Multi-objective water-sediment optimal operation of cascade reservoirs in the Yellow River Basin

Sediment deposition in sediment-laden rivers seriously restricts the normal operation of reservoirs and the socioeconomic development of the basin. Studying the water-sediment joint operation of cascade reservoirs is important for extending the life of reservoirs. The objective of this paper is to provide a sound scientific approach to optimize the water-sediment operation of cascade reservoirs considering multiple objectives. An innovative time-dependent objective function was proposed, in which the sediment release efficiency equations suitable for different sediment inflow scenarios were introduced for sediment flushing calculation. The Sanmenxia (SMX) and Xiaolangdi (XLD) Reservoirs on the Yellow River were selected as case studies to test the proposed method. First, two typical data sets, including high and low flow magnitudes, were taken as model input scenarios. Second, the multiple-objective joint optimal operation model was established. Discrete differential dynamic programming (DDDP) was used to solve the operation model. Finally, the operation results based on different weights were discussed. Results indicate that, for sediment-laden rivers, such as the Yellow River, the proposed model can achieve the maximization of the hydropower generation and sediment flushing benefits for the high flow and low flow series. And the proposed model can guarantee the flood control, ice flood control, water supply, and ecological objectives. For the SMX-XLD cascade reservoirs, when the water resources are abundant, the hydropower generation reservoirs increase significantly. And in flood season, the weight for sediment flushing can be increased appropriately to improve the comprehensive benefits of the reservoir in sediment-laden rivers. In addition, the time-dependent objective function can provide a reference for the multi-objective optimal operation of cascade reservoirs. The optimal operation model provides a model basis for the water-sediment-energy joint operation of large-scale reservoir group in the sediment-laden basins.