a comparative cost analysis of ten shoreprotection approaches at three sites under two sea level...

AComparativeCostAnalysisofTenShore

ProtectionApproachesatThreeSites

UnderTwoSeaLevelRiseScenarios

Preparedfor:

HudsonRiverValleyGreenway

HudsonRiverNationalEstuarine

ResearchReserve

Asapartof:

TheHudsonRiver

SustainableShorelinesProject

Preparedby:

AndrewJ.Rella,&

JonK.Miller,Ph.D.

July2012

i

Acknowledgements

This reportwaspreparedbyAndrewRellaand Jon Miller of Stevens Institute ofTechnology in the course of performingwork contracted for the Hudson RiverSustainableShorelinesProject.

Theauthorswould liketoacknowledgetheSustainable Shorelines coordinating team,especiallyEmilieHauser,DaveStrayer,andKristinMarcellfortheirassistance.Reviewsof the cost estimate approach by KlausJacob,PaulKirshen,andRickGilbertgreatlyimprovedthefinaldocument.

AbouttheHudsonRiverEstuary

TheHudsonRiverEstuary isanarrow,152milearmof the sea thatextends from thesouthern tip of Manhattan north to theTroyDam.Themaximumwidthoftheriveris 3miles in the Tappan Zee, butmost ofthe river is0.51milewide,and theuppersection near Albany is less than 0.5 mileswide.Muchoftheriver is2050feetdeep,and a 32 foot deep navigation channelextendsallthewaytoAlbany.However,theriveralso containsextensive shallowwaterareas thatare less than5 feetdeepat lowtide, many of which support wetlands orbedsofsubmersedvegetation.Muchoftheriver bottom is sand or mud, althoughpatchesofgravel,cobble,relictoysterreefs,anddebrisdoexist.Theaveragetidalrangealong the Hudson River is about 4 feet,peaking at 5 feet at either end of theestuary. In periods of normal freshwaterflows,strongtidalflows(oftengreaterthan2ft/sec)reversethedirectionofwaterflow

every six hours throughout the entireestuary, and are roughly10 times as largeas downriver flow of fresh water. Waterlevelsarealsodeterminedchieflyby tides,but canbe strongly affectedbyhigh flowsfromupriverand tributaries,andby stormsurges. The transition from fresh tosaltwater occurs in the lower half of theriver, depending on freshwater flows andtides.

Forces impinging on the Hudsons shoresinclude winddriven waves, wakes fromcommercial and recreational vessels,currentsfromtidesanddownriverflow,andfloating debris and ice driven onshore bythese forces.Dependingon their exposuretowind,currents,wakes,and ice,andtheirposition relative to the navigation channeland protective shallows, different parts oftheHudsons shores receive very differentinputs of physical energy. Likewise, landusesonthelandwardsideoftheshoreandwaterdependent uses on the riverwardsideof the shore arehighly variable alongtheHudson.As a result, different parts ofthe Hudson place very different demandsonengineeredstructuresalongtheshore.

Theshorelinehasbeendramaticallyalteredover the last150years tosupport industryand other development, contain channeldredgespoils,andwithstanderosion.Abouthalfoftheshorelinehasbeenconspicuouslyengineered with revetment, bulkhead,cribbing or reinforced with riprap. Manyadditional shorelines contain remnantengineeredstructuresfromprevioushumanactivities. The remaining natural

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shorelines (which however have beenaffected by human activities such asdisposal of dredge spoil, invasive species,and contaminants) include a mix ofwooded, grassy, and unvegetatedcommunities on mud, sand, cobbles, andbedrock. Milleretal. (2006)performedaninventory of Hudson River shorelinesbetween the Tappan Zee Bridge and theheadoftideatthefederaldamatTroyandproposeda five levelclassificationscheme.Of the250milesof shorelines inventoried,42% were hard engineered, 47% werenatural, and 11% were natural withremnants of engineering structures. Themost common shoreline structurewas riprap (32%), followed by woody (29%) andunvegetated (16%) slopes. The dominantsubstrate found within the region wasunconsolidatedrock(52%),mud/sand(16%)andmixedsoil/rock(12%).

About the Sustainable ShorelinesProject

The Hudson River Sustainable ShorelinesProject is a multiyear effort lead by theNew York State Department ofEnvironmental Conservation Hudson RiverNational Estuarine Research Reserve incooperation with the GreenwayConservancy for the Hudson River Valley.Partners in the project include CaryInstitute for Ecosystem Studies, NYSDECHudsonRiverEstuaryProgramandStevensInstitute of Technology. The ConsensusBuildingInstitutefacilitatestheproject.

The project is supported by the NationalEstuarineResearchReserveSystemScience

Collaborative,apartnershipoftheNationalOceanic and Atmospheric AdministrationandtheUniversityofNewHampshire. TheScience Collaborative puts Reservebasedscience to work for coastal communitiescopingwiththeimpactsoflandusechange,pollution, and habitat degradation in thecontextofachangingclimate.

Disclaimer

The opinions expressed in this report arethoseoftheauthorsanddonotnecessarilyreflect those of the New York StateDepartmentofEnvironmentalConservationand the Greenway Conservancy for theHudson River Valley or our funders.Reference to any specific product, service,process,ormethoddoesnotconstituteanimplied or expressed recommendation orendorsement of it. Generic shorelinetreatments for specific locations on theHudsonRiverEstuaryarepresentedforthepurpose of developing the relative costanalysis.Theiruse in thisanalysisdoesnotimply regulatory approval of any suchmethod at a particular site. The HudsonRiver isregulatedbyNewYorkStateunderNYSEnvironmentalConservationLaw (ECL)Article15,Part608 (UseandProtectionofWaters), and associated wetlands andadjacentbufferareasmaybe regulatedbyECL Article 24 Part 663 (FreshwaterWetlands) or Article 25, Part 661 (TidalWetlands). Individualprojectproposalsareevaluatedon a caseby casebasisbyDEC,and each project must meet permitissuancestandards.TheUnitedStatesArmyCorps of Engineers also has regulatory

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jurisdiction of adjacent federally regulatedwetlands and the Hudson River as anavigable waterway. Project sponsorsshould contact theUSACOE and request ajurisdictional determination from thatagency.

Terminology

There are many ways to describe bothstandard and innovative engineeringmethods toprotect shoreline. TheHudsonRiver Sustainable Shorelines Project usesthe termecologicallyenhancedengineeredshoreline to denote innovative techniquesthat incorporatemeasures to enhance theattractiveness of the approach to bothterrestrial and marine biota. SomedocumentsandreportsoftheHudsonRiverSustainable Shorelines Project may useother terms to convey this meaning,including: alternatives to hardening, bioengineered, ecoalternatives, green,habitatfriendly, living, soft shorelines, orsoftengineeredshoreline.

SuggestedCitation:Rella,Andrew,andJonMiller,2012. AComparativeCostAnalysisof Ten Shore Protection Approaches atThree Sites Under Two Sea Level RiseScenarios.InassociationwithandpublishedbytheHudsonRiverSustainableShorelinesProject, Staatsburg, NY 12580,http://hrnerr.org.

HudsonRiverSustainableShorelinesProjectNYSDECHudsonRiverNationalEstuarineResearchReserveNorriePointEnvironmentalCenterStaatsburg,[email protected]://hrnerr.orgAuthorscontact:[email protected]

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ContentsIntroduction......................................................................................................................................1

Methodology................................................................................................................................2

Poughkeepsie.................................................................................................................................10

Bulkhead.....................................................................................................................................12

Revetment..................................................................................................................................20

RipRap.......................................................................................................................................22

JointPlanting..............................................................................................................................26

VegetatedGeogrid.....................................................................................................................29

CribWall.....................................................................................................................................32

LiveCribWall..............................................................................................................................36

Sill...............................................................................................................................................39

BowlinePointPark(HaverstrawBay)........................................................................................41

Bulkhead.....................................................................................................................................43

BioWall......................................................................................................................................43

Revetment..................................................................................................................................43

RipRap.......................................................................................................................................47

JointPlanting..............................................................................................................................50


CribWall.....................................................................................................................................53

LiveCribWall..............................................................................................................................53

Sill...............................................................................................................................................53

HenryHudsonPark(AlbanyCounty)..............................................................................................56

Bulkhead.....................................................................................................................................59

Revetment..................................................................................................................................68

RipRap.......................................................................................................................................71

JointPlanting..............................................................................................................................74


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CribWall.....................................................................................................................................80

LiveCribWall..............................................................................................................................84

Sill...............................................................................................................................................87

Summary.........................................................................................................................................91

GlossaryofTerms...........................................................................................................................94

References......................................................................................................................................96

DesignSketchAppendix

CostAnalysisAppendix

StatisticsAppendix

1

IntroductionTheHudson River Sustainable Shorelines Project is focused on bringing together communityleaders, scientists, engineers, and natural resourcemanagers to help peoplemake decisionsabout how to manage community waterfronts, control erosion and respond to increasedflooding andprojectedhigherwater levels. Theproject is generating information about theperformance, cost, and natural benefits of different shoreline management options, in thecontextoftheHudsonRiverEstuaryshumanandnaturalsetting.Theprojectisbeingguidedbytheexpressedneedsandinterestsoflocalgovernments,expertsandconsultants,shorelinelandowners, policymakers, and regulators. The goal of this project is to protect shorelines andassociatedwaterquality,wildlifehabitat,outdoorrecreation,andcommunityqualityoflifeforfuturegenerations.

Insupportoftheaboveobjectives,thisdocument laysoutthemethodologiesandproceduresutilized to perform a comparative cost assessment of ten different shoreline stabilizationapproachesat three sites,under two sea level rise scenarios. The tenapproaches, the threesites,and the two sea level rise scenarioswere selected in consultationwith theSustainableShorelinesProjectteam.Aseventyyeartimeframewasselectedfortheanalysis.

The ten approaches selected include: timber bulkhead, steel sheet pile bulkhead, biowalls,revetments,riprap,jointplanting,vegetatedgeogrids,timbercribbing,livecribwalls,andsills.TheseapproacheswereselectedbasedontheiruseorpotentialuseatsiteswithintheHudson,and cover the spectrum from more traditional approaches such as bulkheads, to moreinnovativeapproachessuchas jointplanting. Itshouldbenotedthatmanyof theapproachesfallintoacategoryofshoreprotectionalternativesidentifiedashybridapproachesduetotheirintegrationofstructuralandnonstructuralelements.

The three sites thatwere selected represent adiverse selectionof shoreline types typicalofthose foundalongtheHudson. Thesitesareactuallyasubsetofthoseanalyzed intheAldenandASA (2006)report.Theadvantagetousingthesesites isthatthemajorityoftherequiredsite information has already been collected, so the focus can be placed on designing thestructuresandpreparingthecostanalyses.TheHenryHudsonParksiteinAlbanyCounty,NewYork isamildmoderatelyslopedsitealongarelativelynarrow (~1000 ft),yetshallow (~20 ft)section of the estuary. The Poughkeepsie site is located along the eastern bank abutting arelativelydeep (~50 ft)sectionof theriver. ThesideslopesatPoughkeepsiearesteep, risingapproximately1footverticallyforevery1.5horizontally.TheBowlinePointParksiteinUpperHaverstrawBay inRocklandCountyrepresentstheoppositeextreme,withamildslopingbank(~1footverticalforevery20fthorizontal)abuttingashallow(~10ft)butwide(15,000ft)reachoftheriver.

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Theproject team selected two sea level rise scenarios for theanalysis. The first is simplyanextrapolation of the current rate over the next seventy years. The National Oceanic andAtmosphericAdministration(NOAA)archivesandanalyzesthedatacollectedbythetidegaugeattheBattery.Themostrecentdataplacestherateofsealevelriseat2.77mm/yr,orroughly10.9 per century (www.tidesandcurrents.noaa.gov/sltrends/index.shtml). Over the seventyyearprojectperiod,thiscorrespondstoapproximately7.6.Thesecondscenarioistherapidicemeltscenario,whichpredicts48inchesofsealevelriseby2080(NewYorkCityPanelonClimateChange,2009).Unlikethecurrenttrendwhichislinear,intherapidicemeltscenariotherateofsea level rise accelerates and the changes become more dramatic towards the end of thedecade.

Methodology

DesignPhilosophyThegeneral characteristicsofeach sitewereobtained from the siteprofilesanddescriptionspresentedinthe2006reportbyAldenandASA(Allen,etal.,2006).Supplementaryinformationsuch as estimates of the wind wave heights for each site was obtained through additionalanalyses. This informationwas used to develop the basic design parameters fromwhich areliablereconnaissancephasecostanalysiscouldbeperformed(USACE,2008). Thepurposeoftheanalysiswastocompareasmanyapproachesatasmanysitesaspossible. Asaresult,some designs were carried out at sites where their applicability is questionable. Only insituations where a given approach was considered extremely unsuitable given the siteconditionswas a design and cost analysis not performed. It should be recognized that thedesignsweredevelopedexpresslyforinputtothecostanalyses,andshouldnotbeconsideredcomplete for construction purposes. Sketches depicting the designs are presented in anAppendix.

CostDevelopmentFor each design, an estimate of the initial construction costwas obtained from one of twoapproaches. Whereavailable,thebulkcostsassociatedwithrecentlycompleted localprojectsof similar dimensionswere used to estimate the cost of protection per length of shoreline.Whenbulkcostswereeithernotavailableordeemed inappropriate,materialand laborcostswereestimatedandusedtodevelopthefinalcostestimate.Insuchcases,thefinalcostswerecrosscheckedagainstsimilarprojectsandestablishedrangestoensurethattheestimateswerereasonable. AnAppendixdetailing the cost information isprovided. Due to the sometimessignificant variation in material and labor costs, every effort was made to be consistentthroughouttofacilitatecomparisonsacrosssitesandmethods.

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The costestimatesweredevelopedusing a lifecycle cost approach. Thebasic lifecycle costswere separated into four main categories. The initial construction (IC) costs are the costsdescribedaboveassociatedwithconstructingeachofthealternativesasdesigned.

Maintenance and repair (M&R) costs refer to the costs associated with inspecting andperformingbasicmaintenanceforeachapproach.SomestructuressuchasbulkheadswillonlyrequireminimalM&Rcostswhileothers,particularly thosewithavegetativecomponentmayrequiremore. AllM&Rcostsare formulated in termsofapercentageof the initialcost. It isassumed thatM&Rcosts forseveraloftheapproacheswill increaseundertherapidsea levelrise scenario. M&Rcosts for shoreline stabilizationalternativeswitha livingcomponent (livecribwalls,vegetatedgeogrids, jointplanting)areassumedto increaseby10%. M&Rcostsforwoodenstructures(cribwalls,woodbulkheads)areassumedtoincreasesby5%.M&Rcostsfortheremainingstructuresareassumedtoremainthesame.Thepercentincreaseisintendedtobereflectiveoftheincreasedstressplacedondifferentmaterialsbyrisingsealevels.

Damage costs (DC) include costsoutsideof the typicalM&R costs created by storm impactsbelowthedesignlevel(50yr).Thesestormsmayhavespecificimpactsthatrequiresignificantmodifications to restore the original function of the shoreline stabilization approach. Jointplantingprovidesperhapstheclearestexample. Whilea10yrstormwillhaveminimalimpactonanadequatelydesignedbasestructure(riprapslopeorrevetment), itwillmost likelywipeout the vegetation. In this case, the damage costswould refer to the cost to replace thevegetationtorestoretheoriginalfunctionofthestabilizationapproach. Duringa50yrstorm,thebasestructuremightbedamagedinadditiontothevegetation,andboththe10yrand50yrdamagecostswouldbe incurred. Thispoint is subtle,but important,as thedamagecostsassociatedwitha50yrstormwillnotalwaysbegreaterthanthoseassociatedwitha40yearstorm. LikeM&Rcosts,damagecostsareformulated intermsofapercentageoftheoriginalcost.

Finally, some structures suchasbulkheadshavea finite lifespan,and regardlessof the stormconditionswillneed tobe replacedonceoreven twicewith the seventyyearperiod. In thelifecyclecostanalysis,thesecostsarereferredtoasreplacementcosts(RC).

SeaLevelRiseThetwosealevelrisescenariosareincorporatedintotheanalysisbyconsideringtheirimpactontheprobabilityofoccurrenceofsignificantstorms.Theapproachdiscussedbelowisasimplifiedmethodof treating returnperiodsandprobability. Additional information ispresented inanAppendix.Eachshorelinestabilizationapproachisdesignedtoresistthe50yearstorm,where50 year refers to the returnperiod (Tr)of the storm. The probabilityof thedesign stormoccurringinanygivenyearis:

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p=1/Tr

Forthe50yeardesignstorm,theannualprobabilityofoccurrenceis0.02.Theprobabilitythatthedesignstormwilloccuroveraperiodofnyearsis:

pn=1(1p)n

Therefore, theprobability that a50 year storm (p =0.02)willoccurwithin the (n=)70 yearanalysisperiod,is0.757.Theexpectedormostlikelynumberofoccurrences(s)duringaperiodofnyearshoweveris:

s=n/Tr

Forthe50yeardesignstorm,themost likelynumberofoccurrencesoverthe70yearanalysisperiodis1.4.

Sea level rise impacts the return period, because it raises the basewater level,making theextremesmoreandmorelikelytooccur.Tohelpillustratethis,theresultsofanextremevalueanalysisperformedontheBatteryParkwaterleveldata,areshowninFigure1.Theplotshowsthe relationshipbetweenwater level (xaxis),and cumulativeprobability,11/Tr (yaxis). Thewater level corresponding to the 10yr return period is approximately 12.25 ft. If the 10yrwaterlevelresultsindamage,overa25yearperiodthatcostcanbeexpectedtobeincurred2.5times. If sea levels rise0.5 ft, thebaseelevation is increasedand itno longer takesa10yrstormtoreachthatelevation.Infact,a5yrstorm,whichwasoriginallyassociatedwithawaterlevelof11.75ft,reachesthesameelevation(11.75ft+0.5ft=12.25ft).Overa25yearperiod,the5yrstormcanbeexpectedtooccur5times,ortwiceasoften,incurringdamagecostseachtime.Thepresentanalysisusesthismethodologytoincreasethefrequencywithwhichdamagecosts are incurred. While climate change is expected to have additional impacts related topotentialchanges inthefrequencyand intensityofstorms,andthedurationandextentof icecover,theseimpactsarenotaswelldocumentedandarenotconsideredhere.

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Figure1ExtremeValueAnalysisofWaterLevelDatafromBatteryPark.

Underthe firstsea levelrisescenario,theexistingrateofchange isassumedtocontinue intothefuture.Underthesecond,therateaccelerates,leadingtoamorerapidincreaseduringthesecondhalfoftheseventyyearperiodunderconsideration.Inordertosimplifytheanalysis,theseventyyearperiodisbrokenintothreeperiods,P1covering20122037(25years),P2covering20372062 (25 years), and P3 covering 20622082 (20 years). The amount of sea level risepredictedatthemidwaypointofeachperiod isusedtomodifythereturnperiodsduringthattimeframe. Thisslightlyoverestimates the returnperiodsduring the firsthalfofeachperiod,andunderestimates themduring the secondhalf,butgreatly simplifies theproblem. As thereturnperiodsarereduced,theexpectednumberofoccurrencesofagivenstormincreasewithtime,asdothepotentialdamages.Thetablesbelowsummarizethesealevelriseadjustments.

Table1SeaLevelriseIncreases.

SeaLevelRiseattheMidpointofEachPeriodPeriod CurrentRate(in) RapidIceMelt(in)P1(20122037) 1.32 9.00P2(20372062) 3.96 24.00P3(20622082) 6.34 41.00

10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 150

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1Extreme Value Analysis of Battery Park Water Levels

CY Water Level (ft StDat)

CD

F

Tr = 10 yrs

Tr = 5 yrs

Tr = 2 yrs

Data (Weibul Plot Pos)GEV DistributionGumbel Distribution

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Table2StormFrequencyModificationBasedonCurrentSeaLevelTrend.

CurrentRateofSLR P1(20122037) P2(20372062) P3(20622082)CurrentTr ModifiedTr #Storms ModifiedTr #Storms ModifiedTr #Storms50 44.9 0.56 33.3 0.75 24.7 1.0140 34.2 0.73 24.4 1.02 19.3 1.3025 22.2 1.13 16.3 1.53 11.7 2.1410 8.8 2.84 6.3 3.97 4.7 5.32

Table3StormFrequencyModificationBasedonRapidIceMeltScenario.

RapidIceMeltRateofSLR P1(20122037) P2(20372062) P3(20622082)CurrentTr ModifiedTr #Storms ModifiedTr #Storms ModifiedTr #Storms

50 18.5 1.35 2.7 9.26 1.0 25.0040 13.1 1.91 2.1 11.90 1.0 25.0025 8.3 3.01 1.5 16.67 1.0 25.0010 3.3 7.58 1.0 25.00 1.0 25.00

Itshouldbepointedoutthatatallthreesites,thedifferencebetweenmeanhighwater(MHW)andthetopofslopebasedontheprofilesintheAldenandASAreport(Allen,etal.,2006)isbetween36and46inches.Undertherapidsealevelrisescenario,theexistingbankatallthreesiteswillbesubmergedathightideatsomepointduringtheseventyyearstudyperiod.Whilethe analysis accounts for this by assuming the damages associated with even the smalleststormsrecuronayearlybasis,thelikelihoodisthatasignificantinterventionbeyondthescopeof this reportwouldbe required. Optionsmight include retreating inland, filling theadjacentareatoraisetheelevations,orconstructingafloodwallorberm.Whenconsideringtheresultsofthecostanalysisundertherapidsealevelrisescenario,considerationshouldbegiventothefactthatonceacriticalelevationisreached,likelynearthestartofperiodP3,criticaldecisionswillhavetobemade,andthepossibilityexiststhatallpriorshorelinestabilizationinvestmentswillbelost.

InflationandDiscountingThelifecyclecostanalysisusesapresentvalueapproachwhereallcostsareconvertedinto2012dollars. Allhistoriccost information isscaledupusingthemethodologyanddatacontained intheU.S.ArmyCorpsofEngineers,CivilWorksConstructionCost IndexSystem (CCWIS)guide.FuturecostsareinflatedusingtheCCWIS,butalsodiscountedata4%annualrateaccordingto

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themostrecent federalguidance (USACE,2012). TheCCWIS tablesonlyextend15years intothefuture.Inordertocovertheperiodofanalysis,therate(1.7%)usedinthetableswasheldconstantandprojectedthroughtheseventyyearprojectlife.Thefollowingexampleillustratestheuseoftheinflationanddiscountratesinthecostestimates.

Assume the cost in 2012 of building a bulkhead is $100,000. The cost in 2012 dollars toreconstructthebulkheadin2072isfirstadjustedtoaccountforinflationaccordingto:

$100,0001 0.017 $274,950

Theinflatedcostisthecostin2072toreconstructthebulkhead;howeverthecostmustalsobeadjustedtoaccountforthediscountrateifapresentvalueanalysisisused.Thisadjustmentisasfollows:

$274,950/1 0.04 $26,251

Thenet result is thecost in2012dollars that takes intoaccount thecompeting influencesofinflationanddiscounting.Error!Referencesourcenotfound.illustratesthatwiththeinflationset at 1.7% and the discount rate set at 4.0%, over time the discount rate has a morepronouncedimpactonthecostintermsofthepresentvalue.

AnexampleofthewaylifecyclecostsarecalculatedisprovidedbelowinFigure3.Thedifferentcolor boxes represent the four different types of costs: Initial (blue), maintenance (purple),damage (green), and replacement (yellow). The analysis is broken up into three differentperiods,withcostscalculatedatthemidpointofeach.Intheexampleshowntherearedamagesassociatedwithtwodifferentstorm levels. Theexpectednumberofstormsofeachtype(andthereforedamages)increasesduringperiods2and3duetosealevelrise.Boththedamageandthemaintenanceareformulatedasapercentageofthe initialcost. Inadditiontothedamageandmaintenance costs, theentire structure is replaced inperiods2&3. Allof the costs inperiods2and3areadjustedfor inflation,andthendiscountedbackto2012dollars. Thefinalcost is then thesumof the initialcost,and the inflatedanddiscountedcostsassociatedwithmaintenance,stormdamage,andreplacement.

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Figure2GrowthoftheInflationandDiscountTermswithTime.

0.0

0.1

1.0

10.0

2012 2022 2032 2042 2052 2062 2072

Infla

tion

/Discoun

tRatio

Date

InflationandDiscountRatioGrowth

CWCCISData 1.7%InflationTACCOMData 4%DiscountRateCombined

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Figure3DevelopmentofLifecycleCost.

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PoughkeepsieThePoughkeepsiesiteislocatedjustsouthoftheMidHudsonBridgealongtheeasternshoreoftheHudsonRiverasshowninFigure4Acrosssectionillustratingthesiteconditionsasof2006whichwaspresented in theAldenandASA (Allen,etal.,2006) report is reproducedhereasFigure5.ThemajorsitecharacteristicsaresummarizedinTable4.AsillustratedinFigure5,theexistingshoreline isbulkheadedwithaconcretecap. ThePoughkeepsieshoreline istypicalofmany of the steep sloped shorelines which have traditionally been bulkheaded. The Aldenreport attributed the erosion of the Poughkeepsie shoreline to scour from ice, waves, andwakes.Runofffrombehindthebulkheadwasalsocitedasaproblem.Windwaveheightswerecalculated using themethodologypresented inChapter 3, Section 6of the Shore ProtectionManual(USACE,1977),assumingawindspeedof50mphandaconstantdepthof50feet.ForthefourfetchesdefinedinFigure4thecalculatedwindwaveheightsareasshowninTable5.

Figure4PoughkeepsieSiteandFetchDelineations.

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Figure5ExistingCrosssectionatPoughkeepsie.

Table4PoughkeepsieSiteCharacteristicsandDimensions.

General Characteristics Width of River 2,600 ft Depth Range 30 125 ft Average Depth 50 ft Current Range 0-3 ft/s Mean Current Velocity (Main Channel) 1 ft/sec Mean Current Velocity (Shoreline) 1 ft/sec Side Slope 1V:1.6H Dimensions Above High Water Level Width 18 ft Height 3.5 ft Slope Length 18 ft

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Surface Area 9,013 ft2

Cross-section Area 31.5 ft2 Volume 15,750 ft3 Dimensions of Intertidal Zone Width 7 ft Height 3.5 ft Slope Length 7 ft Surface Area 3,536 ft2 Cross-section Area 12.25 ft2 Volume 6,125 ft3

Table5FetchesandRelatedWindWaveHeightsatPoughkeepsie.

Length (mi)

Wave Height (ft)

Fetch 1 2.00 2 Fetch 2 0.50 1.0 Fetch 3 0.75 1.3 Fetch 4 2.00 2.5

Inadditiontothecostsdescribedbelowwithineachsection,therewillbeacostassociatedwiththeremovaloftheexistingbulkheadstructureandrock.Asthiscostwillbeincurredregardlessoftheshorelinestabilizationapproachselected,itisnotincludedinthecostanalysis.

BulkheadBulkheadsareoneofthemorecommonshorelinestabilizationapproachesusedalongriverineandestuarinecoastlines. Bulkheadsareverticalsoilretentionstructuresdesignedtoeliminatebankerosionbyencapsulatingthesoilbehindit.Bulkheadscantakeseveralforms,howeverthetwomost common types are cantilevered bulkheads and anchored bulkheads. Cantileveredbulkheadsareusedinrelativelylowheightapplicationsandsimplyrelyontheirembedmentforsupport.Anchoredbulkheadsaresimilartocantileveredbulkheads,onlyananchoringsystemisaddedtoprovideadditionallateralsupport.DuetotherelativelylowgradesateachoftheHudsonRiversites,cantileveredbulkheadswereselectedforeachsite.Afterbalancingtheloadsandpressuresactingonthefrontandrearfacesofthebulkhead,thedesignparameterslistedinTable6wereobtained.

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Table6BulkheadDesignSummary.

HeightofWallAboveSubstrate 13.1ftDepthofPenetration 12.1ftTotalWallHeight 25.2ft

Bulkheadpricesvaryconsiderablydependingonthematerialselected.Costsforwood,steelandconcretebulkheadsareshownbelowinTable7,anddonotincludelaborcosts.Table7BulkheadMaterialCostComparison(Whalen,etal.,2011).

Material Steel Wood Concrete

CostRange/lf $7001,200 $116$265 $500$1000

Althoughnotexplicitlyconsideredinthisanalysis,bulkheadscanbemodifiedtoadapttorisingsealevelsthroughtheadditionofacap.Thecapwillnormallyconsistofeitherwoodsecuredtothe face of the bulkhead, or concrete cast to raise the elevation of the structure. Such amodificationmustbecarriedoutcarefullyhowever;aseffectively increasing theunsupportedlength of the structure changes the pressure distributions onwhich the original designwasbased. Oftentheadditionofananchorwillbenecessary ifthestructure isretrofit. Thecostassociatedwithsuchmodificationscanbesignificant.

WoodBulkheadGiventhesteepsideslopes,proximitytothenavigationchannelandexposuretorelativelylongfetches,anestimateof$265/lfor$132,500wasobtained for thematerialcosts. LaborcostswereestimatedbasedontheprevailingwageformarineconstructionintheStateofNewYork(http://wpp.labor.state.ny.us/wpp/publicViewPWChanges.do). Assuming 400 man hours forconstruction,at$35/hr,anestimateof$14,000for labor isobtained. Inadditiontothecostsassociatedwith thebulkheadconstruction,a lumpsumcostof$25,000 isadded tocover thecostofearthworknotdirectlyrelatedtothebulkheadconstruction. Thetotalestimateoftheinitial costs associated with the construction of a wooden bulkhead at Poughkeepsie is$171,500.Indevelopingthelifecyclecostforwoodenbulkheads,thefollowingassumptionsweremade:

Periodicmaintenanceand repairswillbenecessary. Anestimateof20%of the initialcostissetasideformaintenanceandrepairduringeachperiod.

Itisassumedthatmaintenanceandrepaircostsforwoodstructureswillincreaseundertherapidsealevelrisescenario.A5%increaseisapplied.

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Woodbulkheadsgenerallyhavealifespanofbetween25and40years.Forthepurposeofthisanalysis,a30yearlifespanisassumed.

Woodbulkheads are resilient. The followingdamages are expectedduring significantstorms:

Table8ExpectedDamageWoodBulkhead.

Tr Expected Impacts Damage costs (% IC)

50 Moderate overtopping & scour 10% 40 None N/A 25 Minor scour 5% 10 None N/A

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WoodBulkheadCostEstimate

InitialConstructionCost $171,500

CurrentRateofSLR P1(20122037) P2(20372062) P3(20622082)

Storm Damage #Storms Cost #Storms Cost #Storms Cost TotalCost50 10% 0.56 $7,220 0.75 $5,566 1.01 $4,537 $17,323

40 0.73 $ 1.02 $ 1.30 $ $

25 5% 1.13 $7,302 1.53 $5,686 2.14 $4,789 $17,776

10 2.84 $ 3.97 $ 5.32 $ $

Replacement 100% 0.00 $ 1.00 $74,139 1.00 $44,825 $118,965

Maintenance 20% 1.00 $25,935 1.00 $14,828 1.00 $8,965 $49,728

InitialCost $171,500*#stormsreferstothenumberoftimesthecostisappliedforreplacementandmaintenance TotalCost $375,292

RapidIceMeltRateofSLR

P1(20122037) P2(20372062) P3(20622082)Storm Damage #Storms Cost #Storms Cost #Storms Cost TotalCost50 10% 1.35 $17,524 9.26 $68,648 25.00 $112,063 $198,234

40 1.91 $ 11.90 $ 25.00 $ $

25 5% 3.01 $19,530 16.67 $61,783 25.00 $56,031 $137,344

10 7.58 $ 25.00 $ 25.00 $ $

Replacement 100% 0.00 $ 1.00 $74,139 1.00 $44,825 $118,965

Maintenance 25% 1.00 $32,419 1.00 $18,535 1.00 $11,206 $62,160


16

SteelBulkheadGiventhesteepsideslopes,proximitytothenavigationchannelandexposuretorelativelylongfetches, a cost estimate of $1,200/lf or $600,000which is on the higher end of the rangesobtainedwas selected. Labor costswereestimatedbasedon theprevailingwage formarineconstruction in the State of New York(http://wpp.labor.state.ny.us/wpp/publicViewPWChanges.do). Assuming 350 man hours forconstruction,at$35/hr,anestimateof$12,250 for labor isobtained. Inaddition to thecostsassociatedwith thebulkheadconstruction,a lumpsumcostof$25,000 isadded tocover thecostofearthworknotdirectlyrelatedtothebulkheadconstruction. ThetotalestimateoftheinitialcostsassociatedwiththeconstructionofasteelbulkheadatPoughkeepsieis$637,250.

Indevelopingthelifecyclecostforsteelbulkheads,thefollowingassumptionsweremade:

Maintenanceandrepaircostsforsteelbulkheadsaregenerallyminimal.Anestimateof5%oftheinitialcostissetasideformaintenanceandrepairduringeach.

Steelbulkheadsgenerallyhavealifespanofbetween25and40years.Forthepurposeofthisanalysis,a30yearlifespanisassumed.

Steel bulkheads are resilient. The following damages are expected during significantstorms:

Table9ExpectedDamageSteelBulkhead.



17

SteelBulkheadCostEstimate




40 0.73 $ 1.02 $ 1.30 $ $

25 5% 1.13 $27,131 1.53 $21,126 2.14 $17,795 $66,051

10 2.84 $ 3.97 $ 5.32 $ $

Replacement 100% 0.00 $ 1.00 $275,483 1.00 $166,558 $442,042

Maintenance 5% 1.00 $24,092 1.00 $13,774 1.00 $8,328 $46,194

InitialCost $637,250*#stormsreferstothenumberoftimesthecostisappliedforreplacementandmaintenance TotalCost $1,255,906



40 1.91 $ 11.90 $ 25.00 $ $

25 5% 3.01 $72,567 16.67 $229,569 25.00 $208,198 $510,334

10 7.58 $ 25.00 $ 25.00 $ $

Replacement 100% 0.00 $ 1.00 $275,483 1.00 $166,558 $442,042

Maintenance 5% 1.00 $24,092 1.00 $13,774 1.00 $8,328 $46,194


18

BioWallThe term biowall has been used generically to encompass a suite of shoreline stabilizationapproacheswithsimilarcharacteristics.Mostbiowallsareusedinareasthathavetraditionallybeenprotectedbybulkheads. Biowall can refer to simpleecologicalenhancementsused tomodify traditional bulkheads such as hanging planter baskets, ormore complex approacheswhich incorporate nontraditional materials and design layouts. For the purposes of thisanalysisabiowallwillbedefinedasanecologicallyenhancedconcretepanelbulkheadwhichincorporates threeprecast tidepools. Theenhancementsused tomodify theconcretepanelincluderougheningthesurface,andtheuseof lowPHconcretemixtomaximizegrowth. Thetidepoolsareprecastconcretestructuresthataredesignedtofillupduringhightideandholdareservoirofwateroncethewaterlevelhasdropped.Thismaintainsawetenvironmentthatallowsorganismstogrowinalocationthatwouldnormallybetoodry.Biowalls are a fairly new concept and cost information is extremely limited. In general,ecologicallyenhancedconcretecosts715%morethanregularPortlandcement(ShimritPerkolFinkel, 2012). Traditional concrete bulkheads cost between $500 and $1000 per linear foot(Devore,2010);thereforeanecologicallyenhancedconcretebulkheadcanbeexpectedtocostbetween $575 and $1150 per linear foot. Tide pools for revetment habitat developmentgenerallycostbetween$1000and$1500each (ShimritPerkolFinkel,2012). AtPoughkeepsiewhichisrelativelyhighenergy,thehighendofthesenumbersisusedtodeveloptheestimatedcost. Laborcostswereestimatedbasedontheprevailingwageformarineconstruction intheStateofNewYork(http://wpp.labor.state.ny.us/wpp/publicViewPWChanges.do).Assuming400man hours for construction, at $35/hr, an estimate of $14,000 for labor is obtained. Anadditionallumpsumcostof$25,000isaddedtotheestimatetocoverthecostofearthworknotdirectly related to the biowall. The total estimate of the initial costs associated with theconstructionofabiowallatPoughkeepsieis$618,500.Table10BiowallCostInformation.

EcologicallyEnhancedConcreteBulkheadperlf $1,150TotalCostofEnhancedConcreteBulkhead $575,000CostperTidePool $1,500TotalCostofTidePools $4,500TotalCostofBiowall $579,500

Indevelopingthelifecyclecostforabiowall,thefollowingassumptionsweremade:

Maintenanceandrepaircostsforbiowallsaregenerallyminimal. Anestimateof10%oftheinitialcostissetasideformaintenanceandrepairduringeach.

19

Concrete bulkheads generally have a lifespan of between 20 and 50 years. For thepurposeofthisanalysis,a40yearlifespanisassumedforthebiowall.

Biowallsareresilient.Thefollowingdamagesareexpectedduringsignificantstorms:Table11ExpectedDamageBiowall.



20

BioWallCostEstimate




40 0.73 $ 1.02 $ 1.30 $ $

25 5% 1.13 $26,332 1.53 $20,504 2.14 $17,271 $64,108

10 2.84 $ 3.97 $ 5.32 $ $

Replacement 100% 0.00 $ 1.00 $267,378 0.00 $ $267,378

Maintenance 10% 1.00 $46,767 1.00 $26,738 1.00 $16,166 $89,670




40 1.91 $ 11.90 $ 25.00 $ $

25 5% 3.01 $70,431 16.67 $222,815 25.00 $202,072 $495,318

10 7.58 $ 25.00 $ 25.00 $ $

Replacement 100% 0.00 $ 1.00 $267,378 0.00 $ $267,378

Maintenance 10% 1.00 $46,767 1.00 $26,738 1.00 $16,166 $89,670


21

RevetmentA revetment isa slopedengineered shoreprotectionmethod similar to rip rap;however thedesign is often more involved consisting of multiple layers and/or filter fabric, with theindividual stones placedmore precisely. Revetments tend to use larger stone falling in thebouldercategoryaccording to theWentworth scale. Themedian stone size (D50)andweight(W50) for the revetmentarmor stoneweredeterminedusing thewellknownHudson formula(USACE,1977). TheHudsonformulausesthebalancebetweenthestabilizing(i.e.weight)anddestabilizing(i.e.shearstresses)forcesactingonthestonetodetermineanappropriatestonesize. The largestwindwaveheight(2.5ft)wasselectedas input intotheHudsonformula. AtthePoughkeepsiesite,thecalculatedwindwaveheightisroughlyconsistentwithtypeofwakesthatwouldbeexpected(Brunoetal.,2002).TheresultsfromtheHudsonformularecommendamedianstonesize(D50)of1.09feetindiameterwithaweight(W50)of217pounds.Giventhepropensityfor icescouratthesite,therecommendedvaluewasscaledup20%,resulting inaD50of1.3ftandaW50of363lbs.Sincerevetmentsareconstructedwithuniformlysizedstones,an underlayer, and geotextile filter layer are included to prevent the washout of the finematerial. The tablebelow summarizes thematerialcosts for the two layer revetment. Eachlayer isassumedtobetwostonediameterswithanaverageporosityof40%. Geotextilecostswerecalculatedusingaunitcostof$0.90/sy,whichwhenmultipliedbythetotalsurfaceareaoftherevetmentgives$1,395.

Theplacementof revetment stones is generallymoreprecise and requires specialized labor.LaborcostswereestimatedbasedontheprevailingwageformarineconstructionintheStateofNew York (http://wpp.labor.state.ny.us/wpp/publicViewPWChanges.do). Assuming 400 manhours forconstruction,at$35/hr,anestimateof$14,000 for labor isobtained. Anadditionalcostof$20,000 isaddedtothematerialand laborcoststoaccountforgeneralearthwork,notincludedintheestimate.Thisbringsthefinalinitialcostto$207,538.

Table12MaterialCostsforRevetments(Bids).

Layer Thickness(ft)

Volume(ft3)

Weight(lbs)

Weight(tons)

RockCost(perton)

TotalCost

Armor 2.32 19,253 3,174,253 1587 $97 $153,939Underlayer 0.11 2705 445,970 222 $82 $18,204

Indevelopingthelifecyclecostforrevetments,thefollowingassumptionsweremade:

Maintenanceandrepaircostsforrevetmentsaregenerallyminimal.Anestimateof15%oftheinitialcostissetasideformaintenanceandrepairduringeach.

Revetmentsareresilient.Thefollowingdamagesareexpectedduringsignificantstorms:

22

Table13ExpectedDamageRevetment.


50 Moderate overtopping & scour 15% 40 Additional rock displacement 5% 25 Minor scour & rock displacement 10% 10 None N/A

Althoughnotexplicitlyconsideredinthisanalysis,revetmentscanusuallybemodifiedtoadapttorisingsealevelsbyaddingstonestothecrestofthestructure.Inthiscase,theoriginaldesigncallsforarmoringthebanktothetopoftheexistingslope;thereforeadditionalmeanssuchasinfillingwouldberequiredtocontinuetoelevatethecrest. Normallythecostassociatedwithaddingstonestothecrestofanexistingstructurewouldberelativelyminimal.

23

RevetmentCostEstimate




40 5% 0.73 $5,736 1.02 $4,596 1.30 $3,513 $13,845

25 10% 1.13 $17,672 1.53 $13,761 2.14 $11,591 $43,023

10 2.84 $ 3.97 $ 5.32 $ $

Replacement 100% 0.00 $ 0.00 $ 0.00 $ $

Maintenance 15% 1.00 $23,539 1.00 $13,458 1.00 $8,137 $45,133




40 5% 1.91 $14,974 11.90 $53,404 25.00 $67,805 $136,183

25 10% 3.01 $47,267 16.67 $149,531 25.00 $135,611 $332,409

10 7.58 $ 25.00 $ 25.00 $ $

Replacement 100% 0.00 $ 0.00 $ 0.00 $ $

Maintenance 15% 1.00 $23,539 1.00 $13,458 1.00 $8,137 $45,133


24

RipRapRiprap isamethodofshoreprotectionthatuseswellgradedstonestoarmorthecoast. ThesizeofthestonesgenerallyfallswithinthecobblerangeaccordingtotheWentworthscale.Riprapreliesonitsweightforstabilityanddissipatestheincidentenergyonitsslope.Estimatesofriprap sizebasedon currentvelocitygenerally lead tomaterialmuch smaller thanwouldberequired to resist thepotentialwindand ship generatedwaves at the site. To calculate therequiredstonesize,ariprapspecificversionoftheHudsonformula(USACE,1977)wasutilized.TheHudsonformulausesthebalancebetweenthestabilizing(i.e.weight)anddestabilizing(i.e.shearstresses)forcesactingonthestonetodeterminetheappropriatesize. Thelargestwaveheight(2.5ft)calculatedbasedonthefetchesdefinedaboveforthePoughkeepsiesitewasusedforinputintotheHudsonformula.AtthePoughkeepsiesite,thecalculatedwindwaveheightisroughlyconsistentwithtypeofwakesthatwouldbeexpected(Bruno,2003).TheresultsfromtheHudsonformularecommendamedianstonesize(D50)of1.0footindiameterwithaweight(W50)of173pounds.Giventhepropensityforicescouratthesite,therecommendedvaluewasscaledup20%,resultinginaD50of1.2ftandaW50of285lbs.Fortheriprapslopeprotection,onlyasingle layer(40%porosity)withathicknessequaltotwicethemedianstonediameterisplacedontopofageotextilefilterfabric. Geotextilecostswerecalculatedusingaunitcostof$0.90/sy,whichwhenmultipliedbythetotalsurfaceareaoftheslopegives$1,395.

Table14CostEstimateforRockMaterialtoBuildRipRap.

Layer Thickness(ft)

Volume(ft3)

Weight(lbs)

RockCostPerTon

TotalCost

Armor 2.14 217,772 2,930,079 $97 $142,108

Theplacementofriprapstones isgenerallyveryquickanddoesnotrequirespecialized labor.LaborcostswereestimatedbasedontheprevailingwageformarineconstructionintheStateofNew York (http://wpp.labor.state.ny.us/wpp/publicViewPWChanges.do). Assuming 300 manhours forconstruction,at$35/hr,anestimateof$10,500 for labor isobtained. Anadditionalcostof$20,000 isaddedtothematerialand laborcoststoaccountforgeneralearthwork,notincludedintheestimatethusfar.Thisbringsthefinalinitialcostto$174,003.

Indevelopingthelifecyclecostforriprapslopes,thefollowingassumptionsweremade:

Maintenanceandrepaircostsforripraparegenerally low. Anestimateof20%oftheinitialcostissetasideformaintenanceandrepairduringeachperiod.

Thefollowingdamagesareexpectedduringsignificantstorms:

25

Table15ExpectedDamagesRiprap.


50 Significant overtopping & scour 20% 40 Moderate scour 10% 25 Minor scour 10% 10 None N/A

Although not explicitly considered in this analysis, riprap slopes can usually bemodified toadapttorisingsealevelsbyaddingstonestothecrestofthestructure.Inthiscase,theoriginaldesigncallsforarmoringthebanktothetopoftheexistingslope;thereforeadditionalmeanssuch as infilling would be required to continue to elevate the crest. Normally the costassociatedwithaddingripraptothecrestofanexistingstructurewouldberelativelyminimal.

26

RipRapCostEstimate




40 10% 0.73 $9,618 1.02 $7,707 1.30 $5,891 $23,216

25 10% 1.13 $14,816 1.53 $11,537 2.14 $9,718 $36,071

10 2.84 $ 3.97 $ 5.32 $ $

Replacement 100% 0.00 $ 0.00 $ 0.00 $ $

Maintenance 20% 1.00 $26,314 1.00 $15,044 1.00 $9,096 $50,454




40 10% 1.91 $25,108 11.90 $89,549 25.00 $113,698 $228,356

25 10% 3.01 $39,629 16.67 $125,369 25.00 $113,698 $278,696

10 7.58 $ 25.00 $ 25.00 $ $

Replacement 100% 0.00 $ 0.00 $ 0.00 $ $

Maintenance 20% 1.00 $26,314 1.00 $15,044 1.00 $9,096 $50,454


27

JointPlantingLivestakingorjointplantinginvolvesplantinglivestakesorvegetationintothevoidspacesinariprapslopeorrevetment. Iftheriprapslopeorrevetmentalreadyexiststheonlycostsarerelatedtotheplantmaterialsandthelaborforinstallation.Table16providessomeinformationonthetypicalcostsofmaterialsusedinjointplanting.

Table16CostforStakestobeCoupledwithRipRap(NRPCVT,2004).

Range $2.05$4.78/ft2

SurfaceAreaofSite 9014ft2

CostforPlanting(@$3.00/sq.ft) $27,041Cost $54.08/ft

Labor costs for jointplantingareminimalasupwardsof100 stakes canbeplantedperhourdepending on thework force (USACE, 2001). Assuming four cuttings per square yard (EPA,1993), thePoughkeepsieSitewould requireupwardsof4000plantings. Applyinganaveragelaborrateof$25/hr,thefollowingcostestimateforlaborwasobtained.

Table17LaborCostsforLiveStakes.

SurfaceArea 1002yd2

CuttingDensity 4/yd2

PlantsRequired 4,008InstallationRate 100/hrLaborRate $25/hrLaborCost $1,002

Takingintoaccountthelaborcostsandthematerialcosts,thecostestimateforjointplantingatPoughkeepsie is$28,043,or$56/lf. It isassumedthatthe jointplantingwillbeconstructed inconjunctionwiththeriprapslopediscussed intheprevioussection. Thetotalestimatedcostforariprapprotectedslopewithjointplantingis$202,046or$404/lf.

Indevelopingthelifecyclecostforjointplanting,thefollowingassumptionsweremade:

Theriprapdiscussed intheprevioussectionformsthebaseforthe jointplantingandthe total cost is the cost of constructing the riprap slope plus the cost of the jointplanting.

Jointplantingaddstothemaintenanceandrepaircostsassociatedwithariprapslope.Anadditional5%ofthe initialcost isestimatedforjointplantingbringingtheestimateforariprapslopewithjointplantingto25%.

28

It is assumed that maintenance and repair costs for living structures will increasesignificantlyundertherapidsealevelrisescenario.A10%increaseisapplied.

Jointplantingsarenotespeciallyresilient. Thefollowingdamagesareexpectedduringsignificantstorms:

Table18ExpectedDamageJointPlanting.


50 Significant overtopping & scour 20% 40 Moderate scour 10% 25 Minor scour 10% 10 Loss of plantings 10%

Althoughnotexplicitlyconsidered inthisanalysis,riprapslopeswithjointplantingcanusuallybemodified toadapt to rising sea levelsbyadding stonesandvegetation to the crestof thestructure.Inthiscase,theoriginaldesigncallsforarmoringthebanktothetopoftheexistingslope;thereforeadditionalmeanssuchasinfillingwouldberequiredtocontinuetoelevatethecrest.Normallythecostassociatedwithaddingriprapandvegetationtothecrestofanexistingstructurewouldberelativelyminimal.

29

JointPlantingCostEstimate




40 10% 0.73 $11,168 1.02 $8,949 1.30 $6,841 $26,957

25 10% 1.13 $17,204 1.53 $13,396 2.14 $11,284 $41,884

10 10% 2.84 $43,401 3.97 $34,661 5.32 $28,090 $106,152

Replacement 100% 0.00 $ 0.00 $ 0.00 $ $

Maintenance 25% 1.00 $38,193 1.00 $21,836 1.00 $13,202 $73,232




40 10% 1.91 $29,155 11.90 $103,982 25.00 $132,022 $265,159

25 10% 3.01 $46,016 16.67 $145,574 25.00 $132,022 $323,612

10 10% 7.58 $115,737 25.00 $218,361 25.00 $132,022 $466,120

Replacement 100% 0.00 $ 0.00 $ 0.00 $ $

Maintenance 35% 1.00 $53,470 1.00 $30,571 1.00 $18,483 $102,524


30

VegetatedGeogridAvegetatedgeogrid isconstructedof successive layersof soilwrapped inageotextile fabric.Each layer isstackedupon thepreviousatan inclinedangle to resistany forwardmovement;while vegetation is added between each layer to promote a natural aesthetic and habitatdevelopment. The vegetationonce establishedwill also act to reinforce the strengthof thestructure.Thenumberoflayersandtheamountofwrappingisdeterminedbytheheightofthewall. Themajormaterialcostsforvegetativegeogridsconsistsofthegeotextilefabric,thefillmaterial,and the livevegetation. AtPoughkeepsie it isassumed that theexistingsoilwillbeusedtofillthegeotextilewrapsatareducedcostof$25/ton. ThecostsforeachelementaresummarizedinError!Notavalidbookmarkselfreference..Anadditional$35,000isaddedtothefinalcosttoaccountforearthworknotdirectlyrelatedtofillingeachlayer.Preparingasiteofthiswidthandlengthwillrequireasignificantamountofexcavation.

Table19MaterialCostsforVegetatedGeogridatPoughkeepsie,NY.

GeotextileCosts(HaliburtonCooperative)

NumberofLayers 4WrapLength 7.15ftLengthofgeotextileperlayer 23.45ftTotallength 93.82ft/lfTotalareaofwrap 46,910ft2

AverageCost(Storrar) $0.90/yd2

TotalGeotextileCost $4,691SedimentCosts(SwanRiverTrust)Volumeoffillrequired(40%porosity) 15,600ft3

Unitweightofsedimentfill 165lb/ft3

Weightofstoneneeded 2,574,000lbsAverageCost $25/tonTotalFillCost $32,175VegetationCosts(WSDT,2002)6x2PrunedLiveWillowBranches 5000UnitCost $1.20TotalVegetationCost $6000

LaborcostswereestimatedbasedontheprevailingwageformarineconstructionintheStateofNew York (http://wpp.labor.state.ny.us/wpp/publicViewPWChanges.do). Assuming 500 manhours for construction, at $35/hr, an estimate of $17,500 for labor is obtained. The totalestimatedcostforavegetatedgeogridstructureatPoughkeepsieis$95,366.

Indevelopingthelifecyclecostforvegetatedgeogrids,thefollowingassumptionsweremade:

31

Maintenance and repair costs for vegetated geogrids are generally minimal. Anestimateof20%ofthe initialcost issetasideformaintenanceandrepairduringeachperiod.

Vegetatedgeogridsdonottypicallyhavealonglifespan.Althoughclaimsofaslongas120 years canbe found, given the condition along theHudson, a 20 year lifespan isutilizedintheanalysis.


Thefollowingdamagesareexpectedduringsignificantstorms:Table20ExpectedDamageVegetatedGeogrid.


50 Moderate overtopping & scour 20% 40 None N/A 25 Loss of vegetation 10% 10 None N/A

Althoughnotexplicitlyconsideredinthisanalysis,vegetatedgeogridscanbemodifiedtoadapttorisingsea levelsbyaddingadditional layerstoanexistingstructure. Ifadditional layersareadded,caremustbetakentoensurethatanynew layersaresecuredtotheexistingstructureandanchoringsystemsuchthattheentirestructurebehavesasasingleunit. Inthiscase,theoriginaldesigncallsforarmoringthebanktothetopoftheexistingslope;thereforeadditionalmeanssuchas infillingwouldberequiredtocontinue toelevatethecrest. Normallythecostassociatedwithaddinganadditionallayertoavegetatedgeogridwouldberelativelyminimal.

32

VegetatedGeogridCostEstimate




40 0% 0.73 $ 1.02 $ 1.30 $ $

25 10% 1.13 $8,120 1.53 $6,323 2.14 $5,326 $19,770

10 2.84 $ 3.97 $ 5.32 $ $

Replacement 100% 1.00 $72,109 1.00 $41,227 1.00 $24,926 $138,261

Maintenance 20% 1.00 $14,422 1.00 $8,245 1.00 $4,985 $27,652




40 0% 1.91 $ 11.90 $ 25.00 $ $

25 10% 3.01 $21,720 16.67 $68,711 25.00 $62,315 $152,745

10 7.58 $ 25.00 $ 25.00 $ $

Replacement 100% 1.00 $72,109 1.00 $41,227 1.00 $24,926 $138,261

Maintenance 30% 1.00 $21,633 1.00 $12,368 1.00 $7,478 $41,478


33

CribWallTimbercribbingfunctionssimilartoagravitybulkhead, inthat itsstability isdirectlyrelatedtoitsweight.Thisinturnisdependentuponitsheighttowidthratio,whichshouldbelessthan3(FEMA, 2000). The weight of the crib pushes perpendicularly upon the wooden posts thatcreate the crib, and the allowable stress in thewood determines the capacity of each crib.Generally,thepostsare6to8 feet long (NRCS,2007),withallowablestresses intherangeof200to1000 lb/in2dependingonthespeciesofwood(FEMA,2000). Table21summarizesthecribdesign. A largercribwasselectedforPoughkeepsietocombatthehigherdegreeofwaveenergy at the site. Using 8 foot lengths, 63 cribs would be required along 500 ft of riverfrontage.Thevolumeofeachcribis355ft3.Whenfilledwithstonewithanaverageporosityof40%,thisrequiresnearly1100tonsofstoneandover5,000 logs. Acribwallcoveringanareathis largewillrequireextensiveexcavation;howeverthesoilandstonefromthesitecouldberecycledbackintotheprojectasfillforthecribs. Thecostoftherecycledfillmaterialusedtodeterminethematerialcostsforthestructurewas$25/ton.ThecostsaresummarizedbelowinTable23.Anadditional$35,000isaddedtothefinalcosttoaccountforearthworknotdirectlyrelatedtobuildingandfillingthecribs.Table21SelectionofLogCriteriaforCrib.

LogLength 8ft

LogCrossSection 4.5inx4.5inDesignStress 750lb/in2

CribConfiguration 2x2Capacity 60,750lbsCapacitypereachcontact 15,187lbs

Table22DeterminationofWeightofFilledCrib.

Area 44.44ft2Volume 355.56ft3Unitweightofstone 165lbs/ft3TotalWeightofCrib 29.31tonsTotalNumberofCribs 62.50(500/8)Weightofstone(40%Porosity) 1099tons

34

Table23CostSummaryforTimberCribbing(HaliburtonCooperative).

Theamountoflaborrequiredtoconstructawoodencribwallwillberoughly1.5timeswhatisnecessaryforawoodenbulkhead.Laborcostswereestimatedbasedontheprevailingwageformarine construction in the State of New York(http://wpp.labor.state.ny.us/wpp/publicViewPWChanges.do). Assuming 600 man hours forconstruction,at$35/hr,anestimateof$21,000.ThetotalestimatedcostforconstructingacribwallatthePoughkeepsiesiteis$131,207.

Indevelopingthelifecyclecostforcribwalls,thefollowingassumptionsweremade:

Maintenanceandrepaircostsforcribwallsaregenerallymoderate.Anestimateof20%oftheinitialcostissetasideformaintenanceandrepairduringeachperiod.

Itisassumedthatmaintenanceandrepaircostsforwoodstructureswillincreaseundertherapidsealevelrisescenario.A5%increaseisapplied.

Woodencribshavea lifespanofapproximately2540years. For thepurposesof thisanalysis,completereplacementisassumedafter30years.

Woodencribwallsareresilient.Thefollowingdamagesareexpectedduringsignificantstorms:

Table24ExpectedDamageTimberCribbing.


50 Moderate overtopping & scour 10% 40 Damage to cribs 20% 25 None N/A 10 None N/A

Althoughnotexplicitlyconsideredinthisanalysis,cribwallsandlivecribwallscanbemodifiedtoadapt torisingsea levels through theconstructionofadditionalcribs. Suchamodificationmustbe carriedout carefullyhowever;as increasing theheightof the structure changes thepressure distributions. In addition caremust be taken to ensure that the additionalweight

TimberCribbing(BasedoffDesignof6'wx6'hx500'l) (WSDT,2002)Items #ofUnits Cost/Unit TotalLogs,untreatedD.Fir,CedarorHemlock 5,630logs $6.18/log $34,782SedimentFillMaterial(Upper6ofcrib) 825tons $25/ton $20,625StoneFill(Lower2ofcrib) 275tons $72/ton $19,800TotalCost $75,207CostperLinearFoot $150.40

35

doesnt cause the allowable stress in the timber and the bearing capacity of the earthsupportingthestructuretobeexceeded.Assumingthoseconditionsaremet,thecostofaddinganadditionalcribisrelativelylow.

36

CribWallCostEstimate




40 20% 0.73 $14,504 1.02 $11,623 1.30 $8,884 $35,012

25 1.13 $ 1.53 $ 2.14 $ $

10 2.84 $ 3.97 $ 5.32 $ $

Replacement 100% 0.00 $ 1.00 $56,721 1.00 $34,294 $91,014

Maintenance 20% 1.00 $19,842 1.00 $11,344 1.00 $6,859 $38,045




40 20% 1.91 $37,866 11.90 $135,050 25.00 $171,468 $344,384

25 3.01 $ 16.67 $ 25.00 $ $

10 7.58 $ 25.00 $ 25.00 $ $

Replacement 100% 0.00 $ 1.00 $56,721 1.00 $34,294 $91,014

Maintenance 25% 1.00 $24,802 1.00 $14,180 1.00 $8,573 $47,556


37

LiveCribWallLivecribwallsaredesignedverysimilarlytotimbercribbing;howeveronlythebaselayerisfilledwith stone. The remainder of the crib is filledwith alternating layers of sediment and livebranches.Theresultisaboxlikestructurethatretainsthestructuralintegrityofacribwall,butonethatalsopromoteshabitatgrowth.Thedesignandcostofthecribsisasdiscussedabove,withsoilreplacingthemajorityofthestone.AtPoughkeepsie,itisassumedthatthemajorityofthefillneedscanbefulfilledusingonsitematerial.CostinformationissummarizedinTable25.An averagepriceof$25/tonwasutilized for the costof recycled fillmaterial. An additional$35,000isaddedtothefinalcosttoaccountforearthworknotdirectlyrelatedtobuildingandfillingthecribs.Table25CostSummaryforVegetatedGeogrid(HaliburtonCooperative).

Theamountof laborrequiredtoconstructa livecribwallwillbethesameasforatraditionalcribwallwithanaddedexpenserelatedtoplantingthevegetation.Laborcostswereestimatedbased on the prevailing wage for marine construction in the State of New York(http://wpp.labor.state.ny.us/wpp/publicViewPWChanges.do). 600manhoursareallotted forconstructing and filling the cribs,with an additional50hours added to account forplanting.Usingarateof$35/hr,thelaborcostsareestimatedat$22,750.Addingthelaborcoststothematerialcostsresultsinatotalestimateof$141,678.

Indevelopingthelifecyclecostforlivecribwalls,thefollowingassumptionsweremade:

Maintenanceandrepaircostsforlivecribwallsaregenerallymoderate.Anestimateof25%oftheinitialcostissetasideformaintenanceandrepairduringeachperiod.


LiveCribWall(BasedoffDesignof6'wx6'hx500'l)(WSDT,2002)Items Units Cost/Unit TotalLogs,untreatedD.Fir,CedarorHemlock 5,630 $6.18/log $34,782Willow,prunedlivebranches(6'x2"diameter)

5,000 $1.74/cutting $8,721

SedimentFillMaterial(Upper6ofcrib) 825tons $25/ton $20,625StoneFill(Lower2ofcrib)(40%Porosity) 275tons $72.00/ton $19,800TotalCost $83,928Costperlinearfoot $167.86

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Woodencribshavea lifespanofapproximately2540years. For thepurposesof thisanalysis,completereplacementisassumedafter30years.

Live crib walls are resilient. The following damages are expected during significantstorms:

Table26ExpectedDamageLiveCribWall.


50 Moderate overtopping & scour 10% 40 Damage to cribs 20% 25 Loss of vegetation 10% 10 None N/A

Althoughnotexplicitlyconsideredinthisanalysis,cribwallsandlivecribwallscanbemodifiedtoadapt torisingsea levels through theconstructionofadditionalcribs. Suchamodificationmustbe carriedout carefullyhowever;as increasing theheightof the structure changes thepressure distributions. In addition caremust be taken to ensure that the additionalweightdoesnt cause the allowable stress in the timber and the bearing capacity of the earthsupportingthestructuretobeexceeded.Assumingthoseconditionsaremet,thecostofaddinganadditionalcribisrelativelylow.

39

LiveCribWallCostEstimate




40 20% 0.73 $15,662 1.02 $12,551 1.30 $9,593 $37,806

25 10% 1.13 $12,064 1.53 $9,394 2.14 $7,912 $29,370

10 2.84 $ 3.97 $ 5.32 $ $

Replacement 100% 0.00 $ 1.00 $61,247 1.00 $37,030 $98,278

Maintenance 25% 1.00 $26,782 1.00 $15,312 1.00 $9,258 $51,351




40 20% 1.91 $40,888 11.90 $145,827 25.00 $185,152 $371,868

25 10% 3.01 $32,267 16.67 $102,079 25.00 $92,576 $226,922

10 7.58 $ 25.00 $ 25.00 $ $

Replacement 100% 0.00 $ 1.00 $61,247 1.00 $37,030 $98,278

Maintenance 35% 1.00 $37,494 1.00 $21,437 1.00 $12,961 $71,892


40

SillSillsare typicallydesignedas lowelevationstructuresandareconstructedon flatornear flatbottoms inrelativelyshallowwater. ThesteepsideslopesatthePoughkeepsiesitemaketheconstructionofasillextremelyimpractical;thereforeitwasnotconsideredinthecostanalysis.

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BowlinePointPark(HaverstrawBay)BowlinePointPark is located inHaverstrawBayon thewesternbankof theHudsonbetweentheoildockfortheBowlineGeneratingStationandtheinlettoBowlinePondasshowninFigure6. Acrosssection illustratingthesiteconditionsasof2006whichwaspresented intheAldenandASA(Allen,etal.,2006)reportisreproducedhereasFigure7.Themajorsitecharacteristicsaresummarized inTable27. As illustrated inFigure7,theexistingshorelineatBowlinePointParkhasbeen reinforcedwith rubble riprap. TheBowlinePointPark shoreline is typicalofmany of themild sloped shorelines fronting thewide, shallow sections of theHudson. TheAlden report attributed the erosion of the Bowline Point Park shoreline to wind and wakegeneratedwaves. Wind wave heightswere calculated using themethodology presented inChapter3,Section6oftheShoreProtectionManual(USACE,1977),assumingawindspeedof50mphandaconstantdepthof10feet.ForthefourfetchesdefinedinFigure6,theestimatedwindwaveheightsareasgiveninTable28.

Figure6BowlinePointParkSiteandFetchDelineations.

Fetch1

Fetch2

Fetch3

Fetch4

42

Figure7ExistingCrosssectionatBowlinePointPark.

Table27BowlinePointParkSiteCharacteristicsandDimensions.

General Characteristics Width of River 14,700 ft Average Depth 10 ft Depth at Shoreline < 10 ft Mean Current Velocity (Main Channel) 1.2 ft/sec Mean Current Velocity (Shoreline) 0.5 ft/sec Tidal Flow 130,000 ft3/sec Max Tidal Fluctuation 2.9 ft Side Slope 1V:20H Dimensions of Above High Water Level Width 25 ft Height 4 ft Slope Length 25 ft Surface Area 12,510 ft2 Cross-section Area 44 ft2 Volume 21,875 ft3 Dimensions of Intertidal Zone Width 20 ft Height 3.5 ft Slope Length 20 ft Surface Area 10,012 ft2 Cross-section Area 35 ft2 Volume 17,500 ft3

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Table28FetchesandRelatedWindWaveHeightsatBowlinePointPark.

Length (mi)

Wave Height (ft)

Fetch 1 3.10 2.10 Fetch 2 2.50 2.00 Fetch 3 3.50 2.25 Fetch 4 6.00 2.50

BulkheadBulkheads were not considered a viable alternative at the Bowline Point Park site. Theextremelymildslopeoftheexistingshorelinemakestheconstructionofverticalornearverticalretaining structures (bulkheads, biowalls, timber cribbing, live crib walls, and vegetatedgeogrids) impractical. The nearly horizontal nature of the Bowline Point Park site does notprovide enough natural relief to make these structures costefficient without adding asignificantamountoffill.Doingsowouldchangetheprojectfromashorelineprotectionprojecttoalandreclamationproject,negatinganyusefulinformationthatcouldbeobtainedfromthecostanalysis.ItshouldbenotedthatthissuggestionisconsistentwiththeconclusionsreachedintheAldenandASA(Allen,etal.,2006)report.

BioWallBiowallswerenotconsideredaviablealternativeattheBowlinePointParksite.Theextremelymildslopeoftheexistingshorelinemakestheconstructionofverticalornearverticalretainingstructures (bulkheads, biowalls, timber cribbing, live crib walls, and vegetated geogrids)impractical. The nearly horizontal nature of the Bowline Point Park site does not provideenough natural relief to make these structures costefficient without adding a significantamountoffill.Doingsowouldchangetheprojectfromashorelineprotectionprojecttoalandreclamation project, negating any useful information that could be obtained from the costanalysis. Itshouldbenotedthatthissuggestion isconsistentwiththeconclusionsreached intheAldenandASA(Allen,etal.,2006)report.

RevetmentA revetment isa slopedengineered shoreprotectionmethod similar to rip rap;however thedesign is often more involved consisting of multiple layers and/or filter fabric, with theindividual stones placedmore precisely. Revetments tend to use larger stone falling in thebouldercategoryaccording to theWentworth scale. Themedian stone size (D50)andweight(W50) for the revetmentarmor stoneweredeterminedusing thewellknownHudson formula

44

(USACE,2006). TheHudsonformulausesthebalancebetweenthestabilizing(i.e.weight)anddestabilizing(i.e.shearstresses)forcesactingonthestonetodetermineanappropriatestonesize. The largestwindwaveheight (2.5 ft)calculatedbasedon the fetchesdefinedabove forBowlinePointParkwasusedforinputintotheHudsonformula.AttheHenryHudsonsite,thecalculatedwindwaveheight is roughlyconsistentwith typeofwakes thatmightbeexpected(Bruno). Theresults from theHudson formularecommendamedianstonesize (D50)of0.59feetindiameterwithaweight(W50)of34pounds.Giventhepropensityforicescouratthesite,therecommendedvaluewasscaledup20%,resultinginaD50of0.7ftandaW50of56lbs.Sincerevetments are constructedwith uniformly sized stones, an underlayer, and geotextile filterlayerareincludedtopreventthewashoutofthefinematerial.Thetablebelowsummarizesthematerialcosts forthetwo layerrevetment. Each layer isassumedtobe twostonediameterswithanaverageporosityof40%.Geotextilecostswerecalculatedusingaunitcostof$0.90/sy,whichwhenmultipliedbythetotalsurfaceareaoftherevetmentgives$2,252.

Theplacementof revetment stones is generallymoreprecise and requires specialized labor.LaborcostswereestimatedbasedontheprevailingwageformarineconstructionintheStateofNew York (http://wpp.labor.state.ny.us/wpp/publicViewPWChanges.do). Assuming 300 manhours forconstruction,at$35/hr,anestimateof$10,500 for labor isobtained. Anadditionalcostof$10,000 isaddedtothematerialand laborcoststoaccountforgeneralearthwork,notincludedintheestimate.Thisbringsthefinalinitialcostto$190,896.

Table29MaterialCostsforRevetments(Bids).

Layer Thickness(ft)

Volume(ft3)

Weight(lbs)

Weight(tons)

RockCostPerTon

TotalCost

Armor 1.25 18,810 3,101,096 1,550 $97 $150,350Underlayer 0.106 2,643 435,811 217 $82 $17,794

Indevelopingthelifecyclecostforrevetments,thefollowingassumptionsweremade:

Maintenanceandrepaircostsforrevetmentsaregenerallyminimal.Anestimateof15%oftheinitialcostissetasideformaintenanceandrepairduringeachperiod.

Revetmentsareresilient.Thefollowingdamagesareexpectedduringsignificantstorms:Table30ExpectedDamageRevetments.


50 Moderate overtopping & scour 15% 40 Additional rock displacement 5% 25 Minor scour & rock displacement 10% 10 None N/A

45

Althoughnotexplicitlyconsideredinthisanalysis,revetmentscanusuallybemodifiedtoadapttorisingsealevelsbyaddingstonestothecrestofthestructure.Inthiscase,theoriginaldesigncallsforarmoringthebanktothetopoftheexistingslope;thereforeadditionalmeanssuchasinfillingwouldberequiredtocontinuetoelevatethecrest. Normallythecostassociatedwithaddingstonestothecrestofanexistingstructurewouldberelativelyminimal.

46

RevetmentCostEstimate




40 5% 0.73 $5,276 1.02 $4,228 1.30 $3,232 $12,735

25 10% 1.13 $16,255 1.53 $12,657 2.14 $10,661 $39,573

10 2.84 $ 3.97 $ 5.32 $ $

Replacement 100% 0.00 $ 0.00 $ 0.00 $ $

Maintenance 15% 1.00 $21,651 1.00 $12,379 1.00 $7,484 $41,514




40 5% 1.91 $13,773 11.90 $49,122 25.00 $62,368 $125,263

25 10% 3.01 $43,476 16.67 $137,541 25.00 $124,737 $305,754

10 7.58 $ 25.00 $ 25.00 $ $

Replacement 100% 0.00 $ 0.00 $ 0.00 $ $

Maintenance 15% 1.00 $21,651 1.00 $12,379 1.00 $7,484 $41,514


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RipRapRiprap isamethodofshoreprotectionthatuseswellgradedstonestoarmorthecoast. ThesizeofthestonesgenerallyfallswithinthecobblerangeaccordingtotheWentworthscale.Riprapreliesonitsweightforstabilityanddissipatestheincidentenergyonitsslope.Estimatesofriprap sizebasedon currentvelocitygenerally lead tomaterialmuch smaller thanwouldberequired to resist thepotentialwindand ship generatedwaves at the site. To calculate therequiredstonesize,ariprapspecificversionoftheHudsonformula(USACE,1977)wasutilized.TheHudsonformulausesthebalancebetweenthestabilizing(i.e.weight)anddestabilizing(i.e.shearstresses)forcesactingonthestonetodeterminetheappropriatesize. The largestwindwaveheight (1.8ft)calculatedbasedonthefetchesdefinedabovefortheBowlinePointParksitewasusedforinputintotheHudsonformula.AttheHenryHudsonParksite,thecalculatedwindwaveheight isroughlyconsistentwiththetypeofwakesthatwouldbeexpected(Bruno,2003).TheresultsfromtheHudsonformularecommendamedianstonesize(D50)of0.57feetindiameterwithaweight(W50)of30pounds.Giventhepropensityforicescouratthesite,therecommendedvaluewasscaledup20%,resultinginaD50of0.68ftandaW50of52lbs.Fortheriprapslopeprotection,onlyasingle layer (40%porosity)withathicknessequaltotwice themedian stone diameter is placed on top of a geotextile filter fabric. Geotextile costs werecalculatedusingaunitcostof$0.90/sy,whichwhenmultipliedbythetotalsurfaceareaoftherevetmentgives$2,252.

Table31CostEstimateforRockMaterialtoBuildRipRap.

Layer Thickness(ft)

Volume(ft3)

Weight(lbs)

RockCostPerTon

TotalCost

Armor 1.2 18,272 3,012,494 $97 $146,105

Theplacementofriprapstones isgenerallyveryquickanddoesnotrequirespecialized labor.LaborcostswereestimatedbasedontheprevailingwageformarineconstructionintheStateofNew York (http://wpp.labor.state.ny.us/wpp/publicViewPWChanges.do). Assuming 200 manhoursforconstruction,at$35/hr,anestimateof$7,000forlaborisobtained.Anadditionalcostof $10,000 is added to the material and labor costs to account for general earthwork, notincludedintheestimatethusfar.Thisbringsthefinalinitialcostto$165,357.

Indevelopingthelifecyclecostforriprapslopes,thefollowingassumptionsweremade:

Maintenanceandrepaircostsforripraparegenerally low. Anestimateof20%oftheinitialcostissetasideformaintenanceandrepairduringeachperiod.

Thefollowingdamagesareexpectedduringsignificantstorms:

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Table32ExpectedDamageRiprap.


50 Significant overtopping & scour 20% 40 Moderate scour 10% 25 Minor scour 10% 10 None N/A

Although not explicitly considered in this analysis, riprap slopes can usually bemodified toadapttorisingsealevelsbyaddingstonestothecrestofthestructure.Inthiscase,theoriginaldesigncallsforarmoringthebanktothetopoftheexistingslope;thereforeadditionalmeanssuch as infilling would be required to continue to elevate the crest. Normally the costassociatedwithaddingripraptothecrestofanexistingstructurewouldberelativelyminimal.

49

RipRapCostEstimate




40 20% 0.73 $18,279 1.02 $14,648 1.30 $11,197 $44,124

25 10% 1.13 $14,080 1.53 $10,964 2.14 $9,235 $34,279

10 2.84 $ 3.97 $ 5.32 $ $

Replacement 100% 0.00 $ 0.00 $ 0.00 $ $

Maintenance 20% 1.00 $25,006 1.00 $14,297 1.00 $8,644 $47,947




40 10% 1.91 $23,861 11.90 $85,100 25.00 $108,049 $217,009

25 10% 3.01 $37,660 16.67 $119,140 25.00 $108,049 $264,848

10 7.58 $ 25.00 $ 25.00 $ $

Replacement 100% 0.00 $ 0.00 $ 0.00 $ $

Maintenance 20% 1.00 $25,006 1.00 $14,297 1.00 $8,644 $47,947


50

JointPlantingLivestakingorjointplantinginvolvesplantinglivestakesorvegetationintothevoidspacesinariprapslopeorrevetment. Iftheriprapslopeorrevetmentalreadyexiststheonlycostsarerelatedtothematerialsusedandthelaborforinstallation.Table33providessomeinformationonthetypicalcostsofthematerialsusedinjointplanting.

Table33CostforStakestobeCoupledwithRipRap(NRPCVT,2004).

Range $2.05$4.78/ft2

SurfaceAreaofSite 12,510ft2

CostforPlanting(@$3.00/sq.ft) $37,530Costperlinearfoot $75.06

Labor costs for jointplantingareminimalasupwardsof100 stakes canbeplantedperhourdepending on thework force (USACE, 2001). Assuming four cuttings per square yard (EPA,1993), theHenryHudsonSitewould requireupwardsof5500plantings. Applyinganaveragelaborrateof$25/hr,thefollowingcostestimateforlaborwasdetermined.

Table34LaborCostsforLiveStakes.

SurfaceArea 1,390yd2

CuttingDensity 4/yd2

PlantsRequired 5,560InstallationRate 100/hrLaborRate $25.00/hrLaborCost $1,390

Takingintoaccountthelaborcostsandthematerialcosts,thecostestimateforjointplantingattheHenryHudsonParksite is$38,920,or$77/lf. It isassumed that the jointplantingwillbeconstructed inconjunctionwith theriprapslopediscussed in theprevioussection. The totalestimatedcostforariprapprotectedslopewithjointplantingis$204,277or$408/lf.

Indevelopingthelifecyclecostforjointplanting,thefollowingassumptionsweremade:

Theriprapdiscussed intheprevioussectionformsthebaseforthe jointplantingandthe total cost is the cost of constructing the riprap slope plus the cost of the jointplanting.

Jointplantingaddstothemaintenanceandrepaircostsassociatedwithariprapslope.Anadditional5%ofthe initialcost isestimatedforjointplantingbringingtheestimateforariprapslopewithjointplantingto25%.

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Jointplantingsarenotespeciallyresilient.Thefollowingdamagesareexpectedduringsignificantstorms:

Table35ExpectedDamageJointPlanting.


50 Significant overtopping & scour 20% 40 Moderate scour 10% 25 Minor scour 10% 10 Loss of plantings 10%

Althoughnotexplicitlyconsidered inthisanalysis,riprapslopeswithjointplantingcanusuallybemodified toadapt to rising sea levelsbyadding stonesandvegetation to the crestof thestructure.Inthiscase,theoriginaldesigncallsforarmoringthebanktothetopoftheexistingslope;thereforeadditionalmeanssuchasinfillingwouldberequiredtocontinuetoelevatethecrest.Normallythecostassociatedwithaddingriprapandvegetationtothecrestofanexistingstructurewouldberelativelyminimal.

52

JointPlantingCostEstimate




40 10% 0.73 $11,291 1.02 $9,048 1.30 $6,916 $27,255

25 10% 1.13 $17,394 1.53 $13,544 2.14 $11,409 $42,347

10 10% 2.84 $43,881 3.97 $35,043 5.32 $28,400 $107,324

Replacement 100% 0.00 $ 0.00 $ 0.00 $ $

Maintenance 25% 1.00 $38,615 1.00 $22,077 1.00 $13,348 $74,040




40 10% 1.91 $29,477 11.90 $105,130 25.00 $133,480 $268,087

25 10% 3.01 $46,524 16.67 $147,182 25.00 $133,480 $327,186

10 10% 7.58 $117,015 25.00 $220,773 25.00 $133,480 $471,267

Replacement 100% 0.00 $ 0.00 $ 0.00 $ $

Maintenance 35% 1.00 $54,061 1.00 $30,908 1.00 $18,687 $103,656


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VegetatedGeogridVegetatedgeogridswerenotconsideredaviablealternativeattheBowlinePointParksite.Theextremelymildslopeoftheexistingshorelinemakestheconstructionofverticalornearverticalretaining structures (bulkheads, biowalls, timber cribbing, live crib walls, and vegetatedgeogrids) impractical. The nearly horizontal nature of the Bowline Point Park site does notprovide enough natural relief to make these structures costefficient without adding asignificantamountoffill.Doingsowouldchangetheprojectfromashorelineprotectionprojecttoalandreclamationproject,negatinganyusefulinformationthatcouldbeobtainedfromthecostanalysis.ItshouldbenotedthatthissuggestionisconsistentwiththeconclusionsreachedintheAldenandASA(Allen,etal.,2006)report.

CribWallCribwallswerenotconsideredaviablealternativeattheBowlinePointParksite.Theextremelymildslopeoftheexistingshorelinemakestheconstructionofverticalornearverticalretainingstructures (bulkheads, biowalls, timber cribbing, live crib walls, and vegetated geogrids)impractical. The nearly horizontal nature of the Bowline Point Park site does not provideenough natural relief to make these structures costefficient without adding a significantamountoffill.Doingsowouldchangetheprojectfromashorelineprotectionprojecttoalandreclamation project, negating any useful information that could be obtained from the costanalysis. Itshouldbenotedthatthissuggestion isconsistentwiththeconclusionsreached intheAldenandASA(Allen,etal.,2006)report.

LiveCribWallLive cribwallswere not considered a viable alternative at the Bowline Point Park site. Theextremelymildslopeoftheexistingshorelinemakestheconstructionofverticalornearverticalretaining structures (bulkheads, biowalls, timber cribbing, live crib walls, and vegetatedgeogrids) impractical. The nearly horizontal nature of the Bowline Point Park site does notprovide enough natural relief to make these structures costefficient without adding asignificantamountoffill.Doingsowouldchangetheprojectfromashorelineprotectionprojecttoalandreclamationproject,negatinganyusefulinformationthatcouldbeobtainedfromthecostanalysis.ItshouldbenotedthatthissuggestionisconsistentwiththeconclusionsreachedintheAldenandASA(Allen,etal.,2006)report.

SillStonesillshavebeenusedextensivelyinareasliketheChesapeakeBaysincethemid1980stoprotectlowtomediumenergyshorelines,andtopromotethegrowthofmarshland.Researchhas shown that a typical crosssection developed by the Maryland Department of NaturalResources (DNR,1993),hasworkedwellbothwithinMaryland andwhenappliedelsewhere.ThetypicalcrosssectionisreproducedbelowinFigure8.Therecommendedstonesizesforlow

54

andmediumenergysitesdeterminedbyHardawayandByrne(1999)aresummarized inTable36.ForthelowenergyHenryHudsonParksite,astonesizeof400poundswasselected.UsingtheMarylandcrosssectionasaguide,thedesignparametersshown inTable37wereusedtodevelopthecostforasillattheBowlinePointParksite. Thesuggesteddimensionsresult inasillwithatotalcrosssectionalareaof47ft2/ft.Over500ft,thesillhasatotalvolumeof23,540ft3. The cost estimatewas developed assuming a porosity of 40% for the structure and anaveragerockpriceof$97perton.

Figure8TypicalCrossSectionforSill(DNR,1993).

Table36WeightsforVaryingEnergyRegimes(VirginiaInstituteofMarineScience).

EnergyRegime SuggestedStoneSize

Low(02feet) 300900lbsMedium(24feet) 4001200lbs

Table37SelectedSillDimensionsforHenryHudsonPark.

SeawardSlope 1V:2.0HShorewardSlope 1V:1.5HCrestWidth 5ftSillHeight 5.5ft

55

Table38MaterialCostsSill.

Unitweightofstone 165lbs/ft3

Sizeofstone(Dn50) 2.43ftVolumerequired 14,124ft3

TonsofStone 1,164CostofSill $112,908CostofSillperlinearfoot $225

The placement of sill stones is generallymore precise and requires specialized labor. LaborcostswereestimatedbasedontheprevailingwageformarineconstructionintheStateofNewYork (http://wpp.labor.state.ny.us/wpp/publicViewPWChanges.do). Assuming 500man hoursforconstruction,at$35/hr,anestimateof$17,500forlaborisobtained. Anadditionalcostof$5,000isaddedtothematerialandlaborcoststoaccountforgeneralearthwork,notincludedintheestimate.Thisbringsthefinalinitialcostto$135,408.

Indevelopingthelifecyclecostforsills,thefollowingassumptionsweremade:

Maintenanceandrepaircostsforsillsaregenerallyminimal.Anestimateof10%oftheinitialcostissetasideformaintenanceandrepairduringeachperiod.

Sillsareresilient.Thefollowingdamagesareexpectedduringsignificantstorms:Table39ExpectedDamageSill.


50 None N/A 40 Some stone replacement 10% 25 None N/A 10 None N/A

Althoughnotexplicitlyconsideredinthisanalysis,sillscanusuallybemodifiedtoadapttorisingsealevelsbyaddingstonetobuildupthecrestelevation.Withrapidsealevelrisehowever,itisunlikelythatsedimentaccumulationandmarshgrowthwilloccurnaturally.Thecostassociatedwithaddingstonetoasillwillgenerallybehigherthanforsimilarlandbasedstructuresduetotheadditionalcostsrelatedtomarineconstruction.

56

SillCostEstimate



Storm Damage #Storms Cost #Storms Cost #Storms Cost TotalCost50 0.56 $ 0.75 $ 1.01 $ $

40 10% 0.73 $7,484 1.02 $5,998 1.30 $4,584 $18,066

25 1.13 $ 1.53 $ 2.14 $ $

10 2.84 $ 3.97 $ 5.32 $ $

Replacement 100% 0.00 $ 0.00 $ 0.00 $ $

Maintenance 10% 1.00 $10,239 1.00 $5,854 1.00 $3,539 $19,631

InitialCost $135,408*#stormsreferstothenumberoftimesthecostisappliedforreplacement

a comparative cost analysis of ten shoreprotection approaches at three sites under two sea level...

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