Analysis And Regulation Of Water Temperature Cumulative Effect Of Cascade Reservoirs Based On Basin Water Temperature Line

With the development of economic construction,the demand for energy is increasing day by day.Under the requirement of harmonious coexistence between man and nature,vigorous development of clean energy has become an inevitable trend.Among them,hydropower,as the most effective,mature and representative renewable clean energy,is bound to bear the brunt as the object of development.Therefore,since entering the 21 st century,my country has begun to vigorously build hydropower stations.In order to make full use of water resources for power generation,the development of cascade hydropower has gradually become the main method of hydropower development,such as the Jinsha River Hydropower Base and the Lancang River Mainstream Hydropower Base.The reservoirs of these bases are connected end to end to form a huge cascade reservoir group,which has huge economic benefits in flood control,power generation,and shipping.However,huge water bodies are formed after water storage at all levels of hydropower stations,and their flow patterns and habitat factors have undergone significant changes,which will cause certain impacts on the downstream ecological environment.In particular,changes in water temperature will have a serious impact on the downstream aquatic organisms and species composition.As the largest international river in Southeast Asia,the Lancang River has received extensive attention on the health of its ecological environment.In this paper,the method of combining numerical simulation and field monitoring is used to analyze the law of water temperature changes along the way from the salt well of the Lancang River to the tail section of the Miaowei Reservoir(natural river,that is,no reservoir built),and put forward the idea of "water temperature line in the basin".The main content of the thought includes:(?)In a natural river that has not been disturbed by humans,the change in water temperature with distance can be used as a "watershed water temperature line",and its changes over time form a water temperature surface.This line and the surface formed can be used to determine the health of river water temperature The benchmark of degree.(?)The water temperature line of the basin has the characteristic of continuous variation in space.Based on this characteristic,a method for determining spatial continuity is proposed to analyze the variation of water temperature and the degree of interference.Based on the idea of water temperature lines in the basin,a cascade reservoir model and an inversion natural river model(assuming no reservoir)were established from the end of the Miaowei reservoir to the exit section of the Lancang River.The reservoirs from top to bottom are Miaowei,Gongguoqiao,and Xiaowan,Manwan,Dachaoshan,Nuozhadu,Jinghong.Through the measured water level and flow data and water temperature data,the relevant parameters of the model are calibrated,so that the model can accurately reflect the actual situation,and finally the cumulative effect of the water temperature of the cascade reservoirs is analyzed and evaluated,and the layered water intake scheme is used to alleviate the temperature of the discharged water The cumulative effect was analyzed.The main work and conclusions are as follows:(1)The cumulative effect of water temperature in cascade reservoirs is mainly caused by stratified reservoirs,which account for 87% of the impact.The temperature increase effect is the strongest in winter,with the exit section of Guanlei reaching3.52 ?,and the strongest cooling effect in summer(-1.7 ?);the mixed reservoir and the natural river channel of Guanlei section have the effect of restoring the water temperature,which is equivalent to the layered reservoir.Anti-regulation.(2)In a stratified reservoir,the upstream inflow temperature is low during the low temperature period.It enters the reservoir area along the slope at the bottom,and energy exchange occurs during the intrusion process.The temperature has risen significantly when reaching the bottom of the dam.The first role;assuming that the effect of the reservoir on water temperature can be completely eliminated by setting different water intake layers,the second role is the case where the reservoir has an effect on water temperature due to improper water intake settings.The increase in temperature of the discharged water during the low temperature period(winter)is mainly caused by the first effect,and the decrease of the temperature of the discharged water during the high temperature period(summer)is mainly caused by the second effect.(3)The layered water intake method can eliminate the phenomenon of low-temperature water leakage from the layered reservoir during the high temperature period,but the effect of alleviating the increase in the temperature of the discharged water during the low temperature period is small.This is mainly due to the redistribution of the flow by the reservoir.In winter,the upstream flow is small and the water temperature is low,but the discharge flow from the reservoir is much larger than the upstream flow.In order to meet the discharge flow rate,other layers of water will inevitably participate in the discharge,but other layers of water are often the water bodies accumulated during water storage,and the temperature is higher,which produces a huge warming effect.(4)Based on the idea of basin water temperature line,this paper found that the water temperature restoration mechanism mainly includes two types: one is the gradual restoration of water temperature to its natural state under the action of external conditions such as meteorology and tributaries;the other is the sudden increase of water temperature with distance.In the natural state,the river water temperature gradually increases with distance,and the sudden change value is equal to the water temperature value somewhere downstream,so the water temperature difference gradually decreases along the way until it disappears.