Groynes and breakwaters

Groynes are structures built across a beach, usually from dry land out into the water, while breakwaters are 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 up drift 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.

Since 2001, ten small, geotextile groynes have been built at Somerton Park, a beach that was previously submerged at high tide. At approximately 1.5 metres high and 25 metres long, the structures collect enough sand to raise the beach level on the south side above normal high-tide level. There is no observable adverse effect to the beach down drift of each groyne, and the beach can still be walked on at low tide.

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 sand for trucking to beaches further south.

To build a field of groynes large enough to completely stop the movement of sand along the Adelaide coastline is not feasible. The project would be prohibitively expensive and very damaging to other elements of the environment. The groynes would have to be so enormously long and tall that they would be unsightly in the extreme.

More information 

Refer to our reference material page.