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Guidelines for Erosion Management

Managing shoreline erosion while protecting shoreline resources and the natural movement of sediment in the Pleasant Bay system is a significant management challenge. Under natural circumstances winds, currents and tides hit a coastal bank and, depending on bank profile and vegetation, erode the bank’s sediments. Eroded sediments are transported by winds and currents to the beach at the base of the bank, to elsewhere along the adjacent shoreline, or back out to sea. This natural action ensures that beaches are replenished with sand—which is continually redistributed by tides and storms—and nutrients are added to intertidal and fringe marsh. Without the erosion of coastal banks providing the primary source of sand, nearby salt marsh, beaches, dunes and barrier beaches would rapidly disappear. This in turn would jeopardize landward salt marshes, tidal flats and the extensive plant and animal life they support. Loss of salt marsh also makes upland areas more vulnerable to storm damage.

Coastal armoring, particularly through the use of Coastal Engineering Structures (CES), is intended to prevent erosion of sediments from coastal banks. Often the design of these structures results in a reflection of wave energy in ways that can exacerbate erosion on fronting beaches and down-drift properties and infrastructure. To the extent that they are successful at preventing erosion, hard structures diminish the supply of sediments available for natural beach nourishment. The diffraction of breaking waves around the ends of structures can cause end-scour and erosion of down- drift properties. These combined impacts contribute to lowering the profile of the fronting, adjacent and downdrift beaches. Within Pleasant Bay there is indication of loss of beach and fringe marsh due to the presence of erosion control structures.

The Pleasant Bay Alliance developed Guidelines for Erosion Management in Pleasant Bay to assist property owners, Conservation Commissions and design professionals with evaluating options for managing shoreline erosion in Pleasant Bay. The guidelines seek to ensure that selected measures provide a means for property owners to manage erosion while sustaining the natural process of sediment erosion, transport and deposition needed for a healthy coastal system.

Guidelines for Erosion Management in Pleasant Bay