Study on year-end water level optimization of multi-year regulation reservoirs under uncertain inflow conditions

The year-end water level of multi-year regulation reservoirs is key in harmonizing current-year and future power generation benefits. Taking the multi-year regulating Longyangxia Reservoir and Liujiaxia Reservoir in the upper reaches of the Yellow River as a case study, a multi-objective stochastic optimization model for cascade reservoirs considering the uncertain inflow was established. Then, the best scheme from the Pareto solution set of the current-year power output and the year-end water level was obtained based on the TOPSIS decision-making method. Finally, the effects of runoff frequency and initial water level on year-end water level and power output were investigated, and the reliability of year-end expected water level on multi-year power output was verified. The results show a competitive relationship between the year-end expected water level of Longyangxia Reservoir and the annual expected power output of Longyangxia Reservoir and Liujiaxia Reservoir under the uncertainty inflow scenarios. The lower the frequency of runoff and the higher the year-start water level to Longyangxia Reservoir, the higher the year-end water level of Longyangxia and the higher the power output of Longyangxia Reservoir and Liujiaxia Reservoirs. The optimal year-end water level of Longyangxia Reservoir calculated by the stochastic optimization model should be controlled between 2580~2590 meters, which greatly reduces the range of year-end water level under the current dispatching mode. When the optimal year-end expected water level obtained by stochastic optimization is used to control Longyangxia Reservoir, the reliability of guaranteeing the power generation benefit is above 98%.

Keywords: multi-year regulating reservoir; year-end water level; uncertainty; stochastic optimal operation