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TechnicalMemorandum:Hydrologic&HydraulicStudyforTaylorBayou,HCFCUnitA1040000 <br />December13,2011 <br />Page6of6 <br />Table6.RevisedHECRASModelResultsforHCFCUnitA1041201 <br />RiverPeakFlow(cfs)WaterSurfaceElevation(feet)LowestGround <br />Station10Year50Year100Year10Year50Year100YearElevation(feet)* <br />1875137829253.825.185.75 <br />5405027689103.855.215.778.00 <br />10254877518913.875.235.806.80 <br />1072ShadyRiverRoad <br />10964857488883.965.466.167.30 <br />16324697298674.005.496.197.50 <br />21174557138484.045.526.227.50 <br />25634436988325.016.106.66 <br />30573565416386.137.047.45 <br />3121McCabeRoad <br />31863365065957.008.959.20 <br />35522864194897.179.029.26 <br />40532293243747.459.109.35 <br />Note:TheshadedareasrepresentthecrosssectionsalongtheShadyRiversSubdivision. <br />*GroundelevationatastructurelocationestimatedbasedonLiDARDEMData. <br />SummaryofResults <br />Thecomputed10,50and100yearwatersurfaceelevationsalongTaylorBayou,HCFCUnitA104 <br />0000,andHCFCUnitA1041201likelycauseonlyminorstreetfloodingintheShadyRiver <br />Subdivision.Historicalstructuralfloodinginthesubdivisionwaslikelycausedfromcoastalstorm <br />surgesinGalvestonBay.Itwasbeyondthescopeofthisworktoinvestigateotherfloodingcauses <br />suchas:(1)undersizedstormsewerpipes,(2)inadequatesheetflowsystemforextremeevents, <br />and(3)stormsewerpipefailuresandmaintenanceneeds.Itisourprofessionalopinionthatthe <br />recommendedchannelimprovementsalongTaylorBayou,HCFCUnitA1040000,intheCWDS <br />wouldnotalleviatethehistoricalstructuralfloodingproblemsinthesubdivision.Nonstructural <br />measuressuchasstructureelevations,buyouts,orfloodinsurancearethelikelyfloodriskreduction <br />optionsforthesubdivision. <br />Thehydraulicresultsdidindicateasignificantheadlossof4.8feetduringa100yearstormevent <br />throughtheexisting272inchRCPsatMcCabeRoadandHCFCUnitA1040000.Wewould <br />recommendthereplacementoftheexistingculvertstoeliminatetheoutofbankfloodingupstream <br />ofMcCabeRoad.ThehydraulicanalysisalsofoundinsufficientchannelcapacityalongHCFCUnit <br />A1041201upstreamofMcCabeRoad.OutofbankfloodingwasidentifiedintheForestVista <br />MobileHomeParkfora10yearstormevent.Structuralsolutionscouldincludedetentionupstream <br />inthegolfcourseorchannelimprovementsalongHCFCUnitA1041201upstreamofMcCabeRoad. <br /> <br />