What is a disadvantage of a Groine?

Answer 1

There is a tendency for any currents that run parallel to the shore to eddy when they meet a groine. This causes them to drop any sand they are carrying along. The sand builds up. After a decade or two the groine may be almost completely buried, so that the only part showing is the tops of the posts that support it. That may be fine and dandy for all the kids playing on this new sandy beach, but it has a downside. The sand had to come from somewhere, and this usually means a peninsula a mile or two down the coast. This peninsula erodes, shrinking in time with the growth of the new beach.