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HomeMy WebLinkAbout2017-4 Boun Short Plat - Basin DiversionDenisLawMayorCommunity&EconomicDevelopmentC.E.“Chip”Vincent,AdministratorJune21,2017BrandonLoucks,P.E.BeylerConsulting7602BridgeportWayW.Suite3DLakewood,WA98499RE:BounShortPlat(U16006297)—BasinDiversion-Adjustment2017-04DearMr.Loucks:TheCityofRentonhascompletedreviewoftheadjustmentrequestforBounShortPlat(U16006297)inaccordancewiththeCityadopted2009KingCountySurfaceWaterDesignManual(KCSWDM)andassociatedCityAmendments.Astheapplicant’sengineer,youarerequestinganadjustmentfromthe2009KingCountySurfaceWaterDesignManualtoSection1.2.1,CoreRequirement#1,DischargeattheNaturalLocation.Morespecifically,youarerequestinganadjustmenttodivertstormdrainagefromapproximately8,771squarefeet(0.20acres)oflandareafromdrainingatitsnaturaldischargelocationtoanotherlocation.Findings:1.CoreRequirement#1,DischargeattheNaturalLocationrequiresthatallsurfaceandstormwaterrunofffromaprojectbedischargedatthenaturallocationsoasnottobedivertedontoorawayfromdownstreampropertiesperSection1.2.1oftheCityadopted2009KCSWDM.2.Theprojectsiteislocatedat1012DuvallAvenueNE.TheprojectisasinglefamilyresidentiallanduseandislocatedintheR-8residentialzone.Theprojectsiteis57,499squarefeet(1.32acres)andisundeveloped.Theprojectproposestosubdividetheprojectsiteintosevenlotsforfuturesinglefamilyhomes.Approximately55,007squarefeet(1.26acres)oftheprojectsitewillbedisturbedaspartofthisproject.1055SouthGradyWay,Renton,WA98057.rentonwa.gov Mr.BrandonLoucksPage2of3June20,20173.Theprojectsitecontainstwoseparatethresholddischargeareas.ThresholdDischargeArea#1coversamajorityofthesite.ThresholdDischargeArea#1drainstothesite’ssouthwestcornertowardstheexistingpublicstormdrainagesystemintheChelanAvenueNErightofway.Ofthedisturbedarea,approximately46,236squarefeet(1.06acres,84%ofthedisturbedarea)ispartofThresholdDischargeArea#1underexistingconditions.ThresholdDischargeArea#2islocatedalongtheeasternfrontageofthesite.ThresholdDischargeArea#2drainstothesite’snortheastcornertowardsanexistingstormwaterconveyanceditchlocatedalongthewesternfrontageofDuvallAvenueNE.Theremainingapproximately8,771squarefeetofdisturbedarea(0.20acres,16%ofthedisturbedarea)drainstothislocationunderexistingconditions.4.BoththresholddischargeareasarepartofthelargerMayCreekdrainagebasin.ThedownstreamflowpathscoveragemorethanonequartermiledownstreaminHoneyCreek.TheflowsleavingthesouthwestcornerofthesitefromThresholdDischargeArea#1areconveyedsouththroughanexistingpublicstormdrainagesysteminChelanAvenueNEthatwasconstructedaspartoftheVuongShortPlatdevelopment.FlowsarethenconveyedinCitystormconveyancepipeswestalongNE10thStreet,northalongAnacortesAvenueNE,westalongNE11thStreet,thenfinallynorthalongWhitmanCourtNEtoapipedportionofHoneyCreekunderWhitmanCourtNE.Thedistancefromthesite’ssouthwestdischargepointtoHoneyCreekisapproximately2,700feet.TheflowsleavingthenortheasterncornetofthesitefromThresholdDischargeArea#2areconveyedthroughanopenditchconveyancesystemalongthewesternfrontageofDuvallAvenueNEtoapipedpublicstormdrainageconveyancesystemthatbeginssouthoftheintersectionofDuvallAvenueNEandNE12thStreettoapipedportionofHoneyCreekadjacenttotheStarbucksatthecornerofDuvallAvenueNEandNESunsetBoulevard.Thedistancefromthesite’snortheastdischargepointtothepointonHoneyCreekwherethedownstreamflowpathsintersectisapproximately3,100feet.5.TheTechnicalInformationReportpreparedbyBeylerConsultingnotesthatnorelevantdrainagecomplaintsrelatedtofloodingwererecordedwithinonemiledownstreamofeachthresholddischargeareawithinthelasttenyears.6.PertheCivilConstructionPlanspreparedbyBeylerConsulting,drainagecollectedfromimpervioussurfacesinthesitewillpassthroughacombinationR:\FiIeSys\SWP-SurfaceWaterProjects\SWP-27-SurfaceWaterProjectsfCIP)\27-3129RentonStormwaterManual\ADJUSTMENTS\2017\2017-4BounShortPlat-BasinDiversion.doc1055SouthGradyWay,Renton,WA98057.rentonwa.gov Mr.BrandonLoucksPage3of3June20,2017detention/wetvaultpriortodischargeintothepublicstormwaterconveyancesysteminChelanAvenueNE.7.Theadjustmentproposestodivertapproximately5,760squarefeetofdrainageareafromThresholdDischargeArea#2tothenaturaldischargelocationofThresholdDischargeArea#1atthesouthwestcornerofthesite.OftheareadivertedfromThresholdDischargeArea#2toThresholdDischargeArea#1,onlyasmallportionispotentialroofareaforLots#1-4*4.Lots#1-#4willfrontDuvallAvenueNEwithdrivewaysintherearaccessedfromanextensionofChelanPlaceNE(publicalley)tothenorth.AllofChelanPlaceNEislocatedinThresholdDischargeArea#1.Thus,themajorityoflandintheareathatwillbedivertedwillconsistofgrass,landscaping,andwalkways.TheremainderofThresholdDischargeArea#2(approximately3,011squarefeet)willbegradedtowardstheDuvallAvenueNErightofwayandmaintainthenaturaldischargelocation.8.Theareadivertedwillnotproduceasignificantincreaseinflows(<0.1CFS)tothebasindownstreamofThresholdDischargeArea#1.Theprojectwillbeprovidingflowcontrolusinghistoric(forested)conditionsasthepre-developedallowablereleaseratewhichislessthanthecurrentexistingsiteconditions.9.UsingonefacilityasopposedtotwofacilitiesallowsthedevelopertomakebetteruseofthelandtomeettheR-$singlefamilyresidentialzoningstandards.Decision:Basedontheinformationprovidedintheenclosedadjustmentrequest,theadjustmenttodischargethemajorityofThresholdDischargeArea#2atthenaturaldischargelocationofThresholdDischarge#1isapproved.Ifyouhaveanyquestionsaboutthisadjustment,pleasecontactBrianneBannwarth,DevelopmentEngineeringManager,at(425)430-7299orRonStraka,SurfaceWaterUtilityEngineeringManager,at(425)430-7248.RonStraka,P.E.SurfaceWaterUtilityEngineeringManagercc:IanFitz-James,P.E.,CivilEngineerIllJillDing,SeniorPlannerLysHornsby,P.E.,UtilitySystemsDirectorH:\FileSys\SWP-SurfaceWaterProjects\SWP-27-SurfaceWaterProjects(CIP)\27-3129RentonStormwaterManual\ADJUSTMENTS\2017\2017-4BounShortPlat-BasinDiversion.docSiiBrianneBannwarth,P.E.DevelopmentEngineeringManager1055SouthGradyWay,Renton,WA98057rentonwa.gov