Study On The Reformation Necessity Of Separate System For Old City Combined Drainage System

At present,most urban drainage systems in China save the combined drainage system because of the problems left over by history.When the rainstorm comes,the carrying capacity of the combined pipe network is often limited.Excessive sewage will overflow from the inspection wells and from the ends of the pipe network.Receiving water bodies are seriously polluted,for which it is particularly important to transform the combined drainage system.In this paper,Infoworks ICM software is used to rebuild and simulate the status quo of the combined drainage systems in the study area under separation and low-impact development measures,and the transformation effects are analyzed.The two reconstruction schemes are compared.The main contents are as the following.(1)A combined drainage system model was established by Infoworks ICM ICM software,and related parameters of the model were determined based on the literature both at home and abroad.(2)Based on the data of heavy rainy periods in the study area,the formula of storm intensity is deduced.Under the condition of five kinds of design rainfall recurrences,the city combined drainage system was simulated and found that as the rainfall intensity increased,the overflow of the network gradually aggravated,the discharge peak at the end of the peak increased pollutant emissions Increase,after the sewage treatment plant,the discharge of pollutants have a certain amount of reduction.(3)The separate system was reformed for the combined pipe network in the old urban area.After the reconstruction,the pipe network was simulated and found that due to the direct discharge of pollutants in the rainwater without being treated by the wastewater treatment plant,a large amount of pollutants still overflowed into the river and the pollutants emission reduction effect is not obvious.(4)The low-impact development measures were introduced into the combined pipe network,and it was found that both the node overflow and the discharge of pollutants in the outlet of the combined pipe network with low impact were significantly improved.After the sewage treatment,the drainage volume was further reduced,and the improvement effect was better than that of the separate system,resulting that there was no need to reform to separate system in this study area.