Modelling the effects of joint operations of water transfer project and lake sluice on circulation and water quality of a large shallow lake

Large-scale water conservancy projects are constructed worldwide to mitigate water shortage problems in lakes and/or to improve water quality. However, it is unclear how a lake's ecosystem responds to the joint operations of multiple projects. In this study, we take a first step towards investigating the influence of joint operations involving water transfer and lake sluice projects on current patterns and water quality of Lake Chaohu in China. A coupled 3-D hydrodynamic and biochemical model referred to as an EcoLake was configured and validated. Multiple operation scenarios from the eastern and western routines of the Yangtze River to the Lake Chaohu water transfer project (YCWTP) and the Chaohu Sluice (CS) were generated, based on 'real' water quality and hydrological processes during a water transfer experiment carried out from 15 July to 8 August 2017. The EcoLake model successfully captured the current patterns at most monitoring sites. Numerical experiment results suggest that the operations of YCWTP led to an acceleration of up to 0.90 cm/s in the lake-wide current speed. The joint operations of YCWTP and CS tend to decrease the nearshore current speed and increase the offshore current speed. The effects of the different operation strategies vary considerably among water quality parameters and lake basins. The effects are more evident for the central and eastern basins in terms of both current speed and water quality. YCWTP potentially help decrease the chlorophyll-a (Chla) concentration during the water transfer processing, but the benefits diminish gradually in the following two months. In contrast, when the YCWTP and CS are operated jointly, Chla concentrations tend to increase during the first five to six days in the central and eastern basins, then decrease continuously until mid-August. From then on, the Chla concentrations remain at stable levels throughout the rest of the simulation. This study provides important guidance for optimal operations of water conservancy projects in Lake Chaohu.