Surface and ground waters are scarce in semi-arid and arid regions. Therefore, attempts are made in these regions to collect and preserve rainwater to the maximum possible extent. In arid and semi-arid areas where rainfall pattern is irregular, much of these are lost as surface runoff, and as a result, there is a scarcity of water which results to risk for human beings. Under such conditions, the water harvesting is a substitute and is most important. Water harvesting is a collection of rain and runoff water by using different types of storage structures such as weirs or small dams, primarily for humans, irrigation and livestock consumption. Four sites of special hydrological and geomorphologic characteristics have been chosen and pointed in the drainage map of the studied area for the construction of storage structures on the main channel to impound and harvested rain and runoff water, forming surface storage reservoir and a model of the weir has been designed based on Bligh theory. Geometrical survey has been done for the four sites of the recommended weirs construction, to study and understand the probable size of the reservoir formed by harvested water. The geometrical dimension of each reservoir and bulk volume of water stored behind the weir of the four sites had been measured and calculated. The total volume of storage water behind the dams of the four sites could reach 150000000 m3. The mean output surface runoff of wadi al-kassab basin, for a rainfall storm of 3.22 mm/h intensity of 14.65 h period, has been calculated and is found to be 8.87 m3/s.
Key words: Rain water harvesting, storage structures, reservoir, surface runoff, drainage system.
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