These rocks are intended to keep the sand intact, while the continual tide erodes and removes it moving it onto sandbars or further down the beach. The houses right behind this are in constant jeopardy of falling into the sea. As far as I know there are ridiculous rules about putting sandbags and other protective measures in place. Something about not being allowed to do it at all. I couldn’t imagine the frustration of a home owner here, slowly watching as the sea claims the land under your house.