城市发展进程中不透水率增高影响雨水自然入渗，由此引发了城市内涝、面源污染等问题。国外因而提出了最佳管理措施BMPs、低影响开发LID等降雨径流控制方法与理念，我国近年也提出和推动海绵城市建设。然而目前我国的海绵城市建设仍处于起步阶段，其建设目标多为径流量及污染负荷的总量控制，有必要根据不同城市的实际特点提出针对性的管理、规划、评价和考核方法。平原河网地区具有河道密布、雨水排口众多等特点，降雨径流形成后通过雨水管网就近、分散地排入河道。研究以平原河网地区的降雨径流控制及水环境改善为目标，通过对比分析不同试点省市海绵城市规划、设计导则，构建了适用于平原河网地区的海绵城市目标与评价体系，关注雨水排口出水同时考虑河道调蓄空间。选择苏州市海绵城市建设试点内平江新城区域进行案例研究，在整理、分析区域各类基础数据与文件资料的基础上，制定了区域的海绵城市建设目标，设计了近期对部分项目地块进行透水铺装和下沉式绿地改造的LID情景一和远期对区域进行整体改造的LID情景二两种海绵城市建设情景。研究选取美国环保署（US EPA）开发的SWMM模型和EFDC模型，作为海绵城市情景模拟与分析的工具。使用SWMM模型建立研究区域的地表径流与管网输水模型，使用EFDC模型建立河道水动力水质模型，SWMM模型出水口流量及水质模拟结果作为径流污染源输入EFDC模型中，以模拟降雨径流入河后河道水位和水质的变化情况。在65%年径流总量控制率对应的设计日降雨、2015~2017年降雨时间序列和不同重现期两小时降雨条件下，对两种海绵城市建设情景的区域排水、河道响应进行模拟分析，并使用构建的评价体系对建设情景进行评价。各LID情景在雨量小时效益较好，随着降雨重现增加、降雨强度增大，径流控制率和污染削减率逐渐降低。LID情景一中项目地块可实现径流总量和污染削减的控制目标，但对区域整体及河道水环境改善效果有限。LID情景二可使区域整体达到建设目标，提高了区域排涝标准，除硬性的控制目标外，也可削减峰值流量、污染峰值浓度等，有效改善了区域的水环境。
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 non-point 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.
