Sustainable Management of Reservoir Water Quality and Quantity Through Reservoir Operational Strategy and Watershed Control Strategies

Water quality impairment is a serious health concern for reservoirs; two strategies were used to control reservoir outflow quality: (1) control of reservoir inflows with implementation of structural best management practices (BMPs) at the watershed, and (2) management of reservoir outflows by reservoir operational strategy. To assess the effectiveness of two strategies on reservoir water quality, an extension of the Sustainability Index (SI) for water quality was defined. Additionally, a quantity-based SI for supplying of downstream water demands was defined. So il and water assessment tool was linked to a reservoir simulation model (CE-QUAL-W2), and coupled with multi-objective particle swarm optimization algorithm. The proposed model was applied in four different scenarios on Alavian reservoir and its watershed, in Iran, during a 6-year time horizon. Four BMPs, named detention ponds, filter strips, parallel terraces, and grade stabilization structures, were used. The results indicated that application of the proposed approach provides the best set of solutions for decision makers to manage outflow quality and quantity. Whenever the watershed management strategy is not possible/practical, the reservoir operational strategy in selective withdrawal scheme would improve reservoir outflow quality by up to 77%. On the other hand, when the reservoir downstream water demand satisfaction is necessary, the watershed management strategy, or selective withdrawal scheme would be improved when the reservoir outflow dissolved oxygen concentration SI by up to 30 and 52%, respectively. Among the applied BMPs, filter strip had more effect on reducing nutrient loads and it was the most chosen BMP.