Wetlallds Ecology alld Management 10: 289-302, 2002.@ 2002 Kluwe,. Academic Publishers. Printed in the Netherlands.

289

An integrated habitat enh~ncement approach to shor.eline stabilizationfor a Chesapeake Bay island community

C.S. Hardaway Jr.1.*, Lyle M. Varnell 2, Donna A. Milligan I, Walter'l. Priese, George R.Thomas I and Rebecca C.H. Brindley I

tShoreline Studies Program, Department of Physical Sciences, Virginia Institute of Marine Science, Collegeof William and Mary, P.O. Box 1346, Gloucester Point, VA 23062, UK; 2Centerfor Coastal ResourcesManagement, Virginia Institute of Marine Science, College of William and Mary, P.O. Box 1346, GloucesterPoint, VA 23062, UK; *Author for correspondence (e-mail: hardaway@vims.edu; phone: (804)684-7277;fax: (804)684-7250)

Received 27 November 2000; accepted in revised form 16 August 2001

Key words: Breakwaters, Chesapeake Bay, Habitat restoration, Headland control, Hydrodynamic analysis, Shoreplanform, Shoreline management

Abstract

Shore protection and habitat enhancement along a residential island were the main goals of this shoreline study.The physical and geological factors necessary to design shoreline stabilization structures capable of confidentlysupporting suitable and stable habitat enhancementlrestoration substrate are emphasized since this area of studygenerally may be unfamiliar to wetland resource managers. Erosion along the targeted shoreline is influenced by aunidirectional wave field from the south-southwest. Results of our analyses show that a headland control systemcomprised of headland breakwaters could be used successfully to stabilize the existing shoreline and provideresource managers flexibility in habitat restoration decisions. Headland breakwaters are designed to diffract waveenergy so that shore planform equilibrium is attained and can be sized and positioned to maximize the length ofstabilized shoreline. Maximization of the new shoreline length provides increased subaerial, intertidal, andsubaqueous environments for flexible habitat restoration alternatives. The final restoration design developedthrough this study will create approximately 69,000 m2 of new habitat including stable beach, dune, tidal marsh,scrub shrub, and submersed aquatic vegetation. An additional 2,000 m2 of rock substrate habitat is provideddirectly by the headland control structures.

Introduction

Coastal localities which depend on commercial andrecreational fishing interests and/or nature- basedtourism often face conflicting issues when dealingwith erosion control and shoreline stabilization. Thestabilization strategies which are available to addressthe broad spectrum of shoreline situations often im-pact critical habitats of the same resources whichsupport fishing interests and tourism. However, ifhabitat is considered in the planning process, ashoreline management plan can provide effectiveshoreline stabilization and habitat preservation/en-hancement.

Tidal wetlands, beaches, and dunes in the Virginiaportion of the Chesapeake Bay have experiencedna~9raland anthropogenic losses which have greatlyoutpaced compensatory mitigation of these resources.From 1988-1998, permitted tidal wetland losses fromshoreline alterations associated with development anderosion control have averaged 13.76hectares per year,while required compensatory mitigation has averagedonly 0.70 hectares (Virginia Institute of Marine Sci-ence Wetlands Program 2001). Associated losses ofbeach and dune habitats also have occurred; however,these losses are not generally summarized.

Through this project, a comprehensive shorelinemanagement plan for an island community experienc-

290

ing severe erosion was devel~ped; the plan incorpo-rated a large-scale hab.itat restoration componentwithout compromising shoreline stabilization.Shoreline stabilization projects which are im-plemented over large areas of shoreline can be aneffective vehicle to offset habitat losses and achieveregional or statewide habitat enhancement/restorationgoals.

There are four basic approaches to shoreline man-agement: I) No action; 2) Defend an erosional areawith structures such as bulkheads, seawalls or revet-ments; 3) Maintain and/or enhance existing shorezone features such as beach and dunes that presentlyoffer limited protection or habitat; or 4) Create a shorezone system of beaches, dunes, and fringe marshesgenerally using headland control with stone breakwa-ters (Hardaway and Gunn 1999;Hardaway and Byrne1999). All of these approaches were considered dur-ing this study. When no action is taken to protect ashore, consequences are evident with continued ero-sion, particularly the loss of land and habitat as wellas the threat to upland structures. Shoreline protectionstructures, such as bulkheads or stone revetments,placed upon or against an existing shoreline, at best,maintain the present habitat situation but generallyremove, isolate, or impact existing habitat. Non-struc-tural shoreline erosion control methods such as beachnourishment and marsh fringe creation can effectivelymitigate erosion but generally require frequentmaintenance and associated ongoing costs. Creationof a protected shore zone system using headlandbreakwaters and beach nourishment can reduce futurecosts and maintain a predictable shore planform, butrequires a detailed characterization of local physical,geological, and biological parameters and an analysisof historical and anthropogenic shoreline changes.These data are necessary to understand the erosionalforcing factors which must be compensated for in thedesign of headland breakwaters for shore protection.With proper background data, headland control struc-tures can be designed and positioned in a manner thatallows for a confident prediction of the equilibriumshore planform. Such planforms are necessary forhabitat restoration planning.

Characterization of the local flora and fauna, bothfrom an historical perspective and at the time ofconcern, also are required for habitat restoration plan-ning. Existing natural resources must be analyzed todetermine use characteristics of the littoral marinesystem and the extent of potential direct losses ofexisting habitats from shoreline stabilization. The

amount of direct habitat losses generally are factoredinto restoration initiatives. Analyses of the extent andcharacter of historical shoreline habitats can guide

restoration goals and can be used as a baseline forrestoration planning.

Methods

Study Site

Saxis Island is located on the Bay side of upperAccomack County, Virginia (Figure I). The Town'snorthwestern boundary, which fronts PocomokeSound, has eroded at a rate of approximately 1.52m/year (Hobbs et al. 1975). The mean tide range atSaxis is 0.7 m with a spring range of 0.82 m(NOAA1989). The shore faces approximately northwest withaverage fetches to the northwest, west, and southwestof 4.3 kilometers (km), 15.6km and 34.7 km, respec-tively. The shoreline is characterized as predominant-ly marsh along the southern half, and an impermeablebeach (underlain with marsh peat substrate) along thenorth half with marsh shore re-occurring northward.

Shore Change

Shoreline positions were determined from aerialimage archives (1938, 1942, 1955, 1985, and 1990)and an 1851 topographic map and were compared tothe 1998 shoreline. Shoreline positions and rates ofchange were digitally analyzed using the End PointRate (EPR) method (Fenster et al. 1993), to determinethe overall rate of shore change.

Hydrodynamic Analysis

Wave energy impacting the shore zone defines ero-sional and depositional patterns and guides shoreprotection strategies. Wave climate characterizationrequires knowledge of fetch exposure, dominant winddirection(s), and storm surge frequency. Wind datafrom Patuxent Naval Air Station were used to modellocal wind driven wave fields using procedures de-veloped by Sverdrup and Munk (1947), Bretschneider(\ 958) as modified by Kiley (1982), known as 5MB.Effective fetch, a parameter in wind wave growthrequired for wave field analysis, was determined forthe predominant exposed directions (NW,Wand SW)for Saxis Island (U.S. Army Corps of Engineers1984). Specified storm surges were determined after

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291

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Figure 1. Town of Saxis and study site location.

292

Boon et al. (1978) and range from 0.30 m (returninterval one year) to 2.74 m (return interval 100years).

Offshore, the wind and wave. direction were as-sumed the same. However, at about -4 m mean lowwater (MLW), the waves enter the nearshore shoalingregion and must be evaluated using a hydrodynamicwave refraction model. The predicted significantwave heights and periods for the three subject direc-tions are used as input to the linear wave propagationmodel RCPWAVE(Ebersole et al. 1986). It computeschanges in wave characteristics that result naturallyfrom refraction, shoaling, and diffraction over com-plex topography. Routines to estimate wave energydissipation due to bottom friction were added afterWright et al. (1987). The use of RCPWAVEto modelthe hydrodynamics at Saxis assumes that only theoffshore bathymetry affects wave transformation; theapplication does not include the effects of tidal cur-rents. RCPWAVEcalculates wave heights and direc-tions of propagation (wave orthogonals) along theentire modeled shore. Wave height and direction ofwave approach toward shore at the approximate depthwhere potential offshore structures would be locatedwere used to characterize mean annual conditions atSaxis. The final shape of the shore planform betweenheadlands can be determined with the Static Equilib-rium Bay (SEB) model.

The SEB model is an empirical model that utilizesthe net wave conditions impacting the shore to de-termine the beach planform between headlandbreakwaters. Hsu et al. (1989a) defined bay curvatureutilizing a parabolic bay shape (Figure 2A). Incomingwave crests impinge at an angle ([3)to a straight beach(i.e. the tangential beach). The point of diffraction canbe a naturally occurring headland or it can be the tipof a breakwater. The line joining the point of diffrac-tion to the downcoast limit of the bay (Ro) is termedthe "control line" , and its angle to the incident wavecrest is the obliquity of the waves ([3).When the bay isin static equilibrium, [3is equal to the angle betweenRo and the downcoast tangential beach. Therefore, thevariables which determine bay shape are an arc oflength R angled e to the wave crest line, which isassumed parallel to the tangential beach at the dow-ncoast limit of the bay (Hsu et al. 1989b).

Figure 2B illustrates the connection between thewave climate analysis and SEB model. The waveclimate analysis is necessary to determine the vari-ables needed as input to the SEB model. The windfield for a bay site is used to determine the annual

significant wind and the design storm wind. Waveheight (H) and period (T) are predicted at a pointoffshore of the project by 5MB. The waves generatedin the 5MB model are used as input to RCPWAVEsince wind and wave directions are assumed to be thesame. RCPWAVEmodels wave attenuation across thenearshore region, and the output parameters waveheight and angle (H and a) are exported at theapproximate site of the proposed breakwater project.

Biological Surveys

Present and historical data also were used to assesshabitat losses and develop restoration goals. The timeseries of aerial photographs used in determiningshoreline changes also were used to determine thehistorical character and extent of habitat for SaxisIsland. Assessment of the existing habitats and associ-ated fauna and flora included surveys of vegetationcommunities, birds, nekton and benthic macrofauna.

Recent aerial photographs were used in concertwith a site survey to assess vegetative communitystructure along the shoreline. The photographs weredigitized to determine the relative percent area of eachidentified community. For the purposes of this study,vegetation communities were classified into the fol-lowing categories: beach, dune scarp, marsh, Phrag-mites australis-dominated, scrub shrub, and old field.

Data on birds were collected by roving survey.Birds were identified to species and the subhabitatthey were occupying at the time the encounter waslogged. The entire length of the Saxis shoreline adja-cent to Pocomoke Sound, the upland portions of theisland including the causeway, and the marshes sur-rounding Saxis Island were surveyed four times.Chosen sample dates corresponded with criticalseasonal migratory patterns and included one winter(23 March 1998), two spring (early/mid spring (6May 1998) and late spring (27 May 1998)), and onesummer (25 June 1998) survey.

Six randomly-selected sample sites were seined (5mm mesh) for fish and blue crabs during the spring(27 May 1998) and summer (25 June 1998). Col-lected fauna were enumerated by species.

Sample sites for oyster and clam surveys also werechosen by random distance measurements. An addi-tional random component (offshore distance) extend-ed from mean high water (MHW) to approximately75 m offshore. Three random distances were chosenalong the offshore component at each of six oysterand clam sample sites. A total of 18 separate sites

-

293

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Possible Headla~;Alignment

B

AnnualSignificant

Fetch

RCPWAVEBathymetric

Grid

L,=BW LengthG, =Bay GapM, =IndentationB =Beach Width

Project Upland

Figure 2. Parameters related to A) the Static Equilibrium Bay model (after Hsu et at (1989a», and B) wind/wave generation (SMB). nearshorewave refraction (RCPWAVE), and beach planform prediction (SEB).

294

were sampled for oysters and clams on 18 August1998. At each sample site, an area of approximatelyone square meter was dredged with a hand dredge.The dredge sampled approximately the top 10 cm ofthe substrate which is a sufficient collection depth fornearshore beach environments.

Plan Development

The shoreline management plan will be a result of theconvergence of erosion control design based on shorezone energy models and restoration goals based oncurrent and historical natural resources. Inherent in

both erosion control options and restoration goals arevariables such as community desires and expecta-tions, and costs. Therefore, shoreline managementplans, by nature, must use science-based informationas the basis for conceptual design end points inte-grating all pertinent variables (Figure 3).

The decision to provide long-term erosion control

RestorationGoals

and habit restoration on Saxis Island required thedevelopment of a shore zone system, which consistsof breakwaters, beach nourishment, and vegetativeplantings as a series of headlands and pocket beaches.This methodology of utilizing stable beach planformsas a foundation for coastal habitats has been shown to

be effective (references). The configuration ofbreakwater dimension and placement is based, in part,on the hydrodynamic setting and the known empiricalrelationships between placement and planform. Coun-teracting the erosional forces of storm waves can beaddressed in various structural configurations withoutcompromising erosion control, which provides forflexible restoration alternatives. The level of protec-tion is discerned by the designed storm (based onstorm surge frequency). The minimum design plan-form for shore protection can be enhanced to increasethe aereal extent of vegetative communities. Inherentin pocket beach morphology are elevation gradients,which are also coincident to intertidal and supra-tidal

ErosionControl

Figure 3. Diagram of conceptual integrated shoreline management plan development. Final plan specifications are a convergence of many

factors that build upon science-based information.

estuarine habitats. Integration of erosion control andhabitat restoration therefore entails full vegetative

application at the appropriate elevations within thesubstrate stabilized by breakwaters. To the extent

possible, the offshore limits of the system must not

encroach beyond the what is required for shore

protection.

Results

Shore Change

Saxis Island shoreline change is a result of bothnatural variations in erosional patterns and anthro-pogenic impacts. In 1851, the shoreline may havebeenprimarilymarshjudgingfrom the characteristicundulations (Figure 4). Aerial imagery from 1936shows that the shoreline was primarily marsh, inc\ud-

I250

295

ing several small marsh headlands with little beach.Overall, the shoreline eroded at an average rate ofabout -1.2 m/yr between 1851 to 1942.

Between 1942 and 1968, Saxis's shoreline receded

at an average rate of about -0.4 m/yr which isconsiderably less than the previous time period. Dur-ing the 1960sand early 1970sdredge material deposi-tion upon the southern shoreline and subsequentlongshore dispersal northward increased beach width,and probably is responsible for the lesser overallaverage erosion rate. From 1986 to 1998 the Sax isshoreline regained a higher average erosion rate ofabout 1.16 m/yr (comparable to the rate calculated for1851-1942). Some submersed aquatic vegetation(SAY) and sand bars existed at the site during the late1950s, but both had disappeared by 1965 (Orth andMoore, 1984).

Shoreline conditions for 1985, 1990, and 1998

show little change in land use or shoreline attributes.

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Rate of Change at MHW

Average

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1968-1986 -0.1 m/yr

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I T500 750

Alongshore(m)

I12501000

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Figure 4. Saxis shoreline change and historical shore positions along the southwestern-most section of Saxis Island project site.

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296

The present nearshore zone is relatively shallow withno bars, indicating a general lack of sand in the littoralsystem.

Hydrodynamic Analysis

Long-term wind frequencies indicate that winds blow-ing from the southwest are dominant in the 4-5 mlsrange followed by the northwest, then west. However,as wind speed increases, the northwest componentbecomes dominant while the southwest and west have

similar frequencies. Overall, the northwest componentis slightly more frequent than the southwest, and bothare more frequent than the west condition. The in-fluence of nearshore bathymetry results in a refractionof southwesterly waves of approximately 35° from theoriginal direction of propagation before impacting theshore, with a westerly wave refraction of approxi-

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BFigure 5. Wave vector (orthogonal) plots for annual conditionsfrom the A) West and B) Northwest.

mately 8° from the original direction of propagation.The waves coming from the northwest are alteredlittle by the nearshore; the angle of wave approachonly changes by an average of about 2° and the waveheight does not diminish as rapidly as with otherdirections. Because of the shoreline orientation, the

larger northwesterly waves have angles of about 13°off normal (0°) to the shore, but are shore normalfurther inshore, indicating a possible mechanism foronshore-offshore movement of sand during storms.With the longest effective fetch to the southwest aswell as a high frequency of wind from that direction,waves are generated that significantly impact thealongshore transport system tending to drive sedimentto the north. Current shoreline morphology points to anorthward trending littoral transport system support-ing the wind-wave analysis.

Figure 5 shows typical wave vectors for two exam-ple conditions modeled using RCPWAYE. Figure 5Adepicts waves from the west at a water level justslightly less than MHW. Under these minimal con-ditions, waves diminish in height over the flat near-shore rather than break at the shore. The waves have a

definite angle to the coast, orientated at a positive 20°angle off normal (0°) to the shore (bearing 100° TN).A typical condition using a wave from the northwestis shown in Figure 58. These waves have an averagesignificant wave height of 0.33 m and make an angleof - 12° off normal (bearing 132° TN) with theshoreline. As the wave moves closer to shore theycontinue to bend further toward shore normal before

impacting the shoreline.Individual wave modeling cases must be mean-

weighted with wind frequencies in order to determinethe average annual energy acting on the shoreline.Utilizing the wind analysis and output fromRCPWAYE, the average wave angle impacting theshore bears 107° TN, making a + 13° angle off normalwith the Saxis shoreline. This indicates a northward

net littoral transport of sediment. Wave modelingresults were used to develop equilibrium bay plan-forms for the shore protection system.

Biological Surveys

Historical habitat analyses showed a greater abun-dance of dunes, saltmarsh, scrub-shrub and SAYcommunities relative to the current shoreline. Thelocation and extent of these and other communitieswere used to develop restoration goals.

The Saxis shoreline is dominated by common reed

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(Phragmites austra/is), with significant stands ofemergent marsh, scrub shrub, and old field com-munities (Figure 6). The areal extent of the existingcommunities and its characteristic vegetation arelisted in Table I. Landscape features such as lawn anddeveloped are present adjacent to the Saxis shoreline,but were not included in the study.

Filter feeders (menhaden and anchovies), omni-vores (Atlantic silversides) and forage fishes (summerflounder and croaker) dominate the local nekton. Nospecies was considered unusual or unique to thisecosystem. However, no killifishes were collected,and the absence of species such as the sheepsheadminnow, striped killifish, and the mummichog wasunexpected. Killifishes spawn within areas containingaquatic vegetation (SAY beds or intertidal marshes).Eggs are either attached to aquatic plants or buried inquiescent waters. This shoreline currently provideslittle of the critical habitat for killifishes.

Anchovies dominated spring samples, whereas an-chovies and Atlantic silversides were co-dominant

during the summer sampling period. Relative abun-dances of summer flounder and Atlantic Croaker weregreater during the spring sampling period. Blue crabs

297

and Atlantic menhaden were more abundant duringthe summer sampling period. These data are con-sistent with other local fish population studies (Seaverand Austin 1995).

No live oysters or clams were collected; only sparsecultch was observed at a few sample locations. Theabsence of oysters or clams observed within the studyboundaries also was unexpected.

Birds were represented by a diverse assemblagethat included a mixture of year-round residents, win-tering birds, migrants, and summer nesting birds.There was no one group of birds that dominated theavifauna; pelagic birds, wading birds, waterfowl,raptors, shorebirds, gulls and terns, and passerineswere all well represented. These data are generallyconsistent with the results of other local bird popula-tion studies (Audubon Society Christmas Bird Countsand the U.S. Fish and Wildlife Service Breeding BirdSurvey (Sauer et al. 1997».

With the exception of the narrow beach and non-vegetated intertidal sand community, the Saxisshoreline contains little favorable bird habitat. Theshoreline is dominated by reed grass, and this com-munity provides little functional habitat to the vast

Vegetative Community StructureSaxis, Virginia

xmeters

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~ Marsh

~ Phragmites

k>QI Scrub Shrub

!II]Dune

milOldField

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o SpoilArea

Figure 6. Vegetative community structure along the Saxis shoreline.

298

Vegetated Community Type

Phragmites- Dominated

Table I. Areal coverage and principal plant species characteristic of the major vegetated community types along the Sax is shoreline.

Principal Plant Species

80,547 Common reed - Phragmite.f australis

Marsh 37,254

Scrub shrub 14,307

Old field 4,041

Beach 21,739

RubbleDuneTotal

1,486465159,840

Groundsel tree - Baa'haris halimifolia

Smooth cordgrass - Spartina altemifiora

Saltmeadow hay - Spartina patens

Marsh elder - Iva frutescem'White mulberry - MortiS alba

Black locust - Robinia pseudoacacia

Black Cherry - Prunu.f seratina

Hackberry - Celtis occidentalis

Wax myrtle - Myrica cerifera

Groundsel tree - Baa'haris halimiji)lia

Pokeweed - Phytolacca americana

Horseweed - Erigeran canadensis

Dog-fennel - Eupatorium capillifo/ium

Blackberry - Rubus argutu.f

American beachgrass - Ammophila breviligulata

Bitter panicum - Panicum amartll11

Seaside goldenrod - Solidago .wnpervirens

majority of locally-common birds or those using theAtlantic flyway. Only sparse-scrub shrub com-munities are found along this shoreline.

Plan Development

The initial breakwater system required a minimumdesign beach/dune width for the pocket beach to beapproximately 27m from MLW to the crest of thedune. The dune crest needed to be approximately +6ft above MLW to address the 25-yr storm (the desiredlevel of protection identified by stakeholders). Thissets the minimum distance for MHW from the uplandproperty. The breakwaters are then positioned aroundthe relationship of the beach planform configurationusing the SEB analysis. The resultant stable embay-ment offered increased intertidal, beach and dunehabitat from the current situation. However, by keep-ing the same offshore position, opening the breakwa-ter gap and adding a small inner bay structure, asignificant increase in shoreline length, and conse-quently habitat, is attained. The shoreline manage-ment plan for Saxis Island was designed by buildingupon the minimum beach planform and consists of a

series of headland breakwaters, beach nourishmentand vegetative plantings influenced by the historicshoreline geomorphology, wave climate analysis, andstorm surge frequency (Figure 7).

A diverse coastal habitat supporting aquatic, terres-trial, and avian fauna was the desired restoration goaldeveloped from current and historical natural re-sources data. Optimization of shoreline lengths andelevations needed to both achieve the maximum levelof restored estuarine edge and support the com-munities identified in the restoration goal wasachieved by varying the lengths and heights of theoffshore and inner bay breakwaters, which controlsthe amount and configuration of substrate availablefor community restoration. Bird habitat restorationrequires substrate at the proper elevation and distancefrom the shoreline to support scrub-shrub and her-baceous communities. In response, dune and terraceelements were added to the plan that would supportthese communities. Marsh vegetation requires sub-strate at broad, protected intertidal elevations to in-crease the probability of success and sustainability. Inresponse, offshore and inner bay breakwater length,substrate placement, and tombolo configuration was

299

ExiStingMean HighWater

Scale1 em = 91 m

~ ProposedBeach NourishmentMarsh and DuneHabitat

Figure 7. Proposed Shoreline Management Plan for the Saxis shoreline.

designed to provide optimum conditions in the lee ofthe breakwaters. Nonvegetated beach communitiesrequire substrate placement that maximize intertidaland supra-tidal widths, and beach length. In response,offshore and inner bay breakwater heights and lengthswere designed to provide the necessary stable sub-strate configurations without compromising theamount of area necessary for intertidal marsh restora-tion. SAYcommunities require sandy substrate in aprotected subtidal setting. In response, offshorebreakwater length, height and tombolo configurationwas designed to maximize stable subtidal areas in thelee of the breakwater without compromising theamount of area necessary for either intertidal marsh orbeach restoration.

The final integrated system has seven headlandbreakwaters (91 m crest length) placed about 61 mfrom the existing MLW shoreline and spaced 138 mapart. Relatively large tombolos will be created in thelee of these long breakwaters with beach fill placed asdesigned for community restoration. In order to insurelong-term protection and increase habitat substrateavailability, seven 30.5 m inter-bay breakwaters willbe inset. Typically, the mid-bay areas are higherenergy shorelines which may not support intertidalvegetation as well as areas closer to the largebreakwaters. The small, inter-bay breakwaters in-crease the linear area of stable shoreline by reducingthe characteristic increased energy environments be-tween the large breakwaters.

Approximately 84,I00 cubic meters of beach fill isrequired to meet erosion control and habitat restora-tion goals. A + 1.8 m MLW berm feature will addressa 25-yr storm event, but the overall system willwithstand a 50-yr event with the possible exception of

some sand and vegetation repair. The breakwaterswill remain intact in a 100-yr event while there maybe a need for replacing some sand and vegetationwithin the system. Intertidal marsh will be restoredalong the proposed shoreline from approximatelymean tide level (MTL) to approximately 1.1 m aboveMLW elevation (Figure 8). A mixture of saltmarshcordgmss (Spartina alterniflora) and saltmeadow hay(Spartina patens) is proposed for planting. Generally,saltmarsh cordgrass grows in the Mid-Atlantic regionbetween MTL and MHW, whereas saltmeadow haygenerally is found at slightly higher elevations imme-diately landward of the saltmarsh cordgrass communi-ty. Herb communities (beach mix) will be planted inareas above 3.5 m above MLW. Scrub-shrub (shrubmix) will be planted at the higher (+ 6 MLW)elevations and in lower (+4 MLW) areas protected bydunes.

Discussion

Based on the local needs, desires, and physical settingof the Saxis Island littoral system headland breakwa-ters with beach nourishment are the preferred structur-al option for shore stabilization. A detailed under-standing of local physical and geological factors isnecessary to properly design a headland breakwatersystem. The dimensions and position of any shoreprotection system are dependent on wave climate,costs, what is being protected and what level ofprotection is desired (e.g. for a design storm surge andwave height).

Headland breakwaters have been used extensivelyaround the Chesapeake Bay over the last 15 years for

300

Pocomoke Sound

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Saltmeadow Hay- Spartina patens,Smooth Cordgrass- Spartins alterniflora

Saltmeadow Hay- Spartina patens,American Beachgrass- Ammophilia breviligufataBitter Panicgrass- Panicum amarum

Beach Plum- Prunus maritima, Black Cherry- Prunus serofina,Wax Myrtle- Myrica cerifera, Yaupon- flex vomitoria,Inkberry- flex gfabra

Mean High Water=O.7mUpper Umit Wetlands = 1.1m

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P77I Marshk::L..::IMIx

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0.0 ---------------------~ :.!:30m

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Shrub Red Cedar- Juniperus virginians, Choke Cherry- Aronia melanocarpa,.MI 2 Blueberry-Vacciniumcorymbosum,Groundsel Tree-Baccharis halimifolia,X Sw~chgrass- Panicum virgatum, Persimmon- Diospyros virginiana

Figure 8. Detail of the Shoreline Management Plan with Habitat Enhancement for the Town of Saxis.

erosion control and habitat enhancement (Hardawayand Gunn 1991;Hardaway et al. 1993;Hardaway andGunn 1998). Hardaway et al. (1991) evaluated 15breakwater systems in terms of numerous parametersincluding breakwater length, gap, distance offshoreand the indentation of the adjacent embayments anddemonstrated that a stable beach planform can existwith intertidal attachments. The advantage to an inter-tidal attachment is that wetland habitat is increased inthe breakwater's lee, but beach stability is not com-promised.

The optimized shoreline design provides approxi-mately 72,000 m2 of intertidal, beach and subaqueoushabitats for use by marine, terrestrial, and avian fauna.The accuracy of the amount of restoration area isreasonably assured due to the level of study support-ing the shoreline design. The probability of restora-tion success also is increased due to the level ofsubstrate stability provided by the breakwaters. Thebenefits of flexible habitat restoration alternativesafforded by sound shoreline stabilization have beendemonstrated through this study.

From an ecological perspective, the proposed de-sign provides the fundamental constituents of a struc-turally diverse estuarine ecosystem. Select habitatsand vegetative continua have been designed whichbuild upon the existing ecosystem character and pro-vide opportunities for the development of a self-sus-taining estuarine system (Table 2). The design in-corporates intertidal and protected subaqueous areasthat may provide habitats favorable for the establish-ment of SAV, oyster, and clam resources. Plannedscrub-shrub (wax myrtle, yaupon, highbush blueberry,and beach plum), herbaceous (Saltmeadow hay,American Beachgrass, and bitter panicgrass), andintertidal beach communities are of high relativevalue as food sources, forage areas, and nesting sitesfor a wide range of bird species.

Although of lesser habitat value than natural marinehabitats generally characteristic of the coastal plain,

Table 2. The approximate areas of the habitats that will be producedby the shoreline protection plan.

Habitat Area (m2)

BeachTidal MarshDuneScrub shrubSAYBreakwatersTotal

14,7777,38823,88520,0743.2532,47271,849

301

rock structures provide hard settling substrate andcrevices. Over time, these structures become substrateto a variety of organisms which are important forsupporting base-level food chains. Crevices provideprotected areas of varying size for prey. Also, rockstructures generally attract mobile aquatic faunawhich make them attractive forage areas for wadingbirds. It is our opinion, once mature and fully func-tional, the habitat provided by the proposed rockstructures will compliment and interact well with thenatural-based restoration components and add to theoverall diversity of the system.

Although this shoreline management plan was de-veloped to meet specific erosion control needs andhabitat restoration goals, design changes generallycan be incorporated with relative ease to respond tochanges in stakeholder desires and/or communityneeds. Any changes will necessarily require modi-fications of the original project goals, and unlessproposed changes are significant with respect to ero-sion control needs and/or cost an increase in onesubstrate use will require the sacrifice of all or part ofanother substrate use. For example, if tourism andrecreation needs increase stable public- use beach(es)can be created by removal of one or more inner baybreakwaters and vegetation planting either prior toproject completion or after build out. Also, slightchanges to the offshore breakwater configuration canbe made to alter the amount and configuration ofstable substrate, which can be done to respond todesired changes in the overall vegetation restorationplan.

Acknowledgements

This study was funded in part by the Virginia CoastalProgram of the Department of Environmental Qualitythrough a grant of the National Oceanic and Atmos-pheric Administration, Office of Ocean and CoastalResource Management, under the Coastal Zone Man-agement Act of 1972, as amended. Funding also wasprovided by the Town of Saxis under a grant from theChesapeake Bay Local Assistance Department. Theauthors would like to thank Scott Kudlas fromChesapeake Bay Local Assistance Department as wellas Larry Ives and Mark Hudgins from the U.S. ArmyCorps of Engineers for reviewing the draft report. Inaddition, many thanks to Carl H. Hobbs, III of VIMS,for his efforts in proof reading and suggestions towardthe overall improvement of the report. This paper is

302

Contribution No. 2413 of the Virginia Institute ofMarine Science, College of William & Mary.

References

Boon J.D., Welch C.S., Chen H.S., Lukens R.J., Fang C.S. and

Zeigler J.M. 1978. A Storm Surge Model Study. Storm Surge

Height-Frequency Analysis and Model Prediction for

Chesapeake Bay. Virginia Institute of Marine Science, College of

William and Mary,Virginia, SRAMSOE No. 189, 149 pp. + app.I.

Bretschneider c.L. 1958. Revisions in wave forecasting: Deep and

shallow water Sixth Conf. on Coastal Engineering, ASCE,Council on Wave Research. .

Ebersole B.A., Cialone M.A. and Prater M.D. 1986. RCPWAVE -

A Linear Wave Propagation Model for Engineering Use. CERC-86-4. 260 pp. U.S. Army Corps of Engineers Report.

Fenster M.S., Dolan R. and Elder J.F. 1993. A new method for

predicting shoreline positions from historical data. J. Coast Res.9: 147-171.

Hardaway C.S. Jr. and Gunn J.R. 1991. Headland breakwaters in

Chesapeake Bay Coastal Zone '91. Long Beach, CA, USA, pp.1267-1281.

Hardaway C.S. Jr., Thomas G.R. and Li J.H. 1991. Chesapeake BayShoreline Studies: Headland Breakwaters and Pocket Beaches

for Shoreline Erosion Control. Special Report in Applied Marine

Science and Ocean Engineering Number 313. Virginia Institute

of Marine Science, College of William & Mary, Gloucester

Point, VA, UK, 153 pp.Hardaway C.S. Jr., Gunn J.R. and Reynolds R.N. 1993. Breakwater

design in the Chesapeake Bay: Dealing with the end effects. In:

Hughes S.A. and Magoon O.T. (eds), Coast Engineering Consid-

erations in Coastal Zone Management. American Society of

Civil Engineers, New York, NY, USA, pp. 27-41.Hardaway C.S. Jr. and Gunn J.R. 1998. Chesapeake Bay: design,

installation, and early performance of four new headland

breakwater composite systems 1998 National Conference on

Beach Preservation Technology. St. Petersburg, FL, USA, pp.1-18.

Hardaway C.S. Jr. and Gunn J.R. 1999. Chesapeake Bay: Design

and early performance of three headland breakwater systems

Proceedings of the Conference American Society of Civil En-

gineers: Coastal Sediments '99. Hauppauge, Long Island, NY,

USA, pp. 828-843.Hardaway C.S. Jr. and Byrne R.J. 1999. Shoreline Management in

Chesapeake Bay. Special Report in Applied Marine Science and

Ocean Engineering Number 356. Virginia Institute of Marine

Science, College of William & Mary, Gloucester Point, VA, UK,

54 pp.

Hobbs C.H., Peoples M.H., Anderson G.L., Patton M.A., Rosen P.

and Athearn W.D. 1975. Shoreline Situation Report, Accomack

County, Virginia. Special Report in Applied Marine Science and

Ocean Engineering Number 80. Virginia Institute of Marine

Science, College of William & Mary, Gloucester Point, VA, UK,190 pp.

Hsu J.R.C., Silvester R. and Xia YM. 1989a. Generalities on static

equilibrium bays. Coastal Engineering 12: 353-369.Hsu J.R.C" Silvester R. and Xia Y.M. 1989b. Generalities on static

equilibrium bays. J. Waterway, Port, Coastal, Ocean EngineeringliS: 299-310.

Kiley K. 1982. Estimates of bottom water velocities associated with

gale wind generated waves in the James River, Virginia. Virginia

Institute of Marine Science, College of William & Mary.Gloucester Point, VA, UK.

NOAA 1989. East Coast of North and South America Including

Greenland, Tide Tables 1989. U.S. Department of Commerce,

National Oceanic and Atmospheric Administration, NationalOcean Service.

Sauer J.R., Hines J.E., Gough G., Thomas I. and Peterjohn B.G.

1997. The North American Breeding Bird Survey Results and

Analysis. Version 96.4. Patuxent Wildlife Research Center,Laurel, MD, USA.

Seaver D.M. and Austin H.M. 1995. Monitoring juvenile fishes in

the surf-zone of Virginia, and development of a juvenile bluefish

young-of-the-year index in Virginia: 1994 sampling season. Final

Report to the Virginia Marine Resources Commission. 58 pp.

Sverdrup H.U. and Munk W.H. 1947. Wind, sea, and swell: Theory

of relations for forecasting. U.S. Navy Hydrographic Office,Publ. No. 601.

U.S. Army Corps of Engineers 1977. Shore Protections Manual.

U.S. Government Printing Office, Washington, D.C., USA.

U.S. Army Corps of Engineers 1984. Shore Protections Manual.

U.S. Government Printing Office, Washington, D.C., USA.

Virginia Institute of Marine Science Wetlands Program 200 I. Tidal

Wetlands Impacts Data Home Page. Available: http://www.vim-

s.edul rmapl wetlands.

Wright L.S" Kim C.S., Hardaway C.S. Jr, Kimball S.M. and Green

M.O. 1987. Shoreface and Beach Dynamics of the Coastal

Region from Cape Henry to False Cape, Virginia. Virginia

Institute of Marine Science, College of William & Mary, Techni-

cal Report, 116 pp.