Groins
Groins are artificial structures usually errected perpendicular to the prevailing coastline. Groins are often employed to prevent sand movement from one part of a beach to another as the result of littoral currents, prevailing wave motion and storms.
The success of groins is often a matter of hit or miss where there are both failures and positive outcomes. In recent years the use of groins has been viewed with a good deal of skepticism. Groins are costly and affect a small area of coastline. Longboat Key has experienced stiff resistance from the Florida Department of Environmental Protection to constructing groins at the Islander Club. After five expensive years the permitting has still not been approved.
Groins have both beneficial and deleterious impacts on beaches. In most cases sand builds up on the windward side of the groin and diminishes on the leeward side of the groin.
If there is an inadequate supply of sand, hard structures cannot control erosion. In the absence of an adequate sand supply, hard structures such as seawalls, bulkheads, and revetments are effective in protecting uplands but often at the expense of the beach, reflecting waves sharply, causing greater turbulence, increased sediment in suspension, accelerated longshore currents, and thus a greater erosion rate. ( NOAA )