EVALUATION OF AN OFFSHORE BREAKWATER SYSTEM

EVALUATION OF AN OFFSHORE BREAKWATER SYSTEM ADJACENT TO AND SOUTH OF GREAT KILLS HARBOR

PROJECT GOALS AND ASSUMPTIONS

• Identifyandevaluateapproachesforashoreprotectionsystemthatmaximizesstormprotectionandmarinehabitatvalueandincludesanoffshorebreakwatersystem

• Modeleffectivenessoftwoapproachestoattenuatewavesandotherwiseincreasetheresiliencyoftheshoreline

• Evaluateandsummarizethecosts,benefits,andenvironmentalandsocialimplicationsfortheselectedapproaches

• InformUSACEComprehensiveStudy,ORRinitiatives,andotheragencyprojectsinthearea• Thestudyisnotmeanttolookatstrategiesthatsolelyreducestillwaterflooding,anddoes

notincludewaterqualityandcirculationorsedimentanalysis

BENTHIC SURVEY

COMPARISON OF TRANSECT 1&4: • Transect1istheonlytransectwithhabitatpreferredbynorthernquahog.Habitatvalueis

likelyenhancedbyCrooke’sPointprotection.• OthersouthshoresitesexposedtoopenoceanwavesarelikelytobecomparabletoTransect

4.Breakwaterprotectioncouldencouragehabitatsimilartotransect1.• BreakwaterconstructioninTransect4zonewouldhavelesshabitatimpactduetolongshore

drift.ConstructioninTransect1zonewouldhavehigherimpactswithinconstructionfootprint,butcouldenhancehabitatsontheleesideovertime.

COMPARISON OF TRANSECT 2&3: • Transects2&3hadsimilarsubstrateandreducedhabitatvalueduetoanoxicconditions.• Thesetransectsillustratethereductioninhabitatvaluecausedbypoorwatercirculationand

urbanpollution.

1

2

3

4

MARINE WILDLIFE

Clams

Crabs/Arthropods/Snails

Finfish

Amphipods

gravel + sand

gravel + silt

sand

silt/clay

All benthic data was collected on September 18, 2014 by OCC in the Great Kills Harbor area. Please see the Great Kills Benthic Survey report for more detailed field notes and analysis.

SEDIMENT TYPE

transect

SamplefromTransect1

SamplefromTransect2

Nor’eastermodelingresults,toprow:option0,option1,option2Sandymodelingresults,bottomrow:option0,option1,option2

DESIGN CONCLUSIONS

CROOKE’S POINTactsasaneffectivewaveattenuatorfortheharborinteriorforstormgeneratedwaves.Localwindgeneratedwavescanbeeffectivelymitigatedthroughwavesscreensorcomparablestructures.ThepointiscurrentlymigratingtothesouthintotheUSACEfederalchannel,whichwasdredgedin2014.Couldconsidermovingthechannelsouthwardtoallowpeninsulamigrationtoprovideadditionalprotection.

NICHOLS MARINAwasshowntobeprotectedbyCrooke’sPointandnotimpactedbyoffshorewaves.On-shoreandoffshorestrategiescouldhaveerosionandotherstormprotectionbenefits.

CRESCENT BEACHisvulnerabletostorm-generatedwaves.Neitheroptionstudiedwasoptimal,howeverlessonscanbelearnedfromboth:

-Effectivewaveattenuationcanbe providedbybreakwatersintheCrescentBeacharea

-Option1providesmoreprotectiontosmallersectionofshoreline.

-Option2provideslessprotection,mostlyduetothesizeofthegapsinthebreakwaterdesign.

OPTION 2 BREAKWATER ALIGNMENT

1/10mile

250ft

varia

ble

(73

- 94

ft)

600

ft

EXPOSED BREAKWATER UNDERWATER BREAKWATER FOOTPRINT 11’ NAVD88 height 16’ crest width

DUNE

14’ NAVD88

0.25 0.50.125

miles

N

OPTION 1BREAKWATER ALIGNMENT EXPOSED BREAKWATER UNDERWATER BREAKWATER FOOTPRINT 11’ NAVD88 height 16’ crest width

1/4 mile

1450

ft

600 ft

450 ftfrom channel

1/10mile

1400

ft

0.25 0.50.125

miles

N

DAMAGE ASSESSMENT

ANALYSIS OF ‘DAMAGES AVOIDED’ FOR: • Stormscenariosmodeled• Gradualerosion(basedonhistoricerosionrates)

WHAT CAN / WILL BE ASSESSED:• Sitetobeconsideredastwoseparatepieces:insidetheharbor/outsidethe

harborandwillfocusonareaswhereoffshorebreakwatersshowimpacts: CrescentBeacharea

• Wehavetobeabletoattributethedamagestowaves• Willlookatwavedamageimpactsonbuildings,andpotentiallyshoreline

protectioninfrastructure

PreliminarylookatSandyimpacts:option0,option1,option2

4.5’waveheight 3’waveheight 1.5’waveheight

NEXT STEPS

FINAL RESULTS:Completionandcirculationoffinalresultsandreport

FUTURE STUDY: recommendationsforfuturestudy• Iterativedesignandmodelingadvancingdesignconclusionsofthisstudy• Sedimenttransportmodelingforerosionandsedimentationimpacts

LARGER RESILIENCY RESEARCH NEEDS: Articulationofresearchneeds,suchaswavedamagefunctions

REPLICABILITY: identificationofothersuitablesitesforimplementation

Storm Surge

Normal Tide

Normal Tide

Waves

Storm Surge

Waves

Flood Elevation = surge + waves

Flood Elevation = surge + waves

w/o breakwater

w/ breakwater

Storm Surge

Normal Tide

Normal Tide

Waves

Storm Surge

Waves

Flood Elevation = surge + waves

Flood Elevation = surge + waves

w/o breakwater

w/ breakwater

Storm Surge

Normal Tide

Normal Tide

Waves

Storm Surge

Waves

Flood Elevation = surge + waves

Flood Elevation = surge + waves

w/o breakwater

w/ breakwater

Storm Surge

Normal Tide

Normal Tide

Waves

Storm Surge

Waves

Flood Elevation = surge + waves

Flood Elevation = surge + waves

w/o breakwater

w/ breakwater

waveimpactsduringfrequentnor’easters(top)andhurricaneevents(below)