Revetment

A revetment in stream restoration, river engineering or coastal engineering is a facing of impact-resistant material (such as stone, concrete, sandbags, or wooden piles) applied to a bank or wall in order to absorb the energy of incoming water and protect it from erosion. River or coastal revetments are usually built to preserve the existing uses of the shoreline and to protect the slope. In military engineering it is a structure formed to secure an area from artillery, bombing, or stored explosives. Many revetments are used to line the banks of freshwater rivers, lakes, and man-made reservoirs, especially to prevent damage during periods of floods or heavy seasonal rains (see riprap). Many materials may be used: wooden piles, loose-piled boulders or concrete shapes, or more solid banks. Concrete revetments are the most common type of infrastructure used to control the Mississippi River. More than of concrete matting has been placed in river bends between Cairo, Illinois and the Gulf of Mexico to slow the natural erosion that would otherwise frequently change small parts of the river's course. File:Rock armour revetment Hampton-on-Sea.JPG|Rock armour revetments File:Liliw,Lagunajf5551 01.JPG|Revetment along Oples River ([[Liliw, Laguna]]) Revetments are used as a low-cost solution for coastal erosion defense in areas where crashing waves may otherwise deplete the coastline. Wooden revetments are made of planks laid against wooden frames so that they disrupt the force of the water. Although once popular, the use of wooden revetments has largely been replaced by modern concrete-based defense structures such as tetrapods. In the 1730s, wooden revetments protecting dikes in the Netherlands were phased out due to the spread of shipworm infestations. Dynamic revetments use gravel or cobble-sized rocks to mimic a natural cobble beach for the purpose of reducing wave energy and stopping or slowing coastal erosion. Unlike solid structures, dynamic revetments are designed to allow wave action to rearrange the stones into an equilibrium profile, disrupting wave action and dissipating wave energy as the cobbles move.