Abstract:Reservoirs have to lower their water level in many cases

such as dam overhaul. To quantitatively study the water quality during the process

the method of numerical simulation was taken in this paper. Firstly

a horizontal two-dimensional unsteady dynamic model and a water quality model for large-scale reservoir were developed

and verified by the field data from a typical reservoir. Then the models were used to predict the impact of water-level decline on the water quality during the dam repair period. The simulation results showed that the concentration of pollution factors increased with the lowering water-level

and decreased with the rising water-level. It was clear that the water quality of reservoir was negatively affected by lowered water-level operation. To reduce the negative impact

the quantity of pollutant entering into the reservoir should be controlled strictly. In addition

water-environmental management and monitoring should be strengthened. The simulation results in this paper have theoretical and practical significance for evaluating water quality impact of lowered water-level operation and water quality protection of reservoirs.