Arroyo (watercourse)

For other uses, seeArroyo (disambiguation).

Las CrucesArroyo inNew Mexico

An arroyo in theSonoran DesertofArizona

Aflash floodhits a dry streambed in theGobi Desert

Aerial view ofEl Paso'sArroyo Park, or Billy Rogers Arroyo, providing a path for runoff of rain on theFranklin Mountainsbehind

Anarroyo(/əˈrɔɪoʊ/), fromSpanisharroyo(Spanish:[aˈroʝo],"brook" ), also called awash,is a drywatercoursethat temporarily or seasonally fills and flows after sufficientrain.Flash floodsare common in arroyos followingthunderstorms.

Similar landforms are referred to aswadi(in North Africa and Western Asia),ramblain Spain,chappin the Gobi,laagatein the Kalahari,dongain South Africa,nullahin India,fiumarein Italy, anddry valleyin England.

Thedesert dry washbiomeis restricted to the arroyos of the southwestern United States. Arroyos provide a water source to desert animals.

Types and processes

Arroyos can be naturalfluviallandformsor constructedflood control channels.The term usually applies to aslopedormountainousterrain inxericanddesertclimates. In addition: in many rural communities arroyos are also the principal transportation routes; and in many urban communities arroyos are also parks and recreational locations, often with linear multi-use bicycle, pedestrian, and equestrian trails.Flash floodingcan cause the deep arroyos or deposition of sediment on flooded lands. This can lower thegroundwaterlevel of the surrounding area, making it unsuitable for agriculture. However a shallow water table lowered in desert arroyovalleyscan reducesaline seepingandalkalideposits in thetopsoil,making it suitable for irrigatedfarming.

Natural

In theU.S. stateNew Mexico,theDoña Ana CountyDrainage Ordinance defines an arroyo as "awatercoursethat conducts an intermittent or ephemeral flow, providing primary drainage for an area of land of 40 acres (160,000 m²) 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 yearstormevent. "Research has been conducted in thehydrological modelingrelative to arroyos. Natural arroyos are made through the process known as arroyo-cutting. This occurs in arid regions such as New Mexico, where heavy rains can lead to enlargement of rivers cutting into surrounding rock creating ravines which are dry under normal weather conditions. It is argued, however, whether these excessively stormy periods are the sole cause of arroyo-cutting as other factors such as long-term climate changes must also be taken into account.Further, overgrazing by livestock throughout the 20th century and today has removed vast amounts of surface vegetation which decreases ground infiltration of precipitation and increased runoff, increasing speed and energy of high flow rain events. Coupled with groundwater pumping this increases downcutting in arroyos as well. Arroyo cutting which occurred in the 1900s in the southwestern United States caused serious farming issues such as a lowered water table and the destruction of agriculture lands.

Constructed

Inagriculturalareas in climates needing irrigation,farmerstraditionally relied on small constructed arroyos,acequias,zanjasoraqueductchannels and ditches for the distribution of water.

An example of larger constructed arroyos is inAlbuquerque, New Mexico.There are several miles of open-airconcretelined drainage channels that drain an area into the main North Diversion Channel, atributaryof theRio Grandejoining upstream of Albuquerque. After the San Juan Project Water Treatment Plant here, the Rio Grande's flow exceeding that needed for the river'ssilvery minnowhabitatis available for municipal water supply diversion. Signs are posted at the constructed arroyos warning to keep out due to danger offlash flooding.

TheArroyo SecoandLos Angeles Riverare more famous examples inSouthern Californiaof former natural arroyo seasonal watercourses that became constructed open drainage system arroyos.

See also

• Billabong
• Draw
• Wadi