Estuarine Shoreline Stabilization Options

Estuarine shorelines are dynamic features that experience continued erosion. Land is lost by short term processes, such as, erosion by storms, boat wakes, and tidal currents within the long-term process of rising sea level. As coastal populations encroach on estuarine shorelines, states are required to strike a balance between the need to provide protection to the public from coastal hazards with the need to maintain the integrity of the natural system.

Because estuarine shoreline erosion is common along North Carolina’s broad sounds and tidal rivers, many property owners would like to slow or prevent further erosion by stabilizing their shorelines. Shoreline stabilization is defined as the use of engineered structures, vegetation, or land management practices to provide protection of a shoreline from future or existing erosion. Although the most commonly used method is a bulkhead, there are many other options available. Below are various shoreline stabilization methods allowable in North Carolina. A few of the below methods, such as vegetation, oyster reefs, or marsh sills, can actually improve habitat rather than eliminate it.

Land Planning

Land planning is designing your property around existing conditions and possible erosion. This includes utilizing the land as it exists without construction of shoreline stabilization methods. The most common practices associated with land planning include setbacks, buffers, and no action. Land Planning allows for marsh to migrate and allows for the system to remain natural at minimal cost, but will allow erosion to continue. No CAMA permits are necessary for this stabilization method.

Vegetation Control

Vegetation control (a.k.a.: Wetland or upland plantings) is the use of wetland or upland vegetation to control or prevent further erosion. These plantings include the use of new plantings or preserving existing vegetation and may be planted or allowed to colonize naturally. A final established minimum width of 10-20 feet is preferable to dissipate wave energy and thus control erosion. An additional width of 10 feet of upland or riparian vegetation is also preferred. Marsh grasses dissipate wave energy and wave height through friction and drag, and thus help to reduce erosion further inland (usually on the high ground). The vegetation also increases the marsh habitat and provides food for the lower organisms such as algae and seaweeds, finfish and shellfish, mammals and shorebirds. Planting vegetation is the cheapest and most environmentally sound stabilization method available. No CAMA permits are necessary for this stabilization method unless there is to be filling or grading.

Photo: Bonnie Bendell

Marsh Toe Protection Revetments

Marsh Toe Protection Revetments (a.k.a.: riprap at the waterward toe of marsh) are a shore-parallel, sloping structure constructed against a marsh escarpment to protect the marsh wetland roots from undermining. Placing riprap or stone on the waterward edge of the marsh helps to stabilize or reestablish the marsh vegetation. Marsh grasses dissipate wave energy and wave height through friction and drag, and thus 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.

General Permit for the Construction of Riprap Revetments for Marsh Toe Protection

Sills

A sill (a.k.a.: Marsh Sills or Sheetpile Sills, previously known as Marsh Enhancement Breakwaters) is a shore-parallel, wood or rock structure that is 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 dissipated 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 thus 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. This stabilization method can be permitted through a CAMA Major or General Permit.

General Permit for the Construction of Sheetpile Sills
General Permit for the Construction of the Marsh (Rock) Sills

Groins

A groin is a straight and usually shore-perpendicular structure, 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. Groins are often mistakenly called jetties, which are larger structures designed for the stabilization of navigation channels at river mouths and tidal inlets. This stabilization method can be permitted through a CAMA Major or General Permit.

General Permit for the Construction of Groins

Breakwaters

A breakwater (a.k.a.: Wave Attenuator, Wave Breaks, Wave Fence) is a shore-parallel non-shore-connected structure, designed to trap sand and to attenuate wave energy. Breakwaters are typically constructed of stone, with multiple structures detached or gapped with a distance equal to length of one individual structure. Breakwaters reflect and dissipate wave energy creating a lower wave energy area landward of the structure. A sandy beach is usually created between the structure and shore, but only when longshore transport of sand (movement of sand along a shoreline) occurs. The trapped sand is commonly “stolen” from somewhere downdrift, which then in turn accelerates erosion downdrift of your property. Breakwaters are not commonly used in the NC estuarine system and typically designed for offshore of oceanfront beaches (which is not currently permittable in N.C.). Breakwaters do not have a typical design and require the services of a Professional Engineer (PE). This stabilization method can be permitted through a CAMA Major Permit only.

Riprap Revetments

A revetment (a.k.a.: riprap, sloped structure) is a shore-parallel, sloping structure constructed against a bank/escarpment to protect it from erosion while absorbing wave energy. Revetments are typically constructed on a 1Vertical: 2Horizontal slope. Riprap/Stone can move during storms or wave action and as such the stone used needs to be heavy enough to remain in place. Revetments are very long lasting, durable structures which usually do not need any maintenance after construction. Revetments, when designed to, can withstand a wide range of wave energies from very little to large wave action. Although revetments cause a loss of soft bottom habitat, it causes less habitat destruction and loss than bulkheads and also creates fisheries habitat. This stabilization method can be permitted through a CAMA Major or General Permit.

General Permit for the Construction of Bulkheads and Riprap Revetments

Bulkheads

A bulkhead (a.k.a.: Vertical Structure, Seawall) is any shore-parallel vertical structure designed to prevent erosion, overtopping, flooding, or sliding of the land. Bulkheads are usually placed along an eroding bank or escapement to hold back the land from the water and prevent erosion. Bulkheads are a long lasting, durable structure that can stand up to moderate to high wave energy; but they also prevent the natural migration of wetland vegetation. This stabilization method can be permitted through a CAMA Major or General Permit.

General Permit for the Construction of Bulkheads and Riprap Revetments

For further information or questions please contact the field representative for your area.