Arroyo (creek)
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An arroyo (literally river in Spanish), also called a wash or draw, is a usually dry creek bed or gulch that temporarily fills with water after a heavy rain, or seasonally.[1] As such, the term is similar to the word wadi. Arroyos can be natural or man-made. The term usually applies to a mountainous desert environment.
The Doña Ana County, New Mexico Drainage Ordinance defines an arroyo as "a watercourse that conducts an intermittent or ephemeral flow, providing primary drainage for an area of land of forty acres or larger; or a watercourse which would be expected to flow in excess of one hundred cubic feet per second as the result of a 100 year storm event."
A good example of man-made arroyos can be found in Albuquerque, New Mexico. There are several miles of open-air concrete drainage channels that eventually drain into the main tributary known as the North Diversion Channel that discharges to the Rio Grande upstream of the city. After the completion of the San Juan Project Water Treatment Plant, part of that river flow in excess of that needed for silvery minnow habitat will become part of the city's water supply. Because of the danger of flash flooding signs are posted warning people to keep out, but ditch rescues are a yearly occurrence.
Research has been conducted in the hydrological modeling relative to arroyos.[2]
Man-made arroyos pose a problem for farmers. In areas marginally suited for agriculture, farmers often rely on channels and ditches for the distribution of water. Flash flooding can cause the cutting of deep arroyos and deposition of sediment on flooded lands. This lowers the groundwater level of the surrounding area, making it unsuitable for agriculture. Lowering a shallow water table in river valleys in desert areas however reduces salt and alkali in the topsoil, making it suitable for irrigated farming.
Although not technically an arroyo, the Los Angeles River is a more famous example of this open drainage system.