Flood control channel
Encyclopedia
Flood
A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...
is actually present) open-air channels that extend a ways below the street levels of some larger cities, so that if and when a flood occurs, the flood will run into the channels, and proceed to be drained to the proper body of water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
. Flood control channels are sometimes built on the former courses of waterways as a way to reduce flooding. They are not to be confused with watercourses which are simply confined between levee
Levee
A levee, levée, dike , embankment, floodbank or stopbank is an elongated naturally occurring ridge or artificially constructed fill or wall, which regulates water levels...
s. These structures may be made entirely of concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
, with concrete sides and an exposed bottom, with riprap
Riprap
Riprap — also known as rip rap, rubble, shot rock or rock armour or "Rip-rap" — is rock or other material used to armor shorelines, streambeds, bridge abutments, pilings and other shoreline structures against scour, water or ice erosion.It is made from a variety of rock types, commonly granite or...
sides and an exposed bottom, or completely unlined. They often contain grade control sills or weir
Weir
A weir is a small overflow dam used to alter the flow characteristics of a river or stream. In most cases weirs take the form of a barrier across the river that causes water to pool behind the structure , but allows water to flow over the top...
s to prevent erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
and maintain a level streambed. By definition, flood control channels range from the size of a street gutter
Street gutter
A street gutter is a depression running parallel to a road designed to collect rainwater flowing along the street and divert it into a storm drain. Where a curbstone is present, a gutter may simply be formed by the convergence of the road surface and the vertical face of the sidewalk; otherwise, a...
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 which contains many of these channels is Los Angeles
Los Ángeles
Los Ángeles is the capital of the province of Biobío, in the commune of the same name, in Region VIII , in the center-south of Chile. It is located between the Laja and Biobío rivers. The population is 123,445 inhabitants...
, as they became mandatory with the passage of the Flood Control Act of 1941
Flood Control Act of 1941
The Flood Control Act of 1941 was an Act of the United States Congress signed into law by President Franklin Delano Roosevelt that authorized civil engineering projects such as dams, levees, dikes, and other flood control measures through the United States Army Corps of Engineers and other Federal...
, passed in the wake of the Los Angeles Flood of 1938
Los Angeles Flood of 1938
The Los Angeles Flood of 1938 or 1938 Los Angeles flood was a major flooding event that was responsible for inundating much of Los Angeles, Orange, and Riverside counties, California, during early 1938...
.