The Buffalo River Area of Concern: A Case Study Combining...

The Buffalo River Area of Concern: A Case Study Combining Geological and Engineering Approaches to Understanding Sediment Dynamics

• STAandPTMbothshowthelakeseicheandverifyitsimportanceinmovingsedimentupriver

• BothSTAandPTMshowsedimentmovingbothupstreamanddownstreamandthecomplexinteractionsbetweenriverandlakeflow(thestrongercurrentflowinginthecenterofthechannelandtheweakercurrentflowingalongthebank)

• A3DhydrodynamicmodelthatconsidersthesourceandpathwayofsedimentparticlesisessentialfortheBuffaloRiverwherereverseflowisanimportantprocess

• BenefitscanbederivedbyusingbothSTAandthePTMmodeltounderstandsedimentdynamics.STAvalidatesthePTMandhelpsmodelersidentifyprocessesandareasofspecialinterest.Themodelcanthenbeusedtoanswerenvironmentalmanagementquestionsaboutwhatmighthappenunderawiderangeofflowconditions

• BuffaloRiverservesasacasestudyforotherAOCs

Particle Tracking Model:Athreedimensionalparticletrackingmodelislinkedtoahydrodynamicmodeltosupplyvelocitiesanddiffusivitiesthat,alongwithsettling,controlparticlemovements.Possibleboundaryinteractionsincludereflectionatthesurface,pass-throughboundariesattheupstreamanddownstreamboundaries,anddeposition/erosionalongthebed.Themodelaccountsforvariableupstreamflowsanddownstreamwaterelevation(atLakeErie)todeterminetheflowfield,andcanincorporatevariableloadingsfromeitherupstreamflowsorotherpointandnon-pointsources.Thepresentapplicationdemonstratesclearlythatthree-dimensionaleffectsareevidentinthesedimenttransportcharacteristicsoftheBuffaloRiver,withsedimentcapableofmovinginboththeupstreamanddownstreamdirections,dependingonflowandseicheconditions.Thisresultmayhaveasignificantimpactonevaluatingcandidateareasforenvironmentaldredging.

Figure 12a. Cumulative sediment movement over 24 hours, Case 2; insert shows detail at downstream boundary.

Figure 12b. Detail near downstream boundary, from Figure 12a.

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Abstract:TheidentificationofremediationoptionsandalternativesfortheBuffaloRiverAreaofConcern(AOC)requiresanunderstandingofsedimentationprocessesintheriver.WepresentresultsfromarecenteffortfundedthroughtheEPAGLNPOprograminwhichwecombinedSedimentTrendAnalysis(STA),side-scansonarmappingofriver-bottomfeatures,andthree-dimensionalhydrodynamicmodeling.STAisbasedonastatisticalexaminationofchangesingrain-sizecharacteristicsbetweensamplelocations;forthisparticularstudy,over500sedimentsampleswerecollectedbetweenthemouthoftheBuffaloRiverandtheupperlimitoftheAOC.Thethreeindependentapproacheswereusedincombinationtoelucidate

sedimenttransportpathwaysandflowconditionsintheriver.AllthreeapproachesindependentlyconfirmedthesignificantroleplayedbyLakeErieseichesintransporting

sedimentinanup-riverdirection,andeachprovidedinsightsaboutshort-termandlonger-termprocessescontrollingsedimentationwithintheriver.ResultsfromtheBuffaloRiverstudycanbe

usedinmakingmanagementdecisionsaboutsediment

remediationoptions.Ourworkin theBuffaloRiveralso servesasacasestudyfor otherGreatLakesAOCs.

Prior Work: Side Scan Sonar Surveys, 1990 - 1996Sedimentaryfurrowsarelongitudinalbedforms(grooves)thatparallelthebankandareseparatedbyridges.Furrowformationhasbeenrelatedtosedimenterosion(scouringoffurrow)anddeposition(inter-furrowridge).Furrowshavebeenidentifiedinareascharacterizedbybidirectionalflowregimes(e.g.,largelakes,tidalchannels,continentalshelf,anddeepsea).Furrowsrangeindepthfrom1.5to2.25mandformonlyinonestretchoftheriver.Thefurrowfieldappearstobeverystableandhaspersistedinthesameportionoftheriverfor15years(probablylonger).

Pilot Sediment Trend Analysis (STA), 1990 - 1992149SedimentsampleswerecollectedwithintheBuffaloRiverAOCandgrainsizestatisticsweredeterminedusingaMalvernLaserParticleSizer.AnSTAwasperformedandtwoflowregimeswereidentified(blueandgreenarrowheads,Figureonright).ThereverseflowisdrivenbyLakeEriewatersandrelatedtoseicheevents.

Furrowsexhibit‘tuningfork’patternwithtuningforksopeninthedirectionofcurrentflow.FurrowsintheBuffaloRiveropenbothupstreamanddownstream,indicatingthattheflowregimeisinfluencedbothbytheriverandlakeseiche.

JillSingerDept.EarthSciences,BuffaloStateCollege

PatrickMcLarenGeoSeaConsulting

JosephAtkinsonGreatLakesProgram,SUNY-Buffalo

PatriciaManleyGeologyDept.,MiddleburyCollege

Side Scan Sonar:ReconnaissanceoftheBuffaloRiverusingside-scansonarforthepast15yearsshowsthatthebottommorphologyremainsconsistent.AKleinSonar590dualfrequency(100and500kHz)system(analogpaperrecording)wasusedtoimagetheriverbottomforallsurveysexceptforJuly2005,whenadigitalKlein3000systemwasused.Thepresenceoffurrowsandsandribbonsprovidesconclusiveevidenceoftheredistributionofbottomsediments.

What the furrows tell us about flow in the Buffalo River

Cumulativesedimentmovementover24hours,Lowbaseflowandhighseiche;insertshowsdetailatdownstreamboundary.

Figure 12c. Detail from central part of AOC (Katherine St. Peninsula), from Figure 12a.

Case 3: High flow and high seiche.In this case both the higher flow (50 cms) and the seiche were considered, with the seiche applied as in Case 2. Initially there is little difference from Case 1, and during the initial half of the seiche period (raised lake level) little sediment movement was observed in the simulations. It appears as if the flows related to upstream and to the seiche provide a sort of mitigating effect on each other, in terms of driving sediment transport. The biggest difference, relative to the first two cases, occurs during the second half of the seiche cycle, as the lake level drops. During this period the flows due to upstream and the seiche are additive, causing significant movement of the sediments. This is evident in the 24 hour cumulative plot shown in Figure 13. Relative to either Cases 1 or 2 (Figures 5 or 12, respectively), this case by far shows the strongest sediment transport. The strong downstream movement is highlighted in the details of Figures 13b and 13c.

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Figure 12a. Cumulative sediment movement over 24 hours, Case 2; insert shows detail at downstream boundary.

Figure 12b. Detail near downstream boundary, from Figure 12a.

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Detailneardownstreamboundary.

DetailfromcentralpartofAOC(KatherineSt.Peninsula)

SedimentTrendAnalysis(STA)tellsyouthenetsedimenttransportpathwaysinanysedimentaryenvironment,thedynamicbehaviorofthebottomsediments(neterosion,accretion,dynamicequilibrium,etc.),andthesedimenttransportenvironments(i.e.,sourcesandzonesofinfluence).STAisbasedonthegrain-sizedistributionsofbottomsedimentscollectedovertheareaofinterestinaregulargrid.Twodistinctflowregimesandsixtransport

environmentsareidentifiedfortheBuffaloRiver.

ThetransportpathwaysforTransportEnvironments1,2,and3.

ThetransportpathwaysforTransportEnvironments3,4,5and6.

ThetransportpathwaysforTransportEnvironments5and6.

Conclusions:

Sediment Trend Analysis:

A)RubbersheetedanalogrecordforSeptember2,2004.Furrowsarevisible.B)RubbersheetedanalogrecordforpostfloodofSeptember25,2004.Thefurrowsaremorevisibleandhaveextendeddownstream.C)DigitalrecordfromJuly17,2005.thefurrowsareobservableintheirsameorientationnearCargill’sbutarelessdefinedinthedownstreamreach.

ToLakeErie

UpstreamendofAOC

Cargill’s

Acknowledgements:ThisresearchwassupportedbyProjectNumberGL2004-243throughtheUSEPA-GLNPO.