Waste load reallocation in river–reservoir systems: simulation–optimization approach

Temporal changes in system’s topology and/or socioeconomic criteria may force the authorities to enforce waste load reallocation strategies to sustain water quality standards in a receiving body. This paper proposes a simulation–optimization model to tackle the challenging waste load reallocation in a river–reservoir system. This study links a 2-dimensional process-based water quality simulation model and a surrogate data-driven model with an efficient optimization algorithm to structure a systematic approach and methodology for reallocation of waste loads in a river–reservoir system. Long response time of the reservoir is accounted for by the continuous and long-term simulation of the system for identification of the vulnerable conditions and their consequences. The proposed methodology is particularly suitable for high-dimensional river–reservoir operation optimization with water quality–quantity objectives. To reduce the computational burden, we substitute the simulation model with a surrogate model in an online-dynamically refined routine. The optimum waste load reallocation strategies, for prior and after dam construction, are compared, and their impacts on waste allocation are discussed.