Breakwaters, Headlands, Sills, and Reefs

Other anthropogenic structures that are used to stop or alter natural coastal changes include breakwaters, headlands, sills, and reefs. These structures are composed of either natural or artificial materials, and are designed to alter the effects of waves and slow coastline erosion and change.

A breakwater is an offshore shore-parallel structure that “breaks” waves, reducing the wave energy reaching the beach and fostering sediment accretion between the beach and the breakwater. Made of rock, concrete, or oyster shell, these structures can be floating or fixed on the ocean floor and can be continuous or segmented. Breakwaters can be placed attached to the shoreline as headlands or submerged near the shoreline as sills. Breakwaters allow for the accretion of sediment between the structure and the shoreline, potentially stabilizing wetlands and providing shelter for new intertidal marsh habitat. However, this may impede longshore transportation of material leading to downdrift erosion as well as form intertidal marsh not appropriate for the location, replacing natural sandy beach habitat. Coastal parks hosting historic resources, such as Colonial National Historic Park, can be seen utilizing these techniques to dissipate wave energy and protect inland sites.

Related Links

• Colonial National Historic Park, Virginia—[Geodiversity Atlas] [Park Home]

• NPS—Coastal Geology
• NPS—Beaches and Coastal Landforms
• NPS—Geology
• NPS—Oceans