Research On Water Temperature Distribution And Its Simulation In The Reach Of The Lancang River Before Exiting The Border

For thr past few years,the rapid development of the hydropower industry has emerged in China.The building of dams has not only brought graeat economic benefits,but also caused serious ecological problems.As one of the most typical environmental factors in the river ecosystem,the water temperature of the river reservoir system is bound to change when the reservoir is completed and filled,and it will have a immediate impact on the river ecological environment.Therefore,research the water temperature distribution is meaningful to the design of hydraulic structures and the operation and management of reservoirs.In this paper,Jinghong Reservoir on Lancang River was selected as the study area.Based on the field monitoring data observation,then establish a water temperature model to analyze the distribution of water temperature in the reservoir,and explore the impact of reservoir operation on the water temperature before leaving the country.It provides reference for reservoir operation management and river ecological protection.The main research results of this paper are as follows:（1）As the counter-regulating reservoir of the upstream Nuozhadu Reservoir,the Jinghong Reservoir does not have the ability to adjust for many years.The temperature of the discharged water from the Nuozhadu Reservoir flows into the Jinghong Reservoir area and the water temperature is raised.The annual average measured water temperature after the Jinghong Reservoir was built to store water is about 5 ℃ higher than water temperature in the historical period before dam construction,and the water temperature showed an obvious "gentle" phenomenon.The heating rate of the Nuozhadu-Jinghong section was higher than that of the downstream Jinghong-Guanle section.Guanlei Hydrological Station is less affected by Jinghong Reservoir operation and the water temperature is higher all the year round.The change trend of water temperature in front of the Jinghong Reservoir dam is the same as that of air temperature,but the emergence time of extreme water temperature is lagging behind air temperature.（2）Jinghong reservoir is identified as a weakly stratified reservoir by three methods of water temperature structure.Based on the analysis of the measured data,establish the CE-QUAL-W2 two-dimensional model of Jinghonghui Reservoir.The adjustment results show that the CE-QUAL-W2 model is suitable for the water temperature simulation of Jinghonghui Reservoir.The simulation results are accurate and the water temperature is weakly stratified in the vertical direction,and the stratification has seasonal law.The stratification of water temperature in summer and autumn is more evident,and evenly mixed in spring and winter,the signs of stratification are the weakest in March and the most obvious in July.The water temperature of the downstream channel increases with the increase of the distance,and rises rapidly in flood season.Taking Jinghong Dam as the starting point,the water temperature recovered to the natural water temperature in20 km of the downstream channel.（3）On the basis of the original intake elevation operation,another two simulation scenarios are assumed,the designed water intake elevation was lowered and raised by 15 m respectively,to explore the water temperature distribution of Jinghong Reservoir and the change of discharge water temperature after the operation of the power station.The simulation results show that after the intake elevation drops by 15 m,the shallow water temperature area,and the vertical water temperature stratification weakens.After the elevation increases by 15 m,the shallow water temperature reduces,and the vertical water temperature stratification intensifies.The annual average gradients of vertical water temperature for the three working conditions are 0.02 ℃/m,0.03 ℃/m,and 0.04 ℃/m.The thermocline is formed at a water depth of 3～15m,and the rate of decrease of the thermocline is 0.09 ℃/m,0.12 °C/m,0.1 °C/m,respectively.The elevation of the water intake will also affect the change of the discharge water temperature.In the simulation of this article,the elevation of the water intake increases and the temperature of the discharge water decreases.