Arroyo

An arroyo is a dry creek, streambed, or gullied channel in an arid or semi-arid region that temporarily carries water after rainfall. The term is especially common in the southwestern United States and northern Mexico, where arroyos often form in desert and semi-desert landscapes. In other regions, similar features may be called gullies, washes, or wadis.

Etymology: from Spanish arroyo meaning a small stream or watercourse.

Formation: Arroyos develop through erosion by infrequent but intense runoff. Over time, the channel becomes deeply incised and wide, with steep banks and a broad, often flat bottom. They are typically dry for long periods, with flow occurring during episodic storms, sometimes resulting in flash floods that can transport large volumes of sediment and rapidly reshape the channel.

Geography and hydrology: Arroyos occur in deserts, chaparral, and dry foothill regions. They may host perennial or seasonal vegetation along their riparian margins and in some cases host groundwater-fed flows. Biodiversity can include arroyo willow, cottonwood, tamarisk in some regions, plus birds, reptiles, and invertebrates adapted to temporary waters.

Human interaction: Arroyos are often incorporated into urban and rural planning as drainage corridors. They pose flood hazards during rain events and have commonly been stabilized or channelized with check dams, concrete lining, or restoration projects to reduce erosion and restore ecological function.