Groynes

Above pictures were taken in East Coast beach.

GROYNES



Groynes are built along the beach to protect it from erosion. A groyne is a low wall built at right
angles to prevent materials from being transported away by the longshore drift. This enables the transported materials to accumulate on the side of the groyne facing the longshore drift. The picture below is an illustration of how groynes work.


Types and shapes of groynes

Look at the two photos below, they were taken at exactly same spot on a groyne. As you can see, on the left side of the groyne, the sediment is accumulated and forming a wider beach compare to the right side of the groyne. Thus, groynes are effective to prevent sediment being eroded away from the coast, they also help in the formation of wider beaches.   The wider beaches help to slow down the energy of waves and so reduce coastal erosion of slopes behind the beach to a great extent.



A groyne at the Eastcoast Park

However, there are some disadvantages. Firstly, groynes are expensive to build, each costs about $200 000. Secondly, the beach on the other side of the groynes will not be replenished by materials, creating an asymmetrical beach, which is not pleasing to the eyes and may deter tourists from visiting. What's more the beach further down the coast may be eroded away. Also, it spoils the natural beauty of the beach when a series of groynes are built along it.

*Some matierals are quoted from http://kickessnow.wordpress.com/2011/10/20/river-and-coast-4/.

*Some pictures are taken from Google Map and http://www.coastalwiki.org/coastalwiki/Groynes