Water Quality Simulation of Karkhe Dam Reservoir Outflow by Selecting Appropriate Discharge Level

Nowadays, human is faced with water scarcity and many more problems which are due to population growth and industrial development. Therefore, many people around the world tried to overcome water shortage by dam construction and storing surface water when water is not available naturally. However, such activities together with climate changes may have negative impacts on inflow water quality and quantity.  Nevertheless, the amount of evaporation from surface of water and thermal stratification may also change water characteristics (qualitatively, physically, chemically and biologically). Knowing how water quality changes in long-term period is important. Long-term study of water quality conditions in different layers of the reservoir could help determine the best layer for water intake and also to improve reservoir conditions. In this study, Karkheh Dam was selected as the case study. Using meteorological and river discharges records as well as water quality parameters such as temperature and dissolved oxygen of Karkheh River in different level for a period of 40. For simulation of reservoir behavior, the two-dimensional CE-QUAL-W2 model was used. With the help of this mathematical model the temperature and dissolved oxygen profiles were obtained. The results indicated a strong stratification period from mid of June to late of October in all years. However, a relatively weak stratification was obtained for April, May and November. In addition, in February thermal mixing phenomenon occurs, because, dissolved oxygen is strongly related to thermal stratification and fluctuates vertically according to temperature associated to each layer. Finally, results showed that the best level for water intake during strong stratification was between 170^m to 180^m. Otherwise, there is no limitation for water intake since stratification is not significant.