Optimal reservoir operation based on hydrological and hydraulic methods incorporating the multiple water replenishment process

Abstract

A reservoir usually functions as multi-objectives. Different objective has various requirement in water volume and temporals process due to the fact that some objectives require different constant base flow in different months and some objectives demand ephemeral flood pulse. How to balance reservoir functioning and water allocation of multiple targets has become increasingly significant at present. In the past, the multi-objectives operation was usually designed based on water quantity balance, neglecting the coupling with the hydrodynamic process. Sometimes the coupling is so important for some ecological factors and the neglecting may result in failure to meet the hydraulic requirements of the downstream ecological environment. By coupling the hydrologic and hydrodynamic methods, an integrated reservoir model for multiple-objectives optimal operation was presented including water balance model, one-dimensional unsteady flow model, two-dimensional depth-averaged model and ecological baseflow model. The different process demands include water allocation at the dam site, unsteady flow process at different sections downstream the dam site. Taking a reservoir in northern China as an example, the minimum change of the hydrological process in the river mouth section was set as the objective function for the optimal operation. Regarding the demand for aquatic organisms, the low and high baseflow schemes were suggested by the comprehensive use of different ecological flow methods (the Tennant method, the flow duration curve method and the wetted perimeter method). According to the ecological flooding during the wetland water supplement, the Wetland Water Replenishment Model was applied to calculate the replenishment process under different flood cases. The Lake Water Replenishment Model was used for flow scheduling of the downstream lake. Regarding the wet years, the objective functions at the river mouth section were 16.0% with the low baseflow scheme and 15.5% with the high baseflow scheme, whereas for the dry years, it is 18.2% with the low baseflow scheme and 15.5% with the high baseflow scheme. Comparison showed that the high baseflow scheme was optimal for the reservoir operation. The result could provide a reference for decision-makers in reservoir scheduling design. It shows that the coupling of hydraulic and hydrological methods could provide a more reliable basis for reservoir optimal operation.