Coupled Modelling Of Stormwater Runoff And Water Environment In Suzhou Sponge City Pilot Areas

In the process of urban development,increase of the impervious rate have affected the natural infiltration of rainfall,which has led to the problem of urban floods and nonpoint source pollution.Stormwater runoff control methods and concepts such as Best Management Practices(BMPs)and Low Impact Development(LID)have been proposed in foreign countries.In order to solve the problem caused by stormwater runoff,China has vigorously promoted the construction of Sponge City in recent years.However,China's Sponge City construction is still in its starting stage,and the total amount control objectives have certain limitations.It is necessary to propose targeted management,planning,evaluation,and assessment methods based on the actual characteristics of different cities.Plain river network region has dense river channels and numerous rainwater outlets.Stormwater runoff is scattered discharged into the river nearby.This study aims at the control of stormwater runoff and improvement of the water environment in the plain river network region.Through comparative analysis of Sponge City guidelines of different provinces and pilot cities,a Sponge City planning and evaluation method for the plain river network region was constructed,which pointed out that attention should be paid to the discharge outlets as well as the receiving water channels.Pingjiang New City,Suzhou was selected as the case study area.After analyzing various types of basic data in the region,the construction objectives of the region were formulated.Two LID scenarios were designed: one for permeable pavement and concave green land reconstruction for some project parcels,the other for the overall renovation of the region.This study selected SWMM and EFDC model developed by the US Environmental Protection Agency as the tool for simulation and analysis of the Sponge City construction plan.While SWMM was used to model the surface runoff and pipe network transmission,EFDC was used to model the river hydrodynamic and water quality.The outlet flow rate and water quality simulation results in SWMM were used as the pollution source input of EFDC to simulate changes in water level and water quality when stormwater was discharged into the river network.The two sponge city construction plans were simulated and evaluated under different rainfall conditions(designed daily rainfall corresponding to 65% annual rainfall volume control rate,2015~2017 annual rainfall time series,and two hours rainfall of different return periods).The LID scenarios have a better performance in small rainfall.With the increase of rainfall intensity,the runoff control effect gradually weakened.The LID Scenario 1 can achieve the total runoff and pollution reduction control objectives in project lot,but has limited improvement for the overall region.LID Scenario 2 enables the region as a whole to meet the construction goals and raise the standards for river flood control.While in addition,peak flow rates,peak pollutant concentration,etc.can also be reduced,thus effectively improving the water environment.