| With the development of society,people are increasingly aware of the importance of the ecological environment for our daily life and production activities.This is also true in the development and construction of water conservancy projects.Ecological governance is increasingly valued in water conservancy construction,and water ecological protection is an important part that cannot be ignored in every water conservancy project.The Han to Wei River Diversion Project will play an important role in the development of the Wei River Basin in Guanzhong,Shaanxi,and the Sanhekou Reservoir is an important water source for the project.Therefore,it is crucial to conduct research on the water quality of the Sanhekou Reservoir area.This study takes the Sanhekou Reservoir Area as the research object,and conducts numerical simulation research on the hydrodynamic and water quality of the Sanhekou Reservoir Area based on the MIKE21 model’s hydrodynamic and water quality modules.By constructing a hydrodynamic model for the Sanhekou Reservoir area,the distribution characteristics of the reservoir area under different hydrological conditions were analyzed and studied.Subsequently,a water quality model for the Sanhekou Reservoir area was constructed based on the hydrodynamic model,and parameter calibration and validation were completed using measured data.Based on the model simulation analysis,the spatial distribution characteristics of each state variable under different hydrological year conditions were obtained.The pollution index method was used to evaluate and analyze the water quality in the reservoir area,identifying the main pollution factors,and then proposing suggestions for water environment protection in the Sanhekou reservoir area.The main conclusions obtained are as follows:(1)Based on the monitoring data of various water quality indicators in 2022,the variation pattern of each indicator over time was analyzed.The water quality status was evaluated and analyzed through comprehensive pollution index and single pollution index.The results show that the comprehensive pollution index in each month is less than 1,indicating that the water quality in the reservoir area has reached the target standard;The single pollution index of TN is greater than 1,which exceeds the Class Ⅱ water standard of TN in the water environment standard and is significantly higher than the single pollution index of other water quality indicators,indicating that TN is the main pollution factor affecting the water quality in the reservoir area at present.(2)Based on the measured data,a hydrodynamic model of the reservoir area was constructed using the MIKE21 hydrodynamic module.The parameters were calibrated and validated using the measured data,and the hydrodynamic characteristics of the reservoir area under different working conditions were simulated and analyzed.Evaluate the simulation effect of the hydrodynamic model and calculate a Nash coefficient of 0.77,with an average relative error of 3.8%.The model accuracy meets the requirements.The simulation results show that under various hydrological conditions,the overall flow velocity decreases from the end of the reservoir to the intersection.The intersection area is the area with the relatively smallest flow velocity in the reservoir area,and the flow velocity in front of the dam is slightly higher than the intersection.The average flow velocity in high water years is 0.0068m/s,in normal water years is 0.0033m/s,and in low water years is 0.0028m/s.(3)Based on hydrodynamic simulation,a water quality model for the Sanhekou Reservoir area was constructed using the MIKE21 ECO Lab module,and the spatial distribution characteristics of water quality indicators under different operating conditions were simulated and analyzed.The parameters of the model were calibrated using measured data,and the simulation effect of the model was evaluated.The Nash coefficient during the validation period was calculated to be between 0.69 and 0.79,with an average relative error between 8.8%and 16%.The model is reasonable and reliable.The simulation results show that under different hydrological year conditions,the water quality reflected by DO is in the order of good to bad in high water years,normal water years,and low water years;The water quality status reflected by NH3-N,TN,and TP,from good to bad,is in the order of low water year,normal water year,and high water year.(4)Taking the Class Ⅱ water environment functional zone as the target,the pollution index method was used to evaluate and analyze the water quality status of the reservoir area under different hydrological year conditions.Based on the evaluation results of the water environment in the reservoir area and the actual situation of the reservoir area,suggestions for water environment protection in the reservoir area were proposed.The water quality evaluation results indicate that the comprehensive pollution index under different hydrological year conditions is less than 1,indicating that the water quality in the reservoir area has reached the target standard;From different hydrological years,the water quality is the best in dry years,followed by normal years,and relatively poor in wet years;From different regions,the water quality at the tail of Puhe Reservoir is relatively poor,while the water quality in the middle reaches of Wenshui River and the intersection area of Wenshui River is relatively good;Under the conditions of each hydrological year,the single pollution index of DO and NH3-N is less than 0.5,while the single pollution index of TN is greater than 1.The single pollution index of the other three water quality indicators is less than 1,indicating that TN is the main pollution factor affecting the water quality in the reservoir area and can be used as the basis and direction for future ecological management of the reservoir area. |
