Absecon Brochure Update Planning Process1 [1]

7/27/2019 Absecon Brochure Update Planning Process1 [1]

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The U.S. Army Corps of Engineers Philadelphia Districtpumps sand onto the northern end of Atlantic City in 2012

as part of the first full scale renourishment of the project.

Absecon Is land Coastal Storm Risk Reduction ProjectPlanning Behind the Project

Most residents of Atlantic City, Ventnor, Margateand Longport are familiar with the beachreplenishment project ongoing for Absecon Islandand other projects elsewhere along the New J erseyshoreline.

The Federal Sponsor of the Absecon Island projectis the U.S. Army Corps of Engineers PhiladelphiaDistrict and the Non-Federal Sponsor is the State ofNew J ersey, Department of EnvironmentalProtection (NJ DEP).

But how did the project plan for Absecon Islandcome about? What other alternatives were

considered and what made the U.S. Army Corps ofEngineers who planned and designed the project choose this one?

BACKGROUND

The Absecon Island Coastal Storm RiskManagement project grew out of a larger U.S. ArmyCorps of Engineers feasibility study that wasauthorized by Congress which looked at ways toreduce storm damage due to flooding and waveattack and minimize shoreline erosion betweenBrigantine Inlet and Great Egg Harbor Inlet. The

project has moved forward with at the request andwith support from the local, State and Federalrepresentatives for Absecon Island; and through the

joint efforts of the U.S. Army Corps of EngineersPhiladelphia District (the Federal sponsor) and theNew J ersey Department of Environmental Protection(the non-Federal sponsor). The project wasultimately authorized for Construction by Congressin the Water Resources Development Act of 1996(WRDA 1996).

The Project Cooperation Agreement (PCA) wassigned J uly 31, 2003. This document defines therelationship between USACE and NJDEP in

constructing this project and performing periodicnourishment over the 50-year project life. (The fourmunicipalities on Absecon IslandAtlantic City,Ventnor, Margate and Longportenter into a State-Aid Agreement with NJ DEP that delineates the rolesof the state and respective local governments inmeeting project requirements of the non-federalsponsor). The initial construction of the Atlantic Cityand Ventnor portions of the project was completed in2004

The map on page 2 shows historical shorelines for aportion of Absecon Island. As can be seen in thefigure, the 1870s shoreline was half a blocklandward and consisted of naturally occurring dunesand dune grasses. After development of the arealater in the century, these dunes were flattened andthe beach was extended creating low profilebeaches that were little defense against coastalstorms; Hence the construction over the years of anetwork of bulkheads and seawalls along theshoreline in an attempt to create coastal protection.

The ocean shoreline of Absecon Island, though lowin profile, has experienced relatively stable shorelinelocations in between the Atlantic City and Longportareas of the island adjacent to Absecon and GreatEgg Inlets. This stability is due to the periodicplacement of millions of cubic yards of sand

(beachfill, beach nourishment, etc.) onto thebeach in Atlantic City over the past half-century. Ifsand had not been placed on Atlantic Citys beachesin the past, prior to the start of the Federal project, itis very likely that the other communities on AbseconIsland would have experienced more serious erosionand storm damages than they actually had over thepast several decades


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For more information please see our web page at:www.nap.usace.army.mil/coastal

or contact the Public Affairs Office, Philadelphia District, U.S. Army Corps of Engineers at (215) 656-6515.

PLANNING BEHIND PROJECT

For study purposes, Absecon Island was furtherbroken down into two areas: (1) the Absecon Inletfron tage and (2) the oceanfront, which is thefocus of this pamphlet.

With respect to the oceanfront, Absecon Islandhistorically has been one of the hardest hit of all theNew J ersey barrier islands during coastal storms,especially noreasters like the 1962 Ash Wednesdaystorm. Under state and local funding, Atlantic City

has already seen several large beachfill efforts tomaintain a beach along the northern end, and aseries of groins is in place to help stabilize theshoreline.

The communities of Ventnor and Margate havehistorically low-elevation beaches that are prone toocean side flooding despite the presence ofbulkheads. Longport generally has a narrow beach;shore protection takes the form of a curved-faceconcrete seawall and timber bulkhead. Pastbulkhead failures have resulted in significantproperty damage.

PLANNING PARAMETERSSpecific objectives for the Absecon Island studyincluded the following:

Reduce storm flooding and wave damage alongboth ocean and inlet frontages

Reduce the impacts of long-term beach erosionalong the oceanfront

Improve the retention of beachfill on the ends ofthe project in Atlantic City and Longport

Improve the stability and longevity of beachesand shore protection structures in general

Reduce maintenance of existing hardenedshore protection structures (bulkheads, seawalls)along the shoreline

Preserve and maintain the environmentalcharacter of the areas affected

In evaluating alternatives and selecting a plan thatwould meet these objectives, the Corps projectteam was constrained by a principal guideline: Theeconomic benefits of the project must exceed itscost.

The Absecon Island project is a Coastal Storm RiskManagement projectand is based on an analysis ofreduced damages versus costs. Corps regulationsrequired us to recommend the plan to Congress forauthorization that has a benefit to cost ratio greaterthan 1.0, which has the highest annual net benefitsin the form of reduced damages over the 50 year

period of economic analysis.This is considered theNational Economic Development, (NED), plan. Thiswas the plan ultimately supported by the localmunicipalities, the non-federal cost sharing partner,NJ DEP, and authorized by Congress forconstruction by the Water Resources DevelopmentAct of 1996.
http://www.nap.usace.army.mil/coastalhttp://www.nap.usace.army.mil/coastalhttp://www.nap.usace.army.mil/coastalhttp://www.nap.usace.army.mil/coastal


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THE PLANNING PROCESS

The process of screening many alternatives toidentify the best plan that is technically effective,environmentally sound and economically mostbeneficial consists of three stages or cycles:

Stage 1: Identify various shoreline protection

measures that may satisfy the problem and need.Eliminate from consideration those that obviouslywould not provide the minimum acceptable shoreprotection at a reasonable cost.

Stage 2: For the remaining alternatives, evaluateshore protection benefits, construction costs andenvironmental impact in detail. Make a preliminarycomparison between the cost of each alternativeand the damages that would occurstorm-inducederosion, wave attack and inundationwithout it.

Eliminate those for which the benefits (damagesprevented) do not exceed the costs. Benefits and

costs are expressed on an average annual basis.Net benefits for a proposed plan are measured bysubtracting average annual costs from averageannual benefits.

Stage 3: Develop the designs and calculate damageprojections to produce the optimal plan with thegreatest net benefits.

ALTERNATIVES CONSIDERED (AND WHY EACHWAS REJECTED OR SELECTED)

1. No Action. In other words, maintain status quono measures to provide erosion control,recreational beach or storm damage protection tobeachfront property.

WHY REJECTED: Does not meet any of theprojects objectives.

2. Evacuation from Areas Subject to Erosionand Storm Damage. Permanent evacuation ofexisting developed areas that are prone toflooding involves not only acquiring lands andstructures, but also demolishing or relocatingcommercial and industrial developments and

residential property to another site.WHY REJECTED: The level of development in theproblem areas under study would make thismeasure prohibitively expensive and unrealistic.

3. Regulation of Future Development. Regulationcould be enacted to minimize the impact oferosion on lands which could be developed in thefuture.

WHY REJECTED: Would have little impact becausevirtually all the oceanfront is already developed.

4. Offshore Detached Breakwaters. Typically aseries of stone structures that are visible from thebeach during low tide periods, an offshoredetached breakwater acts as a buffer againsterosion by reducing wave energy on the beachesbehind it. Since it does not protect against storm

surge or flooding, it usually must be accompaniedby an initial beachfill.

WHY REJECTED: This alternative is costprohibitive. All stone must be brought in on bargeswith the resulting additional difficulty of working in anopen ocean environment. It would not providesufficient protection to densely developed oceanfronts. There are also aesthetics and safetyconcerns.

5. Perched Beach. In combination with initialbeachfill, this alternative involves the addition ofan underwater structure to support the offshoreend of the placed beachfill and thus eliminate the

need to place additional sand to meet the oceanbottom. As a result, the actual amount of sand tobe placed is less than in a typical beachfill. Theunderwater structure would act in the same wayas a natural sandbar formed offshore duringstorm events.

WHY REJECTED: Perched beaches are not usuallydesigned for high-wave-energy open oceancoastlines like Absecon Island. Ocean waves wouldscour in front of and behind the offshore structure,


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driving up maintenance costs; sand trapped by theperched beach can cause erosion down the coast,even if only temporarily; and the submergedstructure could pose a safety hazard to swimmersand bathers. The structure would not reducedamages significantly during the most coastal stormevents as the storm surge would allow storm wavesover and impact the shoreline. Costs of construction

would be prohibitively high in comparison to thedamages prevented.

6. Submerged Reef. Interlocking concrete unitsform an offshore reef that is designed both toreduce incident wave energy during storms andto prevent outgoing currents from carrying sandto deeper water.

WHY REJECTED: Similar to the perched beach, thisapproach would not offer significant protection fromstorm surge. Costs of construction would beprohibitively high in comparison to the damagesprevented.

7. Offshore Submerged Feeder Berm. In someareas these near shore berms can supply sandand reduce wave damage for about half the costof onshore beach placement.

WHY REJECTED: Experience with these berms islimited, with mixed results to date. The success ofoffshore submerged feeder berms is affected bysuch variables as wave conditions, long-term sandtransport trends, and proximity to inlets of jetties. Sodespite their lower cost, their benefits are much lesscertain than traditional beachfill. And they affordvirtually no protection from the largest coastalstorms.

8. Beach Dewatering. This concept of draining thebeach face to increase stabilityusing onsitedewatering equipmenthas been tried in bothFlorida and Denmark. Sand in the wet beacharea is typically in a buoyant state, so there isless erosion because of the vertical downwardflow of water. The dewatered sand absorbs thesediment-laden swash, creating a deposit of newsand on the foreshore slope.

WHY REJECTED: This technology is unpredictablefor the Absecon environment. Erosion during astorm would likely expose and damage the

dewatering equipment buried in the beach. Routinemaintenance would also be required for the pumpsystem. It would not provide sufficient protection todensely developed ocean fronts.

9. Seawall. While it would not add any recreationalbeach area, construction of either a curved faceseawall or a massive stone seawall wouldprovide storm damage protection by deflecting ordissipating wave energy.

WHY REJECTED: Costs of construction would beprohibitively high in comparison to the damagesprevented. Also, because seawalls protect only theland immediately behind them, widening and long-term maintenance of the adjacent beach would benecessary to reduce scour and preserve theshoreline for recreational use.

Stage 2

The alternatives listed below did not proceed toStage 3.

10. Extend the Longport Terminal Groin. TheCorps developed a cost estimate for extendingthe Longport Terminal Groinmarking the southend of the Absecon Island oceanfrontfrom 500to 1000 feet. The result showed positive netbenefits because of reduced periodicnourishment requirements.

WHY REJ ECTED: The down drift erosion typical ofgroins in general has been especially pronouncedfor those placed at the southern end of New Jersey'sbarrier islands. More specifically, extending theLongport Terminal Groin seaward of the breakerzone could force sand to flow too far offshore to bereturned to the Great Egg Harbor Inlet ebb shoal.

That in turn would decrease the sand supply to boththe Longport borrow area identified for this projectand the borrow area currently being used for theCorps ongoing Ocean City beachfill project. Thesepotential negative impacts outweigh the benefitsmentioned above.

SELECTING A SHORE PROTECTION PLAN

Only four alternatives remained at the start of thethird stage of the planning process: beachfill withbulkheads, beachfill with groins, beachfill as astandalone option, and beachfill with dunes. Sinceall four methods include a beachfill, the next stepwas to establish the required beach parameters.


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Beach Berm (Towel Area) Elevation: Based onhistorical surveys of the beaches along AbseconIsland the natural berm crest elevations averages atapproximately +7.25 feet above the North AmericanVertical Datum,1988, (NAVD), and was selected asthe design berm elevation for the project.

Beachfill Slope: Based on historical profiles the

average slope from the beach berm to MLW wasselected as the design slope for the project. Beyondthat point the slope follows that of the existing profileto where the design berm meets the existing profile.

Beach Berm Width: For economic evaluation,design widths ranging from 75 feet (the minimum tosupport a small dune) to 250 feet (beyond which thebeachfill construction costs clearly increase fasterthan the benefits) were selected. (SEECOMPARISON OF NET BENEFITS BELOW.)

Dune Heights: For economic evaluation, designheights ranging from +11.25 feet (the minimum to

provide significant added storm damage protection)to +16.75 feet NAVD were selected.

Dune Shape:The dune top width for all alternativeswas 25 feet except for those alternatives with a 75-foot berm width, in which case the dune top widthwas 15 feet. Side slopes were set at 1 vertical to 5horizontal.

Dune Alignment: In Atlantic City the proposed dunealignment follows the existing dunes. In Ventnor,Margate and Longport the proposed dunes will be asfar landward on the beach berm as practical to both

maximize towel area as well as provide a uniformalignment.

Design Beachfill Quantities: Quantities for eachalternative were calculated by comparing theproposed design cross section with existing beachsurvey data. This quantity will be updated and thedesign adjusted accordingly just before constructionof each reach of the project.

Renourishment Volumes:The initial quantity ofsand was intended to provide for maintenance of thedesign beach. Then an additional sacrificial

amount was factored in to account for erosionbetween initial construction and the firstrenourishment. This way, by the end of the firstrenourishment cycleabout three yearsthe beachwill be at its design profile.

Storm Drain Outfalls: In Atlantic City, all outfalls areintact out to approximately the mean low water line;however, several of the existing outfall pipes havebroken off at pipe sections located in the surf zone.

Several outfalls in Ventnor, Margate and Longporthave also suffered damage, and in some caseshave sheared off completely at the bulkhead. Sincethese outfalls are now not long enough to ensureunhindered drainage for beachfill alternatives with aberm width of 200 feet or greater, the analysisincluded the cost of extending them. Using theseparameters, the project team narrowed the options

down to 14 combinations of berm widths and duneheights for the final analysis via computermodelingseven for Atlantic City and seven for theother three communities. Two alternatives wererejected at this point as stated in the followingparagraphs.

11. Beachfill with Bulkhead. A bulkhead protectsshoreline areas from erosion and storm damage,including flooding, but since it does not extend intothe surf area, it does not reduce the flow of sandalong the shoreline. Therefore beachfill would alsobe necessary to limit erosion in front of the bulkheadand provide additional protection.

Since about 60 percent of the Absecon Island oceanfrontage has existing timber or concrete bulkheadsand seawalls parallel to the ocean front, thisalternative examined extending the timber bulkheadwalls along the entire length of the study area. Thiswould require 12,700 feet of new bulkhead toprovide a continuous line of storm protection forAtlantic City. About 1,400 feet would be needed inVentnor, Margate and Longportprimarily at streetendsto replace bulkhead sections that have topelevations below +8.25 NAVD or that are in poorcondition.

WHY REJECTED: A simple matter of economics;the bulkhead offers little more protection than amore natural dune but costs much more. Even ifconstructed beachfill would also be necessary tolimit erosion in front of the bulkhead which woulddrive up the costs even further above the beachfilloptions.

12. Beachfill w ith Groins. Groins are structuresbuilt perpendicular to the shoreline that extend from


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the upper beach face into the surf zone to trap someof the sand moving along the shoreline. When usedin combination with a beachfill, a groin field canreduce both long-term erosion and the requiredfrequency of periodic renourishment.

For such a system to work an adequate quantity ofsand must be moving along the shoreline and the

groins must be designed properlyotherwise, groincompartments at the downward end of the sandsupply may not fill properly and may require periodicaddition of sand. An optimally designed groin willmaximize the amount of sand trapped on its up driftsideclosest to the sand supplywhile minimizingcorresponding erosion of sand on its down drift side.

To supplement numerous groins already in placealong the Absecon Island coastline, the Corpsconsidered adding two groins about 1,200 feet apart

in Atlantic City (southwest of the Ocean One Pier) tostabilize beachfill, and six groins in Longport thatwould also increase the natural beach width.

WHY REJECTED: The one-time cost of groinconstruction turns out to be significantly higher thanthe cost of coming back and adding sand everythree years. Without adding a dune or bulkhead theplan would not significantly reduce damages fromthe more extreme storms enough to justify thesignificantly higher costs.

DETERMINATION OF BENEFITSDamages from hurricanes and coastal storms fallgenerally into three categories: storm-inducederosion, wave attack and inundation (flooding).Using a computer model that simulated storm eventsfrom five- to 500-year frequency, both with andwithout each of the alternative solutions in place, theproject team was able to project monetary damagesstemming from all three categories, subtracting withproject damages from without-project damages tocalculate damages prevented. Both construction(initial beachfill) and long-term maintenance

(renourishment) costs for each alternative were thendeveloped and subtracted from the average yearlydamages prevented to determine the net benefits.Note that the no dune options yielded negative netbenefits; in other words, the damages preventedwould not be enough to recover the costs ofconstruction and maintenance.

COMPARISON OF NET BENEFITS

Atlantic CityNo dune, 150-foot-wide berm $984,34412.75-foot dune, 150-foot-wide berm +$669,80612.75-foot dune, 200-foot-wide berm +$592,05614.75-foot dune, 150-foot-wide berm +$832,01114.75-foot dune, 200-foot-wide berm +$957,29814.75-foot dune, 250-foot-wide berm +$648,38816.75-foot dune, 200-foot-wide berm +$932,573

Ventnor, Margate and LongportNo dune, 150-foot-wide berm $2,196,50111.25-foot dune, 75-foot-wide berm +$206,37012.75-foot dune, 100-foot-wide berm +$592,35212.75-foot dune, 150-foot-wide berm $138,28312.75-foot dune, 200-foot-wide berm $674,61414.75-foot dune, 150-foot-wide berm +$296,10214.75-foot dune, 200-foot-wide berm $272,181

FINAL PLAN FORMULATIONAfter extensive analysis and screening, the field wasnarrowed down to two alternatives: beachfill only

and beachfill with dunes.

13. Beachfill Only. This alternative involves theplacement of sand from an offshore borrow source,directly onto the beach to widen the existing beach.Restoring the beach without sand dunes couldpossibly provide some storm protection by addingsignificantly more sand to the beach to create amuch wider beach berm (the towel area or mainpart of the beach).

However, the addition of a dune would provide amuch greater level of storm protection. The widened

beach is graded to a certain design elevation andwidth to provide the desired level of stormprotection. After the initial widening, the beach willrequire additional sand on a periodic basis to keepthe design beach width and elevation.

WHY REJECTED: This plan was not selectedbecause it is not cost-effective. See comparison ofbenefits above.


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14. Beachfill with Dunes. The beach-restoration-with dune alternative provides the same beachrestoration plan as described above, with additionalsand placed to create a dune at a designedelevation and width. Sand dunes provide additionalstorm surge protection similar to that of bulkheads,but at much lower cost.

They not only reduce flooding in low interior areasby blocking the movement of storm tides and waves

into the land area behind the beach, but also serveas stockpiles to feed the beach. That is becausesand accumulation on the seaward slope of a dunewill either build or extend the dune toward theshoreline; this sand, once in the dune, may bereturned to the beach by a severe storm.

WHY SELECTED: Most cost-effective plan, meetingengineering and environmental requirements. Seecomparison of benefits above.

HOW DUNES AND BEACHFILL WORKTOGETHER

During a coastal storm, the initial wave attack is onthe beach berm in front of the dune. Once the bermis eroded, waves work their way up to the dune. If nodune is in place, oceanfront structures are exposedto both wave attack and flooding. If the attack lastslong enough, then waves can overtop the dune,lowering the dune crest.

Much of the sand eroded from the berm and dune isthen transported directly offshore and deposited in abar formation. This process helps to dissipate waveenergy during a storm. Offshore sand deposits arethen normally transported back to the beach bywaves after the storm. Onshore winds transport thesand from the beach toward the dune area, andanother natural cycle of dune building proceeds. Thegoal is to have a dune of sufficient size so that it willnot completely erode away during a major stormevent.


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THE SELECTED PLAN

The two options with the highest net benefits (onefor Atlantic City and one for Ventnor /Margate/Longport) were completed to come up with the finalAbsecon Island shore protection plan: Beachfill withDunes.

ABSECON ISLANDSELECTED PLAN

AtlanticCity

Ventnor/Margate/Longport

BeachfillBerm Width 200 feet 100 feet

TopElevation

+7.25NAVD(+8.5NGVD)

+7.25NAVD(+8.5NGVD)

Dune

TopElevation

+14.75NAVD(+16 NGVD)

+12.75NAVD(+14 NGVD)

Top Width 25 feet 25 feetSide Slopes 1V:5H 1V:5HDistance

fromBoardwalk 25 feet 25 feet

To aid in the visualization of dune heights: inVentnor the dune will have an elevation about 1 footabove the boardwalk, in Margate it will be onaverage 2.75 feet above the bulkhead and inLongport it will be approximately 2.5 feet above theseawall.

Other key plan elements are as follows:

The initial beachfill for the oceanfront willrequire over 7 million cubic yards of sand tobe placed over a total shoreline length ofapproximately 43,000 feet, followed byperiodic renourishment of about 1.7 millioncubic yards every three years. The beachprofile will taper from a 200-foot to 100-footberm between Atlantic City and Ventnorover a distance of 1000 feet.

Beach access will include natural beachwalkover paths bordered by sand fencing upand over the dunes, and handicappedaccess at required intervals. Thesewalkovers will be placed at most street endsor other traffic areas. Access formaintenance and emergency vehicles will

be provided at specific locations in eachcommunity.

Approximately 90 acres of dune grass willbe planted and about 64,000 feet of sandfence will be erected to protect the dunes.

Documents

Absecon Brochure Update Planning Process1 [1]