Multi-objective and multi-scheme research on water and sediment regulation potential of reservoirs in the upper Yellow River

The problems of the deteriorating relation between water and sediment, and the escalating conflict between water supply and demand in the upper Yellow River (YR), need to be addressed. Reservoirs of Longyangxia, Liujiaxia, and Heishanxia (Long–Liu–Hei) in the upper YR are taken as the research object, and a multi-objective, water–sediment optimal operation model for cascade reservoirs Long–Liu–Hei has been developed. This operation model considers the comprehensive requirements of water supply, power generation, flood control, and especially, water and sediment regulation. The improved Non-dominated Sorting Genetic Algorithms (NSGA-II) method is used to demonstrate the water and sediment regulation potential of three scenario schemes under long-term conditions, and the adjustable water allocation of four schemes under typical year conditions are calculated. It is recommended to use the mode of generating hydropower depending on the available water amount as the best operating mode under the conditions of a long time series and for typical years. This recommended operation mode has verified the rationality and accuracy of the reservoir operations model. At the same time, compared with the calculation results for water and sediment regulation after the construction of the Heishanxia, the current research indicates: (1) Under the recommended model, the potential for water and sediment regulation under the long-term series and typical years is once every four years. (2) Inter-basin water transfer greatly improves the cascade power generation. When the adjustable water volume is converted into the controlled volume for water and sediment regulation, the intensity frequency of water and sediment regulation of cascade reservoirs are improved. (3) With the intensification of the contradiction between the supply of and demand for water resources in the upper YR in the future, the amount of transferable water exhibits a decreasing trend, and the regulation of water and sediment in the upper YR is facing huge challenges. (4) Through joint operation with the Longyangxia and Liujiaxia reservoirs (Long–Liu), Heishanxia will play an important role in the regulation and control of power generation, water supply, flood control, and ice prevention in the upper YR. The current research results can provide a theoretical basis and technical support for water and sediment regulation in the YR basin.