The Burry Port Marina dredging project will start at the end of this month.
Harbour Master Rory Dickinson said that heavy storms in the first three months of the year had caused colossal movements of sand within the estuary.
The harbour was going to be drained for about a week depending on the weather and tides, to allow more work than usual to be undertaken.
Silt and sand removed from the harbour and its sand bank chocked entrance will be used to replenish nearby beaches.
The walls of the west pier or the harbour have also been repaired in the last few weeks as part of the coastal protection works following the storms.
Press Release, April 10, 2014