Coastal Erosion Case Studies PDF

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Holderness Coast – Case Study   

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Geology, fetch, longshore drift and beach material are factors why the coastline is retreating so fast. The geology is varied as the entire coastline consists of unconsolidated bolder clay. Average annual erosion is 1.25m per year, with wide spatial variation between 0 and 6m per year. The variations are a result of: - Coastal defences in locations such as Hornsea, Mappleton and Withernsea which stops erosion. - Sediment starvation, erosion rates increase north to south. South is starved due to the construction of groynes and breakwaters that interrupt longshore drift and trap sediment. - Variations in cliff height and susceptibility to erosion. - Mass movement susceptibility, and debris from previous erosion and mass movements protecting some parts of the cliff. Erosion varies from 0-11m every six months at Hollym, South of Withernsea. Most erosion peaks at the biannual spring measurement, reasons for variations include: - Winter storms, when they coincide with a high spring tide. - Storms are rare in summer so Autumn erosion rates are lower. - North-east storms cause most erosion because of long wave fetch. The shape of the beach can change and promote erosion. Ords are deep hollows running parallel to the base cliff line, they allow waves to directly attack the cliff with little energy dissipation. Ord locations erode four times faster.

Aswan Dam  

Built on the River Nile in 1960s. River discharge fell from 35 billion m3 to 10. Sediment volume fell from 130 million tonnes to 15. These changes were caused by: - Water withdrawals for industry, cities and farming from the reservoir behind the dam. - Sediment trapped by reservoir and dam, slow flowing water allows sediment to deposit.

Akosombo Dam, Ghana   

Constructed in 1965. Reduced flow of sediment down the River Volta from 70 million metres-cubed to less than 7 per year. Had major impacts on longshore drift and coastal erosion in Ghana and neighbouring countries.

River transported sediment is important when maintaining the dynamic equilibrium between deposition and erosion at the coast. As a major sediment source, interference with the flow of sediment down rivers can lead to dramatic coastal change....