Flood walls can be simple or permanent structures used to prevent water encroachment on property. Sandbag walls are easy to assemble but impractical for large areas. The design depends on the area’s long-term condition or crisis level. New Orleans has an extensive series of flood walls built around its perimeter.
A flood wall is a structure designed to prevent water encroachment on residential, commercial or government property. Designs for flood protection walls can be relatively simple and short-term, such as vertical sandbag piles, or they can be long-term, permanent structures in which steel beams and foundation piles are driven into the ground and up sturdy concrete barriers are built of them. In the UK, a flood wall is often referred to as a dyke and can also be a ditch dug below normal ground level to act as a barrier and method of channeling flowing water from a river, lake or bank. excessive runoff of precipitation towards buildings.
An emergency flood retaining wall is often built by volunteers who fill bags with sand and stack them in a vertical and horizontal line around buildings and other structures threatened by rising water. These types of flood walls offer the advantage of being relatively easy to assemble and disassemble and are made of materials that are readily available in many places. Packed sand serves as an effective water barrier, as it is heavy enough to withstand wind and water pressure and composed largely of quartz that does not absorb water like clay or dirt. The downside to a sandbag-built flood wall is that it is labor-intensive to construct and is impractical for cordoning off large areas long-term. A flood wall built with sandbags 300 feet (91.4 meters) long and 3 feet (0.91 meters) high is estimated to require approximately 7,000 average sized sandbags and 250 tons of sand to construct.
The flood wall design is unique depending on the long-term condition of an area or current crisis level. It has been estimated in the United States that 75% of all flood damage occurs from water flowing below 3 feet (0.91 meters) high, so most makeshift wall structures are first built at this vertical level. The construction of flood walls in the UK to protect against periodic flooding of rivers by heavy rains, known as flash floods, is based on the principle that 12 hours of rain will raise water levels to a depth of 6 meters ( 20 feet), so they must be significantly more extensive than a smaller flood retaining wall.
The most extensive versions of the flood wall design are those built to protect large metropolitan areas or major industrial facilities that are located near major waterways such as nuclear power plants and are at or near sea level. An example of this is the US city of New Orleans which has an extensive series of flood walls built around its perimeter, which are also maintained by the US Army Corps of Engineers. After the damage caused to the city and the wall structure by Hurricane Katrina in 2005, the Army Corps of Engineers began rebuilding the wall system to make it capable of withstanding an expected once-in-a-century storm, with a completion date of 2011. Portions of the new flood wall are constructed of reinforced concrete ranging from 15 to 19 feet high (4.6 to 5.8 meters) with a 5-foot (1.5 meter) thick concrete base and pile piles of reinforcements that descend to the ground 12 stories, or about 150 feet (46 meters). The wall is also integrated with tension connectors, expansion joints and waterstop features to allow for flexibility in withstanding the pressure of water surges driven inland by the Atlantic Ocean.
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