FloodinginManayunkNeighborhoodof

Philadelphia

SamuelBrodfuehrer|GISinWaterResources|December8,2017

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Introduction...........................................................................................................................3PhiladelphiaOverview.....................................................................................................................3ManayunkOverview........................................................................................................................4

ProjectObjective....................................................................................................................6

MethodsandDiscussion.........................................................................................................6StageheightsoffloodsatManayunkBrewery..................................................................................6FloodingImpactonManayunk.........................................................................................................7RatingCurveandUSGSGageComparison........................................................................................9

Conclusion.............................................................................................................................11

References............................................................................................................................12

Appendix...............................................................................................................................13

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IntroductionPhiladelphiaOverviewPhiladelphiaisthesixthlargestcityintheUnitedStatesandmostofthecityisborderedbytwomajorrivers,theDelawareandSchuylkill(seeFigure1).Manyneighborhoodsandcommunitiesarelocatedonthebanksofthesetworiverswhichmeanstheyareatriskoffloodingduringmajorstorms.ThecommunitieslocatedalongtheSchuylkillRiverhavehistoricallybeenmoresignificantlyimpactedbyfloodingcomparedtothoselocatedontheDelawareRiver.Floodscanbedeadlynaturalsdisastersthatcanresultinthelossoflifeanddamagetohomes,businesses,andinfrastructure.PhiladelphiahasbeenimpactedbymanyfloodssinceitwasfoundedandTable1showssomeofthemorerecentfloods.TherearetwoUSGSgagesontheSchuylkillRiverthathavebeenidentifiedinFigure1,whichhavecollecteddatarelevanttothisproject1.

Figure1:MapofPhiladelphiawhichidentifiestheManayunkneighborhoodsandlocationofupstreamand

downstreamgages.

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DateofFlood Crest(ft) Streamflow(cfs) Category9/17/1999 14.10 92,500 Moderate3/22/2000 11.04 42,700 Minor6/21/2003 11.43 52,500 Minor9/18/2004 11.33 51,100 Minor9/29/2004 11.86 58,500 Minor4/3/2005 11.74 56,800 Minor10/9/2005 12.07 61,500 Minor6/28/2006 12.51 68,100 Minor4/15/2007 11.34 51,200 Minor10/1/2010 13.05 76,300 Moderate3/11/2011 11.03 47,100 Minor8/28/2011 13.56 83,900 Moderate9/7/2011 12.01 60,600 Minor9/8/2011 12.52 68,200 Minor5/1/2014 13.91 88,300 Moderate

Table1:USGSflooddataforgagelocatedatSchuylkillRiveratPhiladelphia(downstreamofManayunk)2.

ManayunkOverviewThisprojectfocusesonfloodingintheManayunkneighborhoodofPhiladelphiawhichislocatedontheSchuylkillRiver.Manayunkusedtobetextilemanufacturinghubandinthelastcoupledecadesithasgentrifiedsignificantly.Ithasbecomearesidentialareaforyoungprofessionals.Myolderbrother,Ben,isaresidentofManayunkandabusinessacrossthestreetfromhisapartment,theManayunkBrewery,wastheinspirationformyproject.ManayunkBreweryislocateddirectlyontheSchuylkillRiverandhasexperiencedsignificantdamagefromfloodssinceitwasfoundedin1996(seeFigure2a).Ononeofthewallsinsidethebrewerytheyhavehighwaterlinesforfloodsthathavecausedthemostdamagetothebrewery(seeFigure2b).ThethreefloodeventsshowninFigure2bareHurricaneFloyd(1999),HurricaneIrene(2011),andtheFlashFloodof2014.Theheightofthewaterinthebarforeachfloodwas79”,48”,and65.5”respectively(measuredbymybrother).Table1identifieseachfloodasmoderateaccordingtheNationalWeatherService.TheowneroftheManayunkBrewerydidaninterviewinwhichshestatedthatduringsomeofthefloodstheSchuylkillRiverreachedaheightthatwas30feetabovetheriver’snormalstageheight3.Figure3showsamapofManayunkwithlocationsrelevanttotheanalysisdonelaterinthisproject.ThemapinFigure3wasmadebyimportingaPhiladelphianeighborhoodshapefileandanExcelfilewiththeGPScoordinatesofallthebarsinManayunk4.

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Figure2:a)PictureofaunfloodedandfloodedManayunkBreweryb)PictureofHighWaterLinesthataremarkedinManayunkBrewery

Figure3:MapofManayunkneighborhoodwithManayunkBrewery,Ben’sApartmentandotherbarlocationsidentified.

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ProjectObjectiveTheobjectiveofthisprojectistousetheHeightAboveNearestDrainage(HAND)modeltogainabetterunderstandingoffloodingintheManayunkNeighborhoodofPhiladelphia.Thisachievedbydoingthefollowing:

• DeterminingthestageheightforeachfloodattheManayunkBrewerybycombiningtheHANDforthebarandthehighwaterlineswithinthebarforeachflood.

• EvaluatinghowmuchofManayunkwasfloodedduringeachstormusingthecalculatedstageheight.

• GeneratingaRatingCurvefortheManayunkneighborhoodtodeterminetheflowintheSchuylkillRiverandcompareittotheavailableupstreamanddownstreamgagedata.

• Compareresultsfromthisprojecttohistoricalaccountsandreconcileanydifferences.

MethodsandDiscussionStageheightsoffloodsatManayunkBreweryTheproceduredescribedinlectureandExercise5wasusedtodeterminethestageheightofeachflood.LuckilyHANDrastersattheHUC6levelwerealreadymadefortheentireUSbyYanLiuandtheUniversityofIllinois5.TheHUC6whichencompassedPhiladelphiaisshownbelowinFigure4.TomakethismapIimportedtheavailableHANDrasterforHUC020402andadjusteditssymbology.

Figure4:HANDrasterofHUC020402withheightinmeters

TheExtractbyMaskfunctionwasthenusedtocreateanoutputrasterforjusttheManayunkneighborhood.ThisHANDrasterisshownbelowinFigure5.Itshowsthatmostbarsin

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ManayunkhaveaHANDvaluegreaterthan10meters.ManayunkBreweryisoneofthefewbarsthatarebelow10meters.

Figure5:HANDrasterofManayunkwithheightinmeters

ToevaluatethefloodcrestattheManayunkBreweryIusedtheExtractValuetoPointgeoprocessingtooltodeterminetheHANDvalueforit.IsummedtheHANDvaluefortheManayunkBreweryandtheheightofthehighwaterlinesinFigure1todeterminethecrestofeachofthefloodsthathaveaffectedtheManayunkBrewery.TheestimatedcrestsareshownbelowinTable2.

Flood Date Crest(ft)HurricaneFloyd 9/17/1999 29.92HurricaneIrene 8/28/2011 27.33

FlashFloodof2014 5/1/2014 28.79Table2:CrestachievedbyeachfloodbasedonHANDmodelanddocumented

highwaterlineinManayunkBrewery.

FloodingImpactonManayunkThecalculatedcrestsforeachfloodwascomparedtotheHANDvalueofeachbarinManayunktodeterminewhichwouldhavefloodedduringeachstorm.ThesamefourlocationswerefloodedineachstormwhichareshowninFigure6.ThefloodingiscenteredontheMainStreetintheareaaroundtheManayunkBreweryandtherestofManayunkisrelativelysafefromflooding.Photographsfromsomeofthesestormshavebeenpostedontheinternetandthey

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confirmthatthefloodingisonlyaroundtheManayunkBrewery.Thisverifiestheaccuracyofthisanalysis.SomeofthesephotographscanbeseenintheAppendix.

Figure6:MapofManayunkbarsthatarefloodedbya30footcrest

IntheIntroductionitwasmentionedthattheowneroftheManayunkBreweryclaimedthatthecrestsforsomeofthesestormswere30feethigherthantheSchuylkillRiver’snormalheight.ThecrestheightscalculatedinTable2werecloseto30feetbutnoneexceededitsoIdecidedtoinvestigatethisclaimclosertoseeifImadeanerrorinmyanalysis.ConvenientlythisclaimcanbecheckedbecauseaUSGSgagewassetupinManayunkinFebruary,2017.Thedatafromthatgageplacesanormalriverlevelataheightofabout12.5feet.Thismeansthataccordingtotheowner’saccountthecrestduringHurricaneFloydwouldhavereachedapproximately42.5feet.Thefloodingcausedbya42.5footcrestisshowninFigure7.ThereissignificantfloodingallalongtheMainStreetofManayunkandonlyafewbarswouldbeunaffectedbyafloodofthismagnitude.ComparingthisleveloffloodingtophotographsoftheMainStreetitisapparentthattheownermisspokeintheinterview.Shemusthavemeanttosaythatfloodwater“reachedaheightof30feet”notthattheSchuylkillRiverreachedaheight30feethigherthannormal.

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Figure7:MapofManayunkbarsthatarefloodedbya30footcrest

RatingCurveandUSGSGageComparisonTheprocedureinExercise5wasfollowedtogenerateaRatingCurvefortheSchuylkillRiverbytheManayunkneighborhood.Table3belowshowstheparametersoftheSchuylkillRiverbyManayunkandthecalculatedparametersusedtogeneratetheRatingCurveinFigure8.

StageHeight(m) 1 6 10 14As(m2) 66719 276987 1141766 2854414Ab(m2) 66803 281418 1150900 2867259V(m3) 47971 900206 3187810 11491871L(m) 4072 4072 4072 4072A=V/L(m2) 11.8 221.1 782.9 2822.2P=Ab/L(m) 16.4 69.1 282.6 704.1R=A/P(m) 0.719 3.199 2.770 4.008So 0.001749 0.001749 0.001749 0.001749n 0.05 0.05 0.05 0.05Q(m3/s) 7.9 401.4 1291.5 5956.0Q(ft3/s) 279.6 14170.8 45588.4 210248.0

Table3:ParametersusedtogenerateRatingCurve

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Figure8:RatingCurveforManayunkneighborhood

TheRatingCurvewasthenusedtodeterminethedischargeflowforeachfloodbasedonthecalculatedcrestsinTable2.TheseflowswerethencomparedtotheUSGSgagesupstreamanddownstreamofManayunk.TheresultsareshowninTable4.

FloodUpstreamGage

(cfs)DownstreamGage

(cfs)UnofficialManayunkBreweryGage(cfs)

HurricaneFloyd - 92,500 77,600HurricaneIrene 81,400 83,500 67,200FlashFlood2014 90,400 83,900 73,000

Table4:ComparingupstreamanddownstreamgagedischargetothedischargecalculatedfromtheRatingCurve

ThedischargeflowsfromtheRatingCurvearenoticeablysmallerthanboththeupstreamanddownstreamflowsthatweremeasured.IfyourefertoFigure3,6,or7youwillnoticethatthereisastream,theWissahickonCreek,thatmeetstheSchuylkillRiverjustsouthofManayunk.ThisconvergenceiswellbeforethedownstreamgageinTable4.ThereisagageatthemouthoftheWissahickonCreeksoIsummedtheflowsfromthatwiththedischargescalculatedfromtheRatingCurve.TheresultsareshownbelowinTable5.AccountingfortheadditionalflowfromtheWissahickonCreekreducedtheaveragedifferencebetweenthecalculateddischargeatManayunkBreweryandtheobserveddownstreamgagefrom16.2%to3.3%whichisasignificantimprovement.ThisapproachIusedisabasicmassbalanceanditsaccuracysuggeststhattheRatingCurvegivesaccurateflowdischargesforagivenstageheightandviceversainManayunk.

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0.0 50000.0 100000.0 150000.0 200000.0 250000.0

StageHe

ight(ft)

Discharge(ft3/s)

RatingCurve

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Flood DownstreamGage(cfs)UnofficialManayunkBreweryGage+

WissahickonGage(cfs)HurricaneFloyd 92,500 97,400HurricaneIrene 83,900 84,300FlashFloodof2014 85,300 80,900Table5:ComparingdownstreamgagedischargetothedischargecalculatedfromtheRatingCurveand WissahickonCreekgage

ConclusionTheapplicationoftheHANDmodelinthisprojectwassuccessfulingainingabetterunderstandingofhowfloodsaffecttheManayunkneighborhood.IwasabletomakereasonableestimatesforthefloodcrestsinManayunkwhereagagehasnotbeenpresentuntilrecently.WiththesecrestheightsandHANDvaluesofbarsinManayunkIwasthenabletoestimatetheextentoffloodinginManayunkandcomparethemtophotographicaccountsofthefloodstoconfirmmyresults.Finally,IwasabletomakeaRatingCurveandcalculatecorrectdischargesinManayunk.ThisrobustandlightheartedanalysiswasabletobringgreaterknowledgeaboutfloodsinanareathatdidnothaveanexistingUSGSgage.ThisprocesscanbeappliedtootherlocationswherethereareinformalwaystomeasurefloodandsufficientdatatodoaHANDmethodevaluation.

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References[1]UnitedStateGeologicalSurvey.https://waterdata.usgs.gov/usa/nwis/uv?01474500[2]NationalWeatherService. https://www.weather.gov/media/marfc/FloodClimo/SEPA/Philadelphia.pdf[3]ManayunkBrewer.https://www.manayunkbrewery.com/story[4]PennsylvaniaSpatialDataAccess.http://www.pasda.psu.edu[5]YanLiu.http://www.cigi.illinois.edu/yanliu/NFIEHAND.pdf

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Appendix