rebuilding to new base flood elevation requirements after sandy
DESCRIPTION
Mapping Coastal Flood Hazards; Building Requirements in the Flood Zone; Challenges to rebuilding to new standardsTRANSCRIPT
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1RebuildingtoNewBaseFlood
ElevationRequirementsafterSandy
TomHerrington,Ph.DOceanEngineeringDirector
DFISuperPile 2013May1516,2013
OutlineofThisMorningsPresentation MappingCoastalFloodHazards
BuildingRequirementsintheFloodZone
HurricaneSandy AdvisoryBFEs ChallengesinRebuildingtoNewStandards
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2NationalFloodInsuranceProgram TheNationalFloodInsurance
Program(NFIP)wascreatedin1968tohelpprovideameansforpropertyownerstofinanciallyprotectthemselves.
TheNFIPoffersfloodinsurancetohomeowners,renters,andbusinessownersiftheircommunityparticipatesintheNFIP.
ParticipatingcommunitiesagreetoadoptandenforceordinancesthatmeetorexceedFEMArequirementstoreducetheriskofflooding.
TraditionalNFIPServices UndertheNFIP,FEMAconductsFloodInsuranceStudiesthatanalyzetheriskoffloodingandmodelsthehydrologicconditionsduringthe1in100yearfloodevent(1%annualprobabilityevent)
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3FloodInsuranceRateMap(FIRM)
MapModernizationProgram
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4NJCoastalFloodMapModernizationStartedinOctober2009
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5CoastalMapping&Modeling Utilizes:
Highresolutiontopography/bathymetrydata
AdvancedSurgeandWaveNumericalModels
HistoricandSimulatedStormEvents
DevelopsaJointProbabilityofexceedence waterlevels
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6OverlandWaveModeling Oncesurgeandwaveelevationsarecompleted,erosionandoverlandwavepropagationismodeled
RevisedFloodHazardMaps
DepthGrid
WavePropagationGrid
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7PreSandyProjectTimeline
BuildingintheFloodplain FEMAdelineatesthecoastal
floodplainintofourspecificzonesbasedonwaveheightandfloodwatervelocity:
Vzone:waveheights>3ftCoastalAzone:waveheights>1.5ftAzone: waveheights
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8BaseFloodElevationsarebasedonWaveCrestHeight
BuildingRequirementsvarybyFloodZone Vzone:
OpenPileFoundationwiththelowesthorizontalmemberabovetheBFE
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9BuildingRequirementsvarybyFloodZone CoastalAzone:
OpenorclosedfoundationwithfirstfloorabovetheBFE
HurricaneSandy
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SandyLandfall
SandyLandfall
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SandySurge
LocationMap
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SurgeandDamage
LongBeachTownship
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SandyOrtleyBeach
NewJerseyDepartmentofEnvironmentalProtectionBureauofCoastalEngineering ShoreProtectionProgram
Sandy OrtleyBeach
NewJerseyDepartmentofEnvironmentalProtectionBureauofCoastalEngineering ShoreProtectionProgram
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Sandy OrtleyBeachSurfClub
NewJerseyDepartmentofEnvironmentalProtectionBureauofCoastalEngineering ShoreProtectionProgram
Sandy OrtleyBeachSurfClub
NewJerseyDepartmentofEnvironmentalProtectionBureauofCoastalEngineering ShoreProtectionProgram
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SevereDamageMechanism Mostsignificantlydamage
structuresweredisplacedorunderminedduetowavesandhighvelocityflow
Almostallstructureswereslabongrade,piersupported,ormasonryfoundationsconstructedbeforetheNFIPprogram
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BayShoreSurgeBackBay 6ftsurge
NewJerseyDepartmentofEnvironmentalProtectionBureauofCoastalEngineering ShoreProtectionProgram
FEMADamageAssessment
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StillWaterFloodImpacts Sixfootstormsurge
inundatedmanyhomeswith4to5feetofwater
Allutilitiesandmechanicalsystemssubmerged
Waterwickingindrywall
Poststormmoldinfestation
DevelopmentofAdvisoryBFEs PriortoSandy,FEMAwasperformingarestudyoftheNew
JerseyandNewYorkcoastlinewithanticipatedproductstobedeliveredinmid2013.
SincetheeffectiveinformationformanyoftheareasofNJandNYdonotcurrentlyreflectthebestavailabledataandtheregulatoryproductshavenotbeenfinalizedtobedeliveredtolocalofficialsandthepublic,FEMAbelieveditwasvitaltoprovideneartermAdvisoryBaseFloodElevations(ABFEs)tosupportreconstructionefforts.
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AdvisoryMethodology Requirements:
NeededaquickwaytoestimatewaveheightsinordertoleverageupdatedSWELs Advisorydataneededwithinweeks,notmonths ConsistentwithmethodologiesusedforFIS Generallybutnotoverlyconservative Stronginterestin0.2%annualchanceadvisoryelevations
BasedinpartonthemethodologyrecommendedbyNationalAcademyofSciences(NAS,1977) Wavesassumedtobedepthlimited,samecoefficientusedasWHAFIS AdjustforportionofwaveabovetheSWEL Appliedusingboth1%and0.2%annualchanceSWELs
Limitations Noactualmodelingofwaveheights Erosionnotevaluated Doesnotaccountforlanduse (buildings,vegetation) Doesnotaccountforflood/erosioncontrolstructures
AdvisoryBaseFloodElevationMap
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ImpactofMapChanges
ImpactofMapChanges
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ImpactofMapChangesNowHighVelocityWaveZones
ImpactofMapChanges
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ExistingBuildingType
ExistingGrade~2.5to3.0ftNAVD88NeedtoElevate5to7feet
LocalMitigationResponse Homeownersstrugglingto
elevatehomestomeetnewABFEs
CommunitiesapplyingforHMGPfundstohelphomeowners
PossibleuseofHUDcommunityBlockGrants
Statediscussingopenspaceacquisitionfund
Significantconcernoverredevelopmentandchangingcharacterofshore
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LocalMitigationResponse HomesthathavebeenrezonedintoVzonesmustbeelevatedonopenpilefoundations
Manyhomesarelocatedinhighdensityareas Smalllotsize Highimperviouscoverage
VzoneFoundationRequirements OnlydeepopenfoundationsareallowableinthecoastalVzone
Allowsfloodwaterandwavestopassthroughstructurereducingloads
Allowsforsoilerosionandscourunderstructurewithoutundermining
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VzoneFoundationDesign SandySoilswithsubsurfaceorganicstratacommonalongMidAtlanticshoreline
Bearingcapacityofpilesdominatedbyskinfrictionalongpile
Timberpilefoundationsmostcosteffective
VzoneFoundationDesign Lateralloadingismostcriticaldesignelement
StructureneedstobeelevatedabovegradetotheBFE,whichcreatessignificantbendingmomentbetweentheloadpointandthepointoffixity
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FailureMode
NearcollapseduetoinsufficientpileembedmentduringKatrina(DauphinIsland,AL)FEMA55C
ScourandErosion Anunderstandingofthe
maximumwaveinducedscouranderosionisrequiredtosizepilescorrectly.
GoodEstimate: STOT =6xpiledia.or6ftfor
a12india.Pilewithoutgradebeams
InNJexposedpilelengthsinnewVzones: 11to13feet
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DeepFoundationPileRequirements Timberpilelengthsof25
to35feettypicallyusedtoinsurepointoffixitywillresistoverturningmomentaftererosion
Pilesaredrivenformaximumfriction
Canbejettedorplacedinaugered holebutearthpressuresarereduced40%
StiffeningtheFoundation Gradebeamscanbeusedtomovethepointoffixitytowardgrade
Createsresistancetorotationunderlateralloading
Ifexposed,additionalhydrodynamicloadswillbegeneratedatgradebeam
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Challenges
Highdensitydevelopment
Elevatingexistingstructures5to7ftabovegradeon20+footpiles
Obtainingappropriatebearingcapacityandresistancetolateralloads
PossibleSolutions Augering holesunderelevatedstructure
Castinginplacereinforcedconcretepilesandpilecap
Attachingpileorconstructingmasonrysupportcolumn
Issue:Connectionatpilecap
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PossibleSolutions Drillingpileunderelevatedstructure.
Constructingsectionalsteelpile,similartodrillpipe.
Extendpileabovegradetorequiredheight
Issue:Sectionconnections
PossibleSolutions HelicalScrewFoundations
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OtherSolutions?
OpenDeepPileFoundationsWork
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ThankYou!