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... s do to the effect of coastal erosion is a spit. Spits occur when the longshore drift occurs for a long period of time and will eventually form a badmouth bar, which over another long period of time forms a lake. Critical erosion is defined as any coastal erosion that does not threaten or damage man made structures is not classified as critical, even though it might be severe. Driven by a rising sea level, large storms, flooding, and powerful ocean waves, erosion wears away the beaches and bluffs along the 10, 000 miles of United States ocean and Great Lake shorelines. Erosion undermines waterfront houses, offices, and public facilities, eventually making them practically useless.
Within the next sixty years, erosion could destroy approximately 85, 00 houses, not including new development. When moving the shoreline inland, erosion also brings nearby structures very close to the water, often putting them at a greater risk than either their owners or insurers recognize. The erosion hazard was recently researched at the Cape Hatteras lighthouse in North Carolina. When constructed in 1870, the lighthouse was 1, 500 feet from the shore. Protective measures to reduce the rate of beach erosion in front of the lighthouse provided a temporary solution, but by the late 1980 s, the lighthouse stood only 160 feet from the sea and was in danger of collapsing.
In 1999, after several years of debate and lawsuits aimed at blocking a relocation, the National Park service successfully moved the lighthouse back 2, 900 fee at a cost of several million dollars. The Cape Hatters lighthouse examination is just one of many problems that arise when people build different kinds of structures on eroding shores. In Marc 2000, The H. John Heinz III Center for Science, Economics, and Enviroment completed a nationwide study of the impacts erosion has had on the National Insurance Food Program and other federal programs and coastal communities. The new information gathered from this study indicates that property owners need to be informed of the erosion risks they face when moving into a nice luxury house on many different shorelines across the country. Erosion risks need to be incorporated into local land-use planning, state coastal management, and private and public lending and insurance practices.
The Atlantic and Gulf coasts are both bordered by a chain of roughly 300 barrier islands. These islands are composed primarily of loose sand. Barrier islands are the most dynamic land masses along the open ocean coast and have been moving back landward for thousand of years because of the progress of slowly rising sea levels. On the Atlantic coast, beaches are eroding at an average annual rate of two to three feet per year. The beaches along the Gulf of Mexico have the nations highest average annual erosion rates which equal about six feet per year. The Pacific coastline consists of narrow beaches backed by steep sea cliffs composed of rough sedimentary bedrock and are therefore unstable and screwed very easily by wave erosion.
Cliff erosion is site specific. In some locations, cliffs have retreated tons of feet, approximately 50 to 100 feet away, there is no retreat at all. As a result of this variability, long term average annual erosion rates are usually less than 1 foot per year, but these low averages hide the real damage done by large, episodic events. Similar to the shores along the great lakes, bluff and dune erosion rate vary from near zero to tens of feet per year because of annual variability in wave climate and lake levels. Many scientists believe that global sea level will increase twenty centimeters by the year 2050. Absent protective measures, an accelerated rate of sea level rise could result in the increase of rates of inland shoreline retreat and losses of beaches, coastal property, and wetland habitats.
Tide gauge records show no statistically significant evidence to explain that global warming has accelerated sea-level rise in the past 100 years. Short term variations in sea level that endure for a decade or more can distort evidence of sea level rise acceleration. Scientists expect the range of sea level rise forecasts to get smaller as techniques for measuring and modeling changes in sea level, climate, and ice sheets improve. Sea level rise affects all shorelines and is perhaps the most dominant process that determines the long term rate of shoreline movement and position. On the United States East Coast, historical data shows that erosion rates on sandy beaches are about 150 times the rate of sea level rise. During the last century, the global average sea level has risen between ten and twenty-five centimeters.
Along the Atlantic and Gulf coastlines, the average rise was approximately thirty centimeters. Rates are higher in these areas because of natural processes and human activities that cause subsidence of the land surface. In contrast to rising sea levels which move the shoreline inland gradually, severe storm events can move the shore hundreds of feet inland in just a few days. These erosion events are followed by extended periods of accretion, in which the beach partially but not completely builds back to its pre-storm position. Climate records show that the 1970 s and 1980 s, which was a period in which extensive coastal development took place, there was relatively quiet period for hurricanes and other severe storms. In decades before this, hurricanes and other storms caused severe damage to coastal communities.
For instance, in 1954, Hurricane Hazel struck the North Carolina coast with very heavy winds up to 150 miles per hour. This caused the highest tides of the year. The storm killed over twenty people and caused over a 100 million dollars in damage. Everything talked about in this report dealing with coastal erosion is a perfect reason why coastal erosion is so important and effects a wide variety of people every day.
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