Research On Predictive Analysis Of Water Thmperature In Nuozhadu Reservior,the Lancang River

With the hydroelectirc development in china enters in an accelerating development period,hydropower technology will be an important means for China to promote the transformation of energy production and utilization,as well as the fight against climate change.Hydropower is bound to play a more important role in the future energy system.However,while more and more hydropower construction projects bring economy benefits,river ecology and environment also has been changed.Water temperature is a relatively sensitive hydrological element of river ecosystem.The variation of water temperature caused by the construction of dam will have a direct impact on the ecosystem of reservoirs and the downstream environment.To explore the impact of cascade hydropower plants on lower reaches of the Lancang River on water temperature,Nuozhadu hydropower plant which has the largest reservoir capacity,installed capacity and annual energy production is selected as the study area.In this research,by combining prototype observation with mathematical model,the study simulates and analyzes the temporal-spatial variability of water temperature on lower reaches of the Lancang River.In addition,the reasons for the formation of water temperature temporal-spatial variability are deeply studied,which provides data support and theoretical basis for the protection of water ecology and water environment and the operation of hydropower plants.The main results are the following:(1)The operation of the hydropower plants completely have altered the natural water temperature.The increasing temperature process of downstream water temperature is different from that of natural rivers after the construction and operation of Cascade Reservoirs,and the annual range of water temperature was decreased.(2)The paper judged the temperature construction of Nuozhadu reservoir with the Parameter alpha-beta discriminant method,Norton density froude number criterion and the width-depth ratio criterion for reservoirs.The three methods give the same results that Nuozhadu reservoir is a typical stratified reservoir.Then through conducting numerical modeling,the results was confirmed.(3)The variation of water temperature stratification in nuozhadu reservoir varies with month and season.In winter,water temperature of the whole reservoir is lower and lower and the water body of reservoir shows a state of heat dissipation.The area with high surface water temperature is mainly distributed in front of dam,and the thickness of the water layer with high surface water temperature is about 30-40m.The water temperature of suface laver is 16.8 ℃～18℃.The range is about 80km from the front of dam to the upstream.As the upstream water temperature gradually decreases,the range of the water layer narrows.Besides,the thickness of the middle water temperature is directly affected by the upstream water temperature.The water temperature of middle layer is 15.0℃～16.2 ℃.In spring and summer,water temperature of the whole reservoir increases gradually and the water body of reservoir shows a state of heat absorption.The thickness of the water layer with high surface water temperature is about 15～30m.As the upstream water temperature gradually increases,the range of the water layer with high surface water temperature expands and the thickness of the lower water layer with low water temperature increases.The water temperature has been stable in from 16 ℃ to 16.5 ℃.