New England Beaches Erosion
Beach erosion is a chronic problem along many open ocean shores of the United States. As coastal populations continue to grow and community infrastructures are threatened by erosion, there is an increased demand for accurate information regarding past and present trends and rates of shoreline movement. There is also a need for a comprehensive analysis of shoreline movement that is consistent from one coastal region to another. An assessment of coastal change over the past 150 years has found 68 percent of beaches in the New England and Mid-Atlantic region are eroding, according to a U.S. Geological Survey report just released. Scientists studied more than 650 miles of the New England and Mid-Atlantic coasts and found the average rate of coastal change — taking into account beaches that are both eroding and prograding -- was a negative 1.6 feet per year. Of those beaches eroding, the most extreme case exceeded 60 feet per year. The past 25 to 30 years saw a small reduction in the percentage of beaches eroding — dropping to 60 percent, possibly as a result of beach restoration activities such as adding sand to beaches.
Beaches can become eroded naturally or as due to the impact of humans.
Erosion is a natural response to storm activity. During storms, sand from the visible beach submerges to form storm bars that protect the beach. Submersion is only part of the cycle. During calm weather smaller waves return sand from the storm bar to the visible beach surface in a process called accretion. The term erosion conjures visions of environmental damage so the term submersion often replaces it in describing a healthy sandy beach.
Some beaches do not have enough sand available to coastal processes to respond naturally to storms. When there is not enough sand left available on a beach, then there is no recovery of the beach following storms.
Many areas of high erosion are due to human activities. Reasons can include seawalls locking up sand dunes, coastal structures like ports and harbors that prevent longshore drift, dams and other river management structures.
Long-term erosion rates were generally lower in New England than in the Mid-Atlantic. This is a function of the dominant coastal geomorphology; New England has a greater percentage of shore types that tend to erode more slowly (rocky coasts, pocket beaches, and mainland beaches), whereas the Mid-Atlantic is dominated by more vulnerable barrier islands and dynamic spit/inlet environments.
However, the percentage of coastline eroding was higher in New England than in the Mid-Atlantic, highlighting that although rates of shoreline erosion may not be as extreme, coastal erosion is still widespread along this region of the U.S. coastline.
Beaches change in response to a variety of factors, including changes in the amount of available sand, storms, sea-level rise and human activities. How much a beach is eroding or prograding (that is growing by either natural deposition or mad made additions) in any given location is due to some combination of these factors, which vary from place to place.
The Mid-Atlantic coast — from Long Island, N.Y. to the Virginia-North Carolina border -- is eroding at higher average rates than the New England coast. The difference in the type of coastline, with sandy areas being more vulnerable to erosion than areas with a greater concentration of rocky coasts, was the primary factor.
The researchers found that, although coastal change is highly variable, the majority of the coast is eroding throughout both regions, indicating erosion hazards are widespread.
The researchers used historical data sources such as maps and aerial photographs, as well as modern data like lidar, or light detection and ranging, to measure shoreline change at more than 21,000 locations.
This analysis of past and present trends of shoreline movement is designed to allow for future repeatable analysis of shoreline movement, coastal erosion, and land loss. The results of the study provide a baseline for coastal change information that can be used to inform a wide variety of coastal management decisions.
The report, titled "National Assessment of Shoreline Change: Historical Shoreline Change along the New England and Mid-Atlantic Coasts," is the fifth report produced as part of the USGS’s National Assessment of Shoreline Change project. An accompanying report that provides the geographic information system (GIS) data used to conduct the coastal change analysis is being released simultaneously.
For further information: http://www.usgs.gov/newsroom/article.asp?ID=2707&from=rss&utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+UsgsNewsroom+%28USGS+Newsroom%29&utm_content=Google+Reader