Simulation Of Water Temperature Structure Of Guanyinge Reservoir And Prediction Of Water Quality Of Multi-Dam River Under Different Discharge Modes

A large number of hydraulic engineering studies have shown that water temperature stratification often exists in large and medium sized reservoirs,and different water discharge methods have different impacts on the downstream river water environment.At the same time,the construction of river power station and other hydraulic engineering influences the migration and transformation of river material on the basis of adjusting the discharge of Mountain River,which is an important factor causing the difference of water quality between the front of dam and the back of dam.The Guanyinge Reservoir,located in the upper reaches of the hydraulic engineering,is one of the largest reservoirs in Liaoning province.The ecological recharge of the lower reaches of the guanyinge reservoir has been carried out by the way of bottom water drainage since the reservoir was built.The ecological investigation of the affected river under the dam of Guanyinge Reservoir was carried out,the ecological status of the river was identified,and the temporal and spatial variation characteristics of water quality indexes such as the temperature of the downstream river were simulated under different conditions of water discharge modes,it is of great significance to scientifically evaluate the ecological impact of the current reservoir discharge mode on the downstream river.In this study,the area in front of the dam and the Taizi River downstream of the Guanyinge Reservoir are selected as the research objects,the water temperature model in front of the dam of Guanyinge Reservoir and the water quality model of Taizi River in the downstream of the reservoir are established respectively based on the coupling of MIKE21 and MIKE11 and ECO Lab through field investigation and periodic sampling monitoring,the characteristics of water temperature structure in front of the dam and the spatio-temporal variation of water quality indexes under the influence of multi-dam rivers are studied.The main findings are as follows:1)The vertical seasonal variation law of water temperature in front of the Guanyinge Reservoir dam is determined by the empirical formula of dongkeyuan and the method of Mike Mathematical model.In spring,the surface water temperature ranges from 15℃ to 16℃,and the bottom water temperature ranges from 5.2 ℃ to 8.5 ℃.In summer,the surface water temperature is 26～27.5 ℃,and the bottom water temperature is 5.3～9.6 ℃.The surface water temperature is 16～16.5 ℃ in autumn,the bottom water temperature is 8～12 ℃,the surface water temperature is 2～4.6 ℃ in winter,and the bottom water temperature is 5.2～6 ℃.The results show that the temperature difference between the surface and the bottom of the reservoir is large in spring,summer and autumn,but relatively small in winter.The numerical results of the two methods are similar,and the error is only 5.5 ℃.The simulation method is accurate and the results can accurately simulate the real water temperature structure of guanyinge reservoir.2)The current discharge mode of bottom outlet of Guanyinge Reservoir and the temporal and spatial variation of water quality of the downstream river show that the water quality of Taizi River is good.From the time point of view,the annual variation range of water temperature is 2～26 ℃.The annual variation range of Do concentration in water body is from 7 to 14 mg/L.The annual range of Chemical oxygen demand is between 4 and 43 mg/L.The annual variation range of ammonia nitrogen was 0.1～0.66 mg/L.The total phosphorus varied from 0.01 mg/L to 0.17 mg/L.From the space view,the concentration of pollutants in the sample points along the route shows an upward trend.As a result of water storage in front of the dam,the water temperature in front of the dam is higher than that in the back of the dam in Oberburg Power Station and qingshiling power station.The highest water temperature difference between upstream and downstream reaches 3.3 ℃ in April.The dissolved oxygen in front of the dam was lower than that in front of the dam in April and lower than that in front of the dam in November.The highest difference was 3.6 mg/L.The content of Chemical oxygen demand in upstream of sluice dam is higher than that in downstream,and the maximum difference is 15.4 mg/L.The ammonia nitrogen content in the upstream of the dam is higher than that in the downstream of the dam,and the maximum difference is 0.1 mg/L.The content of total phosphorus in upstream of sluice dam is higher than that in downstream,and the highest difference is 0.06mg/L.3)Water quality model based on MIKE11 software coupled with ECO Lab module simulates the influence of different discharge modes on water quality of the lower reaches of Guanyinge Reservoir.The water temperature difference between the two methods was-12～6℃,the temperature difference was higher than 5℃,the dissolved oxygen difference was-1.7～2.9 mg/L,the Chemical oxygen demand content difference was-12.1～10 mg/L,the ammonia nitrogen content difference was-0.09～0.34 mg/L,the total phosphorus content difference was-0.03～0.1 mg/L.4)The difference between surface drainage and bottom drainage is the water temperature.The initial temperature of bottom discharge water is low,and the variation range of water temperature is higher in spring,summer and autumn because of different hydraulic conditions.In winter,the initial water temperature at the beginning of the study area is high,and the water temperature gradually decreases under the influence of air temperature,and is slightly higher than the natural river.The water temperature of the surface outlet is higher in winter,which is closely related to the climate.The water temperature of the river is higher in summer,and the water temperature of the river decreases in winter.