Revetments are a cover or facing of erosion resistant material placed directly on an existing slope, embankment or dike to protect the area from waves and strong currents. They are usually built to preserve the existing uses of the shoreline and to protect the slope. Like seawalls, revetments armor and protect the land behind them. They may be either watertight, covering the slope completely, or porous, to allow water to filter through after the wave energy has been dissipated.
Most revetments do not significantly interfere with transport of littoral drift. They do not redirect wave energy to vulnerable unprotected areas, although beaches in front of steep revetments are prone to erosion. Materials eroded from the slope before construction of a revetment may have nourished a neighboring area, however. Accelerated erosion there after the revetment is built can be controlled with a beach-building or beach-protecting structure such as a groin or a breakwater.
Revetments are commonly constructed using armorstone (high wave energy environments), or rip-rap stone (lower wave energy environments), in combination with smaller stone and geotextile fabrics to act as a filter and underlayer. The filter and underlayer support the armor, yet allow for passage of water through the structure. Toe protection prevents undercutting and provides support for all the above layer materials. A typical design section is shown in the figure to the right.
Other construction materials have also been used to form the armor layer including gabions, poured concrete (usually in stepped fashion), pre-cast concrete blocks, and grout filled bags.