In theory, the groins disrupt ocean currents that typically move parallel to the beach and erode and carry away beach sand. Although the barrier typically disrupts the currents and causes them to drop their loads, the clean water then moves around the tip of the groin and erodes beach sediment on the down current side. Another groin is then required to redeposit the eroded sediment. Erosion would then occur at the end of second groin and a third groin would be required to redeposit that sediment. Not surprisingly, a series of groins may be needed to protect an entire beach.
Beach replenishment involves dredging or pumping offshore sands to buildup eroded beaches.
Although expensive and, in many cases, only temporary, more than 1000 km of U.S. shoreline has been replenished as of 1997. However, the beach washed away in about 2 months. Over the years, Wrightsville Beach in North Carolina has been replenished ten times. In some cases, it s easier and cheaper to control or prohibit the construction of buildings on eroding beaches than to rebuild a beach. In contrast, soils and sediments may erode from coastal regions, accumulate in harbors and interfere with ship navigation.