ocean beach coastal management framework update
TRANSCRIPT
critical reachesSouth of Sloat Blvd
about this project
Although the threat of erosion is chronic and will increase, most areas currently have either:
• adequateinterimprotection(revetments,sandbags,sand,orrubble)or• sufficientdistancebetweentheerodingbluffandtheLakeMercedTunnel
erosion + emergency revetments
project overviewco
asta
l man
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+ SPUR
+ ESA/PWA
+MOFFATT&NICHOL
+ JACOBSASSOCIATES
+AGS,INC
+AECOM
+ SanFranciscoPublicUtilitiesCommission
+ GoldenGateNationalRecreationalArea
+ SanFranciscoDepartmentofPublicWorks
+ CACoastalCommission
+ USArmyCorpsofEngineers
+ SanFranciscoPublicUtilitiesCommission
+ CAStateCoastalConservancy
project team project partners project funders
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theOceanBeachCoastalManagementFrameworkprojectistestingandrefiningthecoastalmanagementconceptsrecommendedintheOceanBeachMasterPlan
it will map out a long-range strategy as well as near-term actions
it is a multi-objective process: that considers coastal access, ecological functions, and aesthetics, in addition to protecting infrastructure
Itishopedthatthisframeworkcanbethebasisofaformalinteragencyagreementtocoordinatethelong-termstewardshipofOceanBeach
sloatparkinglot1990
erosionearly2000’s,rubblereach
emergencyrepair2010,reach1
erosion2012,reach3 sandplacement2012,northlotreach
sandplacement2012,northlotreach
erosion2010,northlotreach
erosion2012,northlotreach
existing conditions
REACH1
REACH2
RUBBLEREACH
EQRREACH
REACH
3NORTHLOTREACH
SFZOO
2010SANDBAGREVETMENT
2010EMERGENCYBLUFFTOEPROTECTION
SLOATBLVD
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2012 SAND PLACEMENT
1997 EMERGENCY BLUFF TOE PROTECTION
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Immediate-TermCoastalManagementPlan(2014-2016)
sand placementThismeasurewouldrepeatthesand
placementthatoccurredin2012,when
73,000cubicyardsofexcesssandwere
truckedfromtheNorthendofOcean
Beach.This“sacrificial”protectionis
expectedtowashaway,butmeanwhile
provides erosion protection while improving
aestheticsandcoastalaccess.Measure
to minimize windblown sand will be
implemented.
sandbag structureSandbags provide a removable and less
intrusiveformofcoastalprotection.Existing
sandbags,placedin2011,haveperformed
well, and are often covered with sand.
rubble consolidationAs a first step toward cleanup of rubble
exposedbyerosion,rubblewouldbe
cleared from parts of the beach and
consolidated close to the bluff toe, where it
would provide a degree of protection from
erosion.
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2
3
erosion + emergency revetments
what’s happening in the short term?
Whilelong-rangeplansarebeingdevelopedandimplemented,OceanBeachisexposedtoerosionhazards.SFPUCanditspartnersareproposingaplantomanagetheerosioninimmediatefuture.Itwill:
•utilizeproven‘softer’interventionsincoordinatedpackage
•barringextremeevents;theseshouldbysufficientatleastthroughspring2016
•theintentistosecurepermitsandclearancesinadvancetoallowforrapidimplementation,and:
•demonstratecommitmenttopro-active/adaptivemanagement
existingrubbleproposedtobeconsolidated
sandbagstructure2012
sandbackpassing2012
3 proposed management actions
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key findings
large scale beach nourishmentnourishment
New analysis is validating the Ocean Beach Master Plan approach, which combines:
•managedretreat
•beachnourishment
•low-profilestructuralprotection
toe of bluff offsetTheengineeringteamandtechnicaladvisorsarepreparingarevised hazard analysis, detailing the probability of coastal erosion threatening theLakeMercedTunnel.
The analysis incorporates climate change,includinglikelysealevelriseandtheincreasedfrequencyandintensityofstorms.
Additionalgeotechnicalworkwillbeconducted,todeterminethepreciselocationandmakeupoferodingmaterials.
hazard analysis
Tunnel Response to Unloading
Subjacent lateral support reduced
r
Distortion Ratio:r / r
r = Radius
ConsultingstructuralengineersareexaminingtheLakeMercedTunnelandtheforcesthatwould act on it if the bluff recedes.
Initialresultsshowthatrequiredbuffer distances can be significantly reduced over earlier,morecautiousassumptions.Thismeansthat more space is available for coastal retreat and surface restoration of the beach and bluffs.
tunnel strucutural modeling
Structures will be installed from above, behind the bluff face, and will be invisibleuntileventuallyexposedbyerosion.Severalavailabletechniquesareunderconsideration.
Several different methods of low-profile structural protection are under consideration, inluding jet grout walls.
Oncestructuralprotectionsegmentsareinplace,existing revetments, sandbags and exposed rubble can be removedinthatarea.Cobble,sand,andnativevegetationwouldthenbeplacedoverthestructuretorestorethesurface.
Ifandwhenerodingbluffsapproachastructure,itwouldbefinishedwithaconcretecapand/orfacing.Evenoncecomplete,structureswouldlikelybeinvisiblemuchofthetime,liketheexistingTaravalseawall.
low-profilestructuralprotection
TheCityandCountyofSanFranciscoiscontinuingtopursuelarge-scalebeachnourishmentinpartnershipwiththeUSArmyCorpsofEngineers,whodredgeapproximately300,000cubicyardofcleansandfromtheMarineShippingChannelnearOceanBeach.
ThispartnershipwouldallowsignificantwideningofOceanBeachinerosion-proneareas,andisanimportantmanagementtoolrecommendedintheOceanBeachMasterPlan.
Permitting efforts are underway.
taraval seawalljet grout wall
Structures to protect the Lake Merced Tunnel will be installed in segments where:
•erosionencroachesondefinedtriggersor,
•wherecleanuporremovalofexistingstructuresisapriority
SFZOO
lakemercedtunnel
50’offsert
100’offset
existingtoeofbluff
SLOATBLVD
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nextsteps
coastal management and protection sequencing-
1-typicalcondition
4-sub-surfacewall
7-nourishment
2-managedretreat
5-beachcleanup
8-restoration
3-sandplacement
6-expectederosion
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A typical existing condition at Ocean Beach showing the Great Highway and stone revetments.
As the beach recedes further, subsurface structural protection is proposed for the Lake Merced tunnel, and the removal of the Great Highway south of Sloat Boulevard to allow surface restoration and coastal access.
Once erosion has reached a significant point, round stone cobble and sand would be placed to create a dynamic dune system, with the ability to dissipate the erosive forces of the ocean.
As the beach recedes, the Great Highway will be narrowed (see transportation study).
With the new structural protection in place and the Great Highway removed, restoration becomes possible.
With the dune system in place, resoration of native vegetation could occur effectively.
Periodic large scale placement of sand (beach nourishment) will slow erosion and maintain the quality of the beach in the near or medium term.
As erosion continues, the protective structure around the Lake Merced Tunnel may become exposed periodically, similar to the Taraval sea wall today.
Thiseffortwilltakesignificanttimeandefforttoplan,reviewenvironmentally,design,fund,permit,andconstruct.Itwillrequireasustainedcollaborationamongcityagencies,GGNRA,theArmyCorps,andtheCaliforniaCoastalCommission.
TheCityandCountyofSanFranciscohasinitiatedaprocesstoupdatetheWesternShorelinePlan,SanFrancisco’s“LocalCoastalProgram”.Thisprocess,subjecttoreviewbytheCoastalCommission,willprovidetheplanningbasisforsustainable,long-termcoastalmanagementatOceanBeach.
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