Shoreline armoring

Shoreline armoring is the construction of barriers or structures for the purpose of preventing coastal erosion and/or manipulating ocean currents. Although they may prevent the deterioration of the immediate shoreline, these man-made structures almost always exacerbate erosion problems at nearby, downstream beaches by changing wave patterns and water flow.

Armoring may also promote the loss of shoreline vegetation, which in turn can degrade the ecosystem that seabirds and other beach and sea-dwelling life depend upon. By altering water flow and erosion and deposition and creating physical barriers, some types of shoreline armoring prevent sea turtles from reaching their nesting sites on shore. Finally, shoreline structures can block sunlight imperative to aquatic plants such as eelgrass , a prime habitat for herring and other marine life.

Shoreline erosion is a natural process determined by a complex array of environmental causes. Weather changes, tidal currents, and sea level adjustments all impact erosion over time. Catastrophic weather events such as hurricanes, tsunamis , and tropical storms can completely change the shape and nature of the coast in one fell swoop. Beach location, currents, and other conditions may also create depositional shorelines, where sand and sediment collect rather than erode. Armoring is a human attempt to minimize the impact of these natural forces on an isolated section of coastal shoreline. Because the coastal ecosystem is extensive and interconnected, these attempts ultimately affect other nearby, unprotected locations.

Common types of shoreline armoring include

• Groins. Long barriers that run perpendicular from the shoreline and are designed to trap sand and deposit it on the adjacent beach.
• Jetties. Similar to groins, jetties are rock structures that are built out from the shoreline. They are often erected for the purpose of keeping ship or boating channels clear of sediment build up by directing currents appropriately.
• Seawalls. These concrete or rock walls act as a barrier between beach and ocean; but increase neighboring beach erosion by deflecting normal wave patterns.
• Bulkheads. Like a seawall, a bulkhead is designed to separate the also promotes erosion further downstream.
• Revetments. A small seawall barrier, often constructed from rocks or boulders.
• Breakwaters. Breakwaters are offshore structures that absorb much of the force of waves before they reach the shoreline. They sometimes serve a dual purpose as navigational aids in boating channels.
• Rip Rap. Rip rap is a rock armoring sometimes used on river beds as well as coastal slopes to deter erosion.
• Docks. Although they are not built for the purpose of preventing coastal erosion, boat dock structures do impact marine life by blocking sunlight crucial for vegetation. Pilings, or posts, for docks can also disrupt sea-floor sediments. Depending on their size, structure, and location, they can also influence natural water flow patterns.

Alternatives to shoreline armoring include maintaining or planting native coastal shrubs, trees, and other plants that have an established root system to help prevent erosion. Beach renourishment , the process of replacing eroded beach with dredged offshore sand, is also used for erosion management. However, renourishment is cost-prohibitive in many cases, and may have a negative impact on marine flora and fauna . It also requires ongoing maintenance, as erosion is a perpetual process. Finally, the relocation of structures placed at risk by severe erosion, sometimes referred to as a retreat strategy, allows the natural processes of shoreline evolution to continue while preserving the public interest.

Shoreline armoring is becoming more widely recognized as an environmental hazard rather than a help. In South Carolina, state legislation entitled the 1988 Beachfront Management Act established a retreat rather than armor strategy for dealing with shoreline changes. The Act states that "[t]he use of armoring in the form of hard erosion control devices such as seawalls, bulkheads, and rip rap to protect erosion-threatened structures adjacent to the beach has not proven effective. These armoring devices have given a false sense of security to beachfront property owners. In reality, these hard structures, in many instances, have increased the vulnerability of beachfront property to damage from wind and waves while contributing to the deterioration and loss of the dry sand beach which is so important to the tourism industry." South Carolina no longer allows the construction of shoreline armoring within its coastal setback area, nor the rebuilding of existing armoring that is more than two-thirds damaged.

[Paula Anne Ford-Martin ]

RESOURCES

BOOKS

Dean, Cornelia. Against the Tide: The Battle for America's Beaches. New York: Columbia University Press, 2001.

PERIODICALS

Dunn, Steve, et al. "Coastal Erosion: Evaluating the Risk." Environment 42, no. 7 (September 2000): 36 (10).

OTHER

South Carolina General Assembly. Beachfront Management Act of 1988. S.C. Code of Regulations. Chapter 30, Section 48-39-320(B). 1998 [cited June 6, 2002]. <http://www.lpitr.state.sc.us/coderegs/c030.htm#30-21>.