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

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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

1

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.

1

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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t4 long term