Application Of Drainage Model For Urban Storm Water Quantity Management

Computer technology propelled the development and application of drainage model software, which becomes a necessary means in urban storm water management. In this paper, the composition and related theories of commonly used drainage models were introduced. InfoWorks CS software was used to establish storm drainage model in order to theoretically and techniquely provide suggestion and reference on the storm water quantity management for Shanghai as well as other cities in China.Correct selection of rainfall-runoff model and corresponding parameters is a premise for successful simulation of urban storm water drainage system. With measured flow data at a residential district of Shanghai, commonly used rainfall-runoff models were calibrated. Sensitivity analysis for major parameters was carried out as well. All these models achieved good simulation results. Parameters were ranked by their effect on runoff volume and peak as well. Lumped model gives a good result with proper storage compensation. The results were used for reference in the later build and calibration of urban drainage models.Storm detention tanks can provide temporary storage of runoff peak and thus mitigate the flooding problem especially for exsiting drainage sysetems with low design return perioud. Zhenru System was chosen as a representative drainage system for Shanghai to study efficiency of detention tank for flooding control in urban areas and the advantage of detention facilities as well. Hydraulic model was used to predict required tank volume if current pipe and pumping station size were maintained. Result shows that, when setting a detention tank volume of 6mm, the key area of Zhenru drainage system can withstand return periods of design storm up to 3yr, and over 50% construction investment can be saved to fulfil the system upgrade. The study can provide reference to other drainage system using detention tank for flooding control.Concerning the efficiency of interception and pollutant removal of detention tanks, hydraulic model was used to predict the long term efficiency of detention tank in Shanghai EXPO area for controlling urban non-point pollution. Simulation result shows that, detention tanks designed of 30m~3/ha can retain about 50% storm runoff annually in average rainfall years in Shanghai. For separate system with storm sewer interception, if interception is allowed during rainfall, the percentage of detention runoff will be higher. This study may provide valuable information on determining volume, operation mode and effects of detention tanks.Hydraulic model of Shanghai's combined Sewerage treatment project Phase I (SSPI) was used to analyze the issue of combined sewer overflows (CSOs) in Shanghai. Result shows that during typhoon storm and high tide level periods of Suzhou Creek, the river water flows backward to drainage networks by the out of date gravity discharge pipes which are not completely blocked after intercepting system put into use. This problem brings great damage to the efficiency of SSPI and measures should be taken for improvement. For most case, the interception pipes and Pengyuepu Pump Station are not the limiting factor for the occurrence of CSOs. By means of increasing interception capacity, optimizing system management, the overflow times of SSPI can be reduced to a lower level. The interconnection between sewer systems, flat pipe slope, and large sewer storage capacity, as well as the spatial difference of rainfall on large catchments, give tremendous detention capability of those combined networks. This lead to the overflow times of CSOs in Shanghai are much less than that of designed and of Japanese counterparts. The overflow pollution load of CSS is not more serious than that of separated sewer systems during wet weather, which is an advantage of CSS in Shanghai with respect to the control of urban non-point pollution. This advantage of CSS may be considered as an option in choice of drainage system for cities like Shanghai.