Detached breakwater

A detached breakwater is a short, shore-parallel structure built in shallow water seaward of the shoreline, not connected to land, used to hold or rebuild a beach. It cuts wave energy in its lee so longshore transport drops and sediment accretes behind it, forming a salient or, if the gap is small and the structure long, a tombolo that ties the beach to the breakwater. Wave diffraction at the roundheads sets the shoreline shape. Design balances crest freeboard, length, gap width, and offshore distance against the target beach response, per the USACE Coastal Engineering Manual. Most are rubble-mound; some are low-crested.