Simulation Research On The Layered Structure Of Longyangxia Reservoir Water Temperature Based On Machine Learning Model

In the past 100 years,the number of high dams and large reservoirs in the upper reaches of the Yellow River has increased greatly,which has a great impact on the ecological environment around the reservoir area.As an important factor affecting the stability of aquatic ecosystems,water temperature not only restricts the reproduction and growth of aquatic plants and animals,It also affects the living environment and population distribution of various aquatic species.In addition,the current prototype observation of water temperature is mainly affected by factors such as the location of the measuring point and the accuracy of the instrument,which has great limitations.Therefore,it is necessary to explore high-precision water temperature simulation methods.It has important reference value for the treatment and protection of reservoir water environment.Taking Longyangxia Reservoir in the upper reaches of the Yellow River as an example,a three-dimensional water temperature numerical model is established by using mike3,and the model parameters are calibrated and verified.The distribution structure of water temperature in Longyangxia reservoir area was simulated,and the simulated values of water temperature at characteristic points were extracted.The results are used as machine learning model training data,and a machine learning model GA-SVR coupled with genetic algorithm(GA)and support vector machine(SVR)is established to simulate high-precision water temperature,and analyzed the change law of water temperature stratification structure in Longyangxia reservoir area.The main research results are as follows:(1)Longyangxia Reservoir is a stratified reservoir.The changes in water temperature stratification can be divided into three periods:water temperature mixing,weak stratification,and strong stratification.Among them,January-March and October-December are the water temperature mixing period,April-May is the weak stratification period,and June-September is the strong stratification period.During the water temperature mixing period,the vertical water temperature structure of the reservoir is a mixture of upper and lower layers.The temperature difference between the surface water temperature and the bottom water temperature ranges from about 1 to 3℃.The temperature continued to drop and the incoming water temperature decreased.The low temperature water enters the reservoir area and the surface water releases heat.As a result,the density gradually increases,and it mixes with the lower layer of high-temperature and low-density water to produce convective motion,which causes the water temperature of the entire reservoir area to become uniform.During the period of weak and strong stratification.Due to the influence of air temperature and sunlight,the temperature of surface water in the reservoir area continues to rise.Due to the high temperature on the surface and low temperature at the bottom,the water body in the reservoir area presents an obvious layered structure.From October to December,the surface low-temperature water body exchanges with the lower water body continuously,the layered structure of reservoir water temperature gradually disappears,and the water body enters into the mixed state until it reaches the isothermal distribution state.(2)The water temperature structure of Longyangxia Reservoir shows periodic changes during the year,and the water temperature stratification in front of the vertical dam is significant.Since the beginning of June,the water temperature in the reservoir area has risen,and the change in water temperature has weakened as the depth increases.The surface water temperature reached its highest in July,while the bottom water temperature was still rising.After the low temperature season in October,the temperature continued to drop,and the surface water temperature dropped rapidly,which in turn caused the lower water body temperature to drop until the water temperature in the entire reservoir area mixed.(3)The GA-SVR prediction model can better predict the vertical water temperature and water temperature structure of the Longyangxia reservoir area;after adding the radiation factor,the GA-SVR model has higher accuracy than the original prediction model;by predicting the water temperature of the Longyangxia reservoir,it is found The Longyangxia Reservoir presents a stable vertical water temperature stratified structure during the year.The water temperature in the surface and middle layers of the water body changes significantly from month to month.The thickness of the thermocline of the reservoir reaches its maximum from July to mid-August and the structure is stable;The impact of temperature changes is significant.(4)In front of the comparison dam,the upper,middle,and tail regions of the reservoir area found that water temperature structure changes are affected by changes in water depth.The deeper the water,the more obvious the water temperature stratification.The water level in front of the dam is the deepest,so the water temperature in front of the dam The delamination is the most obvious.At the end of the reservoir,due to the decreasing water depth,the water temperature stratification is weak and the water temperature structure is unstable.When calculating the gradient of the water temperature in the reservoir area,it was found that,except in front of the dam,the gradient of the water temperature at all other points was the smallest during the period when the temperature was rising,and when the temperature was falling,the gradient change was obvious.(5)The vertical layered structure in front of the water temperature dam of Longyangxia Reservoir is mainly divided into three types:mixed isothermal type from January to February and November to December,transition type from March to May,and June to October(high temperature season)The water temperature is obviously stratified.From June to August,a thermocline appeared at an elevation of about 2560 m,of which the thickness of the thermocline was the most stable from July to August,and the water temperature at the bottom of the reservoir was a stable thermocline.The water temperature stratification in front of the dam is significantly affected by temperature changes.During the warming period,the upper water body absorbs heat,and the temperature difference between the upper and lower layers increases,and the temperature gradient rises easily to form a thermocline.As the temperature drops,the water temperature gradually mixes.