Optimization of Multi-Reservoir Flood Control Operating Rules: A Case Study for the Chaobai River Basin in China

Reservoirs are susceptible to interference from inter-basin water transfer projects intended to relieve serious water shortages. The Central Route of the South-to-North Water Division Project in China has altered the hydrological conditions and water storage status of the terminal reservoir, the Miyun Reservoir, thereby affecting the flood control reliability in the Chaobai River Basin. In this study, a dual-objective five-reservoir operation model was developed, in which reservoir releases are obtained through piecewise linear operating rules. The model considers the flooding risks both downstream of the basin and in the Miyun reservoir area. A parameterization-simulation-optimization approach was employed to obtain the Pareto-optimal front, providing decision-makers with a list of optimal rule parameters to select and match their own risk preferences. All optimized rules could ensure safe operation during the designed floods to be expected once (or more than once) every thousand years. In contrast, the current flood operation schemes largely ignore the water transfer between basins but primarily concentrate on storing water from floods. Thus, the Miyun Reservoir, whose design return period is 1000 years, can easily become filled during a 100-year flood, impeding the system's flood control capacity. Compared to the operating rule optimized in this study, the current schemes result in a 10.5% higher upstream inundation loss and an unsatisfactory 17 million CNY of equivalent water transfer loss.