Study On Water Quality Simulation And Replenishment Scheme Of Wuliangsu Lake

Wuliangsuhai is a natural water regulation reservoir in the Inner Mongolia section of the Yellow River.It is an important flood detention area for disaster reduction and the only drainage area in Hetao irrigation area.It has very important ecological functions.In recent years,due to a large number of untreated industrial and domestic wastewater from cities and towns,the farmland water has been discharged into the Wuliangsuhai Sea,and the ecological environment is seriously insufficient,which makes the ecological environment of the Wuliangsuhai Sea destroyed and the water quality problem increasingly prominent,and has seriously affected the daily life of the residents in the region.Ecological environment water supplement is one of the effective measures to improve lake water quality and restore lake ecology.Aiming at the problems of serious water pollution and insufficient water supply in dry years in Wuliangsuhai Lake,in order to improve the water quality of the lake,the water quality of Wuliangsuhai Lake was simulated and the ecological environment water supplement scheme was studied.The main research contents and results are as follows:(1)Wuliangsuhai water pollution status evaluation and pollution source investigation and analysis.Aiming at the problem of water pollution in Wuliangsuhai Lake,firstly,according to the monitoring data of COD,NH3-N and TP from 2005 to 2018,the single factor analysis method was used to evaluate the water quality of Wuliangsuhai Lake.Then,Pearson correlation coefficient method was used to analyze the correlation between water quality and quantity,and the correlation between inflow and pollutant concentration was analyzed.Finally,the amount of point source pollution and non-point source pollution into the lake was estimated by literature survey and output coefficient method,and their contribution rate was analyzed.The results showed that the main excessive pollutants in Wuliangsuhai Lake were COD and TP,and their concentrations were negatively correlated with the flow into the lake.The main sources of pollution were farmland drainage and livestock breeding.(2)Construction of Wuliangsuhai hydrodynamic-water quality model.Hydrodynamic water quality model is an effective tool for the study of eco-environmental water supplement scheme and the basis for the formulation and evaluation of water supplement scheme.Based on the topographic data of Wuliangsuhai,MIKE21 software is selected as the solution tool to construct the model.Firstly,the model grid is divided according to the actual engineering situation of Wuliangsuhai and the boundary conditions are set.Then,the model parameters of the relevant research area were investigated and counted.On this basis,the initial value of the parameters was set,and the study area was divided into reed area and open water area by remote sensing interpretation.Finally,the rationality of the water quality model parameters is analyzed by calculating the model simulation error and qualified rate,and comparing with the model parameters of the relevant research areas.The analysis results show that the simulation results are in good agreement with the actual data,and the model parameters are reasonable,which can be used to simulate the water quality and quantity of the water supplement scheme.(3)The ecological environment of Wuliangsuhai needs water supplement.First of all,through the analysis of domestic and foreign scholars on lake eco-environmental water demand,combined with the status quo of the study area,the Wuliangsuhai eco-environmental water demand is divided into ecological water demand and environmental water demand.Then,the water balance method and the function method are used to calculate the ecological water demand,and COD and TP are selected as pollutant indexes,and the MIKE water quality model is used to calculate the environmental water demand.Finally,combined with the water status of Wuliangsuhai dry year,the monthly water demand and water demand process were calculated and analyzed.The results show that the natural rainfall runoff supply can basically meet the ecological water demand of Wuliangsuhai,and additional water supply is needed to improve its water pollution status.Among them,the minimum water requirement is 530 million m~3,and the suitable water requirement is 1.040 billion m~3.The water requirement is mainly distributed from January to June.(4)Study on water supplement scheme of Wuliangsuhai ecological environment.Aiming at the problems of serious water pollution and insufficient water supply in dry years in Wuliangsuhai Lake,firstly,according to the current situation of water supply project construction and the characteristics of sub-ling water supply,six kinds of water supply schemes are formulated,including centralized water supply,uniform water supply and camera water supply,and the rationality of the scheme is analyzed from the aspects of water supply on the interval and downstream water safety.Then,the hydrodynamic-water quality model was used to simulate the water replenishment process of different schemes,and the fuzzy optimization method was used to evaluate and optimize each water replenishment scheme to determine the optimal water replenishment scheme.Finally,from the perspective of source control,several better schemes are simulated and evaluated to explore the optimal water supplement method combined with source control and water supplement.The results show that the camera water replenishment scheme based on channel water conveyance is a better ecological water replenishment scheme,and the optimal water replenishment amount is 963 million m~3 when the water quality is replenished to Class IV standard.If considering the source control,combined with structural emission reduction and engineering emission reduction measures,under the planned pollutant emission control level,the optimal water replenishment scheme requires 753 million m~3 water.Finally,the full text is summarized and the problems to be further studied are prospected.