What Is a Longshore Drift?

Longshore drift is the a natural process describing a current that often moves mostly parallel to a beach's shoreline. While this type of phenomenon has always happened, it is largely considered a nuisance because of the way it can change the beach in certain areas. Many refer to this drift as erosion because it moves sediment down the beach and can cause shortages of sand in some areas. Some strategies have been used successfully to stop the effects of longshore drift, but some feel these attempts have ultimately been a detriment to the environment.

The process of a longshore drift begins when the waves hit the beach. Typically, the waves do not hit the shore straight on, but at an angle. As the backwash goes out, it takes with it some sand. The current, which goes the same way as the direction of the waves, takes some of that suspended sand downshore until another wave picks it up and puts it back on the beach. The current rarely changes because of prevailing winds, and therefore the sand typically never returns to its original location.

The main problem with longshore drift relates to the removal of sand from one place and the deposition of it in another. While such things help shape the natural and distinct shoreline of the beach, it can be inconvenient for some property owners. The ones with the most to lose are resort owners, who depend on people coming to enjoy a nice beach. If the drift takes too much sand, it can actually eat away at the permanent land, causing a more serious form of erosion that could eventually threaten structures.

To combat erosion, one of the most common practices is to build a wall that extends from the shoreline into the ocean at an angle of 90 degrees in relation to the shoreline. This helps break up the current and stops the drift from taking place. Some locations may use breakwaters built offshore to stop the waves, but this technique also breaks up the waves before reaching shore, which may be desirable in some locations.

The use of physical barriers to stop longshore drift has also caused controversy. Some groups feel the practice does not allow the natural ebb and flow of the beach to occur. Further, once a person upstream builds a jetty to keep sand, it forces others down the line into taking the same action, or sand will be taken from them but never replaced by more sand from upstream. That often leads to a long series of jetties down the shoreline.