Arroyos

An arroyo is a dry creek, streambed, or gulch that temporarily carries water after rainfall. The term is commonly used in arid and semi-arid regions of the Americas and other dry lands, especially in the southwestern United States and many Spanish-speaking countries. In other arid regions, a similar feature is often called a wadi.

Formation and hydrology: Arroyos form when intense rainfall produces flash floods that erode the channel and transport sediment downstream. The resulting cross section is often V-shaped and the bed may consist of rock, gravel, and accumulated sediment. Between rain events, the channel dries, though groundwater and seasonal springs can maintain flows in some cases. Sediment deposited in arroyos forms alluvial fans at their mouths.

Geomorphology and drainage: Arroyos are typically intermittent or ephemeral, with channels that may be steep and narrow or broad and braided. They are connected to larger basins and can contribute to flash flooding downstream when storms move through the watershed. In arid landscapes, their erosion continually reshapes the landscape.

Ecology and watershed role: Despite being dry much of the time, arroyos support specialized plants and animals adapted to pulse flows. They help recharge groundwater, transport nutrients, and contribute to sediment delivery to downstream rivers and wetlands.

Human interaction and safety: Urban development, mining, and deforestation can increase runoff and flood risk in arroyos. In populated areas, arroyos may be channelized or controlled with flood defenses. Management approaches include flood forecasting, land rehabilitation, revegetation, retention basins, and green infrastructure to reduce erosion and improve infiltration.