    [From the U.S. Government Printing Office, www.gpo.gov]

                            SHORELINE EROSION
                                          IN VIRGINIA

                                                                                00
                                                                                                          V

                                                           Jot

                                                                                   Scott    H ardaway
                                                                                   Gary    Anderson

           G C
           57.2
           .V51 5                                 SEA GRANT PROGRAM
           no. 31                                  Marine Advisory Service
                                              Virginia Institute of Marine Science
                                                 College of William and Mary
                                               Gloucester Point, Virginia 23062

                                                  Copies of this publication may be ordered
                                         for $ 1. 00 each from the Sea Grant Communications Office,
                                      Virginia Institute of Marine Science, Gloucester Point, VA 23062

                                                    SHORELINE
                                    EROSION IN VIRGINIA

                                               SCOTT HARDAWAY
                                                GARY ANDERSON

                                                  Virginia Institute of Marine Science
                                                      Gloucester Point, VA 23062

                                                       Property of CSC Library

                                              U      DEPARTMENT OF COMMERCE NOAA
                                              COASTAL SERVICES CENTER
                                              2234 SOUTH HOBSON AVENUE
                                              CHARLESTON , SC 29405-2413

                                                                            Designed and Edited by Kevin Gray

                             cm
                        N-) Cn                               October 1980
                             C"
                                                  A Sea Grant Advisory Service of the
                             42                      College of William and Mary

                    4@                                 Educational Series No. 31

                                                          ACKNOWLEDGEMENTS

                                      This publication is the result of research sponsored by the Virginia
                                  Institute of Marine Science Institutional Sea Grant Prbgram, supported
                                  by the Office of Sea Grant.

                                      Thanks go to jean Belvin and Cynthia Gaskins for typing the numerous
                                  drafts. Special appreciation goes to Cheryl Teagle for composing the final
                                  manuscript.

                                                 TABLE OF CONTENTS

                 SHORELINE EROSION IN VIRGINIA       .............................................    1

                      CAUSE   .................................................................       I

                      EFFECT   ................................................................       3

                      SHORELINE VARIABLE     ...................................................      4

                      COASTAL PROCESSES    ....................................................       5

                      WIND AND WAVES    ........................................................      5

                      CURRENTS    .............................................................       5

                      BEACH   .................................................................       5

                      SHORE TYPES    ...........................................................      5

                      SEDIMENT BANKS    .......................................................       6

                      MARSH SHORELINES     .....................................................      7

                      BARRIER BEACHES AND SPITS      ............................................     8

                      MAN MODIFIED     .........................................................      9

                 SHORE PROTECTION METHODS        ........   .....................................     11

                      VERTICAL RETAINING STRUCTURES (Bulkheads, Seawalls and Revetments)      ....... 12

                      GROINS AND JETTIES   ...................................................        14

                      BREAKWATERS (Solid and Floating)   ........................................     15

                      SUBMERGED SILL    ......................................................        15

                      DESIGN CONSIDERATIONS      ...............................................      16

                      RIPRAP REVETMENTS    ...................................................        16

                      BULKHEADS    ..........................     ................................    17

                      GABION REVETMENT     ...................................................        18

                      GROINS AND JETTIES   ...................................................        18

                      SUBMERGED SILL    ......................................................        19

                      BREAKWATERS      ........................................................       19

                 VEGETATIVE CONTROL       .....................................................       21

                      MARSH GRASS     .........................................................       22

                      RIVERBANK SLOPE CONTROL      ............................................       22

                                                          iii

                                                            INTRODUCTION

                                Virginia has over 5,000 miles of tidal shoreline. Several different shore
                             types occur in the Tidewater region including the low-lying barrier islands
                             of the Eastern Shore, the ocean front headland -barrier spit of southeastern
                             Virginia, and the shores of the Chesapeake Bay and other estuaries which
                             range from high bluffs to tidal marshes. In order to put shore erosion in
                             proper perspective as a natural phenomenon, one must examine the recent
                             geologic history of the region.
                                Much of shoreline erosion is a direct product of high energy storms
                             like hurricanes and northeasters. The rate and amount of erosion along a
                             specific shoreline may vary from year to year. The rate of erosion will
                             depend upon the following factors: (1) storm frequency; (2) storm type
                             and direction; (3) storm intensity and duration; and (4) resulting wind
                             tides, currents, and waves.      Also, the presence of man-made structures
                             (bulkheads, groins, etc.) will modify the erosion process, increasing or
                             decreasing it to a degree depending on the type, location, design, etc.,
                             of the structure (O'Connor, et al., 1978).
                                The problem of shoreline erosion is most acute when coastal property
                             with improvements is threatened by a rapidly receding shore bank. Many
                             waterfront properties are bought and developed each year with little or no
                             consideration of the shoreline situation. Consequently, additional money
                             must be spent for erosion protection structures.
                                Shoreline protection structures must be adequately designed and cor-
                             rectly placed to be effective under the severest of storm conditions.          In-
                             adequate installation or design may result in failure or deleterious effects
                             to adjacent waterfront properties. In many cases a structure is not needed
                             and protection of a shore bank may be accomplished by vegetative means,
                             such as the planting of appropriate grasses, shrubs or vines to stabilize the
                             bank, beach or nearshore area.
                                Virginia's coast is a dynamic and active environment as well as a beautiful
                             place to live. Sound judgement in coastal development is essential to effec-
                             tive control of shoreline erosion.                          -C. Scott Hardaway

                                                                    v

                                        72W
                    SHORELJ`N.--@.
                    EROSION JN, VIRG IN`j@X

                                                                                                           A

                                                                                                                            V

                                                                                                                                    R
                                                                                                         ----------
                                                                                                        IN&-g

                                                                                                                      7W,
               IM
               I , a
                                                                                                  so,
                                                                                             P"M

                                                                                           "0

                                                                              Ngki 1UM

                                                                                                                                               -fto

               THE CA USE                                   tributary   estuaries  are  a geologi-        melt waters began to raise           the
                                                            cally young portion of the Vir-               level of the oceans.       The rising
                  The Chesapeake       Bay and its          ginia coastal     system.        About        sea level caused the shoreline and
               tributaries are drowned river val-           15,000 years ago, the ocean shore-            coastal system to slowly migrate
               leys of the ancestral Susquehanna            line was about 60 miles east of               upward and westward across the
               River system (Figure 1 ). Drowned            the Virginia Capes and sea level              continental shelf.     Today's estu-
               river valleys where seawater from            was some 300 feet lower than                  aries are formed as the rising sea
               the ocean and freshwater from                it is today. Much of the ocean's              level floods the topographically
               upland rivers mix freely are called          water was locked up in the great              low river and stream valleys.
               estuaries.   The circulation in the          ice   sheets   which covered         the      As sea level continues to rise, the
               estuaries is influenced by the               northern half of North America                coastal lands of Virginia con-
               astronomical tidal conditions, the           during the Late Pleistocene glacial           tinue to flood.
               amount of fresh water run-off                epoch.    As the glaciers began to               The process of shoreline mi-
               and the shape of the basin.                  melt and recede in response to a              gration is better known as shore-
                  The Chesapeake Bay and its                gradually warming climate, the                line erosion.    In the estuaries of

                     Figure 1 - Chesapeake Bay and its tributaries.

                                                                                                                          iij,

                                                                                                   ............

                                                                                                                                                      .. ........

                                                                                                                   .............

                                                                                                                                                            DEL A WA RE

                                                                                                                                                                      Ar

                                                                                           ... ......

                                                                                                 ::3,    Ilk
                                                                                                         V)

                                                                            .. ........

                                                                                     .5i

                                                                                       12,   ....

                                                                                                       2

                      Virginia, shoreline erosion is a
                                                                                                                                                    TABLE 1.
                      continuing prOCC55 which has been
                      operating for several                        thousand
                      years.         Rates of erosion are de-                                          AVERAGE SHORELINE EROSION RATES - TIDEWATER VIRGINIA
                      pendent upon specific shoreline
                      variables and varying storm condi-                                                                                           YORK RIVER
                      tions, according to location. Lo-                                                                 NORTH SIDE                 EROSION RATES                   AVERAGE
                      cally, a shoreline may appear
                      stable or actually accrete sedi-                                                                  Gloucester Co.                 - 0.5 ft/yr                  0.4 ft/yr
                      ments. However, such a situation                                                                  King and Queen Co.             - 0.3 ft/yr                  0.4 ftlyr
                      is     anomalous              and       is      usually                                           SOUTH SIDE                 EROSION RATES                   AVERAGE
                      short-lived.                                                                                      York Co.                         0.9 ft/yr
                                                                                                                        James City Co.                   1.8 ftlyr                 - 1.2 ft/yr
                           Shoreline erosion on a daily                                                                 New Kent Co.                     0.9 ft/yr
                      basis is minimal.                 Severe erosion
                      occurs during periods of high                                                                                                JAMES RIVER
                      energy storms such as northeasters                                                                NORTH SIDE                 EROSION RATES                   AVERAGE
                      and hurricanes.                  Therefore, the                                                   Newport News                     0.8 ft/yr
                      rate of erosion at any specific                                                                   James City                       0.1 ft/yr                 - 0.45 ft/yr
                      location depends upon the fol-                                                                    SOUTH SIDE                 EROSION RATES                   AVERAGE
                      lowing         conditions (Riggs, et al.,                                                         Isle of Wight Co.                1.8 ft/yr
                      1978):                                                                                            Surry Co.                        1 .2 f t/yr               - 1.5 ft/yr
                                 1.     Storm frequency                                                                                     RAPPAHANNOCK RIVER
                                 2.     Storm type and                 direct-                                          NORTH SIDE                 EROSION RATES                   -AVERAGE
                                        ion                                                                             Lancaster Co.                    0.6 ft/yr
                                 3.     Storm intensity and du-                                                         Richmond Co,                     0.6 ft/yr                 - 0.6 ft/yr
                                        ration                                                                          SOUTH SIDE                 EROSION RATES                   AVERAGE
                                 4.     Resulting          wind          tides,                                         Middlesex Co.                    1 .0 ft/yr
                                        current and wave storm                                                          Essex Co.                        1.2 ft/yr                 - 1.1 ft/yr
                                        surge                                                                                                  CHESAPEAKE BAY
                           Seasonal wind patterns vary in                                                               WESTERN SHORE              EROSION RATES                   AVERAGE
                      the Chesapeake Bay region. From                                                                   Gloucester Co.                   0.6 ft/yr
                      late fall to spring the dominant                                                                  Hampton                          1.0 ft/yr
                                                                                                                        Lancaster Co.                    1.4 ft/yr
                      wind direction is from the north                                                                  Mathews Co.                      0.8 ft/yr
                      and northwest.                 During the late                                                    Northumberland Co.               1 .0 ft/yr
                      spring, the dominant wind shifts                                                                  York Co.                         1.5 ftlyr                 - 0.9 ft/yr
                      to the southwest and continues so                                                                 EASTERN SHORE              EROSION RATES                   AVERAGE
                      until the following fall. Northeast                                                               Accomack Co.                     1.5 ft/yr
                      storms which occur from late fall                                                                 Northampton Co,                  0.7 ft/yr
                      to early spring are associated. with                                                              Fisherman's Is.                +11 ft/yr                   - 1 .0 ft/yr
                      eastward          moving storm fronts.                                                            SOUTHERNSHORE EROSIONRATES                                 AVERAGE
                                                                                                     .... .. . .....
                      Frequently there is a period of                                                                   Virginia Beach                   1 .7 f t/yr
                      intense north or northeast winds                                                                  Norfolk                          1.2 ftlyr
                                                                                                                        Nansemond                        1 .2 ft/y r               - 1.4 ft/yr
                      following the passage of the front.
                      Hurricanes can occur from mid-                                             -----------
                      summer to late fall,                      Hurricanes                 shorelines of these tributary es-                                      line exposure to the northwest,
                      are less frequent than other storms                                  tuaries are highly dissected by                                        north        and      northeast directions
                      but sustained winds of 74 knots                                      numerous             lateral         tidal       creeks.               from where the severest seasonal
                      and wave heights of over five feet                                         From about 18SO to 19SO                                          winds originate.                 Individual seg-
                      make hurricanes an unwelcome                                         the Virginia Chesapeake Bay and                                        ments of shoreline have experi-
                      visitor        to     waterfront             property                its tributaries lost over 21,000                                       enced erosion rates of more than
                      owners.                                                              acres of land to shoreline erosion.                                    seven feet per year.                       However,
                                                                                                                                                                  one or two feet per year is more
                      EFFECT                                                                    Average shoreline erosion rates                                   common. For the 2,365 miles of
                                                                                           for this period are shown in Table                                     estuarine shoreline measured, the
                            There       are over 5,000 miles of                            1.      The bay side of the Eastern                                    average       rate of erosion is about
                      shoreline         along the Virginia por-                            Shore, the Peninsula, west side                                        0.7 feet per year (Byrne, et al.,
                      tion of Chesapeake Bay and its                                       of the Bay and the south side of                                       1979).        The Virginia Institute of
                      tributaries.         The major tributaries                           the tributary estuaries have the                                       Marine        Science          defines           5evere
                      are the James, York, Rappahan-                                       highest           relative       erosion            rates.             erosion      as any shoreline segment
                      nock and Potomac Rivers.                             The             This can be attributed to Shore-                                       with a      rate of two or more feet

                                                                                                                        3

            per year (Figure 2).         Shoreline                   (the length of open                         mediately behind the
            erosion becomes a problem when                           water facing the shore-                     sediment beach (if pre-
            coastal property with improve-                           line), the wind speed,                      sent) or shoreline. For
            ments (house, cottage, etc.) are                         direction and duration,                     a given recession rate,
            threatened by a rapidly receding                         and the nearshore water                     the bank height deter-
            shore bank.                                              depth,                                      mines how much ma-
                                                                                                                 terial enters the estu-
            SHORELINE VARIABLES                                2.    Depth   offshore - shal-                    arine system.
                                                                     low water, such as tidal
               Many variables affect the es-                         flats, helps reduce wave               4.   Bank     composition         -
            tuarine shorelands of Virginia.                          energy     better     while                 tight clay or well ce-
            The importance of any given                              deeper water in the                         mented sand resist eros-
            variable   depends on the site.                          nearshore area allows a                     ion better than soft
            Some of the important variables                          greater proportion of                       clay    or     uncemented
            include:                                                 the wave energy to                          sand.
                                                                     reach the shore.
                 7.    Wave height - this vari-                                                             5.   Width   and elevation of
                       able is in turn depend-                3.     Bank height - the height                    sand    beach - a sand
                       dent upon the fetch                           of the shore bank im-                       beach   is a natural buf-
                                                                                                                 fer to wave activity.

                                                                                                            6.   Abundance of vegeta-
                                                                                                                 tion - vegetation (grass-
                                                                                                                 es and vines) on the
                                                                                                                 shore bank nearshore
                                                              CID
                                                                                                                 and beach help hold
                                                                                                                 the sediment and baffle
                                                                                                                 wave action.

                                                                                                            7.   Shoreline geometry -
                                                                                                                 the general shape of the
                                                                                                                 shoreline.         Irregular
                                                                                                                 shorelines like marshes
                                                                                                                 tend to break     up wave
                                                                              V.,
                                                                                                                 energy      better      than
                                                                                                                 straight shorelines.

                                                                                            lo              8.   Shoreline orientation -
                                                                                                                 the general geographic
                                                                                                                 direction the shoreline
                                                                                                                 faces along with the
                                                                                                                 fetch, influences the de-
                                                                                                                 gree of exposure to
                                                                                                                 wind wave attack.

                                                                                                            9.   Boat wakes - waves
                                                                                                                 from boat wakes may
                                                                                                                 severely affect a shore-
                                                                                                                 line which is close to or
                                                                                                                 on a boat channel,

                                        NE
                                         .=Rlj                                                             In addition, the presence of
                                                                                                       man-made structures (bulkheads,
                                                                                                       groins, etc.) modify the process
                                                                                                       of erosion by increasing it or
                                                     NORFOLK
                                                                                                       decreasing it to a degree depend-
                                                                                                       ing on the type, location and de-
                   \/,\-b

                                                                                                       sign of the structure.

                                                                                                       Figure 2 - Green lines indicate erosion
                                                                                                       rates of two or more feet per year.

                                                                            4

                 COASTAL PROCESSES

                 WIND AND WA VES

                     Waves are created by wind.
                 The size of the waves is a func-
                 tion     of  fetch    (distance     over                                                             Ilk
                 water which the wind blows),
                 wind velocity and depth of
                 the water. Storm winds generate
                 large waves which do the most
                 damage to shorelands on the
                 open bay and ocean.              During
                 northeast storms and hurricanes
                 the water level itself may be
                                                                                                                                KEY
                 dramatically       elevated       (storm                                                                         Sand
                 Surge) so the wave attacks the
                                                                                                                                  Clayey-Sand
                 shore at elevations higher than                                                                                  Organic Muck
                 normal.

                 CURRENTS                                           Figure 4    The cypress fringe damping erosion wave forces and trapping sedi-
                                                                    ments is illustrated in this figure. The cypress trees can form a natural bulkhead
                    There are basically two types                   which dissipates wave energy and traps sand.
                 of currents which figure @ro-
                 minently in the coastal processes
                 acting in the Chesapeake Bay                   shore.    It is generated by waves             SHORE TYPES
                 system.    These are tidal currents            which strike a shoreline at an
                 and longshore currents.            Tidal        ngle. Waves and currents work-                    Five basic types of shoreline
                 currents are generated by the
                 periodic    rise and fall of          he       ing along a shoreline mold a shore-            exist    in   the    Virginia coastal
                                                     t          line's configuration and cause the             system. These are:
                 astronomical tide.        These tidal          movement of sediment to and
                 currents are most noticeable at the            from the shore. The movement of                      7.    Swamp forest
                 entrances to harbors and tidal                 sand     either parallel to shore,                   2.    Sediment banks
                 creeks.                                        onshore or offshore is known as                      3.    Marsh
                    The longshore current moves                 littoral transport. Although sand                    4.    Barrier     beaches      and
                 parallel   and    adjacent     to    the       may move along a shoreline in                              spits
                                                                either direction, there is usually a                 5.    Man-modified
                                                                net movement in one direction.
                                                                                                               Their distribution is a function
                                                                                                               of topography and the regional
                                                                BEACH                                          slope of the Chesapeake Bay
                                                                                                               drainage system.
                      P-LE AN.-I
                                                                   Beaches, no matter how ex-                     Swamp forests occur as rivers
                                                                tensive,   are natural landforms               flood plain vegetation (Figure 4).
                                                                resulting from wave action and                 As sea level rises and floods the
                                                                represent a buffer zone between                upland river basins, the flood
                                                                the land  and water. During storm              plains become the receding shore-
                                                                periods,  waves may carry much                 line. In Virginia, extensive reaches
                                                                of the beach sands offshore to                 of swamp forest shorelines occur
                          S,                                    form a bar (Figure 3).              This       in the upper portions of the
                                                                helps    d issi pate the energy of             tributary estuaries and their lateral
                                                       L w
                                                                the   waves    before    they      reach       creeks.
                                         ACCI TI01
                                                   LE A         the shore.     With the return of                   Swamp      forests    contain      a
                                                                calmer weather, the bar sands                  variety of tree species including
                                                                slowly migrate back to the beach.              Bald Cypress (Taxodium disti-
                                                                Longshore sand movement usually                chum), Black Gum (Nyssa syl-
                                         -ET-                   occurs also.      The direction of             vatics), and Tupelo Gum (Nyssa
                                                 'Rol-          beach sands movement must be                   aquatic).      The massive above
                 Figure 3    Creation of nearshore bar          taken into account when designing              ground root system and flared
                 during a storm.                                coastal   structures     for    erosion        trunk of the Bald Cypress make
                                                                protection    (groins, breakwaters             it relatively resistant to wave
                                                                and bulkheads).                                action and erosion.            However,

                                                                                   5

          its vulnerability to flooding makes            tern Shore in South Accomack               off   large  chunks     of fastiand.
          swamp forest shorelines undesir-               County     and        Northampton             Abating active erosion of a
          able for development.                          County.    Low sediment banks              sediment bank requires vegetat-
                                                         ( < 14 feet) occur mostly along            ing the face of the bank.           To
          SEDIMENTBANKS                                  the small creeks and embayments            best accomplish this, the slope
                                                         on the west side of the Chesa-             of the bank should be reduced.
              Sediment banks are composed                peake Bay.                                 A recommended slope gradient
          of varying mixtures of gravel,                   Active erosion - of sediment             is 4:1 (4 horizontal to I vertical).
          sand, silt and clay (Figure 5).                banks produces almost vertical             However, it may be possible to
          They    range    in height from a              exposed scarp with fallen trees            affect vegetative bank stabilization
          few feet to over 100 ft. above                 and logs littering the beach and           on as much as a I: I slope if the
          mean high water.           Usually, a          nearshore area.   Erosion of high          bank is "dry" and has no ground-
          sand beach     will exist along the            banks is caused by rainwash and            water    springs   "weeping"      out.
          base of the    bank with much of               groundwater which saturates the               Once     the eroding bank is
          the    beach   sand coming from                face of the bank causing sliding           stablized by grading, the toe or
          erosion of the bank.                           and slumping.        Wave     action       base must be protected against
              Sediment banks occur as in-                during storms causes additional            waves and high water which will
          terstrearn divides (between creeks)            slumping  by    undercutting     the       undercut the sloped bank and
          in the Chesapeake Bay system.                  base of the high bank. Low banks           eventually renew the erosion pro-
          The higher banks ( > 15 feet) are              are most vulnerable      to wave           blem.     There are basically two
          found along the lateral tributaries            activity which will overtop the            methods for accomplishing this.
          and on the bay side of the Eas-                bank during storms and carry               One is to build up a sand beach,

                                                                                  7-

                                                         KEY
                                                         5-d
                                                                                                         A
                                                      L] cl@y
                                                         Sd Ho6zon

          . ..... .. .....
          Plot,
                    f,        Al
                                                    @Z^P     0,     J

                                                                           ov
                                                                       P
                                                                              __Po@
                                                                                                '7 41t4
                                                                 1@6 4
                                                           &4 04, .4,01
                                                                               r
                                                                                    A

                 Figure 5 - Erosion of sediment banks is the primary source of material for the beaches along the estuarine shoreline.
                 (Upper right) storm waves undercut the high bank causing   slump blocks, along with the vegetative cover, to slide
                 onto the beach. In this illustration, the slump blocks are reduced by further wave action, leaving behind debris of
                 fallen timber.

                                                                          6

                 the other is to harden the toe
                 of the bank (refer to section of
                 "Shore Protection Methods").
                     Sand can be trapped by groins,                                                 W
                                                                                                           %        v
                 submerged sills and breakwaters.
                 Care must be exercised in em-
                                                                                                                  N,
                 placin- those structures to pre-
                 vent sand starvation of adjacent
                 shorelines.    The enhanced beach
                                                                                            "A
                 helps dissipate wave energy against
                 the bank.     However, during large
                                                                                                                          7
                 storms, water levels and waves
                 may overtop an established beach
                 and severely attack the sediment
                 bank.     In many cases, a beach
                 is not enough to prevent bank
                                                                                                                                            4
                 erosion, consequently,        the    toe
                 of the bank must be hardened.
                     Hardening the shoreline can
                 be done by building a bulkhead,
                                                                                                                                                -Z,
                                                   These
                 seawall    o r  revetment.
                 methods are often costly and must
                 be constructed properly to pre-
                 vent premature failure.
                     If a sediment bank shoreline
                 is exposed to small distances of
                 open water, it may be possible
                 to   plant a marsh grass frin@e
                 (Figure 6).        Marsh grass wi
                 baffle wave action and also help
                 trap sand.     This has been done
                 effectively in many areas and it                               - ------
                 can be a viable and relatively
                 inexpensive     measure      to    slow
                                                            TZ,             A
                 shoreline erosion.

                 MARSHSHORELINES

                     Marsh shorelines are extensive
                 marsh (wetlands) plains (Figure 7)
                 or narrow fringes in front or river-
                 ward of sediment banks. Marshes
                 also occur along the flood plains                                                                      7"       P,
                 of embayed lateral creeks. These                                                                                              ;r,
                 creeks are subject to daily tidal
                 fluctuations and usually have a
                 defined channel.

                 Figure 6 - Fringe marshes offer ex-
                 cellent natural buffers to erosion. The
                 marsh grass greatly reduces wave energy
                 acting on the shoreline.

                 Figure 7 - Extensive marsh plains occur
                 along many low lying areas bordering
                 the Chesapeake Bay.

                                                                                 7

              Figure 8 depicts tidal wetlands             10).    This situation exists along             maintain a state of equilibrium.
           of Virginia and the vegetative                 the barrier islands of Virginia's               There is usually little input of
           zonation of plant species. There               Eastern Shore and to a lesser                   sand from actively eroding fast-
           are 212,000-225,000 acres of                   extent along the Bay facing shore-              land.    When a severe storm im-
           tidal marshes in Virginia.             In      line of Accomack, Mathews, and                  pinges on a barrier system, beach
           addition to their value as            an       York Counties.                                  and dune sand can be carried
           essential   link in the estuarine                  Barrier beaches generally ope-              through a breach in the dune
           food chain, marshes also act as                rate with a limited amount of                   line and deposited on the marsh.
           effective buffers to erosion of                sand. The beach and dune system                 These features are called wash-
           the fastland. Their low elevation              react to existing weather condi-                overs.      Washovers reduce the
           and matted root system make                    tions by attempting to attain and               amount of sand available to the
           marshes more resistant to wave
           erosion than sediment banks ex-
           posed to the same fetch con-
           clitions.
              Extensive marshes act as large
           sponges to help reduce the flood
           hazard in some coastal areas.
           Fringing marshes occurring along
           sediment banks greatly reduce
           wave action.        Actively eroding                                                                                        t3
           marsh shorelines are characterized
           by exposed and undercut peat
           banks (Figure 9).         Marshes are
           also valuable to waterfowl as a
           source    of food       and     habitat.

           BARRIER BEACHANDSPITS

                                                            Figure 9     The factors involved in erosion of the brackish marsh shorelineare,
              A beach system is comprised                   illustrated. During low tide, wave action erodes the softer underlying peat (13),
           of a beach, a dune, and a marsh                  undercutting the firm surface layer (A). The peat shelf breaks into blocks that fall
           complex behind the dune (Figure                  into blocks that fall into the water, leaving U-shaped notches along the bank.

                                                 BRACKISH WATER MIXED COMMUNITY TYPE XII
                                                                (excluding upland species - pines, cedars, etc.)

                                                              SALTMARSH CORDGRASS                     SALTBUSH TYPE IV
                                                              TYPE I
                                                                                                      BIG CORDGRASS
                                                              BLACK NEEDLERUSH                        TYPE V
                                                              TYPE III
                                                                                                      SALTGRASS MEADOW
                                                              SALTMARSH BULRUSH                       TYPE 11

                                                              OLNEY THREESQUARE                       SEA LAVENDER

                                                      Figure 8 - Vegetative zonation of plant species.

                                                                             8

                                                                                                                   MAN MODIFIED

                                                                                                                       Man modified shorelines are
                                                                                                                   any of the previous shore types
                                                                                                                   which have been altered in some
                                                                                                                   fashion by man (Figure 73).
                                                                                                                   These alterations or modifications
                r-,        7                                                                                       include      bank     grading,      beach
                                      44,                                                                          nourishment, and protective struc-
                               z
                                                                                                                   tures. Much of Virginia's coast-
                                                                                          J                        line has been developed in one
                                                                                                                   way or another. Over 800 miles
                                                                                                                   of Bay shoreline has a housing
                                                                                                                   density of six or more structures
                                                                                                                   per mile.
                          4"'
                                                                                                                       Shoreline protection to a large
                                                                                                                   degree has been haphazard and
                                                                                                                   piecemeal in nature. Along any
                                                                                                                   given shoreline, the number of
                                                                                                                   different protective -methods often
                Figure  10-    Extensive low-lying dune shorelines occur along bay shores     in Hamp-             equals    the number of people
                ton, Mathews County and Northumberland County.                                                     living there.       This often is in-
                active beach, forcing the beach                   described previously.                            effective in controlling the pro-
                                                                                                                   blem of shoreline erosion.             For
                to react to a reduced sand supply                     Development on          the barrier          example, an improperly designed
                by retreating. In many instances                  beaches and spits         is precarious          or poorly constructed bulkhead
                this retreat exposes the surface                  due to the shifting nature of                    may fail, creating problems for the
                of marsh peat covered by pre-                     sand.     Ocean shorelines are the               owner and adjacent neighbors.
                vious washovers (Figure 11).                      most dangerous because of high                   Groin installations often do well
                    Spits are active sand features                wave    energy potential generated               to protect the updrift shoreline by
                found at the clowndrift end of                    over   long fetch conditions, high               trapping sand, but may cause
                barrier beaches.        They are also             storm surge and deeper nearshore                 serious sand starvation and erosion
                defined as tongues of sand moving                 water depths.         Rigid structures           clowndrift.
                across      the  mouths of lateral                (cottages, bulkheads and seawalls)
                creeks. One example of a spit is                  placed on the dunes and beaches                      Rather than using this ap-
                Willoughby Spit where the Hamp-                   usually    create     adverse      effects       proach, shoreline erosion should
                ton Roads Bridge Tunnel enters                    by causing loss of beach and                     be addressed on a reach basis
                Norfolk. This mile long sand spit                 subsequent undermining of the                    with full consideration for the
                is said to have formed in a single                structure during severe storms.                  net effectiveness of the structural
                hurricane storm in 1806 (Figure
                72).
                    Sand spits may advance across
                small creek entrances if enough
                sand is moving alongshore which
                results in temporarily closing the
                creek.         Larger   lateral     creeks
                maintain their channel opening by
                tidal flushing. However, even these
                naturally maintained channels are                          _4
                not deep enough for continued
                use by some vessels.          This navi-                          ft
                gation     problem      is solved       by
                maintenance dredging of the chan-
                nel and/or stabilizing the inlet                                                                                -r
                with jetties.
                    Some     barrier beaches lack a                  hw
                                                                                                    Z10-
                marsh complex behind the dune
                system.        Such shorelines exist
                along the south shore of
                                                  Chesa
                                                                  rtt;"L

                peake Bay and between Cape                        Figure 11     The  dune   shorelines recede by washovers during storms. This often
                Henry and Sandbridge. They also                   exposes a  peat horizon which was once a living marsh behind the dune system
                retreat by the same process as                    bayward of its current position.

                                                                                      9

            or    other ' methods       employed                                           low
            (Byrne, et al., 1978). A reach is
            a shoreline unit where there is a                                                        '17
            mutual interaction between the
            forces of erosion and/or the sedi-
                                                                       4N7
            ment supply. It may be advan-
            tageous   for   a  waterfront     com-       401@@
                                                                                       T-r
            munity to seek out advisory or
            engineering services, whether pub-
            lic or private, to insure a sensible
            approach to their shoreline situ-
                                                                                                                     17
            ation.

                                                                    &
            Figure 13 - Wooden bulkheads are a           r.. I   F
                                                                   QJP!!R-A@ ajj!F',z',@ip
            popular method of slowing shoreline
            erosion.   If properly installed, they                     0                    N
            will generally last 10-15 years.

            Figure 12     Willoughby Spit as seen
            from the air on March 3, 1973.

            NA
            DV

                                                                        W

                                                                                                          Nz

                                                                VA

                                                                       J,

                                                                          10

                                                                                                                       AIIf

                            kit,                                                                                                                   q Al -qlo-

                                                                     IT
                                                                                                                       Op

                                                                           A"o

                                                                                   I.A

                                                                                                                                                 v
                                                                                                                                                 -k 110
                                                                                                                                                  -, 4",

                                                                              *4 4
                                                                                                         Ft

            SHORE PROTECTION METHODS

               The problem of shore erosion is often overlooked                                  :0j?joio!0-:0:0lolo*       T
            by the prospective or present owner of shoreline                                                     I       I
            property.     Average rates of erosion calculated for
            discrete segments of a shoreline rarely present the
            true picture.     Some areas remain stable for many
            years and then suffer extreme erosion. These erosion                                 0  0 0:1 0! 0 o  0  0 0
            rates reflect the relative severity of erosion in one                                                               WALE
            area versus another. In response to sudden increases
            in the erosion rate, many landowners install forms
            of shore protective structures whether it is the                             PILE                             SHEETING
            proper structure or not.         In many instances im-
                                                                                                 0  0. 0 1' 0a 0  0  0. o:
            proper structures only serve to accelerate the erosion.
            Failures stem from the use of improper materials,
            improper installation, or poor advice.          No patent
            answers exist because each situation is unique; nor
            is there a guarantee that any system will solve the
            problem.     Construction of proper shore protective                                        ELEVATION
            structures is also expensive.        In many cases, the
            cheapest solution is not always the best.              There
            are several protection shore rnethod5 which, if pro-                         WALE,,,,                    dbNPILE
            perly designed for a particular estuarine shoreline,
            can be effective in abating erosion.         Some of the
            methods are:                                                             SHEETING

            VERTICAL RETAINING STRUCTURES
            (BULKHEADS, SEAWALLS, REVETMENTS)                                                                         `*-T I E ROD
                The respective definitions of these structures                                         WALE\
            vary little although different construction materials                                                     I
            are sometimes associated with each structure (Figures
            74A & B, 15, 76A & B). Vertical structures act to
            retain the fastland material and to prevent wave
            induced erosion. In one way, they can be thought of                                        ANCHOR PILES
            as defensive structures. However, in      many situations,                                    PLAN
            vertical structures lead to the loss of   the beach   which
            may front them.

                                                                                                                             %
                                                                                                  AAw"'.,
                                                                       It   'no
                                                                      6@                                                 -Asa
                                                         tie
                                                                                            ING4

                                                                                     kad"APC

            Figure 14A - Wooden bulkhead. Figure 14B (top right) timber sheet -  pile bulkhead.

                                                                           12

                                                                                                                              4f

                                                                                                                 F,@

                                                                                                     TOPSOIL AND SEED
                                                                              4'-66'. ROUNDING                       0.1
                                                                          1'-6" min                        ELEV. 9.0

                                                         ELEV. 8.75'--,,,                                                r
                                                                                                            I'-d' min.
                                          STONE RIP-RAP 2 FT THICK
                                           (25 % 300 1 bs., 25 % 30 bs.                             POURED CONCRETE
                                            50 % wt.   150  lbs.)                                  (Contraction it. every 10'
                                                                    2                     FILTER CLOTH OR
                                                                                     -.q--GRAVEL BLANKET I FT. THICK
                      EXISTING BEACH                                                      (200 SIEVE to 3", 50%       F 1/2
                                A--ELEV. 0.00' M.S.L.                                     OVER REGRADED BANK

                                                                                   ELEV.  1.00'

                                  mppm"wm'm'-
                                              r

                                                                                            4M4jL

                                                                     W

                  Figure 15 - Concrete seawall (top). Figure 16B (bottom) small riprap revetment. Figure 16A (middle) riprap revetment.

                                                                        13

               During times of abnormally high wdter, waves                                     PLANKS
                                                                                              STAGGERED
            may overtop the beach and strike the bulkhead.
            Most of this energy is reflected off the wall. The                                         I- - G. 1. BOLTS
            reflected wave then meets the next incoming wave                                             WATER LEVEL DATUM
            and creates a zone of extreme turbulence where                                                TIMBER WALE
            they meet.      This turbulence causes scouring of
            beach material near the base of the bulkhead. Over
            a period of time, this can lead to the deterioration
            of the beach if there is an insufficient input of                                            TIMBER SHEET
                                                                                      ROUND                 PILING
            sand.   In addition, age or improper construction can                     PILING
            lead to small cracks in a bulkhead. This can result
            in leaching of fine material from behind the bulk-
            head.   In many instances, erosion will continue on
            each side resulting in the flanking of the structure.                             SECTION

                                                                                        ROUND
            GROINS A ND JETTIES                                                          PILES                 G. I. BOLT
                                                                                                                       WALE
               Groins and jetties are vertical structures oriented                                                      -PLANKS
            perpendicular to the shoreline.    Groins are used on                                                            GERED
            open shorelines to trap the littoral transport of sand                                                 \T I BER WALE
            parallel to the beach.     When functioning properly,                                     \WASHERS
            groins will widen and heighten a beach.                                             PLAN
               jetties are structures used to define and protect
            an inlet or harbor entrance from shoaling. Shoaling

                                                                        4, Z'            %
                                   "T

                                                                                                                               _J
            is usually  the product of    the littoral transport   of
            sand towards    and into the inlet.    jetties can also
            serve to make    inlet access easier by reducing wave
            height (Figures I 7A & B).
               Imperative in the success   of groins is an adequate
            supply of sand to quickly     fill the groins and then
            begin bypassing sand.       An inadequate supply of
            sand can lead to accelerated erosion clowndrift of the
            groin. In some cases, this    accelerated erosion can
            flank the groin rendering it totally useless (see Figure
            78).

            Figure 17A    Groin field. Figure 17B (upper right) Timber
            sheet-pile groin.

            Figure 18 - Groin which has been flanked by severe erosion.

                                                                       14

            BREAK" TERS (SOLID AND FLOATING)                                      reduction in wave height can be achieved. The small
                                                                                  waves are the first to be dampened out.
                A solid breakwater is a structure usually con-
            structed of stone, which serves to reduce wave
            height (Figures 19A & B). This reduction of wave
            height reduces the erosive power of the waves striking                SUBMERGED SILL
            the beach or entering a harbor. As solid breakwaters
            work to resist the full power of the incoming waves,                      Although the submerged sill is new to the Chesa-
            the structure must be massive.             If not designed            peake Bay, it was first employed over 40 years
            and placed properly, they can lead to accelerated                     ago.   It consists of a detached structure constructed
            nearshore currents which can cause erosion.               Used        parallel to the shore along the extent of the eroding
            incorrectly, they can halt the parallel littoral sand                 shone.    To date, sandbags, gabions and wood have
            transport leading to accelerated erosion downdrift.                   been used as construction materials.
                A different type of breakwater becoming popular                       The principle involved is known as a perched
            is the floating breakwater (Figure 20).            Numerous           beach. As illustrated (Figures 27A & B) the desired
            designs have been proposed and some have been                         effect is to elevate the profile of the beach. If suc-
            tested.    Two general categories, rigid and flexible,                cessful, a protective layer of sand exists at the base
            have arisen     with various benefits added to each.                  of a cliff or bulkhead.        Because this layer is signi-
            Most designs have a floating structure tethered to                    ficantly   higher than the unprotected backshore
            the bottom. Instead of working to totally eliminate                   height, additional protection is afforded during
            waves from      passing   the structure as does a solid               storm elevated water levels.           This system offers
            breakwater,     floating breakwaters       act as filters to          protection from all wave angles        and at higher water
            the incoming waves by reducing             the wave energy            levels.   In essence, it resembles     a "permanent" bar
            behind the structure.          In some     cases substantial          situated at the step of the beach.

                                                                                                   Varies

                                                                                                                          @*-ARMOR STONE

                                                                                              CORE STONE
                                                                                                (Quarry Run)

                                                                                             CROSS-SECTION

                                                                                                                                    T17

                                                                                                                               _tat
                                                                                                                     04

                                                                                                                        'A

                                               IN-
                                                           v,                                                                                   L

                                4
                                                 11 __411 I'll

                                 Ak

                     Figure 19A - Small stone  breakwater.  Figure 19B (upper   right) generalized cross section of a large stone breakwater.

                                                                             15

                                                                                                   7:7

                                                                                              'V

                                                                         @ngwln

                                                                         -5p,
                                                                         rjW@%JZ

                                                                                                                           Wk

                  Figure 20     Floating
                  tire breakwater.
                                                                      x,
                                                                                                                                    4

                                                                                          A0
                                                 74'

                                                                           N;&

                                                                    RM

                                                                                                                                    A

                                               711

                                                                         FIN

                                                                              Mff 'P'0%-V
                                                                          1000

                 The sources of material to fill the system come            DESIGN CONSIDERATIONS
              from three areas. The first area is that which drifts
              along parallel to the beach. The second area is that          B UL KHEA DS, SEA WA L LS, R E VETMEN TS
              which is   moved onshore from offshore, and the
              third area is that which is introduced by rain runoff            Effective designs for these structures vary with the
              erosion of the cliff face behind the structure. The           forces which these structures must deal with. How-
              percentage of input from these three sources varies           ever, certain considerations may apply according to
              with the location. Beach nourishment can also be              the location.
              used to fill the system.
                 As with any structure, the submerged sill has its          RIPRAP RE VETMENTS
              drawbanks. It can be a swimmer and boating hazard.
              Also, it can be too effective in halting the parallel              1.   The stone or rubble should be placed as
              transport of sand along a beach.           Construction                 opposed to dumped at the site.
              materials such as the sandbag are susceptible to ice                          Rationale: Placing assures good inter-
              damage and vandalism. It is generally restricted to                           locking of the individual stones.
              areas which have significant volumes of sand within                           The proper slope for the material
              the beach system.                                                             can be easily attained.
                                                                        16

                   2.    Stone or rubble of sufficient size to resist
                         the maximum expected wave forces should
                         be used.
                               Rationale:     Many failures of riprap
                               structures stem       from      insufficient
                               stone size.       Waves during storm                          W.W1111
                                                                                        10 1
                               conditions remove the material too
                                                                                                              'NOW"'
                               small, thus leading to failure of the
                               whole structure.

                   3.    A  protective apron      should extend from
                         the toe of the structure.
                               Rationale:        Although the rough
                               nature of    a riprap structure removes
                               a portion    of a wave energy, some is                                           IS-
                               still reflected.    When this reflected
                               wave meets the      next incoming wave,
                               an area of intense scouring occurs
                               immediately in front of the structure.
                               This scour undercuts the structure,                                                A       _Ri               @ 44"t'. r,
                               allows it to slump, and eventually                  Figure 21 A - Sandbag sill.
                               leads to its failure.
                                                                                                      PROFILE BEFORE INSTALLATION OF SILL
                   4.    The use of filter cloth is strongly recom-
                         mended.
                               Rationale:     By their nature, riprap
                               structures are porous.      However, this                                                                MHW
                               porosity can lead to the failure of                                                                      MLW
                               the structure.    The constant flooding                                             SAND VENEER OVERLYING
                               of the structure due to tidal action                NOTE INTERSECTION OF 5TORI 11GII  SEMI- CONSOLIDATED SEDIMENTS
                               and the passage of ground water and                 WIITER ANO SIORe IN Sol. CSE,
                               rain   runoff through the structure
                               can    leach   fastland    material    fro m                           PROFILE AFTER INSTALLATION OF SILL
                               behind it.     Filter cloth acts to pre-
                               vent this leaching of material.         It is
                               emplaced first and then the stone is
                               placed on top of it.                                                ------ SIL-LTO-PE-RCH TH-E- REACH -------------- -STORM HIGH WATER
                                                                                                                                    -MHW
                                                                                                                 - - - - - - -         MLW

                                                                                                 LEVEL OF B@ACH
             BULKHEADS                                                                             BEFORE PERCHING"
                 Vertical sheet pile bulkheads can be constructed                  Figure 21 B - Perched beach concept.
             from a variety of materials. Among these are wood,
             steel, aluminum, asbestos concrete and concrete.
             Gabions can also be used to construct vertical struc-                       2.    As a minimum, depth of penetration
             tu res.                                                                           should be equal to the exposed portion.
                                                                                                      Rationale:      A common cause of
                                                                                                      bulkhead failure is inadequate pene-
             WOOD BULKHEADS                                                                           tration.    Many people assume that
                                                                                                      the beach will remain in front of
                   7.    Vertical tongue and groove sheet pile is                                     the bulkhead.      However, in storms,
                         preferred,                                                                   waves can remove the beach leaving
                               Rationale:     All treated wood warps                                  a minimum length of sheet pile
                               and shrinks after exposure to the                                      penetrating the stable bottom.          The
                               elements.      The tongue and groove                                   weight of the cliff material being
                               configuration     reduces the risk of                                  retained    causes    the   bulkhead      to
                               spaces opening between the sheet                                       topple.    In other cases, the inade-
                               pile   which     would    allow fastland                               quate penetration of the bulkhead
                               material to leach through the open-                                    allows the retained fastland to leach
                               i ng,    Tongue and groove cannot                                      out the bottom of the bulkhead.
                               reduce this risk in cases of faulty                                    To insure adequate penetration, it is
                               construction.                                                          necessary    to    establish   where the

                                                                               17

                                stable layer begins.      In most areas                             return wall joins the fastland.          To
                                throughout      the  lower Chesapeake                               prevent the flanking of the bulk-
                                Bay, this layer generally coincides                                 head, the return        wall   should     be
                                with a reddish brown clay layer which                               entrenched in the fastland.        In addi-
                                exists under the beaches.                                           tion, a riprap cornice may be ne-
                                                                                                    cessary. This riprap serves to reduce
                    3.    Emplacement of filter cloth is recom-                                     the scout of waves focused at the
                          mended.                                                                   ends of the wall.
                                Rationale:    The application of filter
                                cloth behind a tongue and groove
                                bulkhead acts as it does with riprap.              GABION RE VETMENT
                                Because the wood shrinks and warps,
                                small openings can appear between                        7.   GGbions should be entrenched into the
                                the sheet pile. The filter cloth then                         clay  layer below the beach (Figure 22).
                                acts to prevent the leaching of the                                 Rationale:      As with other vertical
                                fastland material out through these                                 structures, some scour can occur on
                                openings.    It is also very helpful at                             the seaward side of the structure.
                                the junction of two structures.          As                         Gabions placed on top of sand will
                                an   added measure of protection,                                   be undermined, causing the structure
                                the bulkhead can be backfilled with                                 to fail.
                                gravel or other coarse material and
                                then regular fill.                                       2.   Filter cloth should be placed under, or on
                                                                                              the   backside of the gabion revetment.
                    4.    Adequate tiebacks and backfill are ne-                                    Rationale:      Gabions are similar to
                          cessary.                                                                  riprap in their use. The filter cloth
                                Rationale:      A common cause of                                   prevents leaching of fine grained
                                bulkhead failure is the lack of sub-                                material from behind the structure.
                                stantial system of tiebacks. Common                                 The filter cloth beneath the structure
                                mistakes are:       tiebacks too close                              helps prevent undue settling of the
                                to the bulkhead, spaced           too far                           structure.
                                apart, tieback material is incapable
                                of resisting the stresses placed on it,            GROINS AND JETTIES
                                and   insufficient size cleadmen or
                                screw anchors.                                        Groin systems vary greatly depending on wave
                                                                                   climate. The following comments concern an imper-
                    5.    Weep holes may be necessary.                             meable, fixed height groin.
                                Rationale:    In certain   areas, ground
                                water collects behind a bulkhead.                        7.   Tongue and groove sheet pile should be
                                It then becomes necessary to release                          used.
                                this pressure by having small openings                              Rationale:       As with a bulkhead,
                                through the bulkhead.        These open-                            the tongue and groove helps pre-
                                ings are stuffed with wads of filter                                vent the leaching of material through
                                cloth to prevent leaching of fine                                   the structure.    In most areas a mini-
                                materials.   They are usually placed                                mum of two-inch thick sheet pile is
                                above the mean high water mark.                                     necessary.
                    6.    Riprap at the toe of the bulkhead may                          2.   Round pile should be placed on alter-
                          be necessary.                                                       nating sides at an equal spacing.
                                Rationale:      In certain high energy                              Rationale: This type of configuration
                                areas,  the     scour   associated     with                         provides good strength and inhibits
                                bulkhead    jeopardizes the integrity                               undue flexing which can result if the
                                of the structure.     To minimize this                              structure does not fill equally on
                                impact, an apron of riprap should                                   each side.
                                be placed at the base of the bulkhead.
                                The approach also provides a re-                         3.   Ratio of sheet pile penetration to exposure
                                medial repair for a failed vertical                           should, as a minimum, be equal.
                                retaining structure.                                                Rationale:      Initially, the groin is a
                                                                                                    free standing structure.        Until it is
                    7.    Return walls should be well tied into                                     full, waves can vibrate a structure
                          the fastland.                                                             out of the bottom if the penetration
                                Rationale:      On an open bulkhead,                                is inadequate. In addition, if the fill
                                waves can be focused where the                                      is differential, i.e., one side only,

                                                                              18

                          the weight of the sand and water                            2.   Sills should be used in areas with good
                          can topple the groin.                                            sand supplied on the beaches.
                                                                                                  Rationale: Insufficient supply of sand
              4.    The groins should be constructed in a                                         to the beach can cause deleterious
                    sequential manner,                                                            effects to clowndrift shores.
                          Rationale:    In most areas, there is
                          a net drift in a certain direction.                         3.   Although not a general rule, the sill is
                          Thus, the first groin should be con-                             usually most effective when placed at, or
                          structed on the downdrift end of the                             near the mean low water line.
                          project.    Construction of the next                                    Rationale:   This position is usually
                          groin should begin when the first                                       sufficient to insure adequate back-
                          groin fills completely. In this way the                                 shore height.   When the system fills
                          beach itself can determine the opti-                                    however, placement too far offshore
                          mum spacing and length of the groins.                                   generally results in failure.
                          While this sequential construction is
                          desirable, repeated contractors' mobi-                BREA KWA TERS
                          lization costs may be prohibitive.                        Rubble mound (riprap) or gabion breakwaters
                                                                                act to build up beach material and reduce wave
                                                                                action against the shoreline during storms. In some
                                                                                cases their benefits tend to outweigh their expense.

                                                                                      7.   Like the riprap revetment, the stone
                                             IT,
                                   -rr,n                                                   should be of sufficient size to resist the
                                                                                           maximum expected wave forces.
                                                                                                  Rationale: Wave forces during storms
                                                                                                  will roll undersize stone off the slope
                                                                                                  of the structure.

                                                                                      2.   For    gapped breakwaters, spacing and dis-
                                                                                           tance offshore must be engineered properly
                                                                                           considering all the design variables for a
                                                                                           given shoreline.
                                                                                                  Rationale:    Breakwaters placed too
                                                                                                  far offshore may be ineffective in
                              . ....                                                              reducing wave forces.      Too wide a
                                                                                                  gap between breakwater units may
                                                                                                  result in increased erosion on the
                                                                                                  shoreline midway between the units.

                                                                                                  ADVISORY SERVICES

                                                                                    In order to   help the shoreline property owners in
                                                                                Virginia, several agencies offer free advice on shore-
                                                                                line problems.    These agencies are:

                                    -r                                              Virginia Shoreline Erosion Advisory Service
                                                     "A"                            P
                                                                                      0. Box 1024
                                                                                    Gloucester Point, VA 23062
              Figure 22 - Gabion revetment.                                         (804) 693-3388

                                                                                    Virginia Institute of Marine Science
                                                                                    Gloucester Point, VA 23062
                                                                                    Attn: Mr. Scott Hardaway
              SUBMERGED SILL                                                        (804) 642-2111, Ext. 280
                 These considerations refer primarily to the use of                 Soil Conservation Service
                                                                                    Warsaw, VA 22572
              sandbags to form the sill. Gabions and mortar filled                  Attn: Mr. Blaine DuLaney
              bags are also effective in perching a beach.                          (804) 333-6931
                    7.    Grain size should be X4 millimeter or larger.             Army Corps of Engineers
                                                                                    804 Front Street
                               Rationale: This size sand is necessary               Norfolk, VA 23510
                               to prevent the bags from loosing                     Attn: Jim Melchor
                               material through their pores.                        (804) 625-8201, Ext. 271

                                                                            19

                                                                               -14

                                                                                  7:1

                                                       1!     A

                                                                 *46

                           AS                                       IN,

                                                                                                     %

                                                                                                            4

                                                                                    xk'44
                                                              tths Lit

                                                                                                @A'

                                                                                                   A6e- 4

                                                                       VIP

                               T,-Aw9t 42M

                         Building a structure close to the Atlantic Ocean may result in severe damage during storm events. The
                      photograph on page 11 showf a Virginia coastal residence with pool in the Summer of 1978. The photograph
                      on this page was taken in October 1979 after a storm of moderate intensity.

                                                                         20

                                                                . . . ...... ......
                                                                                                                                                                                                                                                                                                      21

                                     MA RSH GRASS

                                        Propagation of various species of marsh grass may
                                     be done to curb erosion along an eroding sediment
                                     bank where no marsh exists or to enhance an existing
                                     marsh shoreline. Table 2 lists some plant species
                                     and their adaptability to tidal elevations, water and
                                     soil salinities. Fertilization of new seeds, sprigs or
                                     plugs is essential for good marsh grass growth and
                                     development.
                                        The question arises as to the viability of marsh
                                     grass as an erosion buffer along a given shoreline.
                                     Too much open water where wave forces can build
                                     is not conducive to marsh grass growth. Figure 23
                                     depicts a general rule which may be applied to site
                                     suitability. This does not guarantee success, but
                                     the low cost of the method to abate shoreline
                                     erosion may warrant some experimentation.

                                     RI VERBA NK SLOPE CONTROL

                                        Exposed sediment banks with no vegetative
                                     cover are unstable and susceptible to high rates of
                                     erosion by rainwash, groundwater and wave action.
                                     Getting some type of flora to grow on the surface
                                     of the slope will do much to reduce the erosion.
                                     However, it is often necessary to grade the bank
                                     back to reduce the slope for the planting of grasses.
                                     Table 3 lists some plants which have been used to
                                     control riverbank erosion. Fertilization is almost
                                     essential for a good and quick growth of ground
                                     cover.
                                        Getting vegetation established on a slope is some-
                                     times not enough.  The tow or base of the bank
                                     should be stabilized to insure the rest of the graded
                                     slope remains intact. In areas susceptible to high
                                     storm wave conditions, this toe stabilization will be in
                                     the form of a bulkhead or a riprap revetment.  In
                                     more protected areas, planning a marsh grass fringe
                                     may be all that is needed.

                                            SHORE FACES MORE THAN 5 MILES OF OPEN WATER
                                            AND A IS 15 FEET OR MORE.

                                                                                       NORMAL HIGH TIDE

                                                A

              Figure 23 - Marsh site suitability
                       scheme.
                                            SHORE FACES LESS THAN 5 MILES OF OPEN WATER
                                            AND 8 IS 15 FEET MORE.
                                                  S 15 F@EET O@RMOR@E
                                           A @NA @I

                                                                                       HIGH TIDE
                                                                                                tNORMAL
                                                                                       LOW TIDE 1i

                                                           22

                                           TABLE 2:      MARSH PLANTS AND THEIR ADAPTABILITY TO TIDES AND SALINITY

                                                                                                                                                                               TZ"
                                  Adaptability to                                                                               Adaptability to Water
               2.51,              Tide Elevation             Species                                                            and Soil Salinities

                                  MT - MHW                   juncus roemerianus (Needlerush)                                    brackish and freshwater

                                  MT - MHW; sh               Peltandra virginica (Arrow-arum)                                   freshwater

                                  MT - MHW; sh               Pontederia cordata (Pickerelweed)                                  freshwater
                                                                                                                                                                          z"
                                                                                                                                                                               AL
                                  MT - MHW; sh               Sagittaria latifolia (Duck Potato)                                 freshwater                                . ....
                                  MT - MHW                   Scirpus americanus (Common Threesquare)                            brackish and freshwater
                                  MT - MHW                   Scirpus robustus (Saltmarsh Bulrush)                               brackish and freshwater
                                  MT - MHW                   Spartina alterniflora (Cordgrass)                                  salt and brackish water

                    i@3
                                  MT - MHW; sh               Typha angustifolia (Narrowleaf Cattail)                            brackish and freshwater

                                  M
                                        MHW; sh
                                    T                        Typha latifolia (Broadleaf Cattail)                                freshwater
                                                                                                                                                                               Al
                                  above MHW                  Distichlis spicata (Saltgrass)                                     salt and brackish water
                                  above MHW                  Festuca elatior (Fescue, Kentucky 31                               salt-tolerant
                                  above MHW                  Panicum amarulum (Coastal Panicgrass)                              salt-tolerant
                                  above MHW                  Panicum virgaturn (Switchgrass)                                    salt-tolerant
                                  above MHW                  Spartina cynosuroides (Big Cordgrass)                              brackish and freshwater
                                  above MHW                  Spartina patens (Saltmarsh Hay)                                    salt and brackish water

                                  dune                       Ammophila breviligulata                                            salt-tolerant
                                                             (American Beachgrass)

                                                                                     ---------------                ---- --

                 TABLE 3:
                 RIVERBANK EROSION CONTROL WITH PLANTS                                       *River birch (Betula nigra)

                 by Norman T. Beal, Extension Agent                                   Maple species
                 VPI & SU Extension Division
                                                                                             *Silver maple (Acer saccharinum)
                    Plants are the ultimate controllers of erosion on
                 soils of any slope. They vary widely in their ability                       *Boxedler (A. negundo)
                 to be successfully established on a bank, and to
                 thrive. They hold the soil by one principal means-                   *Fishbait tree (catalpa speciosa)
                 their roots. Following are categories of plants that
                 have been successfully utilized for erosion control.                 *Sweetgum (Liquidambar styraciflua)

                 GRASSES                                                              *Empress tree (Paulownia tomentosa)

                       *Ryegrass (Lolium species)                                     *Elm species
                       *Bermudagrass       t     (Cynodon     clactylon)      tt             American elm (Ulmus americana)
            ffil       *Lovegrass, (Eragrostis species)                                      Chinese elm (U. pumila)
                 SHRUBS                                                         GROUNDCOVERS

                       Indian currant t (Symphoricarpus vulgaris)                     Bamboo t
                       Florida jasmine tt (Jasminum nucliflorum)                             dwarf bamboo (Sasa pygmaea) 18"
                       Trailing roses (Rosa wichuriana, R. max Graf.)                        golden bamboo (Phyllostachys aurea) 2S'
                       Sumac t sp. (Rhus glabra, R. typhina)                                 cane reed (Arundinaria tecta       10'
                       *Lespedeza (Lespecleza sericea)                                Knotweed t
                       Forsythia tt (Forsythia suspensa, f.x "Arnold's                       Mexican bamboo (Polygonum cuspiclatum)
                             dwarf                                                           8)
            pq
                       Rose acacia t (Robinia hispida)                                English   Ivy tt (Lonicera halliana)

                 TREES                                                                Halls honeysuckle (Lonicera halliana)
                       Willow species                                                 Daylily (Hemerocallis species) 2'
                             *black tf t (salix nigra)

            0,               weeping tf t (s. babylonica)
                                                                                             Established from seed
                       Poplar species
                                                                                             Spreads by rhizomes
                             Quaking aspen (Populus tremuloides)
                                                                                      tt     Roots from tips or joints
                             Hybrid poplars ttt (p.x)
             d
                                                                                      ttt    Establish from hardwood cuttings            early
                             Lombardy poplar ttt (p.       nigra italica)                    spring before leaves appear.
            1"d
                                                    V@ r                                                  40-ilvii-i-
                                                    A

                                                                      R
                                                                      ISS
                                                                      ai, ou'll""IrnmEl VIA11-11M

                     - - -- - - -- ... ....,. ... .... . .

                                                                               24

                                                     PHOTO AND SKETCH REFERENCES

                                  Figure 3.   State of California - The Resources Agency, 1976, Shoreline
                                       Protection in California, p. 22.

                                  Figures 4, 5 and 9. Bellis, Vincent, Michael P. O'Connor and Stanley R.
                                       Riggs, 1975, Estuarine Shoreline Erosion in the Albermarle-Pamlico
                                       Region of North Carolina, pp. 27-43.

                                  Figure 8. Marine Resources Commission, 1974, Wetland Guidelines, p. 32.

                                  Figures 15B, 16B, 17B and 19B. U.S. Army Coastal Engineering Research
                                       Center, 1978, Shore Protection Manual.

                                  Figure 20.    DeYoung, Bruce, Enhancing Wave Protection with Floating
                                       Tire Breakwaters.

                                  Figure 21 B. Anderson, Gary L., Robert J. Byrne, David W. Byrd and Gary
                                       M. Chianakas, 1978, Demonstration Project in Low-Cost Shoreline
                                       Erosion Control, p. 13.

                                  Figure 23. Environmental Concern, St. Michaels, Maryland 21663.

                                  Photographs:    VIMS Remote Sensing Center, C. Alston photos.            p. 11
                                   and p. 20.

                                  All other photographs VIMS/Sea Grant Shoreline Erosion Advisory Service,
                                   C. S. Hardaway photos.

                                                                 REFERENCES

                                  Byrne, Robert and Gary Anderson. 1977. Shoreline Erosion in Tidewater
                                       Virginia. Special Report in Applied Marine Science and Ocean Engi-
                                       neering No. 111 of the Virginia Institute of Marine Science, Gloucester
                                       Point, VA.

                                  O'Connor, M. P., V. J. Bellis and S. R. Riggs.      1978. Relative Estuarine
                                       Shoreline Erosion Potential in North Carolina, Department of Geology
                                       and Botany. East Carolina University, Greenville, NC.

                                  Riggs, S. R., V. J. Bellis and M. P. O'Connor    1978. Shoreline Erosion and
                                       Accretion: A Process Response of the Shore Zone and Environment
                                       of North Carolina. Department of Geology and Botany, East Carolina
                                       University, Greenville, NC.

                                                                       25

                                                          DATE DUE

                                                                 K

                                            The College of             William& Mary

                                                             VIMS
                                                             SEA
                                                             GRANT
                                                             PROGRAM

                                                         3 6668 14107 1698