barrier islands so hard that they break right through the island, removing sand, houses and
anything in the way.
Protecting Shorelines
Humans build several different types of structures to try to slow down the regular work of
erosion that waves produce and to help prevent damage to homes from large storms. One
structure that people build, called agroin,is a long narrow pile of rocks that extends out
into the water, at right angles to the shoreline (Figure10.22). The groin traps sand on
one side of the groin, keeping the sand there, rather than allowing it to move along the
coastline. This works well for the person who is on the upcurrent side of the groin, but it