Transcription of Chapter 5 SURFACE WATER - WHO
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Chapter 5 SURFACE WATER - WHO
Chapter 5 SURFACE WATER SURFACE WATER originates mostly from rainfall and is a mixture of SURFACE run-off and ground WATER . It includes larges rivers, ponds and lakes, and the small upland streams which may originate from springs and collect the run-off from the watersheds. The quantity of run-off depends upon a large number of factors, the most important of which are the amount and intensity of rainfall, the climate and vegetation and, also, the geological, geographi- cal, and topographical features of the area under consideration. It varies widely, from about 20 % in arid and sandy areas where the rainfall is scarce to more than 50% in rocky regions in which the annual rainfall is heavy.
annual losses by evaporation alone may be as high as 178 cm (70 in.). Provision should also be made for de-silting facilities through periodic flushing of the reservoirs. It is recommended that the depth of water in a small reservoir at the deeper end should be not less than 1.8 m (6 ft).
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