Hamm Beach

Formation

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Hamm Beach is. like Chesil Beach, a shingle tombolo. While Chesil was formed by material moving south and east from Lyme Bay, the Hamm tombolo was formed by debris falling from the cliffs at East Weares on Portland and being transported northwards to Hamm Beach. This tomobolo can be clearly seen in old postcards dating before the the navy started developing the site. The northern limit of the tombolo was the entrance to the Fleet.

Postcard 1
Postcard dated 1908

Postcard 2
Postcard dated 1911, picture taken during exceptionally low tide.

The pebbles on Hamm are very irregular in shape and size compared with Chesil because of the much reduced wave action.Hamm Beach pebbles
Pebbles on Hamm Beach

The seabed in front of the beach is sand and this is part of the extensive areas of sand in Weymouth Bay. At spring low water large areas of the sand are exposed and strong easterly winds blew this sand onshore to form shallow sand dunes on the shingle tombolo.

layer of sand
In the picture above the layer of sand about 30cms thick can be seen overlaying the shingle. On top is the turf that has formed over the years and which now supports a fragile ecosystem.

When the Portland Harbour breakwaters and naval base were built this cut-off the supply of shingle and sand so Hamm Beach is now a closed system with no fresh supply of material.

The Weymouth to Portland railway line ran the whole length of Hamm Beach and was built by building up ballast on top of the sand and shingle and digging deep drainage ditches alongside the track.Railway trackbed
Trackbed of the railway line

In more recent times a new bridge was built at Ferrybridge and this meant opening a new channel for the Fleet. This has left a short section of Hamm Beach isolated between the new and the old channels.

Chesil Beach is also retreating at about 15cm per year towards Hamm Beach and at the southern limit of Hamm overwash from Chesil Beach has transported Chesil pebbles onto Hamm Beach.

 
     
 
Last updated 20/04/2008 Copyright ©2008 Chickerell BioAcoustics