Groin

A groyne is built on shores and rivers to interrupt water flow.
A consequence for building a groyne is that when the water starts to move the other way its carrying on with more strength and bring destruction with it.

• method, construction. "Groyne - Wikipedia, the free encyclopedia."Wikipedia, the free encyclopedia. N.p., n.d. Web. 10 Jan. 2013. <http://en.wikipedia.org/wiki/Groyne>.