhich again may leadto reductionsin strengthand subsequent failure. 18 sR384 tU04/95 N It shouldbe notedthat there is frequentlya differencein the natureof flow over an embankmentbetween rivers and coastalareas. ln a river spillage overan embankmentfrequently takes place over long lengthsand so the spill dischargecan be high. lt can frequentlybe significantrelative to the total river discharge.In this casethe spillageinfluences the waterlevels in the riverand so limitsthe depthof flow over the embankment.Except in localisedarsas, therefore,in a flwial contextthe depthof flow overan embankmentis normally small. In a coastalcontext, the importantfactor is the seawardwater level. In most casesthe impactof spillson thesewaler levelsis small. Underextreme tidal conditions,therefore, large depths may o@ur over the top of the embankment. 6.2 CIRIAwork on use of grass The rnajorityof UK embankmentsare coveredwith grassor othervegetation and this has a significantetfect on the abilityof a surfaceto withstandshear stresses.CIRIA have carried out a numberof studiesinto the use of grassin an engineeringcontext which are valuablein assessingproblems associated with embankmentovertopping or overflowing(Coppin and Richards,1990). Vegetationreduces or preventssoil erosion in a number of ways. The vegetationincreases the hydraulicroughness of the suface from that of an unvegetatedsurface and hence, for a given discharge,reduces the flow velocities.In additionthe vegetationcan form a protectivelayer over the soil, preventingthe directapplication of shearstress to the soil. The root structure of vegetationmay also act to stabilisethe soil and inhibiterosion. 6.2.1 Hydraulicroughness of grassedsurtaces The hydraulicroughness of a surfacecan be describedby a parametersuch as Manningsn, whichrelates the averageflow velocityto the hydraulicradius R and the slopeS of a channel usingthe equation v=R*So's/n The hydraulicroughness depends upon the nnrphologyof the vegetation,the densityof growthand the heightof the vegetation. When the flow depth is shallowrelative to the heightof the vegetationmost of the energyis dissipated as form lossescaused by the flow aroundthe individualplant stems. As the flow depth increasesrelative to the heightof the vegetation,the plant stems beginto move in the flow, furtherenhancing energy loss. As the flow depth andvelocity increases further the vegetationbegins to be flattenedby the flow. The vegetationthus occupies less of the flowarea and mostof the energyloss arisesfromskin friction. This is normallysignificantly less than the form losses whichoccur at smallerdepths. The generalpattern is thus that as flow depth increasesthe resistanceinitially increases and then reducessubstantially. The hydraulicroughness of shortgrass vegetation is comparablewith that for baresoil. As the grasslength increases the roughnessincreases (Figure 6.1). This can lead to a conflictbetween the needto carry out cuttingto maintain the qualityof the grasscover and the needto maintainthe lengthto increase the roughness. For very shallowflow, in whichthe vegetationis rarelyfully submerged,the roughnessmay be high(Morgan, 1980). '|00,Y95 19 SR384 tr 6.2.2 Protectionfrom hydraulic action provided by grass coveredsurtaces The protectionprovided by vegetationcan be assessedin termsof the velocity of flow, the qualityand lengrthof the vegetationcover and the durationof the flow. Figure6.2 assesseserosion resi$ance in termsof velocityand duration for a rangeof lypes of over. lf theseconditions are exceededthen erosion is likely to occur. Once erosion has been iniliated then further loss of vegetationcover and erosionof the soil will occurrapidly. Hewlettet al (1987) gave the followingrecommendations on permissiblevelocities that can be withstoodby a wellselectedand maintainedgrass @ver. 2mls for prolongedperiods of over 10 hours 3 to 4mls for periodsof a few hours Sm/sfor briefperiods of less than 2 hours. In general, grass can be expectedto provide an adequateprotection for velocitiesup to lm/s. This limitingvelocity is likelyto decrease,however, as the qualityof the grasscover diminishes. The lengthof the grass cover is a major factor in the amountof prolection provided. Otherimpoilant factors are: (a) the densityof the stems,foliage and the sudacemat (b) the state of growth and structureof the sward, this is relatedto the speciespresent and theirmanagement (c) the uniformityof the sward.The presenceof tussocksor clumpscan lead to concentrationsof flow and local weaknesseswhich can significantly reducethe degreeof protection (d) the flexibility and strength of the stems affect both the hydraulic roughnessand the capacityto withstandthe hydraulicforces (e) the seasonofthe year. A furtherimpodant factor that mustbe consideredis the capacityof the grass coverto re@verfrom a flood event.A grasssward will requiresome time to recoverits full strengrthfollowing a flood event. lf two floods occur in quick successionthen the grasscover will not have a chanceto recoverfrom the first attackbefore it is inundatedfudher. ln thesecircumstances, if there is no opportunityto carry out remedialwork then it is the total durationof flooding that is important. 6.2.3 Other forms of embankmentprotection The abovework has been basedupon the assumptionthat the downstream surfaceof the embankmentis grassed. The methodsdeveloped, however, can be apptie-dto consider the risk of eroding any surface. The only requirementis that the hydraulicroughness of the surfaceand the critical velocityfor erosionare known.The equationfor the dischargeoverflowing the embankmentand the Manningsequation still applyto the flow characteristics. The appropriatecalculations can then be performedto determinethe degree of flow over the embankmentthat will resultin sudaceerosion downstream. 20 sR3&+ r00rye6 tr 6.3 Descriptionof flow The flow down the landwardside of the embankmentis determinedby the dischargethat flows over the embankment. An extensivelaboratory study was carriedout by the US GeologicalSuruey on the dischargecharacteristics of embankmentshaped weirs, (Kindsvater, 1964). This study looked specificallyat the hydraulicsassociated with flow over embanlcnents.As pail of the studya seriesof laboratoryexperiments were carriedout at scales rangingfrom 1 in 6 to 1 in 12. Thesetests lookedat manyaspects of the problemincluding: a water-sudaceprof iles, a velocitydistributions, a influenceof boundarylayer development, a influenceof bourdaryform on flow characteristics, a influenceof surfaceroughness, a influenceof geometry. lf more informationis requiredon any of these aspectsthan is containedin this repoil then referenceshould be made to Kindsvater(1964) and the referencescontained therein. The studyidentified different flow conditionsdependent on the influenceof the tailwaterlevel. For low tailwaterlevels, the dischargeis determinedby the upstreamhead. Thiswas referredto as free-flowby Kindsvaterbut usingweir terminologyis now more frequentlyreferred to as modularflow. At high tailwaterlevels, the dischargeis also influencedby the tailwaterlevel. This was refenedto as submergedby Kindsvaterbut the normalweir terminology would now be drowned. ln the case of flow over of embankmentsthe more severeconditions generally occur during modular flow. Dependingon the natureof the landwardconditions and the rate of rise of the river, it is likely thatdrowned conditionswillonly occurfollowing a prolonged period of modular flow. For this study attentionhas, therefore,been restrictedto the case of modularflow. The flow over embankmentsbears some similaritiesto flow over a broad- crestedweir. lt followthat the type of parametersinvolved are very similar: theseare: the profileof the weir, the upstreamwater level, and if the flow is non-rpdular,the downstreamwater level. 6.3.1 Modulanflowdischargeequation Both theoreticalconsiderations of the flow of an idealfluid and compadsons with other weir equationsleads one to the considerationof a discharge equationof the form: Q = CH32 whereq is the dischargeper unitlength and H is the upstreamhead relative to the crestof the embankment.Kindsvater showed thal, for a rangeof heads, the coefficientC had a value of approximately3.0 when q and H were expressedin imperialunits. lt is this equationthat has been used in the SR 384 10ro.Y95 tr subsequentanalysis. Thus the dischargeover the embankmentis dependent on the upstreamhead. In the contextof an en$ankmentthis is the waterlevel on the river or seawardside. For an estuarialor sea embankment,the occurrenceof flow over the embankmentis unlikelyto affect the upstream head. For a river embankment,however, the spillage of water over an embankmentmay influencethe waterlevel. This may leadto a changein the upstreamhead alongthe lengthof the embankment.ln these situationsthe embankmentwill act as a side-weir.For the analysisof such casesreference shouldbe madeto standardhydraulics text bookssuch as Chow (1959). 6.3.2 Flow on landwardface of embankment For modularflowtheunit discharge is determinedby the upstreamhead. The velocityand depth of flow on the landwardside is then determinedby the slope of the embankment and the roughness of the surface. For embankmentscovered with vegetationthe roughnessis determinedby the hydraulicroughness of the vegetation. The CIRIA study of the use of vegetationin civil engineeringprovides informationon the relationshipbetween the hydraulicroughness of vegetation, as expressedby the Manningsn value,and the productof the velocityand depthVR. Differentrelationships are givenfor differentvegetation lengths, see Figure6.1. Fora givenvegetation length this provides an equationlinking the n value with the velocityand hydraulicradius. The further one progressesdown the embankmentthe closer will the flow approximateto normalflow.This can then be usedas a methodof estimating the flow characteristics.The assumptionof normalflowprovides an equation linkingthe velocity,hydraulic radius, slope and roughness. 6.4 Acceptabledegree of overtopping The questionfor normalflow togetherwith the dischargeequation for the embankmentcan be solved to give the conespondingvalue for the flow velocity. The flow velocitiesthat are deriveddepend upon the upstreamhead of water relativeto the embankmentand the slopeof the embankment.The velocitiescan then be comparedwhh the informationon the velocitiesthat can be withstoodby vegetationthat were discussedabove. 6.4.1 Avoidingsupercritical flow on the downstreamface lf supercriticalflow occurson the downstreamface then at or nearthe base of the embankmentan hydrauliciump is likelyto form. This will subiectthe embankmentto highshear stresses and couldcause severe erosion. We will nowderive the conditionsnecessary to preventsupercdtical flow occurringon the downstreamface. We willassumethat: (a) The overtoppingdischarge is givenby. Q=Ch32 (6.1) (b) Sufficientlyfar down the embankmentthe flow approximatesto normal flow. The conditionthat the flow is sub-criticalis thatthe Froudenumber is lessthan 1, thatis, 22 sR 384 t0v04/95 tr V2 . gd. (6.2) Equation(6.1) irplies that vd = C h32. Assumption(b) impliesthat d2tsSo'S, v = n So that Equation(6.3) becomes dzsso'sd=Ch3p n ot, o =[" n%]"u. I so'' ) From Equation(6.3) we havethat 'Jt" c x3t2 v="i =chi*( = C2lsh3/5s3/10. "* [c rr3/2nj n3/5 The inequality(6.2) becomes (\2 v, =[ c h,toI . oo- = o-tso.s [" n:'='"1"', I d ) ) thatis, [gzrs6srsgsno')2 |,c r,ron)t'u f ...... ,,.- | 2 d-[s0.. r- | I nsrs ) ) thusto ensuresub-criticalflow 63/10. 9 ng/s c 1/5s3/10 tr This conditiongives, for a specifieddownstream slope S, the limit on the overtoppingdepth h beforesuper cdticalflow occurs. 6.5 Developmentof a breachin an embankment There is little available informationon the way in which a breach in an embankmentdevelops. As the dischargeover an embankmentincreases the flow velocityincreases and it may reacha point at which the flow beginsto erode the embankment. Normallythis first happens locally. As erosion increasesthe size of the breachand lowersthe crest levels,the discharge increases.The rateof erosioncan be largeand the increasein the sizeof the breachcan be rapid. lf the tailwaterlevel rises or the upstreamlevel falls then the erosionrate will graduallyreduce untilthe flow velocityis unableto erode any fuflher material. Once the breachhas developedso that it is a substantialproportion of the heightof the embankmentthen the highestflow velocitiesoccur immedialely downstreamof the breach. The scourin this area may be substantial. There are limited observationson the width developmentof breaches (Marsland,1984 and CUR, 1990). These demonstratethat breach developmentis most rapid initiallyand graduallyreduces in time, see Figure 6.3. The ultirnatewidth of the gap mustdepend upon upstreamwater levels, the inundatedarea and the compositionof the embankment,but as yet there is no reliablemethod for estimatingthe breachwidth. ln Section6.1 the differencesbetween flow over embankmentin the riverand coastalsituations was discussed. lt is likelythat these differenceswillalso atfectthe developmentof a breach. As a breachdevelops in a river flood embankmentthen the flowthrough the breachwill reducethe riverlevel and so actto inhibitthe breachdevelopment. In a coastalsituation, the upstream waterlevel is frequentlyimposed by the tidal leveland will not be affectedby theflow through the breach.In this situation there are fewer conslraints on the breachdevelopment. ln the shortterm the developmentof a breachis likely to be the samefor bothsituations but the longterm development of the breach is likelyto be very differentbetween the two cases. 6.6 Probabilisticapproach to flow over embankmentsand damages For any embankmentthere is alwaysthe riskthat it will fail. Oneof the rnodes of embankmentfailure is overtoppingand so the riskof ovedoppingshould be considered. An importantdecision that a designer has to take is the appropriateheight of the crest of the embankment. In the past this has frequentlybeen basedon the flood levelswith a specifiedreturn period, with an appropriateallowance for free-board. Though the selection of the appropriateretum period has normallybeen basedon the natureof the area to be protectedil is rare that detailed calculationsare performedof the damagecosts associatedwith overtopping. lf these are carriedout then a sounderbasis for the economicsof the constructionof a flood embankment can be obtained. Such an approachhas been developedand describedin 'Probabilisticdesign of flood defences' which was written by the Dutch Technicaladvisory committee on waterdefences CUR(1990). This section is looselybased on this work. The approachis basedon: 24 SR 384 lU0/Y95 E (a) estimatingthe probabilityof a givenlevelof overtopping (b) for the specifiedlevel estirnatingthe volumeof waterthat overtops (c) convertingthe givenvolume of water into a depthof flooding (d) for the givendepth of floodingdetermining damage costs (e) integratedarnage costs with originalprobabilities to give overallrisk of darnagedue to overtopping The marginalcost of incrementingthe height of the embankmentcan be comparedwith the resultingreduction in damages. As a resultit is possible to determinethe optimume@nomic height of the embankment.lt must be realisedthat such an economb analysisrnay not take into accountall the factorc that rnay affect the degree of protectionotfered. In this sectionattention is restrictedto the risk of overtopping.The method can, however,be extendedto includeother possiblefailure mechanisms. Thusthe probabilityof breachingcan be includedin this typeof analysis. Foreach water level, there is a conditbnalprobability that the embankmentwill breach,which rnay be determinedby, for example,probabilistic slope stability analysis.The breachwilllead to a cefiaindamage cost. Thiscan be included in the riskanalysis by multiplyinglhe waterlevelfrequency with the conditional breachprobability, and integratingthe probabilitieswith cost as above. This is the approachbeing recommended by HR Wallingfordfor use by the NRA. (RiskAssessment for Sea and TidalDefence Schemes, NRA R & D Contract co6/45e). 6.6.1 Probabilityof overtopping The embankmentwill be ovedoppedwhen the water leve! exceeds the embankmentlevel. The probabilityof ovedoppingcan be consideredby assessingthe probabilitydishibutions for the water level and embankment heights. We can definethe functionZ by - - Z=ha- Sv Sp 4, whereh" is the constructionheight of the embankment,Su is the waterlevel, So is the uncertaintyin the water level and Z1 representsthe effect of settlementof the embankment. The probabilityof ovedopping is then equivalentto the probabilitythat Z is lessthen zero. To assessthis probability one musteslimate the probabilityof a givenwater level. Withinthe contextof the UK, the methodsdescribed in the FloodStudies Report can be usedto determineflood hydrographswith a rangeof returnperiods. The outputfrom such an analysisis normallyin terms of dischargebut hydrauliccalculations can be carriedout to determineconesponding water levels. lf consideration is only being given to one point then these calculationswill be relatively straightforward. lf a long reachof a river is beingstudied then recoursewill have to be madeto a numericalmodel. Whichevermethod is adopted,the calculationswill provide the water levels on the channel side of the embankmentduring the flood event. 6.6.2 Volumeof overtopping lf the waterlevels exceed the specifiedembankment height then overtopping will take place. The dischargeover the embankmentfor a given upstream water level can be determinedby regardingthe embankmentas actingas a weir. An extensivelaboratory study was canied out by the US Geological sR384 1ryO4l95 E Survey on the discharge characteristicsof embankmentshaped weirs (Kindsvater,1964). lf the dischargeover the embankmentis substantialthen the impacton the riverdischarge should be considered.These calculations can usuallybe carriedout by hand. lf a numericalmodel is being used to determinethe river levelsthen it is likelythat the same modelcould be used to determinethe overtoppingdischarge. By summingover the hydrographthe total volumeof waterthat overtopsthe embanlfirentcan then be determined. By carryingout this calculationfor a range of hydrographsthe overtoppingvolume associatedwith given return periodscan be determined. lf substantialovertopping occurs then considerationshould be given to the impac'ton the embankment.The downstreamface may be erodedleading to erosion of the crest and possibly even to partial or total failure of the embankment.In thesecircumstances the totalvolumepassing through the embankmentmay increase substantially. Once a breach occurs in an embankmentthen scour can leadto a rapidincrease in the size of the breach. In time the headlossacross the embankmentwill reduceand erosionwill cease. The rate of increaseof the breachand the ultimatesize of the breach willdepend uponthe hydraulicconditions both upstreamand downstreamof the breachand the compositionof the embankmentand sub-soil. 6.6.3 Conveftingthe volumeof overtoppinginto a depth of flooding Once water has overtoppedan embankmentthen its ultimatefate depends uponthe localtopographybehind the embankment.The watermay iust pond immediatelybehind the embankmentor it may flow a considerabledistance. In some cases it may even return to the river further downstream. The assessmentof the fate of such watercan only be basedon a localinspection of the area. In the followinganalysis it will be assumedthat the water will pond in a known area and that for this area it is possibleto determinea relationshipbetween depth and volume. Thus for a given volume of overtoppingthe correspondingdepth of floodingcould be determined. 6.6.4 Determinationof the damagecosfs Damagesdue to floodingare normallyrelated to the depthof floodingand in some casesto the velocityof flow. The amountof darnageis relatedto: (1) the depthand durationof inundationand the qualityof the water, (2\ the characteristicsof the floodedarea in termsof size and nature. CIher factorsrnay be importantin certaincircumstances such as the availability of reliableflood warning. Muchwork has beendone on the assessmentof damagesrelated to flooding, see for example Penning-Rowselland Chatterton (1977) and Parkeret al (1986). Theseworks providemethods to assigndamages to differentdepths of flooding. sR 384 10r0iv95 tr 5.7 Assessmentprocedure There is alwaysa riskthat any flood embankmentwill be oveilopped. There is a further,smaller dsk that the degree of oveiloppingwill be sufficientto cause erosionof the downstreamface of the embankment.To assessthe conditionsunder which erosion could take placeone mustknow the following: (1) the crestheight of the er$ankment, (2) the downstreamslope of the embankment, (3) the natureof the vegetationcover on the embankment, (4) the floodlevels and durations for differentreturn periods. The information given abovecan be usedto assessthe risk of overtoppingresulting in darnageto the embankment: (a) the natureof the vegetationcan be usedto selectan appropriatefigure from Figures6.4 to 6.12, (b) for the selectedreturn period the duration is used to determinethe appropriatecurve on the figure, (c) from the crestheight and the flood level,the amountof overtoppingcan be determined.This together with the downstreamslope can be usedto determinewhether damage will occur. Followingthis procedurecurues have been producedwhich indicate the maximumamount of overtoppingrelative to the crest that can be tolerated beforedarnage is likelyto occur,see Figures6.4 to 6.12. Thereare difierent sets of figuresfor poor, mediumand good vegetationcover. In each set of figuresthere are figuresfor shott, mediumand long grass @ver. ln each figure the maximumovertopping head is plottedagainst downstream slope, with differentcurues for differentdurations. 6.7.1 Use of figures For an existingembankment, the qualityand lengthof the grasscover can be usedto selectthe appropriatefigure. lnformationon the durationof floodsat the site can be usedto selectthe appropriatecurue and then the downstream slope can be used to determinethe amount of overtoppingthat can be toleratedbefore damage is likelyto occur. The figurescan also be usedto assessthe designsof embankments. The engineermust be awareof the problemsthat mightarise due to multiple flood events. Accountshould be taken,therefore, of the frequencyof such eventsand the natureof any maintenancework that mightbe carriedout. The abovecalculations cannot take intoaccount the effectof localfeatures on the flow. Any localfeaturesthat couldact to concentratethe flow will reduce the returnperiod at whichdamage may occur. Also any localdamage to the vegetationcover may also leadto prematuredamage. The dependenceof the limitingvelocity on the state of the vegetationcover highlightsthe needto considerthe maintenanceof the vegetationto ensure that it is alwaysin a fit stateto affordthe requireddegree of protection.Both surfacecover and root densitydecline during dormancy which in the UK is unfortunatelywhen the period of greatest erosion risk occurs. Regular 27 SR 384 t0O/V95 N inspectionis normallyrequired and if thereare areasof vegetationfailure then remedialaction should be takenas soon as possible. 6.8 Maintenance During oveilopping the rnain threat lo embanlcnentscomes from local anornaliesand unevennessin the heightof the embankment.Maintenance shouldbe directedat minimisingthese. A rnaintenanceprogramme should be preparedto maintainthe required propertiesof the vegetation.This programme should address the problemsof the establishmentand continuedmanagement of the vegetation. Such managementis usuallyaimed at controllingthe height and density of the swardand as a contributionto this rnanipulatingthe speciesthat are present. Considerationhas to be givento the impactof cutting,grazing and the use of chemicalsand fertilisers. For more informationon this subiectthe readeris directedto Coppinand Richards(1990). Thereis normallya conflictbetween the needto cut vegetationto maintainthe swardand the desireto maximisethe lengthof the vegetationto providethe greatestdegree protection. Howthis conflbt is resolvedwilldepend upon local circumstancesand the risk of varyinglevels of ovedopping. 7 Conclusionsand recommendations Embankmentsare frequentlyused in the UK for flood defenceof coastalor flood plan areas. As a result the UK has an extensivesystem of flood embankments.A surueywas carriedout by questionnaireof the hydraulic performanceof flood embankments.This questionnairewas circulatedto all the regions of the National Rivers ArXhority. The responses to the questionnaireindicated that the problemsassociated with embankmentsare typically: Groundwaterseepage below or throughthe embankment, Flowover embankments, Sudaceerosion resulting from: . flows overtoppingthe embankment, . riverflood flows, . wave action, . operationof sluicesand gates. Massfailure. Landdrainage problems due lo embankmentsand flap gates. Maintenanceand the controlofvegetation. The directionof this researchproject was alteredin the lightof the responses to the questionnairebut it was not possible,within the constraintsof the proiect,to addressall the problemsthat wereidentified. Consideration should be givento whetherfurther research is requiredon thesetopics, pailicularly: (1) Surfaceerosion resulting from: . riverflood flows . wave action . operationof sluicesand gates. 28 SR384 lO0/Y95 tr (2) Massfailure (3) Landdrainage problems due to embankmentsand flap gates (4) Maintenanceand the controlof vegetation Item(4) falls or.rtsidethe experienceof HR but the othertopics would certainly be amenableto fufiherresearch. The responsesto the questionnairesuggest that such researchwould be economicallyjustifiable. A studywas carried out of the problemof seepagebelow a floodembankment. The study showedhow the dimensionlessconstant used by Singhand Stall (1971)to characteriseaquifers couH be modffiedto characterisethe response of the aquiferto a flood cycle. lf t is the pedodof the flood cycle L is the widthof the flood plain or flood berm S is the aquiferstorage coefficient and T is the aquifertransmissivity then r is givenby Tt / SL2 and the aquiferresponse time c is givenby SL2/ T The natureof the responseof the aquiferto the flood eventcan thereforebe characterisedby compadngthe aquiferresponse time to the durationof the flood event. t > 10t lf r is of the orderof ten timesthe floodcycle period or morethen ihe groundwaterresponse will be small. x = | lf t. is of the same order as the flood cycle period then the groundwaterresponses may be considerableand are liableto cause problems. c S 0.1t lf r* is of the orderof one tenthof the floodcycle period or lessthen the aquiferwill respondfully to the floodhydrograph right across the valley. Whereit is identifiedthat groundwaterresponse may reducethe effectiveness of an embankment,remedial measures should considered. The factors affectingthe stability of an embanlcnentare discussedand methodsto determinethe stabilityare described. In applyingsuch methods it is normal practice to assume steady pore-water pressures in the embankmentcorresponding to normal water levels in the region of the embankment.Analysis using lransient pore-water pressures obtained during the courseof a flood eventindicates that in these circumstancesthe stability of the embankmentmay be reduced. This explains why failures are sometimesobserved to occur duringthe recessionof the flood. Duringthe flood, pore-waterpressures in the embankmentare raised and during the recessionthese are not dissipatedas quicklyas the flood level falls. The transientpore-water pressures act to reducethe stabilityof the embankment. The presentreport indicates that methodsof lransientgroundwater flow and 29 sR 384 iCY0/Y95 tr stability analysis can be used to predict this reduced stability. lt is recommendedthat such a transientanalysis is caniedout whendesigning or assessingembankments so that failuredue to transientpore-water pressure effectsmay be avoidedin the future. Embankmentsare sometimesused to protectagainst floods with relatively modestreturn periods. In these casesthe ovedoppingof such embankment is not unusual. In thesecircumstances the embankmentshould be designed to withstandovertopping. In this repoil previouswork on the abilityof grassto withstandflow and the hydrauliccharacteristics of flow over embankmentshas been put togetherto providecurues which describe the acceptabledegrees of ovedoppingin terms of the embankmentcharactedstics and the conditionof the embankment. Figures6.3 to 6.12 give the acceptabledegrees of overtoppingfor different embankmentgeometries and degreesof vegetationcover. The degreeto whichflow rnaysafely occur over an embankmentdepends upon the nature of the vegetationon the embankment.Thus rnaintenanceof the embankment and the vegetationis impodant. A suitablemaintenance programme should thereforebe prepared. It is also advisableto avoidsupercritical flow developingon the downstream face of the embankment.A conditionis giventhat must be satisfiedto avoid supercriticalflow. Once a breachis createdthere is little informationon the rate at whichthe breachwill develop. The rate at whicha breachdevelops affects the volume and henceextent of floodingthat willoccur in the eventof a failure. Withthe increasinguse of risk analysis in the design of embankmentsthere is increasingemphasis on determining boththe probability and the consequences of a failure. lt is in determiningthe consequencesof failurethat the rate of breachdevelopment is of great impoftance. lt is recommendedthat fuilher researchis carriedout on this topic. ldeallyone wouldcarry out experiments at full scalebut this has manypractical difficulties. lt is likelythat one would have to resodto a combinationof physicalmodel, numerical modelling and materialtestingof the soil propertiesof existingembankments. Such research is necessaryff the risk analysis of river embankmentsis to have any justification. There is alwaysa risk that flow will occurover an embankmentand flooding will result. The design of the embankmentshould take into accountthe probabilityof suchflow andthe damagethat results.A frameworkfor carrying out such an analysisis described. 30 sB 384 &0/V95 tr 8 References 'Slope Anderson,M.G. and Richards,l(.S. (ed.X1987) Stability-Geotechnical Engineeringand Geomorphology'Wiley. Bishop,A.W.(1955). Theuseof theslipcircleinthestabilityanalysisof earth slopes. Geotechnique5, pp 7-17. Brinkgreve,R.B.J. and Bakker,H.L.Q???). Non-linearfinite element analysis of safety factors. Britto,A.M. and Gunn,M.J. (1984. CriticalState soil mechanicsvia finite elements. EllisHorwood Ltd. Britto,A.M. and Gunn,M.J. (1990). CRISP 90. Use/s and Programmers's Guide. Bromhead,E.N. (1986). 'The Stabilityof Slopes'Blackie & Son Ltd. Cedergren,H. R. (1967).'Seepage,Drainageand Flow Nets'Wiley, NewYork. Chow,V.T. (1959). Open-ChannelHydraulics. McGraw-Hill. Cole, J. 1994,Breaching of flood embankments,Program Repoft, O CoppinN.J and Richardsl.G. (1990). Use of vegetationin CivilEngineering. Bufterworths. CUR (1990), Probabilisticdesign of flood defences,Centre for Civil EngineeringResearch and Codes,The Netherlands,Balkema Fellenius,W. (1936)Calculation of the stabilityof earthdams. Trans.2nd Congr.on LargeDams, Washington,4. pp M5-459. HewlettH.W.M, Boorrnan L.A, and Bramley M.E. (1987). Design of relnforced grasswatenvays. GlRlA. Janbu,N, Bjerrum,L, and Kjaemsli,B. (1956). Soil mechanicsapplied to someengineering problems. Norwegian Geotechnique Institute Publication 16. KindsvaterC.A. (1964). DischargeCharacteristics of embankmentshaped weirs. UnitedStates Geological Surueys Water Supply Paper 1617-A. Marsland,A. (1984),Controlled breaching of a fullscaleclay flood bank, Proc IntConf of CaseStudies in GeotechEnging. St Louis,Missouri, USA, 1, p465. Morgan,R.P.C. (1980), Field studies of sedimenttransport by overlandflow. EarthSurface Processes, 5, pp 307-316. Morgenstern,N.R. and Price, V.E. (1965). A numericalmethod for solvingthe equationsof stabilityof generalslip surfaces.Computer Journal 9, pp 388- 393. 31 sR 384 200lg95 tr Naguchi,M. (1989).Hydraulic and HydrologicalProblems in Japan,Nagasaki University,Japan. Nash, D. (198n 'A GomparativeReview of Limit EquilibriumMethods of 'Slope StabilityAnalysis lN Anderson,M.G. and Richards,K.S. (ed.)(l987) Stability- GeotechnicalEngineering and Geomorphology'Wiley. Nutbrown,D.A. and Downing,R.A. (1976)Normal-Mode Analysis of the Structureof BaseflowRecession Curves, Journal of Hydrology,3O, pp 327' 340. ParkerD.J, Green C.H and ThompsonP.M. (1986). UrbanFlood protection benefits: a projectappraisal guide. Penning-RowsellE.C, Chattedon J.B, FarrellS.J, SalvinS.H and WittsH.C. (1977).The benefitsof floodalleviation : A manualof assessmenttechniques. Raudkivi,A.J. and Callander,R.A. (1976). Analysisof GroundwaterFlow. EdwardArnold, London. SkemptonA.W. and DeloryF.A. (1957). Stability of naturalslopesin London Clay. Proc.4thlnt. Con. on SoilMechanics Foundation Engineering, London 2, pp 378-381. Singh,K.P. and Stall,J.B. (1971). Derivationof BaseflowRecession Curves and Parameters,Water ResourcesResearch, 7(2), pp 292-303. Spencer E.E. (1967). A method of the analysis of the stability of embankmentsassuming parallel inter-slice forces. Geotechnique17, pp 11- 26. STABLE.(1992). Programfor the stabilityanalysis of slopes. Mott MacDonaldsoftware. Taylor,D.W. (1948) 'Fundamentals of Soil Mechanics'Wiley, New York. Tezaghi,K. and Peck,R.B. (1967)'Soil Mechanics in EngineeringPractice' Wiley,New York. Watkins,D.C. (1988).Groundwater Flow Beneath Flood Embankments, HydraulicsResearch Repoil No. SR 169. sR 384 t0vqv95 tr Figures SB 384 1CU0.Y95 96/tODt ?8e HS uals^s ,nollJalernpunor6 aql L'earn6lJ sqder6olpfg (p) ,8, lanolJalBir^punoJe - - - ,v, lP lo^gllo^lu - luetrdoleneg luatDluequrf tr 96/!OrOt me US rallnbe;o sed[1 Z'e ornolJ uoprnqro^ou! ocelns ocplns crleoJqd'g Jollnbeu! ocelns culourozord.V (q) ocelns crlEoJLld'E ocelns sulorxozord'v ocBlnsculauozord c (e) aseqrcynby acelns clleolqd 'v acelns crleoJqd '8 acelJnspunoJg ocPIns JolPl papuod 'c tr 6ultsot orerngosu! pasnfulauroa6 lueuquequa lo uolloas-ssoJC 1'9alnEgg <- wt'l ------> tr s6/!oot rae us &lllqelsluauluequa uo ornssard e.lodgo lcedu! orll bultsel ul pasn sacepnscploruozald 7'g arn613 sessedpoop se silel puueqc u! p al lepAA v Weu\ueque p do1seqceet puueqc u! p^al JopltA e 6utsupuuetlc u! l€leAA a puueqcu! leleM oN t luourluequraur asPlns cyleuozeldpue lauuer.lc ul le^olrole6 r_-__.-_il __r_ -'\r-\ '\'=r \ -'-.. .*o:.\. luauluBquS .\ -e tr 'SCSS1 (tSOl rage)selrobalec acueprelorsnoyel rol sprernssser6 lo ocuelslsarleuollclrl l'9 ern6;g Retardancecoefficient, n -i" Lr ; ir. 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E 6 VO )A tl - I o I vo\ - la YX tl t) - lb' t I E G p tl LA -e. tr Appendices tr AppendixA Returnedquestionnaires sR 384 l€v0ly95 -6 [u wua RfCtriV:n f 25 APR1e90 tilvERSA'r:il HYDFii!Liq5"FgWH @ NRA 23 April 1990 N ation aI Riaers Aut hority Anglian Region I C Meadowcroft, Esq Hydraulics Research timited Wallingford 0xon OX1O 8BA Our Ref: AIIB/LS/RC/29 Your Ref: Dear Mr Meadowcroft I refer to clive Magon'g letter to you dated 28 March 1gg0. I am now returning a set of completed proforma, which relate primarily to our Eaetern Area. Yours sincerely f-. Sgcrrcrl dndrew Hunter-Blair rr Regional Co-ordina[or DR.KEVIN EOND RegionolGenerol Monoger King[isherHouse GoldhoyWoy 0rlonGoldhoy Pelerborough Pt2ozR Tel,0/33 37181 I fox:0733 231840 QUESTIONNAIREOII IERSORI{ANC8Or EUBAIf,O{EXT8 Le/02t90 shectuo El f,am of enbanknent sch€ne : location of enbenknent : Rlver Bure at Runham, Nr Great yarnouth tlature of problen : Seepage and instability of toe piling Details of problera : Reoedigl action taken or considered necessary Ad-hoc repalrs !o seepage boreholes and emergency repairs steel piling. to collapsed Person to contact ghould nore infornation be regrired : lrane...JgttT.4fh- -- -'didt;ic'i .- hhg'i"L'e"""''' o" ..' o' Tel llo . . .(.0.6.0.3J..6.63999...... r .. Addresg . Ig.tlgt?l.BlygE"..Agtbgt{lr.. o. o... o.. . 79 Thorpe Road a a a a a a a al a a a o a a a a a a a a a t a a a a a a a a r . a a a o a .yg$ylgE.ryBl.try{...... ,. a o a a a a a a a a a a a o a a o ta a a a a a a a a a a a t a, a a a a a QUESTToNNATRE0I PEREoRilAXCEog EUE XXUEInS 19t0u9a lihect ro El llrm of enbanknent sch@ : North Breydon flood defences. Locatlon of enbanknent : North Breydon, Great yarnouth lfature of problen : Poor water pressure problens leading to liquifactlon. Details of problen : Renedial rction taken or considered necessary Restoratlon of semi-permeable revetment armouring. Person to contact shourdoore inforraation be reqrrired : NED€' ' ' ' :Igtt*'49b ' ' ' ...... Tel lto . . . .(.0.6.0.3J..6f3999. . . - District Engineer ...... Address Aurhoritv -..4 - Jlr!+gpgl-Blvers. a a a t a a a a a a . a a a t. iii-rii/o a o a a. a a a a a . . J9.Tlrgrge.+gEq...... !..... NORI.TICH aa a a a a a a a a a a a o aaaaoaaa a aa a a a a aa.a a a a aa NRI IEI{ o a a a a a a a a a a a a a a a a a aa a a a a a a a a a aa. a a a a a a lrR QUESTIoNNAIREoN pERroRllANcE0F EI{BA}IK}TENTS Le/02/90 - , : sheetuo E Name of enbanknent schene : Location of enbanknent : rightlingsea Railway Embankment, Colne Estuary Nature of problern : erneability problems resulting from change of use of structure. lnerability to froutaL attack of revetment armouring. Details of problen : Renedial action taken or considered necessary s Emergency repairs completed after winter ga1es, 1990. Person to contact should more infornation be required : Nane..!f:::rTgTJ"ll Ter No' ...(0.3.26.)..7.1a,g.!...... o - Distri"t E;;i;;;;'"o"'""'o" Address . . . o. .{g!*g*gl .EirfEtq.4rlt4gr.i.rJ. ., . . . . . Bivers House, Threshelfords aa aa aaa aaaoa aaa a a aa a aa a a arr o o-oii ...... 91:il:E: .lET\,..lqqqr.t\ .4o.qd...... ...... {eET{qg r. .{e.1;e.d.op.r..Es.s.€.4 ...... co5 gsE guliJ 1rvJtilAtJLg gll I&&I9JSIANOE OF EI.IBANKMENTS Le/02t90 sheetxo El llane of enbanlqnent schene : Location of enbanknent : Orplands Marsh Wa1l, Bradwell, Blackwater Estuary. Nature of problen : Dessication and fissuring. Details of problen : Date I The problen remains to be tackled and may be insuperable because of difficulties with economic j ustification. Renedial action taken or considered necessery i Problen has yet to be addressed Person to contact should nore infornation be required : -Na.ne. -- -'-. . . -tiist?'r'ct.C.h.ti.s..R.ausden 'nh'grn!'"r.. -- " " " " " Telllo .....(9?f:).1299q:...... Address National Rivers Authoritv a a a a a a a a a o a a a a a a a a a a a a j a a ia-a a , a a a a a a a a . . . .B.Eo.oh.Eo.d. Fg39...... r ...... r . . . . . Chelnsford a a a a a a a a a a a a a a a a a a a a a a a o aa a a a a a ar a a a a a Essex. ,I2 6NZ a a a a a a a a a a a a a o a a aa a aa a a a a a a a a oa a r a a a a a FIECEIVED 30 MAR1990 NRA RiVEI'ISNEPT nnr.; r-in,t,TE$FAASH xvn N a ti on a I Rioers A u th or i t-y 23rd March, 1990 Anglian Region I.C. Meadowcroft Esq., Hydraulies Research Limited, Wallingford, Oxon, ox10 88A., Our Ref: AHB/JCiRC/29 Your Ref: Dear Mr. Meadowcroft, Hydraulics Performa{rce of {}ood. Emban\p"qnts Thank you for your letter of 19th February. I am pleased to:eturn a set of compleied proforma, which relate primarily to our Northern Area. In respect of our Ceniral Area I would commeRt thai we have hundreds of kilometers of embankments which have been investigated over many years by many eonsultants and organisations. These include for example the Middle and South Level Banks of the gelford Riv,er System and the Tidal Embankments of the River Ouse. We feel that such embankments do not require any further recearch at this stage. I will be grateful to be kept informed about the project. Yours sincerely, Clive Mason, Regional Manager (Flood Defence & Operations). PtTtR8UU.0(K RegionolGenerol llonoget (ingfisherliouse GoldhoyWoy 0rtonGoldhoy Peterborough Pt2olR Iel:0i3337l8ll For0733 231840 qutsurt(,NNAtru; ()N Le/92/90 -;,, .,i.:.i ' '?t Nane of enbankment scheme : oL,,qH"L(l-€ f--€V€-S . Location of enbanknent : 6,r(nil.t, Lol € (l*-rwtl uge f^rftK4{aa'4 LoYe Nature of problen : Details of problen I Date I &Xt L wtru/./b4 "L Ub.d , W ,l k" ur-"k; W La'4 u' J*' L Qt"* k L *b-"t 4 l-']"'rr ct Renedial action taken or considered necessary : Person to contact should more information be required : n r, .6q-L o(flu'V,+S{ t Namg.. r.?..'.:...... o...... oo o.... TgI No o aa a a a a a a a o a a o a a a a a a a a a aaa a a Address a a a a o a a a a a a o a a a a a a a a a a a a a a a a a a.a a a a a a a a aaaaoaa aaaaaa a aa aaaaaa a a a a aa a a a a aa a a a a a a a a a a a a a a a a a o a a a a a o a o a o a a a a HR QUESTIQNNAIREO}I PERFORI'IANC8OF EI,I8ANK}{ENTS L9/02/90 Sheetxo I Name of embankment scheme : Steeping River Revetment Scheme Location of embanknent : Downstream of Wainfleet. Lincolnshire Nature of problen : The river is retained for water resource reasons during the summer and lowered for the winter. Erosion occurred on the unvegetated faces. Details of problen : Date : t978 Wind/wave action and weathering/frost action caused erosion endangering the stability of the embankments. Renedial action taken or considered necessary : Where the batters of the banks were not too steep, revetment was provided in the form of frost resistant stone toe and bank protection laid on a filter sheet. On steeper sections, stone filled box gabions were provided. Person to contact should nore information be required : n"t:. . . |il. L"i}'.f.of ...... o...... o. ret No l}f .ggsb:lT'glgl.(.0:.019?l.8.1.% Address Guy Gibson Hoqse o a a o a a a a a a a a a a a a a a a i a a o a a a a a a aa a a a a a a a Manbv Park a a a o a a a a a a o r o'o o a a a a a a a a a a a a a o a a a a a a a a a Louth a aa a a a ao a a a a at a a a a aa a a a aa a a a aaa a a a a a a a Lincs aaa a aa aa a a a a a a a a a a aa a o a a a a o aa aa a r a a a a a 0N .HR QUESTIQNNAIRE PERSoRMANCEOF EIIBAIIKMENTS L9/02/9A Sheetuo E Nane of embankment scheme 3 River Freshney Location of enbanl Right Bank Upstream of Railway Line, Grimsby Nature of problem : Seepageoccurred during periods of high flow. Details of problen : Date : I 989 Material comprising embankment largely silt and vulnerable to attack by burrowing vermin. Remedial action taken or considered necessary s Bank sealed with clav. Person to contact should nore infonnation be reguired : trema M Pettifor l. alEgg a a a a a a a a a a a a a a a a a a a a a a a a a a a a t a a a a a Te1 tto .s.tj..9,o..]...titlqto,lt !95.0.7.?. 1 ?? AGOreSg Guy Gibson Hopse aaaa a aaaa a a a a aa a a a aa a a aaaa a aa aaaaoa a a a Manby Park a a a a a o a a o a a a a a a aa a aa a a a a a a a a a oa a a a a a a a Louth aaaaa aaaaaaaaaaaaoaaaaaaaoaaaaaaa Lincs aoaa a a aa a a a a a aa aa a a a o a a aoa a a aaa a a a a o a o tiR QUESTIQNNAIRE0N pERrORllANCEOF EIIBANKIIENTS L9/02/90 iJ'e'' Sheet No Narne of embanl River Ancholme Improvement Scheme Location of embanlsoent : South Ferriby to Brandy Wharf - South Humberside/NorthLincolnshire Nature of problen I Seepage occurs during flood conditions and in l98l breaches occurred due to combination of seepage and overtopping. Erosion is also a problem. Details of problen I Date : Current The bank material is variable but generally a light silty soil susceptible to seepage which is made worse by burrowing animals and entails frequent control of vermin. The channel is a navigation and subject to variation in retention level summer/winter. Unvegetated faces between these levels is subiect to weathering/frost damage/wave attack and erosion by wash from boats. Rernedial action taken or considered necessary ! Works planned include the reprofiling of the embankments to improve standard and stability, the insertion of a butyl membrane (vertical) to combat seepage and toe protection consisting of timber toe revetment' filter sheet and backfill to combat erosion. Person to contact should more information be regrrired : n"r:...Y.lgltilgr...... o TerNo .slf .9gsh:lrl'.8i9?.(.0.59!??)..8.10.2. Address Guy Gibson Houpe o a a o a r a a a a a a a a a o a a a a aa a a a a a a Manbv Park a aa a a a a aa a a a a a a a a a aa a a a a a a a a a a a a a a a o a a Louth aa a a a a oa a a a a o a a a a a a a a ao a a a a a a aa a a a a a a a Lincs a a a a a a a a a a a o a a a a a a a a o a a a a a o o a aa a a a a a a a ttl( qUESTTQNNATRE . 0N PERTORUANCE0F EUEAIIKI{ENTS L9/02/eA sheetuo fl Narneof embankment schene ! Vitham Haven Stoning Schemes Location of embanlnuent : Tidal Embankments of the Haven Downstream of Boston Nature of problen : Erosion and slipping of the tidal river banks. Details of problen : Date : Continuous The tidal outfall of the River Witham is also a busy navigable channel serving Boston Docks. Erosion and slipping is caused by weathering, the wash from cargo vessels and high velocity during flood flows. Remedial action taken or considered necessary : A variety of methods have been employed including gabion mattresses, placing of stone on filter sheets and the laying of interlocking panel revetment. Person to contact should more information be required : n"r:...Y.Y.1i1".Y...... ,...... TelNo .lix:tL!0.5.12.).:l?|qq...... Address Aqua House . aa a a a a a aa a aaa a oa a aa aaaaa aaa a a a Harvey Street a a a a a a a a a a a a a a a a a a a a aa a a a a aa a Lincoln a aa a aa a a a a a a a a a a a a a a o a a i a a a a o oa a oa a a a a LNI ITF a a aa a a a a a a a a a a a a a a a a aa a aaaa aa a a a a a NK qulDrrvNNArK!; 9N ftsliguKr.tANcE oF E}{BA}IK}1ENT5 L9tszt9{) Sheetuo I Narne of embankment scher[e i River l[itham - Greetwell to Fiskerton Location of embanlsinent : Downstream of Lincoln Nature of problen : Erosion of the berm on the riverside of the embankment endangered the stability of the embankments in periods of high flows. Details of problen : Date : 1989 The River Witham is an embanked channel, a navigable river, protecting very large areas of grade I and 2 arable land. The banks are generally of light silty soil and are afforded protection by the berm. The berm was eroded by a combination of waterbourne traffic, grazing stock and weathering/frost damage/wave action. Reruedial action taken or considered necessary : Berm revetment provided by installation of Enkomatt supported by timber piles driven along the edge of berm and backfilled with dredged material. Top edge of berm also given protection after settlement. Person to contact should more information be required r r?--- M Whilev AAIIlg...... r . . i . . r . ! ...... Tel No .fii:*1.!0i.?.:1.3.1.0.0...... Address Aqua House , a a a a aa a a o a a a a a a a a a a o a a a a o a a a a a a o a a a a a a Harvey Street a aa a a a a aa a a a a aa a a a a a a o o a a a a a a aa a a a a a a a Lincoln aaa a a a a a a a a a a a a a a a a a o a a a a a a a a aa a a a a o a a LNI ITF o a a a a o a a a a a a a a a a a a a a a o a a a a r a a aa a a a a o a a HR QUESTIQNNAIRE0N pERFoRl'tANc808 EI.IEA}IKUENTS L9t02/90 Sheetuo E Nane of embanlcmentscherne : River Vitham - Kirkstead to Tattershall Location of embankment : Both Banks of the Witham near Woodhall Spa, Lincs Nature of problem : Erosion of the berm on the riverside of the embankments endangered the stability of the embankment in periods of high flows. Details of problen : Date : 1978 The River Witham is an embanked channel, a navigable river, protecting large areas of Grade I and 2 land. The banks are generally of light silty soil and are afforded protection by the berm. The berm was eroded by a combination of weathering/wave action and boat wash particularly in the unvegetated zone between summer and winter retention levels. Renedial action taken or considered necessary ! Berm protection was provided by placing frost resistant limestone on a filter sheet to rebuild the toe. Person to contact should more information be required : Name....l{.Ybtlgy...... ,...... Tel uo .L!t]9o.1!.10.5??.21?1.90.. Address Aqua House . aa aaoa a a aa o a a aa.a aa.a a aa a aa aaaaaa aa a a a Harvey Street a a a o a a a o a a a a a a a a o a a a o o a a a a a a a aa a a a a a a o Lincoln ..a.. .aaaa.o..o.aa.aaaa.l LNI ITF a a a a a a a a a a a a a a a a a a a a a a a o a a o o a aa a a a a a a a HR qUESTIQNNATRE0N PERFORMANCE08 El,tEAliKllENTS L9/02/90 Sheetuo E Narne of embankment scheme : South Forty Foot Drain Location of embankrnent : Upstream of Boston, Lincs Nature of problen : Erosion of the berm on the riverside of the embankments is endangering their stability and causing access problems. Details of problen : Date : t99l Soils are light Grade I fenland silts and the berms are susceptible to erosion by weathering and wave/wind attack. Renedial action taken or considered necessary : Revetment (form yet to be decided) to be provided after reinstatement of the berm. Person to contact should more information be regrrired : n-r tr- Lincoln (0522) 513100 n"t:....l{.Ylllgy...... l€ll llO ...... o..o.o... Address Aqua House . a a a a a a a a a a a a a a a a a a o a o a a a a a a a a aa a a a a a a a Harvey Street aa a a a a aa a a a a o a a a a a t a a a a aa a a a a a a o a a o a a a Lincoln a a a a a a a aa a a a a a a a a a a a a a a a a a a a a a a o a a a o a a LNI ITF aaoa a a aa a a a a a a a aaa a ao a a a a a a aa aa a a a a o a a HR qUESTIQNNAIRE0N PERFORI.IANCE0F EMBAIiKMENTS L9/02/90 Sheetuo I Nane of enbanl Kyme Eau Location of embanknent : Upstream and Downstream of South Kyme, Lincs Nature of problen : Seepage occurs during periods of flood flow. Details of problen : The embankments are founded on silt and peat which permits seepage during high flows. Remedial action taken or considered necessary : Seepage remedial works yet to be decided possibly in the form of a membrane inserted in the bank. Person to contact should more information be reguired : n"r:...1{.Y!tIgY...... o. o r ...... TerNo .fi19oJl.(0.5.?. Address Aqua House , a a a a a a aa aaa a a aaaa a aa aaa a aa a a a Harvev Street a a a a a a a a aa o a a o a a a a a a a a a Lincoln a_a a a a a a a e a a a a a a a a o a a o a a a a o a a a a a a a a a a a a LNI ITF a a aa ao a a a a a a a aa o a a aa a a a a aa a aoaa a a o a a a a HR QUESTIQNNAIRE0N PERFORIjANCE08 EHBAIIKI{ENTS L9/02/90 sheetuo fl Narneof embanl Branston Delph Bank Improvement Location of enbankrnent : East of Lincoln (Tributarv of the River Witham) Nature of problen : The banks are on a deep peat area and susceptible to seepage at high water levels. Details of problen : Date 1994 An embanked channel serving as a highland carrier across the fen between the River Witham and higher land to the south west, it is therefore dependent on levels in the River Witham for discharge and high water levels are retained for long periods in storm events. Renedial action taken or eonsidered necessary : The banks have been clayed in the past but a more reliable system is required to prevent or significantly reduce seepage. Person to contact should more infonnation be reguired : M Whiley Lincoln (0522)5l 3100 Nane. Tel No a a a a a a a a o a a a a a a a a aa a a Address Aqua House . oaaa aa a aaa a a o a a aa a aa aa aaaaa aa aaa aoa a a a Harvey Street o aa a a a a a a a a a o a a a a a a a a o o a a a a a a a a a a a a a a a Lincoln a a a a aa aa a a a a a a a a a a a a a a aa a a a a a a a a a a a a a a LNI ITF a a a a a a a a a a a a a a a a aa a a a a a aaa a a aaaoa a a o a a ni( qijEsl'j,ONiiAii(E 0N PEE.IOri{A}lCE 0l' EyrtsA.}i.G'1lN'IS 19/02/90 Sheetxo I Nameof embankmentscherne T]DAL WELLAND Location of embanbnent : FROM WASH OUTFALL TO SPALDING Nature of problern : EROSION OF BERM AND BANKS DUE TO TIDAL AND SHIPPING ACTION Details of problen : THE TIDAL CHANNEL IS ARTIFICIAL AND RUNS THROUGHSILT SOILS SUSCEPTIBLE TO EROSION. PAST PROTECTIONHAS BEEN AFFORDEDBY TRADIT]ONAL THORN FAGGOTS. THESE ARE NOW COMING TO THE END OF THEIR USEFUL LIVES AND RE- SULTING IN AN INCREASE IN LOSS OF BERM AND BANK. Renedial action taken or considered necessary 3 REINSTATEMENTOF BERM AND BANK W]TH PROTECTTONNOW GIVEN BY RANDOM PITCHED STONEBATTER AND BANK. Person to contact should nore infornation be required I lJarne...J.'. .U.L.Y.AIL.. oo . o... o...... Tel No pB+l,plN9.tA771I .ZQ?],??... o. Address STEPPING STONE WALK a a r a a a a a a a a a o a aa a a a a a aa a a r a a a a a r a aao a a ...... l'tll\FFF.Y. AyFJ.{.UF.. . o. . . . . o o .. o r o . . . o.....SRAIDfAIG.o...... o o... o r. . . . o. . .LI.ryC.O.L.NF.HJ.R.E.. r...... i:rt PEii!0zu'fi.itcE0F ElitsA\iolirN,Is 19/ a2/90 Sheetuo E Narneof embanlment scheme TIDAL NENE Location of embanknent : WASH TO FOUL ANCHOR Nature of problern : EROSION OF BERM AND BANKS DUE TO TIDAL AND SHIPPING ACTION Details of problen : Date : tg88 THE TIDAL CHANNEL IS ART]FIC]AL AND RUNS THROUGHS]LT SOILS SUSCEPTIBLE TO EROSION. PAST PROTECTIONHAS BEEN AFFORDEDBY TRADITIONAL THORN FAGGOTS. THESE ARE NOWCOMING TO THE END OF THEIR USEFUL LIVES AND RE- SULT]NG IN AN INCREASE IN LOSS OF BERM AND BANK. Remedial action taken or considered necessary 3 REINSTATEMENTOF BERM AND BANK WITH PROTECTIONNOW G]VEN BY RANDOM PITCHED STONE BATTER AND BANK. Person to contact should nore information be required : Nang..J.o.H.\ .U.L.Y$ILo. o o . r o o . o.. ... TelNo . ?l+!?1ry9 .10.77,7),,?,24r.??. ... . Address STEPPING STONE WALK o a a a a a a a a a o o a a a a a a a a a a a a r a a a a ar a t a a o o a WINFREY AVENUE o a a a a a a a o a a a a o a a r a a a a a aaa a a a a ao, a a a, a, .. o...SBAT-DTJW r. o..... r.o. o.... r.r.... LINCOLNSHIRE a a o a a a a a a a a a a a a a aa a a a a oaa o a a a a a a a aa a a a ili, QUES'JIONjiAI]iE0N PitRf ORifillcE 0i' E1{BA}-jCI1INTS L9/42/90 Sheet No Narne of embankrnent scherne MAXEY CUT Location of embanlonent: BETWEENPEAKIRK AND TALLINGTON Nature of problen : EROSION OF FLOOD BANKS Details of problen : Date : 1985 THE BED OF THE MAXEY CUT FALLS RAP]DLY FROM ITS HEAD AT TALL]NGTON TO ITS OUTFALL ]NTO THE WELLANDAT PEAKIRK. ]TS FUNCTION IS TO ACT AS A FLOOD RELIEF CHANNELTAKING HIGH FLOWS OFF THE MAIN WELLANDCHANNEL. THE BED AND BANKS ARE MADE UP OF GRAVELS AND SANDS AND IN TIMES OF FLOOD LARGE SCOURHOLES WOULDRAPIDLY APPEAR WITHOUT WARNINGTHREATENING THE SAFETY OF THE EMBANKMENT. Renedial action taken or considered necessary ! PROTECTTHE BANKS FROM SCOURBY APPLY]NG AN ENKAMATREVETMENT SYSTEM AND STABILISING THE BED BY ]NSTALLATION OF WEIRS. Person to contact should nore inforrnation be required : Natne..J0HN. ULYATT.. o... oo.....,...... Tel No .SBALDtrIIG.(QZZ5).J12J2A.,.. . a- Address ...... SIEPBING.$TQNE.U/41,K...... t wrnFnny AVENUE a a a a a a o a o a a a a o a a a a a a a o aa o a, a a ar a aa a a, r .. o. o.. FPAI'PJN9..,.,.. o...... I r..... ...... JJNCOLNSHIRE'o.o...... hi( QliEStiOJiliAUG 0N PitiJ0i]/rAil CE 0i' El'rtsA.\X}irNTS t9/ a2/9A Sheetuo E Narneof embankmentscheme DEEP]NG HIGH BANK CRADGEBANK Location of ernbanlsnent: 'RIVER WELLANDU/S OF SPALDING Nature of problero : BANK AND BERM CONS]STS OF SILT MATERIAL SUSCEPTIBLE TO LONG TERM EROSION Details of problem : Date L982 AN ARTIFICIAL CHANNELWAS CUT IN 1950. THE BANKS WEREPROTECTED AT THAT TIME AND S]NCE BY THORNFAGGOTSTO RESIST WAVE ACTION AT NORMAL RETENTIONLEVEL. THE FAGGOTSARE NOWFAILING LEADING TO A LOSS OF BERM W]DTH AND EMBANKMENT. WORKIS ONGOING. Remedial action taken or considered necessary : REINSTATEMENTOF BERM WIDTH AND PROTECTIONOF RIVER FACE USING A VARIETY OF METHODSINCLUDING:- (a) Asbestos Piles (b) Random Pitched Stone (c) Duracem Piles IIU U U99I I IIgD Person to contact should rore infornation be required Nar8e..J.gryry .U.L.Y.AJJ.. r . . . .. oo, ...... , rel No . FP$J.PJII9.!97771.7Q?+??. Address STEPPING STONE a a a a WALK a a a a o a a a a o a a t a a a a a a a a a a a a aa a a o a a a a . o . . . .Wtr,lI4BqY.AVLI\UE . . . o o . . . . . o ...... QDAT NTNIA ur nLUIllu, a o a a a o a a a a a o a a a a a a o a a a oa o a a a a o a o a,a a a o ...... Ic{IIqqL.ryS.H.I.R.q...... oo...... HR QIIESTIONNAIREON PERTORI.TANCEOF E}'BA}IIC.fENTS Le/02/90 sheetNo tr Name of embankrnent scheme : R,$*q["^^-tS-tA trA"r"$,?,r#,t";^^ Location of embankment : Vu 9ro ?=ic> fi, l.jo ?7t Si+ Nature of problem : Details of problern : t?gs, (F\rELluwa Z ;- 1, cL yaroAl (h_un \\ elu< Remedial action taken or considered necessary : Person to contact should ruoreinfornration be required : Name..N--d.eJ,AdI(E Address N.,Il. \, N.eRTK0.r{,gt& u. . R rqraav FtDr)rrJ...t:{,ep.sr ReqsI!:c-..9.sxx-te fostro.r.lr.K [.I ptucA5ttE OPoP Tr7\tE I{R QUESTIoNNAIREON PERFOR}fANCEOF EI.t8A}TKMENTS L9/02/9A Sheet No Narne of embankment scheme : Location of embanknent : \A^f-€cra Nature of problen : 4+{a'@*L-Q;";; o Tjtd" - a- cer.ri,.^^a:-4.^= Details of problem : Renedial action taken or considered necessary : Person to contact should more infornation be required, : relNo o.?L..u3.A2A6...... Address NI.R. A. N setqvxcR-tx. ..Reqoo,i Rtparu.. I&00g.R .,.R-n4a;ur. €86-rme, Qqk&--efl N.st-r,A*fLE .. (JP.Q.N/. .Td"F HR QI'ESTIONNAIREON PERTORMANCEOF EI,IBAI{K}IENTS L9/02/9A sheet No E Narne of embankment scheme : GceaTHn{ Ceeet< Location of embankment : 'TibM- Q(enfr+*a eee€K EretSArsKh4€NT Nature of problem : -Trb€ ?eld€.Ar,os lr{ sTo&vt Cmr\rTrors S Details of problem : Date : -InCouqH Ulnfea- Pe*areRTrr.tQ, Er,\SANrKMeNTs (c"srstaocre\ .1eTAL rtrF:ffi"l) Rasuurrr.rc|ril couuAPs€ &Ppe.'... 4 Jan*u1 lilreer'&r-s Remedial action taken or considered necessary : ?.ePrnc=' B(enc,H ulrrH er-*1 ' Person to contact should more infornation be required i ar- o3aY'.+(o(41 Name....)..S.1L15:.... rerNO .. Anrrtt'rtetrrl Address ilAttooe'q R'nyeCS .. . s-r(.".{:s*!*. ..:. I.S...... SilrPe t-Anse. I .{, ; HR QIIESTIONNAXREO}I PERI.ORMANCEOF EI,I3A}IK}{ENTS L9/02/90 sheet No E Name of enbankment scheme : Newl[,-^ , )lotm. ' l2tver"6et Location of embankrnent: ttlz Ne"rsL^ 0 , Vor^ C)"uol"n& or,l Q,eFfi,oo€ 3Zoi. Nature of problen : See cnC Details of problern : Date : Se. enclosqf rcPort' Renedial action taken or considered necessary See o*Joso Person to contact should nore infornation be required : r{8o84q N.'"3 : SIy.kS: relNo g?tr. Ad'd'ressrJJ,o,ol Qrvers Autto''f)' .tf:r.qhlrs. .5.4\t. ..1q,ip*...l*rs ..0|+gly.ql! /l\rl ..U.qr.ttlX!91r.. Co-turtrn. wwtulr,^4 Ourref FDll/12lPWlSSt fruu*.ttlrP Yourre{ 25 APR1$gU f,i.1'd'ii,'r+$ l-l[N; Oofe23rd April 1990 rNntiiff"di*gn*slt NRA National Riaers Authorilg Ian Meadowcroft Esq North West Region River Engineering Department Ilydraulics Research Wallingford Oxfordshire ox10 8BA Dear Mr Meadowcroft EY-DRATILIC PBRFOR},IANCE OT TLOOD EMBANKIIEII'fS PLease find enclosed a completed questionnaire on the hydrauJ.ic performance of embankment,s in respect of our Northern Area. I understand that my Central and Southern Area Managers have already replied to you directly and this completes the response from the North west Region. Yours sincerely WtA"& DR PETER D WALSH Regional Flood Defence Manager { P.0.Box l2 RichordFoirclough House Knutsford Rood Worringron WA4 Il|G Tel, (0925) 53999 Ielex, 628425 Fox: (0925) 4.l5961 0N .HR QUESTIQNNAIRE PERSoRMANCEOF EIIBAIIKMENTS L9/02/9A Sheetuo E Nane of embankment scheme 3 River Freshney Location of enbanl Right Bank Upstream of Railway Line, Grimsby Nature of problem : Seepageoccurred during periods of high flow. Details of problen : Date : I 989 Material comprising embankment largely silt and vulnerable to attack by burrowing vermin. Remedial action taken or considered necessary s Bank sealed with clav. Person to contact should nore infonnation be reguired : trema M Pettifor l. alEgg a a a a a a a a a a a a a a a a a a a a a a a a a a a a t a a a a a Te1 tto .s.tj..9,o..]...titlqto,lt !95.0.7.?. 1 ?? AGOreSg Guy Gibson Hopse aaaa a aaaa a a a a aa a a a aa a a aaaa a aa aaaaoa a a a Manby Park a a a a a o a a o a a a a a a aa a aa a a a a a a a a a oa a a a a a a a Louth aaaaa aaaaaaaaaaaaoaaaaaaaoaaaaaaa Lincs aoaa a a aa a a a a a aa aa a a a o a a aoa a a aaa a a a a o a o ' E FIPR 98 lBt ?4 TO CHERTSEYH PRGE. EAE 19/02,/90 HRqUE$TrolrHArRs oN PEESORHANCEoF EHBAII/OfiNTS Sheet No Nane of embanknent scherqe MiIIorn Ernbarrkrnent(gEA' DEFENCE) Location of embankment : From I'til1on, North Eaet for 3l(m. Nature of o Details of probl"em:r' Date llarch 199O grass' the embankment is construeted of sand/eilt and protected vitfi The The front face nas origlnally turf,ed and the back face eeeded' grass has been slowly replaoed by moss Remediaiaction taken or considered necessary I be f,olloued bY U Last year, the enbanknent r"as lined end this wllL fertiliser. nris is a Problen with other ernbarrkrnents in South Cumbria. Person go coniect shor.rld lssrs informaiion be reguired : n i\' Nerue.. . .Y. ,Y. .\N.:\s.cr. ret No . . . .qq3:q.69.5.67. Address Beathwaite, . ..,.i,ey.ep.s.r. Cunbria. 'gE 6 fPR lE:85 TO CHERTSEYH PAGE. BS3 |e/02190 HR QTTESTION}IAIREON SERT'ORUINCEOF 8}'3A}{ruENTS sheetxo El Nane of enDenkment schene I of erobanJ HelsLngton PooI Erifue * Low Pool Eridge llature of Structrrral faiLure. o Itlarch L99O Details of problenr ; Date r This embanknent sa,e raised about 10 years ago, Extensive cracke havs occu.med paralleL to the enbankment on bqth faces. Renedial acticn t,akerror considered necessary : o Three nonths ago the cracks trere fil.Ied with the silts similar to the embanlsaent congtructiong and the site is being nonitored for anY firrther movement. j Person Eo cailtect should nore informatien be required (-)t.\ril\ \./ \t \ .-r \\ a^-. 1r_ 05395 60567 Nane..,. .[. r).: .S,:\)*- Tei No Ad Beattruaite, i"'r .....Levens,.. Kenda.l-, Cumbria. LAg SNL. E FFR '39 I E: Z5 TO CHEETSEYH PAGE. gE4 Lei02/90 HR qUES?T0MAIREoli P8R^FORIiANCEOF ElEAliiQ{8NTS sheetNo tr enbar*ment scheme l. River Kent (tidaL eection) adjacent to Sanpool Caravan Parlc Erosion of.rlver bed and lwoer banks adjacent to a flood embankment- o Date ; ,March L99O Details of problen r: Thia section is subject to erosion from freshwatef'flows which are rrndernlning the river bank, whiLst the adjacent fl.ood barrk (tldal) is endangered. It is not possible beeauee of, the proxtrnity of, etatic caravan to move the flood bartk. : Reroediai.eciion taken or considered necessery It Placirrg of large rocks in the bed. : Person to caniec t sirould more iirfornaiicn be required' t\ 60567 Qrr r r \\ O53SS ...... Narne. qr Y ,.. -VJ r\\n-.- ?eI No ". A HR QMSTION}IAIREO}I PERIORI{ANCEO8 E}B${ruENTS 19/02/90 sheet No n Narseof embankment scheme : I{OSSBAND GRETNA Location of enbanlcment : BET!{EENRrVER SARK AND RrVER ESK, APPROX.Ny 330 652 & Ny 335 650. Nature of problen : Erosion of inland face of bank. Details of oroblem : Date Over-topping causing erosion of inland face of bank and conseguent reduction in top width on this grassed bank. Renedial action taken or considered necessary : Backfil ind repair. Raising of bank. Person to contact should nore infornation be required : tlane. . .G.' A. NOONAN Tel No Adciress IIR QUESTIONNAIREON PERE'ORUANCBOF EUEA}IKMEIITS L9/02/90 Sheet No Nane of enbanknent scheme DURRANHILL BECK FLOOD STORAGERESERVOIR Location of enbanlsnent : NORTH OF WARWTCKROAD, CARITSLE - N.G.R. NY 423 562. Nature of problern : Seepage into storage basin reducing its capacity. Details of problen : Date seepage is through underground gravel layers fed by ground water from the River Eden. Reme Cut-off of gravel layers by bentonite or butyl seal. Person to cont,act should more information be required : Narne.. S.'. .A.' NOONAN TeI No Ad Ourrel 556. R/JF./Jv Yourrel R/S/0OL3F' Fi ;j i;: i_ , 0$ ftPR1*{i\j Dole 2nd April, NRA 1-990 Rllifi::' ."i irl.ii i" Aut futr i I f Hydraulics Research Lim National Riuers Y Wallingford, Norlh West Region Oxfordshire, oxLo 8BA Dear Sir, Please find enclosed a completed copy of your embankment perfornance questionnaire which I hope will be of use to you in your current research project. Should you require further information do not hesitate to contact this office. Yours faithfully, ,,\ \ rynryLh^ H. T. DAVIDSON, SENIOR ENGINEER, SOUTH FI,OOD DEFENCE AREA. This matter is being dealt with by Mr. J. Ruckledge. Mirwell'Iorrington Ione Sole M33 5Nt Tel, (061)9732237 F0x: (061) 973 4601 tiR QttEsrroNNArRSON PERI'OF}{A}ICE03 Et{tsANn'IENTS 19/02/90 Sheet No Name of ernbankroent scheme : RIVER MERSEYREHABILITATION SCHEME Location of embankment : BETWEENASHTON WErR (SJ 773 936) AND STOCKPORTE.T.W. (S.l 870 890) Nature of problem : EROSION AND SILT DEPOSITION DURING FLOOD FLOWS Details of problem : Date : BANK EROSION AT FLOODFLOWS. SILT DEPOSITION, CAUSING REDUCTIONIN FLOWCAPACITY OF CHANNEL. Remeiial action taken or considered necessary : REMOVALOF SILT OVERBURDENAND RECONSTRUCTIONOF BANKS. Person to contact should more infornation be required : ., JOHN RUCKLEDGE \,^ 061 973 2237 (Ext. l-68) NaJite. ltv A;,.1-^- - NATIONAL R]VERS AUTHORITY, SOUTHFLOOD DEFENCEAREA, MIRWELL, CARRINGTONLANE, SALE, M33 5NL, UII-BJN-Lt1E . lrui Ourref BFW\LR301\OL Yourrel @ Dofe 26 March 1990 NRA National Ritnrs Au t h or i t Y River Engineering Departmentr North West Regilnt Hydraulics Research Ltd Wallingford oxLo 8BA L fft..f;fiftffi111f;il) For tbe attention of lrtr Ian lleadowcroft 2?MARM I$[}{} Fl\,ri::l g.p.'i1,1q,r.!.rii; Dear Sir H;"i:.1:'. '.";.ii BYDRAULTCPERFORUATCE OF FIOOD EUBENKMENT Further to your letter of the 19 February 1990 to our Regional Flood Defence Manager I attach details of two problems of possible interest vours TLtrrfuLLy WLU / B F WHELAN AREA MANAGER CENTRAL FI'OD DEFENCE lostock11ouse Holme Rood Bomber Bridge Preston PR5 6AI Tel:(0772)39882 tox: (07/2) 627730 HR QUESTIONNAIREON PERFORMA}ICEOF EMBANIC{ENTS 8/A2/90 Sheet No Name of embanlcrnentscheme : SLUICE Et'tsANKlmNT Location of embankrnent BETI'EEN SLUICE & BACK DRAIN SOUTH OF WATER LANE, CROSSENS Nature of problem : SEEPAGE FROM HIGH TEVEL CARRIER TO tOW LEVEL DRAIN, BOTH IN CROSSENS PTJMPEDSYSTEM Details of problem : Date 223/3/9O THE WATERLEVET DTFFERENTIALrS ABOUT2.1M TO 2.4Nt, SEEPAGEIS MONITOREDBY INSPECTION AND WORKSARE TJI{DERTAKENAS NEEDEDTO CONTROLTHE FLOWAND STABITISE THE BATTER Rernedial action taken or considered necessary : OLD METHOD WAS TO SUPPORT SLIPPING EMBANKMENT USING TIII'IBER REVETUENT AND STONE BACKING - SIOW AND COSTLY. CI'RRENT MUCH CHEAPER AND EFFECTTVE METHOD UTILTSES TCI FILTRAM IN A TRENCH PARALLEL TO THE I.INE OF THE EI'tsANKMENT TO INTERCEPT THE SEEPAGE. Person to contact should more information be requi-red : Narne.. . .PTTry++P.lTT$ry Te1 No Address . . . .u4TTqryA+.tsMBS.AVTrlqBlTy LOSTOCK HOUSE HOLME ROAD BAMBER BRIDGE PRESTON PR5 6AE HR QI'ESTIoNNATRE0N PERFoRMANCEOF EMBATKI{ENTS L9/02/gCI sheet No H Name of embankrnent scheme : RIVER DOUGLASTIDAL EI'tsANKI'IENT Location of embankment : NORTH OF 459, BANK HALL BRIDGE, TARLETON Nature of problem : LOSS OF I',IATERIAL FROM LOWER BATTER AND BERM DUE TO SLIPPAGE CREATES A POTENTIAL PROBLEM OF SECURITY OF TIDAL EMBANKMENT Details of problem : Date t23/z/9o V. FINE SILTY MATERIAL HAS LITTLE STRENGTH AND STABILITY WHEN LT'BRICATED. Remedial action taken or considered necessary : FMAVY STONE TOE PITCHING - EXPERIMENTAL LENGTH TO BE UNDERTAKEN IN 1990. Person to contact should more i-nformation be required : Narne.. . ?.T+ry9gry re1No . .o.77?.:.?9gg? Address . . . . tIATIAryAr-,.BMB$.4gTqq4r.Ty LOSTOCK HOUSE HOLME ROAD .BAUBEB.BBIDGE. PRESTON PR5 6AE HR ON PERFORMANCE L9/02/90 QI'ESTIoNNAIRE 'L' r" '".' i.{t.i ,i - i t I lu""' 1*ituiAill it*il sheet uo E Name of embanknent scheme : f.tW(L Ptoz,1> Er,lgAuk_n€:r\fis -fe QltreLS oo9€, ADUfL < A{Lut\y' Location of enbankment : : * x./ewi\a.v€N./ to 'Bx(LLc xG€ - 6'9.rL tho'?-€\,N!-r Ac, $€pfr€\-D I \UU rt\.,, ,\)** - LrTf!€L\\tletoFt -fa Pr:'-?.":f?cizr Nature of problem : Ltt \k- ,t r*-:*\-r-"\ \^\- €€.1xe F*t\c*. 7e\- '.. d rylulfl **aftr -s+s,a -\^"L rA$-.,. b,*1*e-Fh \.- h^\^.* b'"t/ (**t*l .^^-r^ a sAU*-]'r\ & ^-:f-*) 5r*t\r* I Details of problen g .'- 2e'*zr.^ Date avs€ \r.,|^t.e- ^oFt'* $L€qr."+, \zr.*L \v^\*gr. +.Ar- I $.",6 "6r-^h- gr.*t<. h^\^-*- )a.* 199c7 '.1- S-ffie^u<" G*LuL^>* ,*J1g^*) ,$.*.I.n-* , i^J l-o.^^g. .*.^*.,* '*.-.-;5. g,ctU*.' ) **o-.--;€ g*!.\r-t *he Lo*L t" \^'H\'th'"(tt) SylJ Sr-a-<- q.kru4--$*l $o* <-',-* CL^^^J'-\ ^**En) *z{t-V+ ,\-t.*;. r ,\oJ 6*\'\r-' Remedial action taken or considered necessary : ow';E'-': Sxr**\ *'\r. t^\----;:; )#)f:l:- s ,* -\J\,- "i*r*J^v -*,\. \-.*t ^.r.-J f'^,- ^***\b ry '(l) t g^lLr-. f4y! *.,.,f,-.,*L t.,L,.o.^^--' Person to contact should more information be required : Name..Noczr*r..%*:t: rel No \^r(TArl.?LkZ:.1). .*?.691* Address t{flr\ 9.,\tTF\e&-N) fZqteNJ ClV \iegou R-N€ Na'g'>s- C,tl Affgr*'s.Zt\\ QD ttl( qUESTTQNNATRE . 0N PERTORUANCE0F EUEAIIKI{ENTS L9/02/eA sheetuo fl Narneof embankment schene ! Vitham Haven Stoning Schemes Location of embanlnuent : Tidal Embankments of the Haven Downstream of Boston Nature of problen : Erosion and slipping of the tidal river banks. Details of problen : Date : Continuous The tidal outfall of the River Witham is also a busy navigable channel serving Boston Docks. Erosion and slipping is caused by weathering, the wash from cargo vessels and high velocity during flood flows. Remedial action taken or considered necessary : A variety of methods have been employed including gabion mattresses, placing of stone on filter sheets and the laying of interlocking panel revetment. Person to contact should more information be required : n"r:...Y.Y.1i1".Y...... ,...... TelNo .lix:tL!0.5.12.).:l?|qq...... Address Aqua House . aa a a a a a aa a aaa a oa a aa aaaaa aaa a a a Harvey Street a a a a a a a a a a a a a a a a a a a a aa a a a a aa a Lincoln a aa a aa a a a a a a a a a a a a a a o a a i a a a a o oa a oa a a a a LNI ITF a a aa a a a a a a a a a a a a a a a a aa a aaaa aa a a a a a HR qUESTIQNNATRE0N PERFORMANCE08 El,tEAliKllENTS L9/02/90 Sheetuo E Narne of embankment scheme : South Forty Foot Drain Location of embankrnent : Upstream of Boston, Lincs Nature of problen : Erosion of the berm on the riverside of the embankments is endangering their stability and causing access problems. Details of problen : Date : t99l Soils are light Grade I fenland silts and the berms are susceptible to erosion by weathering and wave/wind attack. Renedial action taken or considered necessary : Revetment (form yet to be decided) to be provided after reinstatement of the berm. Person to contact should more information be regrrired : n-r tr- Lincoln (0522) 513100 n"t:....l{.Ylllgy...... l€ll llO ...... o..o.o... Address Aqua House . a a a a a a a a a a a a a a a a a a o a o a a a a a a a a aa a a a a a a a Harvey Street aa a a a a aa a a a a o a a a a a t a a a a aa a a a a a a o a a o a a a Lincoln a a a a a a a aa a a a a a a a a a a a a a a a a a a a a a a o a a a o a a LNI ITF aaoa a a aa a a a a a a a aaa a ao a a a a a a aa aa a a a a o a a ni( qijEsl'j,ONiiAii(E 0N PEE.IOri{A}lCE 0l' EyrtsA.}i.G'1lN'IS 19/02/90 Sheetxo I Nameof embankmentscherne T]DAL WELLAND Location of embanbnent : FROM WASH OUTFALL TO SPALDING Nature of problern : EROSION OF BERM AND BANKS DUE TO TIDAL AND SHIPPING ACTION Details of problen : THE TIDAL CHANNEL IS ARTIFICIAL AND RUNS THROUGHSILT SOILS SUSCEPTIBLE TO EROSION. PAST PROTECTIONHAS BEEN AFFORDEDBY TRADIT]ONAL THORN FAGGOTS. THESE ARE NOW COMING TO THE END OF THEIR USEFUL LIVES AND RE- SULTING IN AN INCREASE IN LOSS OF BERM AND BANK. Renedial action taken or considered necessary 3 REINSTATEMENTOF BERM AND BANK W]TH PROTECTTONNOW GIVEN BY RANDOM PITCHED STONEBATTER AND BANK. Person to contact should nore infornation be required I lJarne...J.'. .U.L.Y.AIL.. oo . o... o...... Tel No pB+l,plN9.tA771I .ZQ?],??... o. Address STEPPING STONE WALK a a r a a a a a a a a a o a aa a a a a a aa a a r a a a a a r a aao a a ...... l'tll\FFF.Y. AyFJ.{.UF.. . o. . . . . o o .. o r o . . . o.....SRAIDfAIG.o...... o o... o r. . . . o. . .LI.ryC.O.L.NF.HJ.R.E.. r...... hi( QliEStiOJiliAUG 0N PitiJ0i]/rAil CE 0i' El'rtsA.\X}irNTS t9/ a2/9A Sheetuo E Narneof embankmentscheme DEEP]NG HIGH BANK CRADGEBANK Location of ernbanlsnent: 'RIVER WELLANDU/S OF SPALDING Nature of problero : BANK AND BERM CONS]STS OF SILT MATERIAL SUSCEPTIBLE TO LONG TERM EROSION Details of problem : Date L982 AN ARTIFICIAL CHANNELWAS CUT IN 1950. THE BANKS WEREPROTECTED AT THAT TIME AND S]NCE BY THORNFAGGOTSTO RESIST WAVE ACTION AT NORMAL RETENTIONLEVEL. THE FAGGOTSARE NOWFAILING LEADING TO A LOSS OF BERM W]DTH AND EMBANKMENT. WORKIS ONGOING. Remedial action taken or considered necessary : REINSTATEMENTOF BERM WIDTH AND PROTECTIONOF RIVER FACE USING A VARIETY OF METHODSINCLUDING:- (a) Asbestos Piles (b) Random Pitched Stone (c) Duracem Piles IIU U U99I I IIgD Person to contact should rore infornation be required Nar8e..J.gryry .U.L.Y.AJJ.. r . . . .. oo, ...... , rel No . FP$J.PJII9.!97771.7Q?+??. Address STEPPING STONE a a a a WALK a a a a o a a a a o a a t a a a a a a a a a a a a aa a a o a a a a . o . . . .Wtr,lI4BqY.AVLI\UE . . . o o . . . . . o ...... QDAT NTNIA ur nLUIllu, a o a a a o a a a a a o a a a a a a o a a a oa o a a a a o a o a,a a a o ...... Ic{IIqqL.ryS.H.I.R.q...... oo...... HR QI'ESTIONNAIREON PERTORMANCEOF EI,IBAI{K}IENTS L9/02/9A sheet No E Narne of embankment scheme : GceaTHn{ Ceeet< Location of embankment : 'TibM- Q(enfr+*a eee€K EretSArsKh4€NT Nature of problem : -Trb€ ?eld€.Ar,os lr{ sTo&vt Cmr\rTrors S Details of problem : Date : -InCouqH Ulnfea- Pe*areRTrr.tQ, Er,\SANrKMeNTs (c"srstaocre\ .1eTAL rtrF:ffi"l) Rasuurrr.rc|ril couuAPs€ &Ppe.'... 4 Jan*u1 lilreer'&r-s Remedial action taken or considered necessary : ?.ePrnc=' B(enc,H ulrrH er-*1 ' Person to contact should more infornation be required i ar- o3aY'.+(o(41 Name....)..S.1L15:.... rerNO .. Anrrtt'rtetrrl Address ilAttooe'q R'nyeCS .. . s-r(.".{:s*!*. ..:. I.S...... SilrPe t-Anse. E FFR '39 I E: Z5 TO CHEETSEYH PAGE. gE4 Lei02/90 HR qUES?T0MAIREoli P8R^FORIiANCEOF ElEAliiQ{8NTS sheetNo tr enbar*ment scheme l. River Kent (tidaL eection) adjacent to Sanpool Caravan Parlc Erosion of.rlver bed and lwoer banks adjacent to a flood embankment- o Date ; ,March L99O Details of problen r: Thia section is subject to erosion from freshwatef'flows which are rrndernlning the river bank, whiLst the adjacent fl.ood barrk (tldal) is endangered. It is not possible beeauee of, the proxtrnity of, etatic caravan to move the flood bartk. : Reroediai.eciion taken or considered necessery It Placirrg of large rocks in the bed. : Person to caniec t sirould more iirfornaiicn be required' t\ 60567 Qrr r r \\ O53SS ...... Narne. qr Y ,.. -VJ r\\n-.- ?eI No ". A Sheet No Name of ernbankroent scheme : RIVER MERSEYREHABILITATION SCHEME Location of embankment : BETWEENASHTON WErR (SJ 773 936) AND STOCKPORTE.T.W. (S.l 870 890) Nature of problem : EROSION AND SILT DEPOSITION DURING FLOOD FLOWS Details of problem : Date : BANK EROSION AT FLOODFLOWS. SILT DEPOSITION, CAUSING REDUCTIONIN FLOWCAPACITY OF CHANNEL. Remeiial action taken or considered necessary : REMOVALOF SILT OVERBURDENAND RECONSTRUCTIONOF BANKS. Person to contact should more infornation be required : ., JOHN RUCKLEDGE \,^ 061 973 2237 (Ext. l-68) NaJite. ltv A;,.1-^- - NATIONAL R]VERS AUTHORITY, SOUTHFLOOD DEFENCEAREA, MIRWELL, CARRINGTONLANE, SALE, M33 5NL, UII-BJN-Lt1E . HR ON PERFORMANCE L9/02/90 QI'ESTIoNNAIRE 'L' r" '".' i.{t.i ,i - i t I lu""' 1*ituiAill it*il sheet uo E Name of embanknent scheme : f.tW(L Ptoz,1> Er,lgAuk_n€:r\fis -fe QltreLS oo9€, ADUfL < A{Lut\y' Location of enbankment : : * x./ewi\a.v€N./ to 'Bx(LLc xG€ - 6'9.rL tho'?-€\,N!-r Ac, $€pfr€\-D I \UU rt\.,, ,\)** - LrTf!€L\\tletoFt -fa Pr:'-?.":f?cizr Nature of problem : Ltt \k- ,t r*-:*\-r-"\ \^\- €€.1xe F*t\c*. 7e\- '.. d rylulfl **aftr -s+s,a -\^"L rA$-.,. b,*1*e-Fh \.- h^\^.* b'"t/ (**t*l .^^-r^ a sAU*-]'r\ & ^-:f-*) 5r*t\r* I Details of problen g .'- 2e'*zr.^ Date avs€ \r.,|^t.e- ^oFt'* $L€qr."+, \zr.*L \v^\*gr. +.Ar- I $.",6 "6r-^h- gr.*t<. h^\^-*- )a.* 199c7 '.1- S-ffie^u<" G*LuL^>* ,*J1g^*) ,$.*.I.n-* , i^J l-o.^^g. .*.^*.,* '*.-.-;5. g,ctU*.' ) **o-.--;€ g*!.\r-t *he Lo*L t" \^'H\'th'"(tt) SylJ Sr-a-<- q.kru4--$*l $o* <-',-* CL^^^J'-\ ^**En) *z{t-V+ ,\-t.*;. r ,\oJ 6*\'\r-' Remedial action taken or considered necessary : ow';E'-': Sxr**\ *'\r. t^\----;:; )#)f:l:- s ,* -\J\,- "i*r*J^v -*,\. \-.*t ^.r.-J f'^,- ^***\b ry '(l) t g^lLr-. f4y! *.,.,f,-.,*L t.,L,.o.^^--' Person to contact should more information be required : Name..Noczr*r..%*:t: rel No \^r(TArl.?LkZ:.1). .*?.691* Address t{flr\ 9.,\tTF\e&-N) fZqteNJ ClV \iegou R-N€ Na'g'>s- C,tl Affgr*'s.Zt\\ QD t o o EI{BANKMENTS L9/02/90 Sheet No \) o.,\\,.J.,^ < \ , B"\,.U Co-\ 2--f Location of ernbanknent : 3o\^un.'.^- €* ^(\r$d., r^^o..B"-f ,* R. !\ l"- , Nature of problem : Q..,.,..^4".-\-'- t--lrK. \^*,(y €.*\ .^*\^*^"^L , Details of problem : Date : T;- \hc\o Remedial action taken or considered necessary : <-.^\ \L....=r^ q=-s.'-.*.1..^--s' \*1--, Person to contact should more information O" required <-. ^ - I \',l' '"t-1rc-re \,*e- Name. S' Tel No t-a-c &-- GrCo tq( Address 1(t L.L S *.^K.-- t--e-< d--2 L-s\ 2-Qq )Lc, r2* &KA QUESTIONNAIREON PERFORI.'ANCEOF EI{BANKMENTS 19/02/90 Sheet No Name of embankment scherne : E^ B"& -B;\,.u ce.-\ (o .\^ Location of embanknent : \-lo1-sc 61a \n-r.osr- TL* Q- d!r.,.-sL, S.'^\- toAnnr-i^- , Nature of problem : \\r,..--(-O-5 Al. (! \ -^.-.\\ t-^v , Details of problem : Date : raE I \g N.\ * *. .r^€ a\V- c.- }- S\ .-- .*rg ia \- .,r * NA b^^k *Q- s^- \^.r \ \-e .i*.*-\- A .*\ c^^\,a.-cL A, \\; *:..S"---':S t^S.q.^\- *r.^---*\.. *\ . Remedial action taken or considered necessary : \t r-{ D*1.t \. *-o'-r Cq<)\s s= JN ^^ *A "*-r*^;\L r.-:\.rr5 fr\ .'1.^^.,,.ao-^\-.L .6\.L*_1 r\^*\-o-- [,^-L.*\\-.-* { ) t Person to contact should more infonnation be required : Narne.. .-,, C\4.'..8..**.'"b-4-. . . Ter No Address }-\ $rjt z:\ bgc"la