The coast has taken a pounding by huge waves which have altered the shape of the coast. Work started late on Friday to install ‘rock armour’ along the coast next to Preston Beach Road.
The Environment Agency is spending £100,000 on the operation at Preston Beach alone.
A spokesman said: “The defence at Preston consists of a concrete wall with shingle in front. A lot of the shingle has been taken away as it has soaked up the wave energy.
“When that washed away the wall took a bit of a beating which is why boulders have been brought in to replace the shingle and reduce the risk of damage.”
The Environment Agency spokesman said the situation at Chesil Beach had to be approached differently as it is protected heritage coast.
He said: “What you have in place there is gabion baskets full of stone which have been joined up to form a barrier.
“Some of those baskets have been shattered by the waves and emptied of stone.
“So the work we are doing there is to repair the baskets, plus we also have three long-reach diggers and three bulldozers working to move material and replenish the parts of the beach which have been lost through wave action.
“If it was left long enough the material would return from the sea. The guys have been nipping down there when the tide is right.”