Study On The Characteristics And Influencing Factors Of Water Temperature Evolution In Longqing Section Of The Upper Yellow River

The section from Longyangxia to Qingtongxia is the most intensively developed section of the cascade hydropower station group on the mainstream of the Yellow River.In the past 60 years,more than 20 hydropower stations of different scales have been built,which has caused significant changes in the water temperature status of the river.The cascade development process has been proved The temporal and spatial evolution of the water temperature in the middle channel and the main influencing factors can provide an important reference for river water ecological environment protection.Based on the meteorological,hydrological,water temperature,and cascade reservoir operation data in the Longqing section of the upper reaches of the Yellow River,this paper combines prototype observations,statistical analysis,and numerical simulation to analyze the temporal and spatial changes of river water temperature,and explore the effects of reservoirs.The variation characteristics of river water temperature reveal the main factors affecting river water temperature.The main results achieved are as follows:(1)The law of temporal and spatial evolution of water temperature in Longqing River section is proved.The natural water temperature of the river course tends to a weak upward trend;the river section with significant influence of cascade reservoirs shows a fluctuating downward trend in summer water temperature,and an upward trend in winter water temperature;in the section below Liujiaxia Reservoir,the fluctuation of summer water temperature and winter water temperature increase weakens.Compared with the water temperature along the river course before the construction of the reservoir,the water temperature along the river course has basically increased steadily.Aflcr the construction of the reservoir,the water temperature along the river course has the characteristics of cooling in winter,alternating temperature changes,and an increase in the temperature increase rate along the course in summer.(2)Analyzed the variation characteristics of river water temperature affected by cascade reservoirs.Three typical years were selected,and the PCA method was used to explore the basic characteristics of the reservoir's impact on river water temperature,including five aspects:cooling in summer,warming in winter,lack of seasonal water temperature,delay in the water temperature process,and temporal fluctuations in the threshold,revealing the impact of reservoir interference Changes in strength and weakness have a significant effect on the spatial distribution of water temperature in the lower reaches of the river,and the influence of cascade faucet reservoirs on the fluctuation of water temperature in the lower reaches of the river is basically eliminated in the lower reaches of Liujiaxia Reservoir.(3)It reveals the influence of temperature changes and reservoir operation on river water temperature changes.The temperature and water temperature of the river section not disturbed by the reservoir have a significant correlation;the influence of the operating water level of the reservoir,different types of reservoirs and the discharge flow of the reservoir on the water temperature of the river is discussed.The operation change of the cascade faucet reservoir has a dominant influence on the water temperature of the Longliu section Effect;the change of water temperature in the Liuqing River section is restricted by the discharge temperature of Liujiaxia Reservoir;the increase of the daily variation of the discharge flow of the reservoir will cause the fluctuation of the water temperature of the downstream river to increase.