Study On Water Quality Improvement For Urban Lakes Based On Water Resources Allocation

The deterioration of water quality in urban rivers and lakes has seriously affected the image of the city and people's quality of life,even restricted the development of the city,and become a serious social problem.With the development of irrigation districts,besides traditional agricultural production,how to exert greater economic and social benefits is also the goal of irrigation districts.Irrigation area is rich in water resources.It is of great practical significance to study water diversion under the condition of ensuring agricultural production for improving the water environment of urban lakes and improving the economic benefits of irrigation area.Firstly,on the basis of considering industrial,agricultural,domestic and other water users in the irrigation area,the optimal allocation model is established and the ecological environment water is obtained.Then,in order to make full use of the water for ecological environment,a two-dimensional hydrodynamic water quality model of urban lakes was established,and the water diversion of urban lakes under different conditions were simulated by various diversion schemes.Finally,through the evaluation index system of diversion,the optimal water diversion flow is selected.This study takes Nanchang City and Ganfu Plain irrigation area as the research object.The main research contents are as follows:(1)The optimal allocation model is established to provide basis for water diversion.Considering the water consumption of agricultural,industrial,living and urban ecology users in irrigation area,and aiming at maximizing social and economic benefits of irrigation area,an optimal allocation model is established.The model was solved by the combination of constraint method and weight method,and the optimal allocation results were obtained at the two time scales of the whole year and the peak period of water use.The results of optimal allocation of water resources in Ganfu Plain show that the irrigation area can provide a certain amount of clean water for water diversion into Nanchang City,but the amount of water available is greatly affected by the situation of incoming water and decision-making tendency.(2)A two-dimensional hydrodynamic-water quality coupling model was established to simulate water diversion.Based on the measured bottom topographic data of Qingshan Lake,Xianghu Lake and Aixi Lake in Nanchang City,a two-dimensional hydrodynamic water quality model was established by using MIKE 21.The important parameters of the model are calibrated by the measured water level and water quality data,and then the model is validated.Various schemes are used to simulate the water diversion of lakes.The simulation results of the three lakes show that the model can accurately simulate the hydrodynamic and water quality of the lakes,and the simulated water diversion schemes can provide reference for the actual water diversion.(3)The evaluation index system of water diversion is constructed,and the scheme is optimized.A multi-objective evaluation index system considering the time,quantity,water quality and hydrodynamic conditions of water diversion is established,which can calculate the optimal flow for water diversion of urban lakes.After applying the index system to Qingshan Lake,Aixi Lake and Xianghu Lake in Nanchang City,the optimal water diversion flow of three lakes under different conditions is calculated,the water requirement for single diversion of water in Nanchang City is obtained,and the water requirement for the ecological environment of Nanchang City is evaluated.The results show that the optimal water diversion flow of the three lakes in Nanchang is quite different when they are in different water quality and quantity states,and the ecological environment water supply in Ganfu Plain irrigation area is insufficient.