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  • Sonoma Valley Stormwater Management and Groundwater Recharge Scoping Study

    Parker Groundwater

    Screening Evaluation and Prioritization Memorandum

    PreparedfortheSonomaCountyWaterAgencyby

    ESAPWA DanielB.Stephens&Associates

    ParkerGroundwater

    April30,2012

    DW02050.00

    SonomaCreekatGlenEllen,followingthepeakofthe20052006floodevent.ImagefromtheSonomaValleyHistoricalEcologyArchive.ElaineNealley,photographer.

  • SonomaValleyStormwaterManagementandGroundwaterRechargeScopingStudyScreeningEvaluationandPrioritizationMemorandum

    2 Parker GroundwaterParker Groundwater

    [Thispageisintentionallyblank.]

  • Sonoma Valley Stormwater Management and Groundwater Recharge Scoping Study

    Parker Groundwater

    TABLEOFCONTENTS Page1 Introduction..........................................................................................................................................11.1 Projectpurpose.............................................................................................................................11.2 Efforttodate.................................................................................................................................11.2.1 Projectdeliverables...............................................................................................................21.2.2 Projectobjectives..................................................................................................................2

    1.3 Projectprocess..............................................................................................................................31.4 Purposeofthismemorandum......................................................................................................41.5 Structureofthismemorandum....................................................................................................4

    2 Projecttypesconsidered......................................................................................................................42.1 Requirements................................................................................................................................52.2 Sources..........................................................................................................................................52.3 Potentialprojecttypesormeasures.............................................................................................52.3.1 Measuresthatdecreasefloodflows.....................................................................................62.3.2 Measuresthatincreaseconveyance.....................................................................................92.3.3 Measuresthatmodifysusceptibilitytoflooding................................................................102.3.4 Measurestoenhancegroundwaterrecharge....................................................................112.3.5 Measurestoreducegroundwaterpumping(inlieuofpumping)......................................132.3.6 Measurestomimicnaturalsitehydrology(Lowimpactdevelopment,orLID).................14

    3 Screening.............................................................................................................................................153.1 Effectiveness...............................................................................................................................163.2 Physicalfeasibility.......................................................................................................................173.2.1 Floodhazardreductionpotential.......................................................................................173.2.2 Rechargepotential..............................................................................................................20

    3.3 Screenedprojecttypesbylocation.............................................................................................224 Prioritization.......................................................................................................................................244.1 Approach.....................................................................................................................................244.2 Step1:Implementationfeasibility..............................................................................................254.3 Step2:Greatestpotentialcorebenefits.....................................................................................284.3.1 Floodhazardreductionbenefitsconsiderations................................................................284.3.2 Rechargebenefitsconsiderations.......................................................................................294.3.3 Combinedfloodhazardreductionandrechargebenefits..................................................30

    4.4 Step3:Supportingobjectivesandabsenceofwaterqualityconcerns......................................324.5 Prioritylistofprojectconcepts...................................................................................................33

    5 NextSteps...........................................................................................................................................346 References..........................................................................................................................................35TablesTable1.Measurestoreducefloodhazardsandenhancegroundwaterrecharge.......................................5Table2.Retainedprojecttypesbyhydrologicsubbasin............................................................................22Table3.Projecttypes,bylocation,foradvancementtoprioritizationStep2...........................................28Table4.Projecttypes,bylocation,foradvancementtoprioritizationStep3...........................................31Table5.Potentialforprioritizedprojecttypestoaddresssupportingobjectives.....................................32Table6.Projecttypes,bylocation,foradvancementfromStep3totheprioritylist...............................33

  • SonomaValleyStormwaterManagementandGroundwaterRechargeScopingStudyScreeningEvaluationandPrioritizationMemorandum

    ii Parker GroundwaterParker Groundwater

    FiguresFigure1.Projectdevelopmentprocess........................................................................................................3Figure2.Flowchartofscreeningandprioritizationprocess.........................................................................4Figure3.Groundwaterrechargemethods.................................................................................................13Figure4.Surfacewaterhydrologymodelschematic,upperandmiddleSonomaCreekwatershed(fromPWA,2004).................................................................................................................................................18Figure5.SubbasincontributionstopeakfloodflowsonSonomaCreekattheoutletofsubbasinSon4(belowDowdallCreek,derivedfrommodelofDecember31,2005floodeventdescribedinPWA,2008)....................................................................................................................................................................19Plates(includedfollowingthereporttext)Plate1. FloodHazardReductionPotentialbySubbasinsPlate2. AreaswithSlopeLessthan10PercentandAreaswithGeologicRechargePotentialGreaterthan

    orEqualtoFairPlate3. FloodHazardReductionPotentialbySubbasinsandPhysicalFeasibilityScreeningPlate4. AreaswithSlopesLessThan5and10PercentandAreaswithGeologicRechargePotential

    GreaterthanorEqualtoFairPlate5. AreaswithSlopesLessThan5and10PercentandAreaswithGeologicRechargePotential

    GreaterthanorEqualtoGoodPlate6. ProjectPrioritizationwithFloodHazardReductionandPhysicalFeasibilityPlate7. ProjectPrioritizationwithFloodHazardReduction,PhysicalFeasibility,andAreasof

    GroundwaterDepression

  • SonomaValleyStormwaterManagementandGroundwaterRechargeScopingStudyScreeningEvaluationandPrioritizationMemorandum

    \\Sfofile01\esapwa\Data\projects\2050_Sonoma_Valley\ProjectConcepts\Sonoma_Scoping_Screening_Memo_Final_043012.docx4/30/2012

    1Parker GroundwaterParker Groundwater

    1 Introduction TheSonomaCountyWaterAgency(WaterAgency)seekstoidentifypotentialprojectswithintheSonomaValleythatcanmeetstormwatermanagementandgroundwaterrechargegoals.TheWaterAgencyhascontractedwithESAPWA,DanielB.Stephens&Associates,ParkerGroundwater,andothersubconsultantstodeveloptheseprojectconcepts,vetthemwithSonomaValleystakeholders,andhelpidentifypotentialfundingsources.

    1.1 Project purpose AnimmediateactionoftheWaterAgencys2010WaterSupplyStrategiesActionPlanisidentificationofprojectswithinWaterAgencyfloodcontrolzonesthatreducefloodingandincreasegroundwaterrecharge.AnimportanttoolinidentifyingandimprovingwaterresourcemanagementintheSonomaValleyisthe2007GroundwaterManagementPlan(GMP).TheGMPidentifiesstormwaterrechargeasakeyactiontowardsachievinggroundwatersustainability.OtherkeyactionsidentifiedintheGMPincludegroundwaterbanking,increaseduseofrecycledwaterandconservationandotherdemandreductionmeasures.TheSonomaValleyGMPgoalgroundwatersustainabilitycannotbereachedwithoutimplementationofeachoftheseactions.

    ThegoaloftheSonomaValleyStormwaterManagementandGroundwaterRechargeScopingStudyistodeveloponeormorestormwatermanagement/groundwaterrechargeprojectsthataddresstheKeyProjectPurpose:reducingfloodhazardsandincreasingopportunitiesforgroundwaterrechargewithintheSonomaCreekwatershed.

    Forthepurposesofthiseffort,aprojectmayconsistofeitherasinglefacilityorasuiteofelementsthatfunctionphysicallyasstandaloneprojectsbutcollectivelyaddresscoreprojectobjectives.Forexample,asinglefacilityoptionmightbearetentionbasinforstormwaterthatreducesthesizeofafloodpeakwhileenhancinggroundwaterrecharge.Amultipleelementprojectmightincludeaprojecttocreatead