An arroyo is a dry creek or stream bed that temporarily or seasonally fills with water after heavy rainfalls, commonly found in arid and semi-arid regions. Arroyos can be sites of flash flooding, and their presence is indicative of episodic water flow and erosion in dryland environments. They are significant in the study of desert hydrology and sediment transport.
Reference: Bull, W. B. (1997). “Discontinuous Ephemeral Streams.” Geomorphology, 19(3-4), 227-276.