Study On Water Quality Evaluation And Simulation Of A Typical Pumped Storage Reservoir In Ningxia

Water quality evaluation and prediction are important works of the water environment management,which is the main theoretical basis to make a scientific and reasonable water quality control scheme and plays a vital role in water environmental protection.Yazidang Reservoir is a typical Pumped Storage Reservoir in Ningxia.In this paper,base on analysis of the water quality indexes,uncertainty methodolodgy was used for comprehensive evaluation of water quality of reservoir.Base on field testing reservoir bottom tepography,both of flow field and water quality were simulated.（1）Some water quality index were monitored monthly.Water quality comprehensive analysis showed that concentration of COD_Cr,NH₃-N and DO meet Class Ⅲ waterbody requirements,Both BOD₅ and TP are part of the violation,and TN was 100%of overweight.Using the grey correlation method to evaluate reservoir water quality,the results showed that the Yazidang Reservoir basically belong to Class Ⅲ waterbody,and the result would be more realistic when S_t valued by Ⅲ class standard rather than the average of five types of water quality standard.（2）Base on sampling and monitoring,With spatial interpolation of Inverse Distance Weighted in ArcGIS software,the spatial distribution of COD_Cr,NH₃-N,TN and TP were draw out.The results showed that due to ice melting and water mixed convection,the contaminant spatial difference is small in April,but it become markedly in July and October.While COD_Mnand NH₃-N can satisfy the requirement of water body function,but the TN in the 100%more than the standard limit of 1 mg/L,part of the TP concentration exceed the standard limit of 0.05 mg/L.Relative to the aimed at each sampling point of single point of data analysis,the spatial distribution characteristics of more comprehensive.（3）With Real-time Kinematic（RTK）as positioning technology and advanced "rivercat "equipment measured the topography and section velocity in Yazidang Reservoir,the two-dimensional turbulent numerical model was established base on triangle mesh to simulate the flow field.The simulation results showed the as a typical Pump Storage Reservoir,there are different flow characteristics under two operation condition of.inflow and no inflow in Yazidang Reservoir.When inflow,there is a obvious mainstream from the inlet to the intake tower,and forming a water circulation near the water intake tower due to the intake power.The velocity can reach to 0.02～0.03 m/s in areas near the water intake and water intake tower;and the velocity is small in other areas,the lowest velocity appear in the southwest of reservoir area,where the velocity is 0.004～0.008 m/s.When no inflow,there is no mainstream and only a circulation near the water intake tower.Circulation flow velocity is still can reach to 0.02～0.03 m/s,while velocity is small in other area.Water velocity when inflow in reservoir area is bigger than no inflow.By setting different operation conditions,further simulation results showed that the throughput flow and wind current obviously affect the reservoir flow field of Yazidang Reservoir,and wind current is the initiative power.（4）The two-dimensional pollutant transport numerical model was established base on triangle mesh to simulate the distribution of pollutants.The simulation results showed that there are different change law of water quality when inflow and no inflow in Yazidang Reservoir.high concentration area concentrated near the water intake when inflow,and along the direction of the mainstream gradually reduce.The concentration of COD_Crand NH₃-N was about 10 mg/L and 0.25 mg/L respectively near the water intake tower.When no inflow,spatial heterogeneity of the pollutants concentration decreases.The water quality is poorer when inflow than no inflow.By setting different operation conditions,further simulation results showed that throughput flow,wind field and inflow water quality had a great effect on the spatial distribution of COD_Crand NH₃-N.Under various working conditions,high concentration areas concentrated near the inlet when inflow.So,control feed water quality is important for reservoir water quality management.（5）There are some water quality problems in Yazidang Reservoir,such as some water quality indexes are excessive,water quality is poor when inflow,and the space-time distribution of the pollutants concentration are inequality.To protect the water quality of reservoirs,some physical countermeasures should be carried out,such as,promotion of ecological restoration and biological purification technology,digging sediment in inlet area,bottom aeration,strengthening reservoir water quality monitoring and water quality assessment,doing some research on correlation between the source of Yellow River water quality and the water quality of reservoir,and research of nitrogen source pollution related to control the eutrophication of water body.Meanwhile,some no-physical measures also needed,such as,strengthen management,increase the water source protection publicity and law enforcement,estimating the reservoir environmental capacity,and improving the system of water source emergency plan and supervision,preventing the water environment pollution accident.