Engineering Side Effects

On coasts with a strong net sand transport in one direction, any interruption of the sand transport will lead to new patterns of sedimentation and erosion. The beach will start to change, adjusting to the new conditions. If left alone long enough, a new near equilibrium situation will eventually develop.

A typical such disturbance is the dredging of a coastal inlet, and the construction of jetties to prevent sand from the beach to fill up the channel too fast. The sand will accumulate on one side, and make the beach aggrade until it has reached near enough ot the end of the pier that the sand can get into the channel. On the other side the sand transport capacity exceeds the sand input, so the beach will erode.

Another man-made reason for coastal erosion is the decrease of sand supply to the shore from land, due to the regulation of rivers. The sand gets trapped in reservoirs behing dams instead of reaching the beach. This has negative consequences not only in terms of land loss, but also as fertility loss. The inundations in many rivers were important for agriculture in that they brought in new nutrients to the flood plain.

It has been estimated that 80% of the beach erosion problems on the U.S. Atlantic coast are caused by the man-made interruption of the natural sand transport along the coast.