Multi-objective optimization to manage reservoir water quality and quantity via selective withdrawal and watershed control

A new approach was presented to manage simultaneously reservoir outflow quantity and quality. Two strategies were used to control reservoir outflow quality: (1) reservoir inflow control with Best Management Practices (BMPs) in the watershed and (2) outflow management by reservoir operational strategy. Soil and Water Assessment Tool (SWAT) model was linked to a reservoir water quality simulation model (CE-QUAL-W2), the linked watershed-reservoir model was coupled with Multi-Objective Particle Swarm Optimization algorithm (MOPSO) to find the best set of decisions to optimize the reservoir outflow quality and quantity objectives. The approach was applied to Alavian reservoir and its watershed, in Iran, for a 6-year time horizon. The results show the proposed approach could reduce reservoir outflow phosphorus concentration while increasing downstream water supply. The implemented BMPs outperformed the reservoir operational strategy in terms of reservoir outflow quality reducing outflow phosphorus concentration up to 45% comparing with current conditions. Among the four applied BMPs, filter strips had more effect on reducing nutrient loads.