Methodology that improves water utilization and hydropower generation without increasing flood risk in mega cascade reservoirs

The optimal dynamic operating flood limiting water levels (FLWLs) of cascade reservoirs are the critical driver for satisfactorily compromise flood control and hydropower needs. We proposed an adept multi-objective dynamic operating FLWLs methodology based on an evolutionary algorithm with a modified aggregation-decomposition method for optimal operation of three cascade reservoirs. The modified aggregation-decomposition method is used to identify the upper boundary of FLWLs of cascade reservoirs by extending the flood routing process for multiple time-delay inflows - single outflow patterns. The non-dominated sorting genetic algorithm-II (NSGA-II) was then used to efficiently counterbalance the risks of flood control and hydropower generation in the dynamic operation of cascade reservoirs. Three mega cascade reservoirs in the Yangtze River basin of China are selected as a case study. The optimal solutions of cascade reservoirs operation are compared with those of single reservoir operation. The results indicate (1) the minimum power generation risk solution could largely improve the water utilization and hydropower generation by 5.43% and 6.48% (3.71billion kW·h/year), respectively, as well as mitigate the power generation risk by 5.8% with a small cost of increasing flood risk by 0.3%; and (2) the minimum flood control risk solution could reduce the flood risk and power generation risk by 0.4% and 0.7%, respectively, and enhance the water utilization and hydropower generation by 0.64% and 2.18%, respectively. We demonstrate the proposed methodology could largely improve the water utilization and hydropower generation without increasing flood risk. Moreover the widespread Pareto front solutions allow decision-makers to determine the best compromising solution with counterbalanced risks of flood control and hydropower generation. The hydropower generation indeed would provide extensive economic benefits and contribute to growth in social well-being with low environmental impact. Thus, the proposed methodology can be used as a basis of analysis for a large number of constructed and under-constructed mega dams in upper Yangtze river to overcome the bottleneck of new energy development and water resources sustainability management.