The topic that I chose to do my geology extra credit paper on is coastal erosion. There are many different types of coastal erosion and are all very important. There has been a lot of research done on coastal erosion and all have been very helpful in understanding it clearly. The first attempts to stop coastal erosion were to build sea defenses, and this has been going on for many decades now. Researchers first thought the attempts were successful, but after several years it was understood that the power of the sea was too powerful for any kind of human defense. Huge costs were involved, but the only thing that produced was protection.
Many methods around the British Isles have taken place in the last fifty years only to occur in many different failures. It is very rare to find a coastline with a decrease in the rate of erosion after many years after defenses have been put into place. The fact that the erosion process actually speeds up in the different places that these defenses have been set up comes from different research. Coastal erosion is the natural process of erosion, transportation, and deposition. Interfering with these natural processes could be the blame for the rise in erosion on the coasts of some areas.
One way that has been helpful in the management of coastal erosion is the building of groins. Groins have been built out to sea in many areas of the British coastline. The reason for doing this is to trap material and thus slow down the rate of longshore drift. The downside to these groins is that they have been blamed for the rise in erosion rates further down the coast. People are complaining that the erosion occurs more rapidly after these groins have been made.
One of the only ways to stop this is to just start building more groins. There is a coastline in Humberside where erosion is taking place about two meters per year. There is a strong action of longshore drift taking place along this coastline. Over many many years, this has caused a spit to form on the southern tip of Holderness, which is called the Spurn Head spit. The spit is over four kilometers long and 100 meters wide. A majority of this coastline is made up of a soft fragile material called till.
This glacial till is easily eroded. It was not thought that the till was the reason for the very fast rate of erosion. Human interference was a thought to be another cause of the erosion, this is a result of the sea defenses that were put into place. A rock groin was built right around the same area to create a wider beach. The building of this groin in turn would help protect the coastline, by absorbing the wave energy. Another way that has been tested to try to stop the erosion of coastal erosion was to build a sea wall with a splash back and boulder rip-rap in front of it.
These different defenses only in the long run caused many different problems with the coastlines surrounding them. The groin meant that material moving down the coast by longshore drift would get stuck behind the groin. This did protect the initial area where the beach was created. These groins proved that less sand and material did move down shore than in the past. Beaches are the main reason for the building of these groins. Hotels and different types of businesses would do pretty well if the were on the side before the groin but if they were built after the groin, they would pretty much be out of luck.
The sea wall and rip-rap also helped the initial area surrounding it by stopping the erosion. This also meant that less sand and material was moving down the coast. This in turn meant that it was actually hurting the coastal environment further down along the coast. The beaches along the Holderness coast were already pretty small, as only about thirty percent of the glacial till eroded and was heavy enough to be deposited and form a beach.
The beaches that are down coast from these different defenses usually begin to shrink in size because of material that is deposited there is either not eroded or stuck behind a groin. The reason for this is because the waves concentrated all their energy on the base of a weak cliff and the beaches were not big enough to withstand very big waves. This causes cliffs to erode at a faster pace, threatening whatever kind of business is in the area. If these buildings thought at one point that they were very safe, they were sadly mistaken. The only thing to do with these businesses once it gets to the point of having no beach around them, is either move to a completely different area or build some kind of their own defense that might help in the long run. There are many different examples of businesses in this kind of situation.
There is an example of a farm just down from where a groin has been built. The farm is about to fall into the sea. Erosion has increased as a direct result of the defenses, there is practically no visible beach remaining at the foot of the cliff. There are many other properties that have either already fallen into the sea or are about to.
Gravel extraction occurs in many different offshore areas around the world. This is a process that involves the removal of gravel in large volumes for commercial purposes each year. There was about 20 billion tons that have been dredged in the last few years. The removal of the gavel was thought to be good method, because there would be no protests from the local people. But the problem with moving all this sand and gravel is leading to the gradual wearing of shores and cliffs, this adds to the effect of coastal erosion.
When large amounts of material are removed from the seabed, the direction of the current moves more material back into the dredged area. The area dredged will be replaced with other material, material that has been taken from somewhere else further down along the coastline. Most areas suffer from coastal erosion at an alarming rate. Another geologic feature that occurs 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 bay mouth 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 Hatter us 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 nation's 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.