Flood control channels are large and empty basins which let water flow in and out (except during
flood
A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrol ...
ing) or dry channels that run below the street levels of some larger
cities
A city is a human settlement of notable size.Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Penguin.Kuper, A. and Kuper, J., eds (1996) ''The Social Science Encyclopedia''. 2nd edition. London: Routledge. It can be def ...
, so that if and when a flood occurs, the water will run into these channels, and eventually drain into a
river
A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of w ...
or other body of
water
Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
. Flood channels are sometimes built on the former courses of waterways as a way to reduce flooding.
Levees
Flood control channels are not to be confused with watercourses which are simply confined between
levees. These structures may be made entirely of
concrete
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wid ...
, with concrete sides and an exposed bottom, with
riprap
Riprap (in North American English), also known as rip rap, rip-rap, shot rock, rock armour (in British English) or rubble, is human-placed rock or other material used to protect shoreline structures against scour and water, wave, or ice erosion. ...
sides and an exposed bottom, or completely unlined. They often contain grade control sills or
weir
A weir or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. Weirs are also used to control the flow of water for outlets of l ...
s to prevent
erosion
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is dis ...
and maintain a level streambed.
Distribution
By definition, flood control channels range from the size of a
street gutter to a few hundred or even a few thousand feet wide in some rare cases. Flood control channels are found in most heavily developed areas in the world. One city with many of these channels is
Los Angeles
Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the List of municipalities in California, largest city in the U.S. state, state of California and the List of United States cities by population, sec ...
, as they became mandatory with the passage of the
Flood Control Act of 1941 The Flood Control Act of 1941 was an Act of the United States Congress signed into law by US President Franklin Roosevelt that authorized civil engineering projects such as dams, levees, dikes, and other flood control measures through the United ...
passed in the wake of the
Los Angeles Flood of 1938
The Los Angeles flood of 1938 was one of the largest floods in the history of Los Angeles, Orange, and Riverside Counties in southern California. The flood was caused by two Pacific storms that swept across the Los Angeles Basin in February-Ma ...
.
See also
*
Drop structure
A drop structure, also known as a grade control, sill, or weir, is a manmade structure, typically small and built on minor streams, or as part of a dam's spillway, to pass water to a lower elevation while controlling the energy and velocity of the ...
*
Urban runoff
Urban runoff is surface runoff of rainwater, landscape irrigation, and car washing created by urbanization. Impervious surfaces (roads, parking lots and sidewalks) are constructed during land development. During rain , storms and other precip ...
*
Weir
A weir or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. Weirs are also used to control the flow of water for outlets of l ...
*
Levee
External links
LA River Flood Control Channel
Flood control
Environmental engineering
Rivers
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