Here's an interesting related word from Dr. Bill [wwh]:

On Cape Cod, to reduce erosion of beach sand, large stones are piled perpendicular to the shore, as much as six feet wide and six fee high and 100 feet long. Called groins. Groynes is probably an older spelling.

groyne

n : a protective structure of stone or concrete; extends from shore into the water to prevent a beach from washing away [syn: breakwater, groin, mole, bulwark, seawall, jetty]

http://dictionary.reference.com/search?q=groyne

Thanks, Dr. Bill.