This can erode the beach in one area and build it in another. Unfortunately a considerable amount of sediment is dumped into shipping channels and harbors, which requires expensive dredging to remove. Rip currents are formed when longshore currents, moving parallel to the coastline, are deflected seaward by bottom irregularities, or meet another current deflecting the flow to seaward. Development depends upon wave conditions. Large incoming waves on a long, straight beach will produce rips.
Rip currents consist of feeders, a neck, and a head.
The feeder is usually the longshore current that flows parallel to the beach inside the breakers. The neck is the main channel of the rip current where feeder currents converge and flow outwards at a speed of one to three knots through a weak point in the breakers. The head is where the current widens and slackens outside the breaker line. A number of swimmers are lost every summer when caught up in rips and swept out to sea. If trapped in this situation, swim parallel to the shoreline until out of the rip rather than swimming directly into the current, then swim back to shore.