The Theories And Methods Of Water Quality Prediction In The Middle Route Of South To North Water Transfer Project Of China

The safety of water delivery and water quality in the South to North Water Transfer Project of China is important to northern China.The effective method to solve water quality problem is water quality model with high predicting accuracy,so it is necessary to study the rule and mechanism of water quality change and build an adaptive water quality model.In this paper,the rules and mechanism of water quality in the main channel of the middle route of South to North Water Transfer Project was studied by theoretical and experimental research.It was found that the water quality is affected by both the external and internal factors,and it was possible that sudden-happened and non-sudden water pollution incident occur in this channel.So this paper studied the theory of channel quality changes in different pollution situations,built the water quality models of two different water pollution situations,and improved the predicting accuracy of models by the optimization algorithm and data assimilation mathematical algorithm.The main contents and conclusions are as follows:(1)The water quality is affected by the external factors named illumination,temperature,atmospheric deposition and water quantity,at the same time,the process of sulfide decay,organic matter decay and oxygen consumption and recovery all have an influence on the water quality.The coupling equations of water flow and water quality were studied and the numerical methods solving equations were classified in this paper.(2)Three experiments were conducted to study the rules of contaminant transport in channels with different boundary conditions.It was found that contaminant diffuse along the channel,the solution concentration in downstream monitoring section increase rapidly and decrease slowly and the peak concentration become lower along the channel.In the actual contaminant transport process,the concentration-time curve fit skewed distribution,and the complicated boundary will increase the turbulent diffusion affection.At the same time,the concentration-time curve of suspended contaminant also fit skewed distribution,but it was smoother because suspended contaminant precipitate along the channel.(3)On non-sudden water pollution condition,the systematic model is available to solve water prediction problem.The General Regression Neural Network(GRNN)was studied and the best value of each spread in GRNN was found via genetic algorithm that depends on the degree of impact of the output.Then,a GA-GRNN model was constructed.After using the water quality data from the middle route of the South to North Water Transfer Project,it was found that GA-GRNN had good network stability,high learning speed and strong approximation ability.(4)On sudden water pollution condition,the contaminant transport model is available to solve water prediction problem.Data assimilation techniques have been proven as an effective tool to improve model forecasts by combining information about observed variables.Data assimilation algorithm could be used to improve the accuracy of model,and a water quality model with three dimensional variational data assimilation(3DVAR-WQM)were developed in this paper.A contaminant transport experiment was conducted for the purpose of verifying the accuracy of the water quality model with 3D VAR,and it was found the accuracy of model increases after assimilation.(5)A demonstration project was conducted in the middle route of South to North Water Transfer Project to simulate the process of pollution accident occurring and being treating.The monitored solution concentration were used to verify the accuracy of water quality model after assimilation.It was found that the model function well in the area of predicting the arrival time and value of peak concentration,root mean square error and forecasted error in the simulated results.As a conclusion,this paper studied the water quality changing theory in middle route of South to North Water Transfer Project and built water quality models dealing non-sudden and sudden water pollution accident.Optimization algorithm and data assimilation mathematical algorithm were studied to improve the accuracy of water quality model,and it was verified by experiments that the optimized model functioned better.Therefore,this paper plays an important role in the water security of the South to North Water Transfer Project.