For one named stretch of coastline, comment on the success of coastal defences. (10 marks)
An example of a stretched coastline is the Holderness coastline it consists of different coastal defences along the coastline to help slow down erosion by the use of both hard and soft engineering techniques.
Firstly if we look at the Cliff defence (sea walls) and then the failure of groyens at Sewerby we can start to compare and contrast the use of different coastal defences in different areas and if they have or haven’t succeeded. The first defence system in Sewerby was built 150 years ago- sea wall, destructive waves and corrasion caused it to collapse as it became weak however it was then replaced and rebuilt in a much improved way, as the bricks were structured securely together and the wall was flat not a stair type design as it was in the past, the positive about this is that it is able to protect the cliff base against erosion as big waves crash into it and slows down the process of erosion. On the other hand the sea wall was built curved and over a long term period it will collapse again as the energy of the wave is reflected back into the sea the wave power remains but the sea wall is a barrier between the boulder clay and the sea. Groynes have also not been a great success over a long period of time the process of long shore drift has caused sediment to cover them which has then created a second beach, I personally think this was a waste of money to invest in two short term sea defences when money could have been spent on more worthy long term investment such as rip rap at the bottom of the sea wall as a way to dissipate energy to prevent scouring although tourist may find them unattractive.
Moreover sea defences at Mapleton consists of hard engineering such rock groynes, the boulders were imported from Norway as Norwegian granite and were laid out like groynes parallel to the coast to prevent the removal of beach sand by long shore drift to decrease erosion but also was re- graded to make it less steep therefore more stable this was seen as a long term resolution but not long after sediment starvation increased erosion causing ripple effect by terminal groyne syndrome, over all this wasn’t such a well invested technique as the erosion rate increased from 2.5 meters a year to 3.8 meters a year between 1991 and 2007. Nevertheless a successful coastal defence system was put up in Withernsea that slowed down the movement of erosion which were: building a sea wall, the first sea wall they put up was straight rather than absorbing the way energy it reflected it, over time it was eroded by wave energy and scoured the base of the wall undercutting it causing it to collapse just like the wall in Sewerby although they rebuilt a re-curved wall which was effective and successful as it caused the wave energy to dissipate decreasing the erosion and the base off the cliff but also extending its life this is a strength because it is a long term investment and the government won’t have to find another way to slow down erosion for a long time. The cost benefit analysis showed it was beneficial as they over weighed the construction costs, another great success was the groynes, the groynes were placed in a T shape this reduces erosion at the downdrift side and can trap sediment meaningless sediment is lost and beach nourishment isn’t needed. One of the other strength is that can perform well to protect the beach in different wave directions over all, in my opinion this can be seen as a long term investment and doesn’t cost as much as normal laid out groynes.