Study On Water Quality Risk Evaluation And Monitoring Point Optimization Of Mountain City Water Supply Network

With the continuous improvement of China’s economic level and people’s living standards,water quality safety had increasingly become a concern of the whole society.The water supply pipeline network was responsible for delivering to various users in compliance with the national water quality standards.However,due to water retention in the pipeline network and pipeline corrosion,it was easy to cause the water quality to deteriorate.How to use the limited water quality monitoring points to reflect the water quality of the whole water supply network as much as possible was an urgent problem to be solved.This study is based on the project"Research and Demonstration on Key Technology of Urban Water Supply Security in the Three Gorges Reservoir Area"(2017YFC0404706).Taking the water quality safety of the water supply pipe network as the starting point,the water quality risk assessment and monitoring point optimization of the water supply pipe network in mountainous cities were studied.Firstly,A detailed investigation was carried out on the status of the water supply pipe network in Chongqing,including the material,diameter,service life and water consumption status of the pipe section,and the water quality data such as residual chlorine and turbidity at the current water quality monitoring point were recorded.Combined with the typical characteristics of"double water source+mixed zone"of the water supply network in Chongqing,the water supply network was dismantled according to the zones.The hydraulic water quality models based on Epanet 2.0 software were established respectively.The models were guaranteed to reflect the real operating state of the water supply network through verification.The spatial and temporal distribution characteristics of residual chlorine and turbidity in the water supply network were analyzed based on the data of current water quality monitoring points,flow rate,velocity and water age obtained by the model.The turbidity model was obtained by nonlinear fitting of water age,residual chlorine and turbidity with 1stopt software.The goodness of fit evaluation index RSME of the model was 0.022 and R~2 was 0.938,indicating that the model could better simulate the change of turbidity of water supply network.Secondly,in view of the difficulties that it was difficult to quantify the water quality risk assessment of the water supply network,the comprehensive evaluation system of water quality risk was established by comprehensively considering the factors affecting the water quality risk of the water supply network.The fuzzy comprehensive evaluation method and BP neural network algorithm were respectively used to evaluate the water quality risk of the water supply network in Chongqing.Compared with the fuzzy comprehensive evaluation method,the BP neural network has the advantages of objective evaluation and convenient application.The results of water quality risk assessment show that the current water quality monitoring points of the water supply pipeline network in Chongqing were all at a low level of water quality risk.Finally,according to the requirements of the optimal layout of water quality monitoring points in the water supply network,the evaluation indexes and weights in the water quality risk assessment model of the water supply network were adopted to establish a two-objective optimization model with the maximum water quality risk of the covering nodes and the minimum error of the comprehensive evaluation of water quality risk.The idea of ideal point method was used to solve the optimization model with genetic algorithm toolbox in MATLAB software.The results showed that the model and solution method can meet the actual situation of the pipe network well in Chongqing,and the selected water quality monitoring points have high representativeness,which could better reflect the water quality of the whole pipe network.