Optimisation plan for ecological water replenishment in water-deficient rivers – a case study of Yongding River, China

In view of the subjectivity and limitations of scenario setting, as well as the time-consuming nature of computations and difficulty of obtaining global optimal solutions, this paper proposes an ecological water replenishment optimisation model by coupling a hydrodynamic model and an optimisation algorithm. The proposed model aims to obtain the most optimal water replenishment plan to meet specific objectives, by using the hydrodynamic model to obtain relationship curves between various hydrodynamic indicators (e.g. water level, discharge, flow velocity) and different ecological water replenishment flows, and combining these curves with the optimisation algorithm. The model was applied to the Beijing section of the Yongding River. The minimum water replenishment flow at the cross section of Guanting Reservoir is 30 m3/s, to meet the goal of full-channel waterflow connectivity in the Beijing section of Yongding River. A comprehensive optimal ecological water replenishment plan is proposed under the consideration of three objectives in the best state possible, i.e. the maximum guaranteed rate of suitable ecological flow, the highest monthly average ecological water replenishment efficiency and the maximum guaranteed rate of full-channel waterflow connectivity. This study provides novel insights and methodologies for the formulation of ecological water replenishment plans for water-deficient rivers.