Water harvesting in the arid countries: The “widan” (rivers) in Algeria and their management

Algeria, a large country which extend from parallel 18° to parallel 38° and as long as 2000 km. Algeria’s climates are varied but have a tendancy to dryness and sporadic rains which cause devastating flooding of the word “oued” (plural widan) means a river which:-is a temporarly dry during part to the year. A bed which stays mostly dry and floods once a year -and in some cases once in ten years. Sometimes it’s a “fossil valley” from a large saharian fluvial artery which bears in it! and/or in it’s vegetation, the marks of big rivers from the quaternary era-and last, a saharian river where the watershed moves according flooding periods; the bed of the river may rise because of the sand deposited by floods. It is said to shift its course (in french: divaguer). Hundreds of this kind ofrivers exist in the Sahara. A past from the known cases of Watersheds in the Northern part in Algeria, which can be improved and arranged by introducing sheam correction, benches and the planting of trees. Other examples, in others parts of the country can be mentioned. “Madjan” on the oued Mina (North West of the country), which is a pocked digged down a slope in order to collect rain waters. “Rasfa” which is used on the widan which has a sharp slope from the Saharian the south and which keeps water from evaporating. “Mahder” alluvial cone, on the High Plateaux, which goos in the “sebkha” or “chott” (depression which collect briny water). “Sed” and “Chebka” which are dams built in the area of M’zab, in order to irrigate palm groves and to supply the underground water reservoirs; the system to water haversting in the area of M’zab is very ingenious. During these last decades of mastering deep diggings and using to the profusion fossil water which renew it self only after millenaries, all this must remind us that in this regions, water is something very rare, and we must preserve it and used with parcimony. Some new innovations like lateral drilling in the “ergs” and sand bottoms, in the Sahara, building “barrages” in the North and also in the Hoggar mountains, must be done. In conclusion, in the light of modern knowledge (remote sensing, G.I.S.) as well as new materials associated with ingenious traditional practices we can hope, taking into account the growth of the population and the droughtness and desertification, that real progress willlead us to resolve the serious problems of shortage in water, in order to safeguard linked resources. Water, soil, vegetation for the future of the balance of Nature.