For the more information about the geologic resources of the National Park Service, please visit http://www.nature.nps.gov/geology/.


Soft Engineering

Beach nourishment
Beach nourishment (NPS photo)

Beach Nourishment

Beach nourishment is the process of placing additional sediment on a beach or in the nearshore. A wider beach can provide storm protection for coastal structures, create new habitat, and enhance the beach for recreation. However, beach nourishment can also have significant negative impacts and every effort should be taken to avoid and/or mitigate impacts.

Beach nourishment is often needed to mitigate the effects of hard coastal structures (jetties, groins, seawalls, etc.) because structures may increase downdrift erosion rates. The need for beach nourishment after human alteration is evident at many sites within the National Park System, including Assateague Island National Seashore (ASIS) and Cape Hatteras National Seashore (CAHA).

In the case of ASIS, in the 1930's a jetty system was established to stabilize the Ocean City Inlet. The northern jetty acts as a barrier to sediment transport (north-to-south), and has caused sediment accretion on the north side of the jetty and erosion on the south. The deterrence of alongshore sediment transport to ASIS has had numerous detrimental impacts on the island's biological, geological and cultural resources. Both short-term and long-term beach nourishment plans are in place to mitigate the destructive effects of jetty placement.

At CAHA, beginning in the 1920's, Highway 12 was constructed along the entire length of the park to provide access to the barrier island. According to North Carolina statutes, Highway 12 is mandated to exist in its current position, which disrupts the natural evolution of the barrier island. Dune building and filling of inlets is necessary at CAHA in order to maintain the highway.


Dredging

Dredging is the removal of material, including sand, silt, gravel and other subaqueous materials with the purpose of disposing them at a different location. Dredging is often used to keep waterways and ports navigable and the effects are not fully understood.

Inlets are vital passageways to the ocean for both recreational and commercial users. However, creating and maintaining navigation channels can affect the stability of adjacent shorelines, sediment transport, and currents in the vicinity.

Historically most dredged sediment was placed offshore, removing it from the active sediment system. Removing sediment from the system may contribute to long-term shoreline erosion on downdrift beaches. Fortunately, many recent projects are now placing dredged material in the nearshore, directly on beaches (if the material is compatible), or reusing it in other projects.


Beach Scraping

Beach scraping (grading, bulldozing) is the process of reshaping beach and dune landforms with heavy machinery. The creation of dunes is intended to protect property from storm overwash and erosion. During the summers the man made dunes may be bulldozed flat, providing water views to property owners. The effects of beach scraping on coastal environments are not fully known.

Beach scraping has occurred irregularly at private communities within Fire Island National Seashore, located on a barrier island on the south coast of Long Island, New York. Natural, undeveloped park lands are immediately adjacent to the developed areas on Fire Island, so any human modifications in the developed areas can affect park resources. A study in 2010 investigated the impacts of beach scraping at Fire Island (report PDF - 1.31 MB). Results indicate that where homes are built directly on the dunes, man made (scraped) dunes are ineffective protection because they can not be built high enough. In other areas, man made dunes are larger than the natural dunes and more material is transported alongshore, causing accretion downcoast.


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Last Updated: August 16, 2011