What Is Coastal Erosion of a Coastline?

Man-made structures often increase the rate of coastal erosion.

Coastal erosion is the process by which coastal land is worn away by natural forces. Coastal erosion is an issue for people living on or near the coast as well as marine organisms in bays, estuaries, and shallow coastal waters.

Causes

The main cause of coastal erosion is tidal. Coastal erosion can be the most severe when the direction of the tide runs parallel or at an angle to the coastline. Steep waves break on sea walls or cliffs with greater force than smaller waves and cause a high rate of erosion. The rising of sea levels is also a significant factor. As levels rise, the upland area is slowly eroded. Sediment deficiencies, usually a result of human influence, also contribute to coastal erosion. Certain rock types are susceptible to corrosion from the carbonic acid in seawater and secretions from algae. Wind and rain can also contribute to cliff and coastline erosion, as well as storms, hurricanes, and tsunamis.

Rates of Erosion

Coastal erosion is not always consistent. Much beach erosion is specific to episodic events, including severe storms and hurricanes, which cause large amounts of erosion in small periods of time. Erosion occurs sporadically. During a storm, different areas erode at different rates. Some coastal areas consistently erode at fast rates. Other areas have a much slower average annual rate of erosion.

Sporadic Erosion: A Case Study

A case study of the Cape Cod bluffs between the Pamet River and Beach Point, published in 2008, and conducted by geologist Dr. Elazar Uchupi and coastal specialist Dr. Graham Giese, highlights the sporadic nature of coastal erosion. The study shows that the long-term erosion rate for the area is less than half a foot annually. However, when erosion does occur, it occurs at high rates over short periods of time. The study suggests that the bluffs in the area erode ten to fifteen feet over a two- to seven-year span and subsequently remain fairly stable for a period of forty to fifty years.

Sporadic Erosion Examples

There are many noted instances of sporadic erosion. The Mississippi Delta region has areas that erode meters per year while certain areas on the rocky West Coast erode at an average of inches per year.

Human Influence

The human influence on coastal erosion is vast. Dams store sediments needed to replenish beaches. Man-made structures, such as seawalls built to prevent sand loss, increase erosion in the long term. Sand in front of seawalls erodes, and waves eventually reach the walls, creating turbulence, increasing erosion rates and undercutting the walls. Navigation channels through barrier islands interrupt the natural flow of sediment, leading to erosion in certain areas and the growth of beach in others. The destruction of vegetation along the coast, including mangroves, leads to greater rates of erosion.

References

• Coastal Erosion Definition
• Coastal Erosion
• Coastal Erosion (2)
• Coastal Erosion (3)
• Case Study

Resources

• Coastal Erosion Case Study