Actually this is a GROYNE. A groyne is an active structure extending from the shore into the sea, most often perpendicular or slightly oblique to the shoreline. The main function of a groyne is catching and trapping part of the sediment moving in a longshore direction in the surf zone. This groyne is catching flint pebbles and quite large pieces of flint in chalk. Some of the wood lower down is heavily weathered, and the construction bolts are very rusty.