Portland Bill to Selsey Bill

Location and Geology

This area of coast stretches from the Isle of Portland, which is on the Dorset coast and is next to Weymouth, all the way to Selsey Bill, which is not far to the East of Portsmouth. Portland Bill and its surrounding areas are mainly limestone, with sandstone and mudstone deposits on the beaches. This suggests that the area is mainly resistant to erosion, as limestone is a relatively resistant rock. In contrast Selsey Bill is mainly sand, silt and clay, some of it being superficial deposits, suggesting that this area is more vulnerable to erosion.

Land forms

  • Headlands and Bays- There is lots of evidence for headlands and bays forming due to alternating rock strata, such as Swanage Bay and Durlston Head.

  • Spits and Double Spits- Because there are so many rivers that feed into the English Channel on the south coast, spits form because water loses energy when it encounters an opposite flow. Examples of double spits include those formed at the mouth of the River Piddle and the River Frome, and those at Christchurch Harbour. Hurst Castle is also built on a spit, which has a salt marsh behind it (an important habitat). There is also a spit at the end of the Beaulieu River and a recurved spit at the end of Calshot Beach, which also has a salt marsh behind it.

  • Coves- Lulworth Cove is a key example of this land form and shows that erosional processes are happening.

  • Islands- these have formed due to rives cutting land off, for example Hayling Island

Coastal defences

There are groynes all along the stretch of coast, which are in place to prevent longshore drift. They vary from wooden to rock groynes, and are an example of hard engineering. They are also indicative of the wind direction and show which areas of the coast are the most vulnerable to erosion

How is each process in a sedimentary cell shown along this coast?

  • Inputs- erosional land forms such as Lulworth Cove and Swanage Bay are evidence that erosion is happening.

  • Transfers- you can see that longshore drift is happening because there are coastal defences, such as groynes, which show the build up of sediment in the direction of the prevailing wind.

  • Outputs- erosional land forms, such as spits and beaches, have formed.