ABSTRACT
Water is an essential natural resource for the sustenance of vegetal, animal and human life on the Earth. In the world, the water volume is estimated to be 1.45 × 109 km3 in total, of which 94% is sea water and only 6% is land water. Romania is an European country with limited water resources. In South Africa, the average annual rainfall is about 500 mm, well below the world average of 860 mm; 65% of the country receives less than 500 mm of rain annually and 21% receives less than 200 mm. The water stored in reservoirs is not stagnant but is in a state of continuous movement or circulation. The water circulation in reservoirs generally is non-uniform, gradually varied flow and is multi-directionally developed. The permanent water movements in reservoirs develop as internal and/or shore currents, being mainly caused by the direct inflows of the main river and its tributaries into the reservoir basin.
