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Arroyo (watercourse)

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An arroyo is a dry watercourse that flows only seasonally or temporarily.

Las Cruces Arroyo
Las Cruces Arroyo

These landforms are common in xeric and desert climates. They are defined by their intermittent or ephemeral flow. This means the water does not flow constantly. Instead, it fills after sufficient rain falls. In the United States, the desert dry wash biome is restricted to these arroyos. They are vital because they provide a water source to desert animals.

Sonoran Desert Arroyo Sahuarita Arizona 2013
Sonoran Desert Arroyo Sahuarita Arizona 2013

Natural arroyos are created through a process known as arroyo-cutting. This process occurs in arid regions like New Mexico. During heavy rains, rivers can enlarge significantly. The moving water cuts into the surrounding rock. This action creates deep ravines that remain dry under normal weather conditions. Some researchers argue that excessively stormy periods are the primary cause of this cutting. However, others suggest that long-term climate changes must also be considered. These environmental shifts can change how the land reacts to water.

GobiFlood
GobiFlood

Other human activities can also speed up the process of arroyo-cutting. Throughout the 20th century, overgrazing by livestock changed the landscape. Animals removed vast amounts of surface vegetation. Without plants, there is less ground infiltration of precipitation. This means the soil cannot soak up the rain as well. Instead, it creates increased runoff. This runoff increases the speed and energy of high-flow rain events. When coupled with groundwater pumping, these factors increase downcutting in arroyos. This deep cutting can cause serious problems for farming. It can lower the groundwater level in the surrounding area. This makes the land unsuitable for agriculture. However, a shallow water table in some valleys can actually reduce saline seeping. This can make the topsoil better for irrigated farming.

Arroyos are not always natural landforms. They can also be constructed flood control channels. In agricultural areas that need irrigation, farmers use man-made channels. These are sometimes called acequias, zanjas, or aqueduct channels. They are used for the distribution of water. In urban areas, arroyos often serve different purposes. Many communities use them as parks or recreational locations. These parks often feature linear multi-use trails for bicycles, pedestrians, and horses.

Billy Rogers Arroyo Park
Billy Rogers Arroyo Park

Constructed arroyos can be quite large and complex. In Albuquerque, New Mexico, there are several miles of open-air concrete-lined drainage channels. These channels drain an area into the North Diversion Channel. This channel is a tributary of the Rio Grande. The Rio Grande's flow can exceed what is needed for the silvery minnow habitat. This extra water is then available for municipal water supply diversion. While these channels help manage water, they carry significant risks.

Flash flooding is a major danger in both natural and constructed arroyos. A dry channel can turn into a roaring river in under two minutes. This can happen even if there is no rain in the local area. Because of this, signs are often posted to warn people to keep out. The danger is very real in urban settings. From 2017 to 2021, twelve people were killed by sudden flooding in Albuquerque's drainage channels. This happened despite most residents being aware of the risks. In Southern California, the Arroyo Seco and the Los Angeles River are famous examples. These were once natural seasonal watercourses that became constructed drainage systems.

Different cultures have unique names for these dry watercourses. The word arroyo comes from the Spanish word for brook. In North Africa and Western Asia, they are called wadis. In the Gobi Desert, they are referred to as chapp. In the Kalahari, they are called laagate. In South Africa, they are known as donga. In India, they are called nullah. In Italy, the term is fiumare. In England, they are simply called dry valleys. These names show how common these landforms are across the globe.

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🖼️ Images & Media (4)
File:Las Cruces Arroyo.jpg
Las Cruces Arroyo.jpg
File:Sonoran Desert Arroyo Sahuarita Arizona 2013.jpg
Sonoran Desert Arroyo Sahuarita Arizona 2013.jpg
File:GobiFlood.JPG
GobiFlood.JPG
File:Billy Rogers Arroyo Park.jpg
Billy Rogers Arroyo Park.jpg
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