In the case of cross-shore related erosion problems, the construction of a seawall can be considered. Seawalls are built parallel to the coast. They protect the coast by preventing the erosion of the land behind them. However, this goes with more severe erosion in front of the seawall (see Fig. 84). Thus a seawall does not
prevent erosion, but limits it to the sea side of the wall.

A major design criterion for a seawall is the expected erosion depth at the toe of the structure. If the erosion exceeds the construction depth, the wall will fail. Another important criterion is the acceptable rate of wave overtopping (see Fig. 85). The acceptable overtopping discharge depends upon the activities normally performed in the lee of the structure, the economic consequences of flooding, and the need to prevent erosion of the rear face of the seawall.

A seawall is not necessarily vertical, but is often stepped (see Fig. 84) or curved (see Fig. 86) to reduce wave overtopping and scour. Many types of construction exist: stone masonry walls, steel and wooden sheet piles, monolithic concrete walls, interlocking concrete slabs and rubble mound seawalls.

A seawall does not "work" if the underlying problem is loss of sediment induced by long shore transport.