Two spits of land, Hengisbury Head and Mudeford Quay, create the entrance to Christchurch Harbour. These spits of land are the result of deposition from the River Stour and River Avon and longshore drift. When these rivers reach the sea they slow down, much of the sediment that they carry is released, this sediment settles behind the spit creating marshland. The spit itself off Hengisbury Head was created by longshore drift, man has also helped its development by building groynes that trap sand inbetween them slowly increasing the land area occupied by the spit.
The diagram above shows how a spit is formed, in turn creating a marsh and new land behind it.
· Longshore drift causes sediment to create a spit on the far side of the headland. This continues to grow as more and more sediment is added.
· Short term changes is wind direction cause the spit to bend in, towards the bay creating an area of sheltered water.
· As sediment is deposited by the river as it slows down when it reaches the sea it is deposited in the ‘low energy’ are behind the continually growing spit.
· This sediment creates a salt marsh behind the spit, as plants colonise the marshland and the pH is lowered, soil develops and more plants start to grow until the once marsh is part of the mainland.
Christchurch Harbour and Hengisbury Head
Time to test yourself...
Home
Chesil Beach
Fleet Lagoon
The Isle of Portland
Lulworth Cove
Bournemouth and Barton-on-Sea