In some cases, it is necessary to build various structures like groynes, breakwaters and seawalls that are engineered to aid in effective coastal management such as trapping sand and protecting infrastructure.
Groynes are structures built across a beach, usually from dry land out into the water. Breakwaters are usually built parallel to the beach. Both of these structures interrupt the alongshore movement of sand. A groyne acts as a physical barrier across the beach and collects sand on the updrift side, in what is called a fillet.
Small groynes are useful for raising beach levels on a small scale. Their height can be adjusted to trap enough sand to improve beach levels without being obstructive.
Seawalls act as a last line of defence and protect coastal infrastructure and property from storms. Early seawall designs were often solid concrete structures, but since the 1960s most seawalls have been built and repaired using large boulders and rocks. This allows them to better absorb wave energy. Along Adelaide’s metropolitan coast, ongoing beach replenishment has slowed the eventual damage to seawalls. However, the forces of the sea are such that many of the older seawalls will need repair in the future.
At Semaphore Park, a trial geo-textile sand bag breakwater was built in 2004. The trial proved so successful at trapping sand that the breakwater was armoured with heavy rocks in 2009. This area provides a source of beach replenishment sand to beaches further south.