Groyne – A wooden or concrete barrier built out into the sea to stop the longshore drift of sand and shingle and so cause the beach to grow
His groin (groyne) was in agony. He had slipped and hurt himself on the wooden barriers at the beach.
Swash – Think of swash as water coming from the side and washing the sand.
Backwash – Think of backwash as water coming back after washing the sand.
Swash – Material is carried up the beach at an angle.
Backwash – Material is carried straight down the beach as the water retreats.
So, a groyne is a barrier built down the slope of a beach to prevent movement of the sand along the beach by longshore drift.
They do this by interrupting the action of waves that pass over the foreshore at an angle.
Groynes can help to build up the amount of sand on a beach.