Breaching the sea defences would allow salt marshes to form

The Environment Agency said the shingle accumulates because of natural coastal processes, but the build-up will block the river unless it is moved.

Sussex area flood defence manager Andrew Gilham said the work would be carried out in daylight during low tide, as in previous years.

"During winter months, the threat of flooding is never far away," he said.

What is certain is that forecast rises in sea level will mean that the current maintenance regime is untenable Andrew Gilham

"It is crucial that these works take place before the shingle has a chance to block the river.

"Although the Cuckmere Valley is mainly rural, there are isolated properties that are at risk of flooding if the river is unable to discharge to sea."

He said the agency was continuing to look at options for the long-term management of the valley and further technical studies are taking place.

"What is certain is that forecast rises in sea level will mean that the current maintenance regime is untenable."

Plan opposed

The Environment Agency has put forward plans which would see the valley, created by the Victorians in 1846, turned into a salt marsh and nature reserve.

Residents living near the valley have been fighting the scheme since 2003.

People living nearby announced last year they were submitting their own planning application for the area, to build defences which would keep the valley in its current state.

They say the agency's plan will destroy wildlife, footpaths and parts of the local beach.