A beach has been cordoned off after strong tides breached recently completed sea defences.
Solent Coastguard said flood defences at Pagham beach had been breached and part of the shingle bank washed away.
People have been urged to keep away from the area which is very dangerous, a spokesman said.
Arun council was responsible for the sea defence which was completed in December
Large areas of the shingle bank and large boulders, which all formed part of the flood defence scheme, have been washed away over the past week in the poor weather.