Hydrological Action
Modern English usage differentiates a wadi from another canyon or wash by the action and prevalence of water. Wadis, as drainage courses, are formed by water, but are distinguished from river valleys or gullies in that surface water is intermittent or ephemeral. Wadis, cut by stream in a desert environment, generally are dry year round except after a rain. The desert environment is characterized by a sudden but infrequent heavy rainfall often resulting in flash floods. Crossing wadis at certain times of the year can be dangerous because of unexpected flash floods. Such flash floods cause several deaths each year in North America and many Middle Eastern countries.
Wadis tend to be associated with centers of human population because sub-surface water is sometimes available in them. Nomadic and pastoral desert peoples will rely on seasonal vegetation found in wadis, even in regions as dry as the Sahara, as they travel in complex transhumance routes.
The centrality of wadis to water - and human life - in desert environments gave birth to the distinct sub-field of "Wadi Hydrology" in the 1990s.
Read more about this topic: Wadi
Famous quotes containing the word action:
“There has never been in history another such culture as the Western civilization M a culture which has practiced the belief that the physical and social environment of man is subject to rational manipulation and that history is subject to the will and action of man; whereas central to the traditional cultures of the rivals of Western civilization, those of Africa and Asia, is a belief that it is environment that dominates man.”
—Ishmael Reed (b. 1938)