Wadi is a traditional Arabic term for a valley. The term can also refer to a wet (ephemeral) riverbed that contains water only during heavy rains.
Wadis are located on gently sloping, almost flat parts of the desert. The water that appears in them periodically leaves sediment dams on which wind-borne material then settles, forming sedimentary structures. Wadi sediments can contain a range of materials, from gravel to mud - they are the most diverse of all desert environments.
Unlike canyons, gullies, and dry riverbeds, wadis are generally dry throughout the year, except after rain. Desert environments are characterized by sudden but infrequent torrential rains, which often cause flash floods (being in a wadi during such a period can be dangerous).
