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N.C. Department of Environment and Natural Resources

NC Department of Environment and Natural Resources
Coastal Management - Bulkheads and Estuarine Shoreline Stabilization

Coastal Management

    Bulkheads and Estuarine Shoreline Stabilization

    Shoreline erosion is common along North Carolina's broad sounds and tidal rivers, and many waterfront property owners look for methods to slow or prevent it. The Estuarine Shoreline Stabilization section of DCM’s website provides property owners with a simple interactive guide to help determine the best stabilization method for a particular shoreline. There are several approved methods for stabilizing estuarine shorelines.

    1. Planting vegetation along the estuarine shoreline is the cheapest and most environmentally sound stabilization method. Plants slow wave energy and trap sediments. They also increase the marsh habitat and provide food for lower organisms such as algae and seaweeds, finfish and shellfish, mammals and shorebirds.
    Because of the variety of shoreline types and plant species in North Carolina estuaries, your project should be evaluated for the appropriateness of planting vegetation and for specifics on how to plant properly. If the shoreline does not require preparation – i.e. grading – a permit is not required for planting vegetation. For large projects or for projects on areas that need preparation, contact Coastal Management, and check with the North Carolina Sea Grant Program for information about plantings. (See Section 9 for contact information.)

    2.Stone riprapor revetments also dissipate some wave action, but they often increase erosion along the front and sides of the revetment. Because the stones or rocks of a revetment will settle and readjust with storms or waves, riprap material must be heavy enough or securely tied down to remain in place through storms and normal tidal and wave movement. In fresh water, you can further stabilize riprap sites by planting vegetation in the spaces between the stone using soil bioengineering techniques.

    Riprap material must be clean and free of pollutants. Although riprap causes less habitat destruction and loss than permanent seawalls, riprap replaces soft bottom habitat with hard bottom habitat, and it changes plant and animal diversity and abundance.

    3.Sills are shore-parallel, wood or rock structures that are designed to protect existing or newly planted wetland vegetation. A sill is placed offshore of existing marsh to help reduce the erosion of the waterward edge (escarpment). If there is not marsh already on the property, a sill is placed just offshore of where marsh would or could grow and is planted. The sill helps to protect the marsh by dissipating enough wave energy so that the marsh can establish. Once established, the marsh grasses dissipate wave energy and wave height through friction and drag, and help to reduce erosion further inland (usually on the high ground). Marsh vegetation also increases the marsh habitat and provides food for the lower organisms such as algae and seaweeds, finfish and shellfish, mammals and shorebirds.

    4.Groins are straight and usually shore-perpendicular structures, constructed with stone (riprap) or as a freestanding vertical wall to trap sand along one side. Trapped sand becomes a wave energy dissipation zone during daily wave action or sacrificial buffer during storms. Groins can be constructed either singly or in a series. Groins function only when longshore transport of sand (movement of sand along a shoreline) occurs and thus traps sand. Groins produce accretion of beach material along the updrift side and erosion on the downdrift side. A saw-toothed shaped shoreline is created with a series of groins. The trapped sand is commonly “stolen” from somewhere downdrift, which then in turn accelerates erosion downdrift of your property. 

    5.Bulkheads or vertical retaining walls are not the most desirable method of shoreline stabilization, because they can encroach into estuarine waters or public trust areas and can prevent the natural landward migration of coastal wetlands. Although bulkheads block or reflect wave energy, they also may block normal sand migration, increasing erosion along the front and sides of the wall. In addition, bulkheads can lead to the destruction of shallow-water habitat.
    Bulkheads must follow the general CAMA rules for coastal wetlands, estuarine waters and public trust areas, and the following specific guidelines {15A NCAC 7H .0208(b)(7)}:

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    • Where possible, sloping riprap or vegetation should be used rather than vertical bulkheads.  Riprap and vegetation can be less expensive and more effective at slowing erosion than bulkheads, depending on the characteristics of the shoreline. Sloping shoreline structures help dissipate wave energy as a wave strikes the shoreline, reducing the wave's ability to carry away soil. Vertical bulkheads do not dissipate wave energy as well; they can direct that energy to adjacent properties and to the base of the bulkhead, causing additional erosion and damage.

    • To keep the shoreline stable, shoreline stabilization measures should be aligned with, or landward of, the normal high water or normal water level (see Figure 4.4). The normal water level is the ordinary extent of high tide, based on the location of the apparent high tide line and site conditions, such as the presence and location of vegetation that is distributed by tides (wrack line). Shoreline stabilization measures located waterward of this line encroach on the public's right of access to those lands and waters.

    Figure 4.4

    Illustration showing proper bulkhead alignment

     

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      • Bulkheads or other shoreline stabilization structures may be permitted below the normal water level if all of the conditions below are met:

        • The property has an identifiable erosion problem or has unusual features, such as a steep bank;

        • Coastal Management has documented the need for shoreline stabilization below the normal water line;

        • The shoreline stabilization measure extends beyond the normal water line no more than necessary to: resolve the hardship resulting from unusual features; align with adjacent shoreline stabilization measures; or allow backfill of the area eroded in the year before the date of the permit application;

        • The shoreline stabilization measure will not significantly impair public trust rights or damage adjacent waterfront properties; and

        • The property is not on the oceanfront.

      • If you are installing a shoreline stabilization measure, you must build the structure landward of marsh areas (see Figure 4.5). In those areas where a shoreline stabilization measure is proposed immediately waterward of the marsh, it may be allowed if it is placed no more than 6 inches above the elevation of the adjacent marsh substrate, and involves no backfilling or altering of the wetland. Marshes are vital to the health and productivity of fish and shellfish, and they depend on regular flooding for nutrients and for carrying away sediments and pollutants. Bulkheads may block this essential exchange and stimulate the gradual filling of the state's coastal wetlands.

      • If you are installing a shoreline stabilization measure with backfill, the fill material must be from an approved upland source – not the state's wetlands, estuarine beaches, or sound and river bottoms. All backfill material must be confined behind the structure.

      Figure 4.5

      Illustration showing bulkhead placed landward of marsh

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