Determination of the Optimal Level of Water Releases from a Reservoir to Control Water Quality

Abstract

The increase of pollution loads and of the diversity of pollutants threatening water resources calls for sophisticated management of water resources. This paper shows that the thermal stratification of water in reservoirs and the variation of its density with reservoir depth make it possible to manage sudden water-pollution events by controlling water release as a function of lake depth to minimize effects associated with the release of polluted water from reservoirs. The best outlet level of a reservoir to release polluted water is selected in this paper using the technique for order performance by similarity of ideal solution (TOPSIS). The latter is a multicriteria decision-making (MCDM) tool for managing water quality in reservoirs. The application of MCDM is illustrated with the management of reservoir releases to cope with the sudden spill of 30 m3 of methyl tertiary butyl ether (MTBE) into the Amirkabir reservoir (Iran). The CE-QUAL-W2 calibrated model is used to simulate the spreading of MTBE in the reservoir. Pollutant spreading is predicted under four seasonal pollution scenarios and one scenario considering all seasons simultaneously. This allows for the consideration of the effects of climatic and water demand conditions on reservoir water quality. This paper’s results show that the water should be released from the low-elevation gate in spring and winter and from the high-elevation gate in summer and autumn to optimally manage the sudden release of MTBE spills in the Amirkabir reservoir.