What effects does seawall have on sand beaches?
Seawalls have a number of effects on the beach.
Firstly, most seawalls will reflect the wave energy striking them, this means that there is an increases backwash, which is able to carry away sediment (i.e. sand) and so sand is removed from the area of the seawall. Ultimately this can lead to the undermining of the base of the seawall and its failure. Many seawalls now have a layer of rip-rap which serves both to protect the wall itself, but also reduces the amount of energy reflected by the wall by absorbing the energy of the waves and releasing the backwash more slowly as it exits from the blocks of rip rap.
A second effect is that by preventing erosion of the land behind the wall the seawall will reduce the amount of sediment available. This is less important where the seawall is short, but long stretches of seawall can have a significant effect on sediment supply, leading to sediment starvation and narrower beaches, which increace the wave energy reaching the seawall, which increaces scouring, which reduces the width of the beach.............
