aldot ditch check practices using testing techniques

ResearchReportNo.1ProjectNumber:930‐826R

EvaluationofALDOTDitchCheckPracticesusing

Large‐ScaleTestingTechniques

Large‐scaleChannelTesting(ASTMD7208–modified)

ofEvaluationofVariousWattleInstallationConfigurationsusing

a20in.WheatStrawWattleover

PoorlyGradedSand

December2012

Submittedto:AlabamaDepartmentofTransportation

1409ColiseumBoulevardMontgomery,Alabama36110

Submittedby:Dr.WesleyC.Zech,Ph.D.

&Dr.XingFang,Ph.D.

HighwayResearchCenterSamuelGinnCollegeofEngineering

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DISCLAIMERSThecontentsofthisreportreflecttheviewsoftheauthorswhoareresponsibleforthefactsandaccuracyofthedatapresentedherein.ThecontentsdonotnecessarilyreflecttheofficialviewsorpoliciesoftheAlabamaDepartmentofTransportationortheAuburnUniversityHighwayResearchCenter.Thisreportdoesnotconstituteastandard,specification,orregulation.Commentscontainedinthispaperrelatedtospecifictestingequipmentandmaterialsshouldnotbeconsideredanendorsementofanycommercialproductorservice;nosuchendorsementisintendedorimplied.

NOTINTENDEDFORCONSTRUCTION,BIDDING,ORPERMITPURPOSESDr.WesleyC.Zech,Ph.D.

&Dr.XingFang,Ph.D.ResearchSupervisors

ACKNOWLEDGEMENTS

ThisprojectwassponsoredbytheAlabamaDepartmentofTransportation.Materialcontainedhereinwasobtainedinconnectionwitharesearchproject“EvaluationofALDOTDitchCheckPracticesusingLarge‐ScaleTestingTechniques,”ALDOTProject930‐826R,conductedbytheAuburnUniversityHighwayResearchCenter.Thefunding,cooperation,andassistanceofmanyindividualsfromeachoftheseorganizationsaregratefullyacknowledged.

EXECUTIVESUMMARYLinearconstructiontypicallyusesdrainageconveyances,suchasroadsideditches,toconveystormwaterrunoffawayfromconstructionsitestoneighboringwaterbodies.Thesemaybeunstabilizedandhighlysusceptibletoerosiveshearstressesinhighvelocityrunoff.Therefore,bestmanagementpractices,suchaswattleditchchecks,areusedtohelpreducechannelerosioncausedbyhighvelocityflowwhilepropagatingsedimentdepositionwithinthechannel.

TheAuburnUniversityErosionandSedimentControlTestingFacility(AU‐ESCTF)wasusedtoevaluateandimprovewattleditchcheckinstallationpracticeperformancetohelptheAlabamaDepartmentofTransportation(ALDOT)bettermaximizewattleditchcheckperformanceinthefield.Onecontroltestandsevendifferentinstallationswereevaluated.Theseveninstallationswere:(1)DownstreamStaking,(2)TeepeeStaking,(3)DownstreamStakingw/Trenching,(4)TeepeeStakingw/8oz.FFandTrenching,(5)DownstreamStakingw/FF,(6)TeepeeStakingw/8oz.FFand(7)TeepeeStakingw/8oz.FF+Staples.

Statisticalanalysesindicatedthattrenching,stapling,andafilterfabricunderlaysignificantlyaffectedwattleperformancewithtrenchingbeingdetrimentaltoperformanceandstaplingandunderlayimprovingperformance.Itshouldalsobenotedthattrenchingcausesgreatererosiondownstreamandmayactuallyincreasetheeffectsofundercutting.

ThisstudyconcludedthatALDOT’scurrentinstallationofonlystakingawattletoanunstabilizedchannelcanbeimproved.Withtheadditionofafilterfabric(FF)underlaytoprotectthechannelbottomattheinstallationareafromscourandusingsodstaplesinadditiontoteepeestakingtosecurethewattleinplacewhileincreasinggroundcontact,channelerosionandundercuttingofthewattlecanbereduced.Therefore,itistherecommendationofthisstudythatthe‘Teepeew/8oz.FF+Staples’installationbeusedtoinstall20in.diameterwattlesasditchchecksformaximumrunoffcontrolperformance.


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TableofContents1 INTRODUCTION.............................................................................................................................................................1 2 BACKGROUND.................................................................................................................................................................1 2.1 FieldEvaluationsofDitchCheckPerformance........................................................................................2 2.2 StandardSHA’sWattleDitchCheckDetail................................................................................................3

3 TESTINGMETHODOLOGY..........................................................................................................................................4 3.1 TestChannel...........................................................................................................................................................4 3.1.1 PreparationoftheTestChannel...........................................................................................................5

3.2 ConstantFlowTest..............................................................................................................................................5 3.3 InstallationEvaluationRegime......................................................................................................................5 3.3.1 MaterialsforInstallations.......................................................................................................................5 3.3.2 ControlTest...................................................................................................................................................6 3.3.3 WattleInstallationTests..........................................................................................................................6

3.4 DataCollected........................................................................................................................................................8 3.5 StatisticalAnalysis...............................................................................................................................................8

4 RESULTSANDDISCUSSION.......................................................................................................................................8 4.1 StatisticalAnalysisResults.............................................................................................................................12

5 CONCLUSIONS...............................................................................................................................................................12 6 RECOMMENDATIONSFORIMPLEMENTATION.............................................................................................13 7 ACKNOWLEDGEMENTS............................................................................................................................................13 8 REFERENCES.................................................................................................................................................................13

ListofTablesTable1:ComparativeResultsofEachWattleInstallationConfigurationandtheControl.....................11 Table2:StatisticalRelationshipsofInstallationComponents...........................................................................12

ListofFiguresFigure1:ComparisonofALDOTandNCDOTWattleInstallationPractices...................................................3 Figure2:DitchCheckTestChannelDimensionsandConfiguration..................................................................5 Figure3:ControlandAllWattleInstallationsTested..............................................................................................7 Figure4:ComparisonsofEGLandWSEforVariousInstallations......................................................................9 Figure5:TestComparisonofTrenchedWattleConfigurations........................................................................10 Figure6:InstallationComparisonwithandwithoutStaples..............................................................................11


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1 INTRODUCTIONTheconstructionofroadwaystypicallyconsistsofmassclearingandgradingleavingmanysiteareasunstable,lackinggroundcovertoprotectagainstrainfallinducederosion.Aslinearroadwayprojectsprogress,unstabilizedareas(i.e.,roadbeds,cutandfillslopes,andotherembankments)tendtobehighlycompactedtherebyreducinginfiltration.Thismayincreasesediment‐ladensurfacestormwaterrunofffromtheseunstabilizedareas.Stormwaterrunofffromunstabilizedgradingoperationsonconstructionsitescanyieldsedimentlossesof35to45tons/acre(13to16.5tonnes/hectare)peryear(1).Erodedsedimentfromconstructionsitesisoneofthemostharmfulpollutantstotheenvironmentresultinginover80milliontons(73milliontonnes)ofsedimentwashingfromconstructionsitesintosurfacewaterbodieseachyear(2).Inlinearconstruction,stormwaterrunoffistypicallydivertedtoaseriesofconstructedstormwaterconveyances(i.e.,berms,swales,andditches),whichmayalsobeunstabilizedpriortovegetativeestablishment.Therefore,runoffcontrolmeasuresmustbeinstalledtominimizechannelerosion,especiallyduringpeakperiodsofastormevent.Stormwaterrunoffcontrolisthepracticeofmanagingconcentratedflowsandreducingpeakrunoffcausedbymodificationofthesitetopography.

Ditchchecks,whicharerunoffcontrols,aredefinedaseitherpermanentortemporarystructuresconstructedacrossrunoffconveyances,intendedtoslowandimpoundstormwaterrunoff,reduceshearstressesthatcausechannelerosion,andcreatefavorableconditionsforsedimentation(3,4,5,6,&7).Awattle,whichmaybeusedasaditchcheckorslopeinterceptdevicedependingonsite‐specificrequirements,isamanufactured,tubulardevicecomposedofnaturalorsyntheticfillers(i.e.,compostmaterial,wheatstraw,excelsior[woodshaving],coir,carpetfiber,orrecycledrubbertires)encasedinanaturalfiberorsyntheticnetting.Theadvantagesofusingwattlesasditchchecks,overothertypesofditchchecks(i.e.,rock,haybales,siltfence,etc.)include:(1)itsbiodegradability,(2)typicallylightweight,(3)easeofinstallationusingminimumresources,(4)economical,and(5)availableinvariousdimensionsmakingthemadaptabletositespecificconstraints.Somelimitationsofusingwattlesasditchchecksinclude:(1)theirellipticshapemayreducesurfaceareaavailableforgroundcontactwiththechannelresultinginunderminingandscour,and(2)thepotentialforlightweightwattlesbecomingbuoyant,reducingadequategroundcontactwhilesubjectedtoconcentratedflows.

Thepurposeofthisreportistoexamineandsummarizetheeffectsvariouswattleinstallationconfigurationshaveonawattle’soverallperformancewhenusedasaditchcheck.Sevendifferentwattleinstallationtestsarecomparedtoacontroltest(i.e.,nowattleinstallation)todetermineperformanceimprovementbasedonvelocityreduction,impoundmentlength,andstructuralintegrity.Eachditchcheckinstallationwastestedusingfield‐scale,replicabletestprotocols.

2 BACKGROUNDAliteraturereviewwasperformedtodeterminerelevantstudiesfocusingonvariouswattleditchcheckapplicationsandevaluationsofoverallperformance.Severalstatehighwayagencies(SHAs)standardditchcheckpracticeswereinvestigatedtodeterminevariouswattleinstallationpractices.McEnroeandTreff(8)statethatsuccessorfailureofditchchecksoftenreliesuponlocation,placement,installation,andmaintenancepracticesemployedonconstructionsites.Thisisespeciallytrueforwattlessincemostarenotmanufacturedwithdedicatedanchorstoaidinsecuringtheminplace.Thereforeinstallingwattlescapableofimpoundingwater,slowingrunoffvelocity,reducingchannelerosion,andallowingforsedimentationtooccurisimportant.Unfortunatelythereisalackofrelevantresearchpublishedontheperformanceofwattlesbaseduponinstallationpractices.Manyhighwaydepartments,municipalities,andmanufacturershaveinstallationdetailsandrecommendations,typicallydevelopedbasedonfieldevaluationsandtrial‐and‐error.However,McLaughlinetal.(9)states,“fieldtestingofexistingandnewsedimentand


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erosioncontrolproductsorsystemshasbeenproblematicwhenconductedonactiveconstructionsites.Uncertaintyaboutrunoffquantityandqualityduetoweatherpatternsandconstructionactivitiesmakesobjective,replicatedexperimentsverydifficult.”Thereforeaneedexistsforevaluatingtheinstallationofditchchecksusinglarge‐scaleexperimentaltestingprocedurestogainanunderstandingofperformancewhileattemptingtomakeimprovements.

2.1 FieldEvaluationsofDitchCheckPerformanceMcEnroeandTreff(8)performedaqualitativestudy,basedonfieldobservations,investigatingtheeffectivenessofKansasDepartmentofTransportation’s(KDOT)temporaryerosionandsedimentcontrolmeasures.Thepracticesevaluatedincludedsiltfenceandhaybalesusedasditchchecks,perimetercontrols,andinletprotectiondevices.Thequalitativeperformanceofthesemeasureswasbasedon:preventingerosion,sedimentcapture,preventionofoff‐sitesedimentmigration,observedfailuremodes,andwhetherimprovementscouldbemademakingthecontrolsmoreeffectiveandlessexpensive.Themajorityoffailuresobservedwerecausedbyimproperimplementationwithdesignandplacement,useofsubstandardmaterials,andlackofattentiontodetail.Fieldpersonnelindicatedthaterrorsmaybeattributedtoabasicmisunderstandingofhowerosionandsedimentcontrolpracticesareintendedtoperform.Fromthis,theauthorsconcludedthatthesuccessofthesepracticesislargelydependentoninstallationandmaintenancepractices.

Asaresultoftheirresearch,McEnroeandTreff(8)implementedseveralnewditchcheckpracticesforfieldevaluationtocompareagainsthaybaleditchchecksincludingaTriangularSiltDikeTM(TSD),rockditchchecks,andbio‐logs.ATSDisatriangularpolyurethanefoaminsertwrappedingeotextilefabricwithageotextilefabricapronsewntothebottom.TheapronprotectsthechannelfromscourupstreamanddownstreamoftheTSD.Thisdevicewasdeemedanimprovementtocurrentpracticeduetoeaseofinstallationandtheapronsabilitytoprotectthechannelfromscourattheditchcheck.Rockditchcheckswerealsoevaluatedandrecommendedforsteepslopedchannelsand/orchannelsthatareconveyinghighflowratesduetotheirinherentstructurallystabilityversushaybaleditchchecks.Bio‐logs,erosioncontrolblankets(ECBs)rolledupandplacedacrosstheditchspan,essentiallyaprimitivetypeofwattle,werealsofieldevaluated.Bio‐logsweredeemedineffectiveduetoextensiveundermining.

McLaughlinetal.(10)performedastudytoevaluatetheeffectivenessofwattleswithandwithouttheuseofpolyacrylamide(PAM),forreducingsedimentandturbidityinrunoffwateronconstructionsiteswhilecomparingthesepracticestostandardrockcheckdams.Thesesitesemployedsmallsedimenttrapsconstructedofrockditchchecksprecededbysumpsandtwodifferentwattletypescomposedoftwodifferentmaterials,coirandwheatstraw.Onecoirwattlewasinstalledforeverythreewheatstrawwattlesbecausethecoirwattleswerelarger,sturdier,andinstalledincasethewheatstrawwattlesfailed.Thecoirlogswere12in.(30cm)indiameterand10ft(3m)long.Thestrawwattleswere9in.(23cm)indiameterand10ft(3m)long.Bothwattleswereinstalledusingstakesandsodstaplestosecureinplace.GapsbetweenthewattlesandgroundwerefilledwithpiecesofECBs.Channelsatsite1werelinedwithECBsduetochannelsteepness,whilesite2channelswereunlined.ExcelsiorECBunderlayswereinstalledforsite2wattles,extending3ft(1m)downstreamofthewattlestopreventdownstreamscour.Eventhoughtheprimaryfocusoftheirresearchwassedimentcontrolperformanceofditchcheckinstallations,someerosioncontrolobservationswerenoted.McLaughlinetal.(10)concludedthatwattlesperformedbetterinlowflowconditionsthanrockditchcheckswhilerockditchcheckstypicallyhadlittletonopoolinlowflowconditionsresultinginupstreamchannelerosion.

McLaughlinetal.(10)concludedthattheidealditchcheckspacinghaswaterimpoundingbackuptheslope,totheimmediatedownstreamsideoftheprecedingupstreamditchcheck.Therefore,thespacingisafunctionofditchcheckheight(ordiameter)andchannelslope.Thiscreatesaseriesofsubcriticalflowingpoolsthatreduceshearforcealongthechannelbottom,reducingchannelerosion.Energyistransformedfrompotentialenergy(i.e.,subcriticalflow)back


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tokineticenergy(i.e.,supercriticalflow)aswaterflowsthrough,over,and/orundertheditchchecks.Sincethegreatestenergytransfersoccurattheinterfaceofthewattleandchannelbottom,sometypeofchannelarmoringisrecommendedtodissipateenergyandmaintainchannelintegrity.

2.2 StandardSHA’sWattleDitchCheckDetailALDOT’sstandardwattleinstallationpracticecanbefoundon‘ESC‐300DitchCheckStructures,TypicalApplications,andDetails’(4)andisshowninFigure1(a)alongwithNCDOT’sstandardwattleinstallationdetailinFigure1(b)(11).

(a)ALDOTStandardWattleDetail(4)

(b)NCDOTStandardWattleDetail(11)

Figure1:ComparisonofALDOTandNCDOTWattleInstallationPractices.


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ALDOT’swattleinstallationspecifiesa20in.(51cm)diameterwattleplacedperpendiculartoflowacrossatrapezoidalchannel.Thewattleistobestakedinplacebyanchoringthestakethroughthenetting.Thestakesaretobedrivenintothegroundonthedownstreamsideofthewattleaminimumof1.5ft(0.45m)withamaximumstakespacingof3ft(1m).Thedetailrecommendstrenchingofwattlesifpipingunderthewattlebecomesevident.ThemaindifferenceintheALDOTandNCDOTdetailsisthestakingpatternanduseofanunderlayforchannelprotection.ALDOT’sstakingmethodpiercesthedownstreamsideofthewattle,makingitadestructivestakingpractice.NCDOT’spracticecallsforstakestobedrivenintothegroundontheupstreamanddownstreamside,angledtowardsthewattleinanA‐shapeorteepeeconfiguration.Thisconfigurationdoesnotpiercethewattleandisconsiderednondestructive.

Limitedresearchhasbeenconductedoncontrolled,large‐scaletestingofditchchecksinchannelizedapplications.Nostudieswereidentifiedthatfocusedonevaluatingperformancecharacteristicsofvariousditchcheckinstallations’abilitytoincreaseperformance.Asmoretemporaryditchcheckoptionsbecomeavailablewithintheindustry,determiningthemosteffectiveinstallationforeachtemporaryditchcheck,suchasawattle,hasbecomeincreasinglyimportant.Themosteffectivewattleinstallationhasthepotentialtomaximizeitsabilitytoreducechannelerosionandcreatefavorableconditionsforsedimentdepositiontooccurwithinthechannel.

Basedontheliteraturereviewedandaneedtofurtherunderstandwattleperformance,afield‐scaleditchchecktestingmethodologywasdevelopedandappliedtoevaluatetheimprovementeffectsvariouswattleinstallationconfigurationshaveonwattleperformance.

3 TESTINGMETHODOLOGYAlltestsconductedaspartofthisresearchwereperformedattheAuburnUniversityErosionandSedimentControlFacility(AU‐ESCTF)locatedattheNationalCenterforAsphaltTechnology(NCAT)inOpelika,AL.Toproperlyevaluatetheaffectvariousinstallationconfigurationshaveonwattleperformance,thesamewheatstrawwattlemanufacturerandtypewereusedforalltestsperformed.

ThestandardtestmethodreferencedforthedevelopmentofthetestingmethodologyusedinthisstudywasASTMD7208‐06:StandardTestMethodforDeterminationofTemporaryDitchCheckPerformanceinProtectingEarthenChannelsfromStormwater‐InducedErosion(7).

3.1 TestChannelTheAU‐ESCTFhasatestchanneldedicatedtoperformancetestingofditchchecksinconcentratedflowapplicationsandisshowninFigure2(a)and2(b).

(a)ElevationView

Metal Section

Earthen Section

Concrete Section

......

CS1CS2

CS3CS4

CS5CS6 CS7 CS8

Ditch Check

3 ft3 ft

3 ft3 ft

3 ft3 ft

CL

5%


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(b)Cross‐SectionalView

Figure2:DitchCheckTestChannelDimensionsandConfiguration.

Theditchchecktestingchannelhasatrapezoidalcrosssectionwithatopwidthof13ft(4m)andabottomwidthof4ft(1.2m)with3H:1Vsideslopes.Thedepthofthechannelis1.5ft(0.5m)andis39.5ft(12m)long.Thechannelisdividedintoagalvanizedsteelplatedsection24.5ft(7.5m)longandanearthensection15ft(4.6m)long.Thelongitudinalslopeofthechannelis5%.Theearthensectionallowedforfieldqualityinstallationsandperformanceobservationsoftheditchchecks.Themetallinedportionedallowedtheditchcheckstobetestedandevaluatedregardlessofchannelperformance.

3.1.1 PreparationoftheTestChannelBeforeeachtest,the15ft(4.6m)earthensectionistilledusingareartinetiller,handraked,handtamped,andthenmechanicallycompactedusinganuprightrammerhammerwithacompactionplateof14x11.5in.(36x29cm),ablowcountof600blows/minuteandacompactionforceof2,700lbs(1,225kg).ThesoilwithintheearthensectionwasclassifiedasapoorlygradedsandusingtheUSGSSoilClassificationSystem.Themaximumdensityof123.8lbs/ft3(19.44kN/m3)wasdeterminedbythemethoddescribedinASTMD698‐07,StandardTestMethodsforLaboratoryCompactionCharacteristicsofSoilUsingStandardEffort(12).In‐placedensitysamplesweretakenwithadensitydrivehammerandthinwalledShelbytubestoverifythatatleast95%+/‐2%compactionwasachieved.

3.2 ConstantFlowTestThetestforwattleinstallationevaluationsforthisstudyusedasustained,constantflowof0.56cfs(16L/s)ofcleanwaterforadurationof30minutes.Priortotesting,eightlevelstringlineswerestretchedacrossthechannelat8cross‐sectional(CS)locations(Figure2(a):CS‐1toCS‐8),sixupstreamandtwodownstreamoftheditchcheck.Themeasurementpointswerespaced1ft(0.3m)apartalongeachstringline.Thesestringlineswereusedtotakewaterdepthandvelocitymeasurementsatpoints4,5and6inFigure2(b)duringeachtest.

3.3 InstallationEvaluationRegimeAseriesofconstantflow,large‐scaleditchcheckexperimentswereperformedtoevaluateeachinstallationconfiguration.Theseweredonetocomparativelyanalyzethesevendifferentwattleditchcheckinstallationconfigurations.Foreachinstallationconfiguration,includingthecontrolwithnowattleinstalled,threereplicatetestswereperformed,totaling24large‐scaleexperiments.

3.3.1 MaterialsforInstallationsThefollowingisalistofmaterialsusedforthevariouswattleinstallationconfigurations: wattle:20in.(50cm)diameter,20ft(6m)longwheatstrawwattlewithsyntheticnetting, woodenstakes:1in.x2in.x3ft(2.5cmx5cmx1m),usedtosecurethewattleinplace,

1 2 3 4 5 6 7 8 9

1 ft 1 ft 1 ft 1 ft1 ft 1 ft1 ft 1 ft

13

4 ft4.5 ft

1.5 ft


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sodstaples:11gaugemetal,6in.longx1in.(15cmx2.5cm)wideU‐shapestaples,usedtosecurethefilterfabricunderlayandthewattle,and filterfabric(FF)underlay:8oz.(225gram),nonwovenFF,7.5ft(2.3m)long,15ft(4.6m)wide.Extends3ft(1m)upstreamfromtheupstreamfaceofthewattleandkeyedinaminimumof5in.(0.13m)deepinanarrowtrench.Thefabricunderlayextends3ft(1m)downstreambeyondthewattle.Thetrenchedendoffabricwasfirmlytampedtoensureadequatecompaction.TheupstreamanddownstreamedgesofFFweresecuredwithsodstaplesspaced10in.(25cm)apartandlongitudinallyalongeachsideandthecenterlineofthefabricspaced1.5ft(0.45m).

3.3.2 ControlTestAbaresoilcontroltestwasperformedthatconsistedofthechannelbeinggradedandcompactedtoexperimentalspecificationswithoutaditchcheckinstalled.Thistestestablishesabaselineforflowvelocitiesandwaterdepthsundersupercriticalflowconditions(i.e.,noimpedanceofflow)ateachcrosssection(CS1‐CS8)asshowninFigure2(a).

3.3.3 WattleInstallationTestsThechannelwaspreparedtoexperimentalspecificationsforalltestsperformedonthesevendifferentwattleinstallationconfigurationssodirectcomparisonscouldbemadewiththecontrolandvariousconfigurations.Thefollowingsevenwattleinstallationconfigurationsweretested:(1) DownstreamStaking:currentALDOTinstallation,wattleisplacedacrossthechannelinaU‐

shape,concaveupstream,andsecuredwithwoodenstakesdrivenintothegroundaminimumof1.5ft(0.45m)andpositionedevery2ft(0.6m)onthedownstreamsideofthewattlepiercingthenetting.

(2) TeepeeStaking:mimickedNCDOTstakingpractices(Figure1(b))creatinga“teepee”orA‐frameoverthewattlebydrivingthestakesintothegroundaminimumof1.5ft(0.45m)nexttothewattlewithoutpiercingthewattleorwattlenetting.Thesestakesweredriveninatanangletowardsthewattlesecuringthewattleinplace.Aminimumoftwostakeswereinstalledupstreamandaminimumof5stakesinstalleddownstreamwithamaximumstakespacingof2ft.(0.6m).

(3) DownstreamStakingw/8oz.FF:wattlewasinstalledwithan8oz.(225gram)filterfabricunderlayandsecuredinplaceusingALDOTstakingpractices.

(4) TeepeeStakingw/8oz.FF:wattlewasinstalledwithan8oz.(225gram)filterfabricunderlayandsecuredinplacefollowingNCDOTstakingpractices.

(5) DownstreamStakingw/Trenching:entirewidthofthewattlewastrenchedintochannel2in.(5.1cm)deep,perpendiculartotheflowofwaterandanchoredusingALDOTstakingpractices.

(6) TeepeeStakingw/8oz.FFandTrenching:a2in.(5.1cm)deeptrenchextendingtheentirewidthofthewattlewasexcavatedandcoveredwithan8oz.(225gram)filterfabricunderlay.ThewattlewasinstalledandsecuredusingNCDOTstakingpractices.

(7) TeepeeStakingw/8oz.FF+Staples(12):wattlewasinstalledexactlyasdescribedinconfiguration(4),alsosecuringthebottomoftheupstreamanddownstreamfaceofthewattletochannelusingsodstaplesalongeachside,spaced12in.(0.3m)aparttoimprovecontactwiththechannelbottom.

Figure3providesaphotographiccomparisonofthecontrolset‐upandseveninstallationconfigurationspriortotesting.Figure3showstheFFunderlaythatwasusedtopreventerosionwithinthechannel(Figures3(d),(e),(g),and(h))andthetwostakingpatterns.


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(a)Control (b)DownstreamStaking

(c)TeepeeStaking (d)DownstreamStakingw/8oz.FF

(e)TeepeeStakingw/8oz.FF (f)DownstreamStakingw/Trenching

(g)TeepeeStakingw/8oz.FF+Trenching (h)TeepeeStakingw/8oz.FF+Staples

Figure3:ControlandAllWattleInstallationsTested.


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3.4 DataCollectedOncesteady‐stateflowconditionswereachieved,waterdepthandvelocitymeasurementsweretakenatcrosssectionalmeasurementpoints4,5and6foreverycrosssection(CS1‐CS8)showninFigures2(a)and2(b).Thesepointswereaveragedtodeterminetheaveragewaterdepthandaveragevelocityforeachcrosssection.Thedistancefromtheupstreamfaceofthewattletothehydraulicjumpwasalsorecordedoncesteadystateconditionswereachievedtodeterminesubcriticalflowlengthcreatedbytheinstallation’sabilitytoimpoundwater.

Usingthecollecteddata,theslopeoftheenergygradeline(EGL)forthewaterprofilewasplottedasspecifiedbyASTMD7208‐06.TheEGLisdefinedbyEquation1(7).

EGL=WSE+v2/2g (1)where, EGL =energygradeline(ft) WSE =watersurfaceelevation(ft) v =averagewatervelocity(ft/sec) g =gravitationalconstant(32.2ft/sec2)TheslopeoftheEGLforlong,unimpeded,continuousflowchannelsshouldcloselymimicthechannelslope.Whenthechannelisimpeded(e.g.,byaditchcheck),theslopeoftheEGLwithintheimpoundmentareabecomessmallerthanthechannelslopeaspondingdepthsincreasetowardsthewattle.Thepotentialenergybuiltupbythesubcriticalflowisreturnedtokineticenergyastheimpoundedwatergoesunder,through,and/orovertheditchcheck.Inadditiontoimpoundingwaterandreducingerosionduetoshearstresses,theinstallationmustalsowithstandhydrodynamicpressureforceinthefrontfaceofthewattleandpossibleliftingforceunderneaththewattlewhilesimultaneouslymaintainingtheintegrityoftheinstallationandditch.

3.5 StatisticalAnalysisThestatisticalanalysismethodforthisstudyusesamultiplelinearregressionmodeltodeterminethesignificanceofthevariables(i.e.,wattleinstallationcomponents).Themultiplelinearregressionmodelindependentlyevaluatestheeffecteachvariablehasonincreasingthelengthofimpoundedwater(i.e.,lengthofsubcriticalflow).Themodeldevelopspartialregressioncoefficientsthatreporthowstronglythatdependentvariable(i.e.,trenching,stapling,staking,ortheunderlay)affectstheindependentvariable(i.e.,subcriticalflowlength).ThemultiplelinearregressionmodelusedfortheseanalysesisshowninEquation2. f(x)=β0+β1x1+β2x2+...+βnxn (2)where, f(x) =dependentvariable(e.g.,subcriticalflowlengthorimpoundmentlength) xi =independentvariables(e.g.,trenching,stapling,staking,ortheunderlay) βi =theordinaryleastsquarescoefficients

Usingthismodel,themosteffectivemeansofincreasingthesubcriticalflowlengthcanbedetermined.

4 RESULTSANDDISCUSSIONThefollowingsectionisasummaryoftheresultsandcomparisonsthatweremadefromtheexperimentsusinga0.56cfsconstantflowrateforalllarge‐scaletestsperformed.

ThecurrentALDOTinstallationpractice,referredtoasDownstreamStaking,isconsideredadestructiveinstallationpracticebecausestakespierceandpotentiallydamagingthewattlenetting.ThisstakingpatternwastestedandcomparedtothenondestructiveTeepeeStakingpattern.Data


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analysisdeterminedthatstakingpatternhadlittleeffectontheaveragesubcriticalflowlengthwhencomparingtheDownstreamStakingpatternof10.3ft(3.1m)totheTeepeeStakingpatternof10.7ft(3.3m).Visualdocumentationnotedthatduringtesting,forbothstakingpatterns,amaximumimpoundmentlengthwasachievedearly,thenrecededtoashortersteady‐statesubcriticalflowlengthasthetestcontinuedduetoexcessiveundercuttingandpipingoccurringattheinterfaceofthewattleandchannelbottom.Topreventthepipingeffect,theteepeeanddownstreamstakingweretestedusingan8oz.(225gram)filterfabric(FF)underlaythatwasintendedtoprotectthechannelbottomatthewattleinstallation.ThedatacollectedshowsthattheTeepeeStakingw/8oz.FFinstallationincreasedsubcriticalflowlengthto16.5ft(5m)incomparisontothepreviouslydiscussedTeepeeStakinginstallation.TheDownstreamStakingw/8oz.FFinstallationalsoincreasedsubcriticalflowlengthto15ft(4.6m)whencomparedtotheDownstreamStakinginstallation.Notehowever,thatthoughtheFFincreasedthesubcriticalflowlengthforbothinstallations,bothsubcriticalflowlengthswereonceagainsimilar(i.e.16.5ft(5m)forTeepeeStakingw/8oz.FFand15ft(4.6m)forDownstreamStakingw/8oz.FF).Theseinstallationsareeachcomparedtothecontrol(nowattleinstallation)asshowninFigure4.TheEGLandwatersurfaceelevation(WSE)areplottedforeach.InFigures4(a)and4(b),therearetwoEGLsplottedforeachinstallation.ThesetwoEGLsarearesultoftwodifferentflowconditions(i.e.supercriticalorsubcritical)thatfellwithinthemeasurementcross‐sections.TheupstreamEGLsrepresentsupercriticalflow.ThesesupercriticalEGLpointsareabovetheWSEpointsandindicatehigherkineticenergyfromgreaterflowvelocity.However,thedownstreamsubcriticalflowEGLsshowlesskineticenergysincetheEGLpointsfallalmostdirectlyontopoftheWSEpointsindicatingimpoundmentofflow.Thisdecreaseinkineticenergyistheidealcircumstanceforchannelprotection.ThisimpoundmentlengthofsubcriticalflowincreaseswiththeinclusionoftheFFunderlay.

(a)DownstreamStakingvs.Control (b)TeepeeStakingvs.Control

(c)DownstreamStakingw/FFvs.Control (d)TeepeeStakingw/FFvs.Control

Figure4:ComparisonsofEGLandWSEforVariousInstallations.


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ALDOTandmanymanufacturersrecommendtrenchingthewattleifpipingbecomesevident(4,13).ThisinstallationwastestedusingtheDownstreamStakingw/Trenchinginstallationandresultedinadecreaseinimpoundmentlengthwithanaveragesubcriticalflowlengthof9ft(2.7m)whichwas1.3ft(0.4m)shorterthantheDownstreamStakinginstallationalone.Visualdocumentationalsoobservedpipingandscourunderthewattle,alongwithhigheramountsoferosionoccurringonthedownstreamsideofthewattleduetothetrenchbeingwashedoutasshowninFigure5(a).AnticipatingbetterperformancebyonceagainusingtheFFunderlay,theTeepeeStakingw/8oz.FFandTrenchingwasalsotestedandshowninFigure5(b).However,trenchingwithFFdidnotincreaseperformance;rathertheaveragesubcriticalflowwasreducedto8ft.(2.4m)longcomparedtotheTeepeeStakingw/8oz.FFimpoundmentof16.5ft(5m)long.Thisseemstosuggestthattrenchingreducesthewattle’sgroundcontactwiththechannelbottom,allowinganeasierpathforwatertoflowunderthewattle.

(a) DownstreamStaking+Trenching (b) TeepeeStaking+Trenching+ FF

(c) DownstreamStaking+Trenchingvs.Control (d) Teepeestaking+Trenching+FFvs.Control

Figure5:TestComparisonofTrenchedWattleConfigurations.

Thefinalinstallationtested,TeepeeStakingw/8oz.FF+Staples,mimicstheNCDOT’swattledetail(11).ThisinstallationusesaFFunderlay,teepeestaking,and12in.(30cm)sodstaplesanchoringthewattletothechannelwhichisintendedtoimprovegroundcontactandminimizeundercutting.Thisinstallationresultedinanaveragesubcriticalflowlengthof20.5ft(6.2m).Figure6showsthehydraulicresultsofthistestcomparedtotheTeepeeStakingw/8oz.FFinstallation.Theinclusionofstaplestoincreasegroundcontactappearstosuccessfullyimprovewattleperformanceasevidentbytheincreaseofsubcriticalflowlengthandvisualobservations.Becausethesodstaplesincreasedgroundcontact,undercuttingwasreducedandincreasedflowwasvisuallynotedasflowingthroughthewattleinsteadofunder.Thisassumptionwasfurtherverifiedbystatisticalanalyses.


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(a) TeepeeStakingw/FFvs.Control (b) TeepeeStakingw/FF+Staplesvs.Control

Figure6:InstallationComparisonwithandwithoutStaples.

TheimpoundmentlengthsaswellastheEGLslopesaretabulatedinTable1.ASTMD7208‐06saystodeterminetheEGLbyfittingaregressionlinethroughEGLelevationpointsdeterminedateachcrosssection(7).Nofurtherguidanceforinterpretingoranalyzingthedataisgiven.Thiscouldbeproblematicifahydraulicjumpiswithinthemeasurementcrosssectionssincesteady‐statesupercriticalEGLslopestypicallycloselymatchthechannelslopewhilethesubcriticalEGLslopeisflattenedoutbytheimpoundmentcausedbythewattle.Usingasingletrend‐linetomimictheEGLslopeacrossthehydraulicjumpwouldmakeitinaccuratesincethesupercriticalflowEGLismoreaffectedbythewatervelocitywhilethesubcriticalflowEGLismostaffectedbyWSEorwaterdepth.TheonlyinstallationsthatresultedinthehydraulicjumpextendingbeyondthemeasurementthresholdwasTeepeeStakingw/8oz.FFandTeepeeStakingw/8oz.FF+Staples(Fig.6).Thebaresoilcontrolisallsupercriticalflow.However,evaluatinginstallationsbasedonsubcriticalflowsonlycanalsobeproblematicbecausetheshorterpoollengthstypicallyhaveEGLslopesapproachingzero(Fig.4(a)and(b),Fig.5(d)).Longer‐pondingEGLslopestendtobesteeperslopedwhichisevidentwhencomparinglongersubcriticalflowstoshortersubcriticalflowsasshowninTable1.TheEGLandWSEshouldmimicimpoundmentssuchasdammedreservoirsorsluicesandshouldhavesmallslopesalongtheflowdirection;insteadofthesteeperimpoundmentslopesshowninFigure6.Thisanomalymaybecausedbythecomplexflows(e.g.,threedimensionalflowcirculationsobservedduringtesting)createdbyundercuttingandthewattlesporousmaterial.Thisshouldbefurtherinvestigatedinafuturestudy.

Table1:ComparativeResultsofEachWattleInstallationConfigurationandtheControl.

Treatment

LengthofSubcriticalFlow(Impoundment) EnergyGradeLineSlopes(ft/ft)

Length(ft)

PercentDifference(%)[a]

BasedonASTMD7208[b]

SubcriticalFlowsOnly

Teepeew/8oz.FF+Staples 20.5 99.0 ‐0.0166 ‐0.0166Teepeew/8oz.FF 16.5 60.2 ‐0.0250 ‐0.0250

Downstreamw/8oz.FF 15.0 45.6 ‐0.0302 ‐0.0210Teepee 10.7 3.9 ‐0.0197 ‐0.0060

Downstream 10.3 ‐‐ ‐0.0277 ‐0.0063Downstreamw/Trenching 9.0 ‐12.6 ‐0.0457 ‐0.0250

Teepeew/8oz.FF+Trenching 8.0 ‐22.3 ‐0.0275 ‐0.0077BareSoilControl N/A N/A ‐0.0514 ‐0.0514

Notes: [a]Percentincrease/decreaseincomparisontotheDownstreamStaking installation; [b]ASTMD7208‐06EGLslopewasasinglelineartrendlinethroughallEGLpointsupstreamthewattle(including bothsupercriticalandsubcriticalflow).


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4.1 StatisticalAnalysisResultsAmultiplelinearregressionmodelwasusedtodeterminetheeffectofthedifferentinstallationconfigurationsonoverallwattleperformance.Eachoftheinstallationswereclassifiedbydifferentcombinationsoftheindependentvariablesconsideredintheanalysis:(1)trenching,(2)underlay,(3)downstreamstaking,(4)teepeestaking,and(5)stapling.Fortheregressionmodel,thedownstreamstakingpatternwasusedastheanalysisbase,fromwhichallotherinstallationcomponentsarecompared.ThiswasselectedbecausethecurrentALDOTpracticeissimplystakingthewattlewithdownstreamstakingonly.Theresultsofthisanalysisalongwithcorrespondingp‐valuesareshowninTable2.

Table2:StatisticalRelationshipsofInstallationComponents

InstallationComponentStatisticalSignificance

Coefficients p‐value[a]

Select1StakingOption:

DownstreamStaking Base ‐‐TeepeeStaking ‐0.833 0.389

SelectAnyTreatmentsthatApply

FilterFabricUnderlay 3.500 0.002Trenching ‐4.667 >0.001Stapling 5.583 0.001

Notes:[a]a99%confidencelevelwasusedtoestablishstatisticalsignificance

UsingthemodelinTable2,wattleperformancecanbedeterminedbycreatingarepresentativemodel.Sinceteepeestakinganddownstreamstakingarenotsignificantlydifferent,eitherpatternmaybeusedforinstallation.Aninstallationthatusesfilterfabricunderlayandstaplingwillseeanincreaseinpoollengthof9.083ft(3.5+5.583)baseduponthemodelinTable2.However,includingtrenchingintheinstallationwouldresultinareductionof4.667ftinpoollength.

Basedupontheseresultsthefollowingconclusionsaremadebasedonstatisticalsignificanceofthemodel:(1)becausethecoefficientforstakingisnotstatisticallysignificant,wecanconcludethatthestakingpatterndoesnotsignificantlyaffecttheperformanceoftheinstallationforincreasingsubcriticalflowlength,(2)trenchingthewattlehasasignificantlydetrimentaleffectonperformance,asevidencedbythenegativecoefficient,and(3)theunderlayandstaplingsignificantlyimproveperformancebyincreasingthesubcriticalflowlength.

5 CONCLUSIONSAsthisstudyhasshown,determiningthemosteffectiveinstallationisdifficultbecauseopinionscanvarybasedonmanufacturerrecommendationsorSHA’sstandardpractices.Reevaluatinginstallationproceduresinthefieldcanberiskybecauseinstallationfailureoftenresultsinincreasederosionalongwithgreatersedimenttransport.Thereforeevaluatingwattleinstallationinacontrolledenvironmenthelpsalleviateriskwhileprovidingamorecontrolledandscientificplatformtotestvariousinstallationconfigurations.

Evaluatingtheinstallationsrequiresdeterminingthegreatestmitigatingfactorthatdefinesthewattlesperformanceasaditchcheck.TheslopeoftheEGLisplottedtoevaluatetheenergyreductionoftheexperimentalflow,askineticenergy(i.e.,v2/2gofthesupercriticalflow)changesintopotentialenergy(i.e.,WSEofthesubcriticalflow)bytheditchcheck.However,recognizingthatincreasedimpoundmentlengthmeansincreasedsubcriticalflowisalsorelevantfordeterminingperformance.Forchannelizedflow,reducingtheerosiveforcescausedbysupercriticalflowsinanearthenchannelwhilealsopromptingsedimentdepositioninthesubcriticalflowareaistheidealscenario.Thiscanbeaccomplishedbymaximizingthesubcriticalflowlength,thereforeminimizinghighlyerosivesupercriticalflows.


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Onecontroltestandsevendifferentinstallationswereevaluated.Theseveninstallationswere:(1)DownstreamStaking,(2)TeepeeStaking,(3)DownstreamStakingw/Trenching,(4)TeepeeStakingw/8oz.FFandTrenching,(5)DownstreamStakingw/FF,(6)TeepeeStakingw/8oz.FFand(7)TeepeeStakingw/8oz.FF+Staples.Hydraulicevaluationofthetests’resultsshowedthatevaluatingperformancebasedsolelyonEGLslopereductionmayleadtoimproperconclusions,especiallyiftheEGLcrossesthehydraulicjump.Perhapsabettermethodforperformanceevaluationwouldbetoevaluateditchchecksperformancebasedonsubcriticalflowlength.

Usingamultiplelinearregressionmodeltoevaluatethemostsignificantinstallationcomponentforincreasingsubcriticalflowlength,fiveindependentvariableswereidentifiedandcompared.Thesevariableswere:(1)trenching,(2)downstreamstaking,(3)teepeestaking,(4)underlay,and(5)stapling.Themodelshowedthatthestakingpatterndidnotsignificantlyaffectthewattlesperformance.Themodeldidshowthattrenching,stapling,andunderlaydidsignificantlyaffectwattleperformancewithtrenchingbeingdetrimentaltoperformanceandstaplingandunderlayimprovingperformance.Itshouldalsobenotedthattrenchingcausesgreatererosiondownstreamandmayactuallyincreasetheeffectsofundercutting.Thereforetakingthestatisticalsignificanceintoconsiderationwhilealsolookingatthelargestincreaseinsubcriticalflowlength,itistherecommendationofthisstudythatthe‘Teepeew/8oz.FF+Staples’installationbeusedtoinstall20in.diameterwheatstrawwattlesasditchchecksformaximumstormwatercontrolperformance.

6 RECOMMENDATIONSFORIMPLEMENTATIONAsaresultofthistestingeffort,theresearchteam’sfirstrecommendationistoincorporatethe‘Teepeew/8oz.FF+Staples’installationintotheALDOTStandardDrawings.Basedupontheresultsofthetesting,staplingthewattleincreasedthedevicescontactwiththeground,resultingina99%increaseinimpoundmentlengthincomparisontocurrentstandardinstallationof‘DownstreamStaking’only,andgreatlyreducedflowvelocitiesupstreamoftheinstallation.Boththeincreasedimpoundmentandareductionofvelocitywillmaintaintheintegrityofanearthenchannelupstreamoftheinstallationwhichisadesirableoutcome.However,duringaworkinggroupmeetingassociatedwiththeproject,ALDOTrepresentativesstatedthatitwasunlikelythatcontractor’swillincludestaplestofastenthewattlesecurelytotheground.TheALDOTrepresentativesalsobelieveditwouldincreaseoverallinspectioneffortsofwattleditchcheckinstallations.Therefore,thesecondrecommendationoftheresearchteamistoincorporatethe‘Teepeew/8oz.FF’installationintothestandarddrawings.The‘Teepeew/8oz.FF’installationresultedina60.2%increaseinimpoundmentlengthincomparisontothecurrentALDOTstandardinstallationof‘DownstreamStaking’only.

7 ACKNOWLEDGEMENTSThisreportisbasedonastudysponsoredbyALDOT.Theauthorsgratefullyacknowledgethisfinancialsupport.Thefindings,opinions,andconclusionsexpressedinthisreportarethoseoftheauthorsanddonotnecessarilyreflecttheviewofthesponsor.

8 REFERENCES1.AmericaSocietyofCivilEngineers(ASCE)andWaterEnvironmentFederation(WEF),Designand

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2.Novotny,V.2003.WaterQuality:DiffusePollutionandWatershedManagement.NewYork:JohnWiley&Sons,Inc.

3.U.S.EnvironmentalProtectionAgency(EPA),MenuofBMP’s:CheckDams,May2006http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm.AccessedFebruary9,2012.

4.ESC‐300DitchCheckStructures,TypicalApplicationsandDetails,AlabamaDepartmentofTransportation(ALDOT),Montgomery,AL,2012,sheets1&4of7.


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5.TemporaryRockSiltCheckTypeBSpecification,ErosionControlandRoadsideDevelopment,NorthCarolinaDepartmentofTransportation(NCDOT),Raleigh,NC,2012,1633.01.

6.ManualforErosionandSedimentControlinGeorgia,GeorgiaWaterandSoilConservationCommission(GWSCC),Athens,GA,2000,pg.7ofchapter2.

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8.McEnroe,B.M.,andB.J.Treff.PerformanceofKDOTTemporaryErosionControlMeasures,ReportNo.K‐TRAN:KU‐97‐2FinalReport,KansasDepartmentofTransportation,December1997.

9.McLaughlin,R.A.,N.Rajbhandari,W.F.Hunt,D.E.Line,R.E.Sheffield,andN.M.White.SoilErosionResearchforthe21stCentury,TheSedimentandErosionControlResearchandEducationFacilityatNorthCarolinaStateUniversity,ProceedingsoftheInternationalConferenceofAmericanSocietyofAgriculturalEngineers(ASAE)Pub#701P0007,2001

10.McLaughlin,R.A.,S.E.King,andG.D.Jennings,ImprovingConstructionSiteRunoffQualitywithFiberCheckDamsandPolyacrylamide,JournalofSoilandWaterConservation,Vol.64,2009,pp.144–154.

11.WattleDetail,RoadsideandEnvironmentalUnit,NorthCarolinaDepartmentofTransportation(NCDOT),Raleigh,NC,2012.

12.ASTMStandardD698,2007,StandardTestMethodsforLaboratoryCompactionCharacteristicsofSoilUsingStandardEffort,ASTMInternational,WestConshohocken,PA,2007.

13.AmericanExcelsiorCompany:EarthScienceDivision.TechnicalSupportLibrary:CurlexSedimentLogsChannel,http://www.americanexcelsior.com/erosioncontrol/library/CAD%20Details/Curlex%20Sediment%20Logs%20Channel.PDF.AccessedJuly30,2012.

aldot ditch check practices using testing techniques

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