Multiobjective Reservoir Operation for Water Quality Optimization

Abstract

Total dissolved solids (TDS) may enter reservoirs at high concentrations during flooding events. The release of TDS from reservoirs depends on water quality stratification within them. This paper presents an approach for the optimal operation of a reservoir with two objectives: (1) the minimization of TDS in reservoir releases, and (2) the minimization of the temperature difference between inflow to the reservoir and released water from the reservoir. The Karaj reservoir in Iran is operated to optimize these two objectives. The reservoir has two water outlets with an elevation difference equal to 40 m. Water quality and 2D hydrodynamic modeling is carried out with the model CE-QUAL-W2, which is coupled with the nondominated sorting genetic algorithm-II (NSGA-II) to produce a simulation-optimization method. The simulation-optimization method is applied to the Karaj reservoir operation under four scenarios (seasons). The paper’s results indicate enhanced reservoir operation with two-outlet releases compared with one-outlet releases. Specifically, the TDS in reservoir releases and the temperature difference between inflow into and released water from the reservoir achieved with two-outlet operation are 11.81 and 4.02% lower than those achieved with single-outlet operation, respectively.