Coastal Erosion

For many decades the approach to rapid coastal erosion was to build up sea defences, to try and slow down or even stop the erosion. Initially the attempts were thought a success, however after some years it was realised that the power of the sea and waves could overcome human attempts. Only could protection be a success if huge costs were going to be involved. Many methods around the British Isles have taken place in he last 50 years with many failures occurring. It is very rare to find a coastline that shows a decrease in the rate of erosion over many years after defences are in place. In fact in places the defences seem to have speeded up the erosion process. Coastal erosion is a natural process of erosion, transportation and deposition, interfering with this balance could be to blame for the rise in erosion on the coasts of some areas.

Groynes have been built out to sea in many areas of the British coastline. Their aim is to trap material and thus slow down the rate of longshore drift. However, these groynes in some areas are been blamed for the rise in erosion rates further down the coast.

On the Holderness coastline in Humberside, erosion is taking place at a rate of about 2 metres per year. Along this coast there is a strong action of longshore drift taking place, which over centuries has produced a spit to form on the southern tip of Holderness, called Spurn Head spit. The spit is over 4km long and 100 metres wide. The majority of this coastline is glacial till, a soft fragile material, which is easily eroded. This however is not thought of as the only reason for the rapid rates of erosion. Human interference is thought to be another cause, as a result of the sea defences put in place. A rock groyne was built at Mappleton, to create a wider beach. This in turn would help protect the coastline, by absorbing the wave energy. Then at Withernsea a concrete sea wall with a splashback and boulder rip-rap in front of it was created. These defences were to cause great problems. The groyne meant that material moving down the coast by longshore drift would get stuck behind the groyne. This protected the initial area as a beach was created. Although this meant less material was heading further down the coast than it had done in the past, it created a beach as it was trapped. The sea wall and rip-rap protected the initial area, by stopping the erosion. Although in turn this meant less material was been carried down the coast, because there was less been eroded by the sea. The beaches along the Holderness coast were already very small, as only 30% of the glacial till eroded is heavy enough to be deposited and form a beach. The beaches down coast of the defences began to shrink in size, as material usually deposited there was either not eroded, or stuck behind the groyne. This meant that the waves concentrated all their energy on the base of the weak cliff, because the beaches were not big enough to absorb the waves. This caused the cliffs to erode at a faster rate, threatening many buildings once thought of as safe. At Easington, the Gas terminal is under threat sitting right on the edge of the cliff, with no beach to protect it. They will either have to move it, or build some of their own sea defences. Cowden Farm just down the coast from the Mappleton groyne, is starting to fall into the sea. Here erosion increased as a direct result of the defences, there is almost visibly no beach remaining at the foot of the cliff. Many other properties have already fallen into the sea or are about to do so soon.

Gravel extraction occurs in many offshore areas around Britain, gravel is removed in large volumes for commercial purposes each year. More than 20 million tonnes were been dredged in 1989. The removal of this gravel was thought to be a good method, as no extra quarries would have to open therefore creating no protests from any local people. The problem is removing all this sand and gravel is leading to the gradual wearing away of shores and cliffs, adding to coastal erosion. When large amounts of material are removed from the seabed, the directions of currents move more material back into the dredged area. The area dredged will be replenished with material, and this material will be taken from elsewhere along the coastline. Dredging is taking place offshore from Barton on Sea, near the Isle of Wight. Like Holderness, Barton on Sea suffers from coastal erosion at an alarming rate, and longshore drift is also present. At Barton, a spit has also developed because of the longshore drift. Barton is also an area that has suffered heavily from landslides on the coast in the past, because of the layers that make up the cliff. Heavy rain causes the initial problem, infiltrating into the permeable material. It can then not pass through the clay layer, so flows outwards horizontally emerging as a spring. This lubricates the layer, removing the friction between layers. When the weight becomes too much, the cliff slips creating a landslide. Many things have been done to the coastline to slow the rate of erosion, but the construction of a groyne at Hengistbury Head has made matters worse. Sediment travelling east to west has become stuck on the east side of the groyne to form a beach. This has limited the amount of sediment moving further along the coast by longshore drift. So now, the only sediment to reach Barton is silty material brought into Christchurch Harbour by the rivers Stour and Avon. And, material which is eroded from the cliffs at Plateau Gravels. Therefore, with the building of the groyne and removal of offshore gravel, erosion rates have increased at Barton. This is because a reduce in the amount of available sediment for the beaches, leads to the beaches shrinking. This means that the wave energy is concentrated more on the base of the cliffs, and the beaches cannot absorb as much energy from the waves as they originally did. With the base of the cliffs attacked more than usual, the rate of erosion is faster and material supporting the upper cliff is removed. Therefore, the upper cliff is even more likely to slide, as there is no base to support it. This means when the cliff slides the amount of friction between the layers is greater than what it was in the past. As previously the base supported some of the cliff, so friction levels had to be low for the landslide to occur. However because of indirect links to human activities, landslides will now happen with higher amounts of friction due to there been no base to help support the weight of the cliff. Therefore, in theory the time gap between the landslides on the Barton coastline will decrease.

We have seen examples by which coastal erosion has been made worse because of human intervention. In the years when new methods were been experimented with little did people realise that in fact they were making the situation worse. Still these methods were carried forward and constructed around the British Isles for many years. Only has it been in the last 10 years that we have started to learn more and more about the coastal system. Today we have realised that in fact most of the methods we try on the coasts are in fact causing more damage than they are preventing it. We now understand that protecting one particular area will almost certainly lead to the putting another at risk. The good news is that now the councils and government are only protecting valuable areas that are under threat, and are refusing to give new licences to dredge material from offshore. This is also been accompanied by a new attitude towards coastal erosion of managed retreat. With sea levels expected to rise in the future, and Britain slowly subsiding into the sea this new method involves retreating from the coast. Meaning no new buildings are to be constructed unless they are a certain distance from the coastline. Also sea defences will be moved inland to higher ground, to compensate the rising sea levels. This will also reduce the money spent on sea defences every year, which can be put to much better uses within Britain. There may be people who oppose this idea like farmers and householders on the coasts, but even to compensate them will mean still saving millions of pounds every year. In normal circumstances, no one ever receives compensation for properties lost to the sea.