Water Temperature Regulation And Simulation Of Different Inflow In Manwan Reservoir

Manwan Hydropower Station is located in the middle reach of Lancang River,1 km downstream of Manwan Estuary at the junction of Yunxian County and Jingdong County in Western Yunnan Province,China.The upstream of Manwan Hydropower Station is Xiaowan Hydropower Station.Based on CE-QUAL-W2 model,the laterally averaged two-dimensional water temperature model of Manwan Reservoir and Manwan natural river were constructed.The laterally averaged two-dimensional water temperature model of Manwan Reservoir was calibrated by using the surface water temperature of Manwan Reservoir and the vertical water temperature monitoring data of typical sampling sites.The simulation results of outflow water temperature of Manwan Natural River and Manwan Reservoir were compared,and the evolution process of water temperature of Manwan Reservoir under different inflow and air temperature conditions was analyzed.Based on the study of water temperature evolution process of Manwan Reservoir,under the conditions of high-temperature inflow water or low-temperature inflow water,the operation scenarios of Manwan Reservoir were set.The diversion port at 949.5 m,the spillway tunnel at 970 m,and the diversion port and the spillway tunnel at the same time were selected to set different outflow scenarios,and the regulating effect of the operation mode of Manwan Reservoir on the outflow water temperature under Manwan Reservoir was studied.The main conclusions were as follows:(1)Calibration results showed that the model could accurately simulate the vertical water temperature and surface water temperature of Manwan Reservoir,among which the vertical water temperature was better.(2)In Manwan Reservoir,15 km to 60 km upstream of Manwan Dam had shallow water depth and large discharge,and there was no water temperature stratification.0 km to 14 km upstream of Manwan Dam had deep water depth,and water temperature stratification may appear there.(3)The outflow water temperature of Manwan Reservoir was higher than that of Manwan natural river in 2017 except December under the same inflow water temperature,inflow discharge and meteorological conditions.Under the condition of high air temperature from June to September,reservoir outflow water temperature increased by 0.20 ℃,0.27 ℃,0.23 ℃ and 0.20 ℃ compared with natural river.Under the extreme conditions,outflow water temperature of Manwan Reservoir was 0.42 ℃ higher than that of Manwan River.(4)In the case of high-temperature inflow water or low-temperature inflow water,water temperature stratification may occur in front of the Manwan Dam.Increasing air temperature would strengthen water temperature stratification in front of the dam,and increasing inflow discharge would weaken water temperature stratification in front of the dam.(5)When water temperature stratification occurred in front of the Manwan Dam,the barrier effect of water temperature gradients was formed,and the upper water body in front of the dam can not be taken from the diversion port.Influenced by the outflow from the middle and lower layers of water,there was a circulation in the surface water in front of the dam due to momentum conservation.When the outflow discharge was increased,the diversion port had a strong water intake capacity for the surface water in front of the dam,breaking through the barrier effect formed by the water temperature gradients,and making the surface water with higher temperature in front of the Manwan Dam flowed out of the reservoir.(6)Because Manwan Reservoir had a very weak regulating capacity for flow discharge,the outflow discharge water temperature of Manwan Reservoir under different outflow modes had little difference under the conditions of high-temperature inflow water or low-temperature inflow water,and the operation mode of Manwan Reservoir had almost no regulating effect on the outflow water temperature of Manwan Reservoir.