Seems to me they're much the same as the riprap seawalls, jetties, and groynes you'd find down the shore in parts of the US. They're pretty effective, and USACE

Seems to me they're much the same as the riprap seawalls, jetties, and groynes you'd find down the shore in parts of the US. They're pretty effective, and USACE seems to approve of them being there.