| At present,the drainage system of the old urban area in China mostly adopts the intercepting type confluence system,while the drainage system of the new urban area and the reformed urban adopts is the diversion system.The improvement of the drainage system makes the receiving water better protected.However,when it rains,the intercepting combined sewerage system will make the influent water quality of the sewage treatment plant fluctuate greatly.The direct rainwater collected by the separate drainage system(especially the initial rainwater)will cause the pollution of the receiving water and the waste of resources.Therefore,the study of rainwater runoff and pollution control is of great significance to effectively solve the problem of rainwater pollution and resource utilization.Based on the analysis of the existing drainage system,according to the different rainwater closure mode,two new drainage systems of mixed intercepting diversion system and non-mixed intercepting diversion system are put forward.Taking an industrial park in Shaanxi Province as the research object,based on the drainage pipe network planning and design,the regional related elevation data,underlying surface data,pipe network topology data and rainfall data were preprocessed,and the regional pipe network model,runoff model and water.quality model were constructed,and the change process of runoff,pipe flow and four pollutants such as chemical oxygen demand,suspended solids,total phosphorus and ammonia nitrogen in regional and partial molecular catchment areas are analyzed.At the same time,the green ecological rainwater system composed of the optimal non-mixed intercepting diversion system and low-impact development facilities is used to optimize the control of rainwater runoff and pollution in the study area,making the rain in the region gets the biggest degree of infiltration,storage,purification and utilization.The specific conclusions are as follows:(1)According to the difference of rainwater closure mode,two new drainage systems of mixed closure type and non-mixed closure type are proposed,which can effectively solve the problems of initial rainwater pollution and rainwater resource utilization.Through the analysis,it is considered that the non-mixed closure diverting system is the best drainage system.(2)Based on the validation method of similar areas,the hydrological,hydraulic and water quality model of the verification area are constructed.Meanwhile,on the condition that the error between the simulated value and the measured value at the drainage outlet was within the allowable range,relevant parameters such as impervious coefficient,initial rainfall loss,hydrological coefficient in the model were determined.(3)Based on the industrial park planning and design,the present situation of regional hydrologic and hydraulic and water quality model are built,and the surface runoff,network overload running situation and regional water quality present situation are analyzed.The results show that in the original planning and design return period 1 year,although no inspection shaft overflow occurs,but the network has more than a third of the pipeline has been in a state of overload.When the design return period is 5 years,the number of overflow inspection wells is nearly 3/4,and almost all pipe segments are in overloaded operation state.The length of overloaded pipe segment accounts for 97.49%of the main pipe length,while the length of normal load pipe segment only accounts for 2.51%of the main pipe length,and the drainage capacity of the pipe network is low.Meanwhile,the concentration of chemical oxygen demand and suspended solids for the initial precipitation in the region is high,while the concentration of total phosphorus and ammonia nitrogen is low.The concentrations of chemical oxygen demand,suspended solids,total phosphorus and ammonia nitrogen are 3.56 times,40.40 times,1.35 times and 1.28 times of the standard for reuse water,respectively.Therefore,the receiving water has a higher risk of pollution.(4)In view of the existing problems for the current drainage capacity,initial rainwater pollution and insufficient resource utilization of an industrial park,optimized control of rainwater runoff and pollution is carried out by the green ecological rainwater system composed of non-mixed closure type diversion system and low-impact development facilities,and preliminary design of rainwater reuse facilities is carried out.The results show that:①After the transformation of the regional drainage system,the peak water level before the outfall decreased by about 33.39%,the water storage time of the pipeline was delayed by 12 minutes,and the peak time was delayed by 10 minutes.It shows that the non-mixed interception diversion drainage system can alleviate the overload operation of pipeline to a certain extent and reduce the risk of waterlogging,but the runoff reduction has no significant effect,only in the aspect of off peak storage.②Taking the annual runoff control rate of 85%and the maximum efficiency of green facilities as the objectives,the ecological rainwater system was optimized,and the optimized utilization rate of green facilities is close to 100%.And the reduction rate of total runoff,peak runoff and pollution load is about 70%except that the peak reduction rate of ammonia nitrogen is 96.43%.It shows that the load of the regional pipe network has been alleviated and the effect of runoff and pollution control is better.③After the green ecological rainwater system regulation,according to the initial rainwater pollution,the pipeline flocculator,rainwater sedimentation tank and pipe filter and other process facilities are preliminarily designed to effectively control the rainwater runoff pollution and improve the utilization rate of resources. |
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