Effects of Change in Hydrological Conditions on Water Quality inReservoir of Ilam Dam

The assessment of water quality in reservoirs is essential because reservoirs are often one of the main sources of water for human consumption and irrigation. In this paper، a two-dimensional، laterally averaged CE-QUAL-W2 model was used to simulate the water surface elevation، water temperature، and water quality parameters such as dissolved oxygen and nutrients in the Ilam dam reservoir. After simulating the water level، the temperature and dissolved oxygen were respectively simulated with an average absolute error 0. 76°C and 1. 41mg/L during the calibration period and 1. 18°C and 1. 18 mg/l during the verification period. The model results showed relatively good agreement between the measured and simulated data. After model calibration and validation، in order to investigate the hydrological changes on reservoir water quality، two inflow scenarios were simulated based on the dry and normal years. The results of the dry year indicated a six-month stratification period from April to September. Due to increase of water retention time in the dry years، Chlorophyll A concentrations increased in summer so that the reservoir conditions changed from mesotrophic to eutrophic. A similar pattern was observed between the temperature and dissolved oxygen profiles. In the normal year، stratification period included seven months from April to October. Due to decrease of water retention time in reservoir in the normal year، Chlorophyll A concentrations decreased in summer so that the reservoir conditions changed from mesotrophic to oligotrophic condition.