EPA(Environmental Protection Agency, 环境保护署)SWMM(storm water management model，暴雨洪水管理模型)是一个动态的降水-径流模拟模型，主要用于模拟城市某一单一降水事件或长期的水量和水质模拟。其径流模块部分综合处理各子流域所发生的降水，径流和污染负荷。其汇流模块部分则通过管网、渠道、蓄水和处理设施、水泵、调节闸等进行水量传输。该模型可以跟踪模拟不同时间步长任意时刻每个子流域所产生径流的水质和水量，以及每个管道和河道中水的流量、水深及水质等情况。 SWMM自1971年开发以来，已经经历过多次升级。在世界范围内广泛应用于城市地区的暴雨洪水、合流式下水道、排污管道以及其它排水系统的规划、分析和设计，在其它非城市区域也有广泛的应用。当前最新版本是在以前版本基础上进行了全新升级的结果，可以在Windows操作系统下运行SWMM5提供了一个宽松的综合性环境，可以对研究区输入的数据进行编辑、模拟水文、水力和水质情况，并可以用多种形式对结果进行显示，包括对排水区域和系统输水路线进行彩色编码，提供结果的时间序列曲线和图表、坡面图以及统计频率的分析结果。 最新的版本开发由国家环境保护署国家风险管理研究中心实验室下属的供水和水资源研究中心资助，同时也得到了来自CDM咨询公司的协助。
EPA’s Storm Water Management Model (SWMM) is used throughout the world for planning, analysis, and design related to stormwater runoff, combined and sanitary sewers, and other drainage systems in urban areas. There are many applications for drainage systems in non-urban areas as well.
SWMM is a dynamic hydrology-hydraulic water quality simulation model. It is used for single event or long-term (continuous) simulation of runoff quantity and quality from primarily urban areas. The runoff component operates on a collection of sub-catchment areas that receive precipitation and generate runoff and pollutant loads. The routing portion transports this runoff through a system of pipes, channels, storage/treatment devices, pumps, and regulators.
SWMM tracks the quantity and quality of runoff made within each sub-catchment. It tracks the flow rate, flow depth, and quality of water in each pipe and channel during a simulation period made up of multiple time steps. SWMM 5 has been extended to model the hydrologic performance of specific types of low impact development (LID) controls. The LID controls that the user can choose to include the following green infrastructure practices:
- Rain gardens
- Bioretention cells (or bioswales)
- Vegetative swales
- Infiltration trenches
- Green roofs
- Rooftop (downspout) disconnection
- Rain barrels or cisterns (rainwater harvesting)
- Continuous permeable pavement systems
The updated model allows engineers and planners to accurately represent any combination of LID controls within a study area to determine their effectiveness in managing stormwater and combined sewer overflows.
Running under Windows, SWMM 5 provides an integrated environment for editing study area input data; running hydrologic, hydraulic and water quality simulations; and viewing the results in a variety of formats. The latter includes color-coded drainage area and conveyance system maps, time series graphs and tables, profile plots, and statistical frequency analyses. SWMM 5 was produced in a joint development effort with CDM, Inc., a global consulting, engineering, construction, and operations firm.
SWMM accounts for various hydrologic processes that produce runoff from urban areas, which include the following:
- Time-varying rainfall
- Evaporation of standing surface water
- Snow accumulation and melting
- Rainfall interception from depression storage
- Infiltration of rainfall into unsaturated soil layers
- Percolation of infiltrated water into groundwater layers
- Interflow between groundwater and the drainage system
- Nonlinear reservoir routing of overland flow
- Runoff reduction via LID controls
Spatial variability in all of these processes is achieved by dividing a study area into a collection of smaller, homogeneous sub-catchment areas. Each of the areas contains its own fraction of pervious and impervious sub-areas. Overland flow can be routed between sub-areas, between sub-catchments, or between entry points of a drainage system.
SWMM contains a flexible set of hydraulic modeling capabilities used to route runoff and external inflows through the drainage system network of pipes, channels, storage/treatment units and diversion structures. These include the ability to
- handle drainage networks of unlimited size;
- use a wide variety of standard closed and open conduit shapes as well as natural channels;
- model special elements, such as storage/treatment units, flow dividers, pumps, weirs, and orifices;
- apply external flows and water quality inputs from surface runoff, groundwater interflow, rainfall-dependent infiltration/inflow, dry weather sanitary flow, and user-defined inflows;
- utilize either kinematic wave or full dynamic wave flow routing methods;
- model various flow regimes, such as backwater, surcharging, reverse flow, and surface ponding; and
- apply user-defined dynamic control rules to simulate the operation of pumps, orifice openings, and weir crest level
SWMM can estimate the production of pollutant loads associated with stormwater runoff. The following processes can be modeled for any number of user-defined water quality constituents:
- Dry-weather pollutant buildup over different land uses.
- Pollutant wash-off from specific land uses during storm events.
- Direct contribution of rainfall deposition.
- Reduction in dry-weather buildup due to street cleaning.
- Reduction in wash-off load due to best management practices (BMPs).
- Entry of dry weather sanitary flows and user-specified external inflows at any point in the drainage system.
- Routing of water quality constituents through the drainage system.
- Reduction in constituent concentration through treatment in storage units or by natural processes in pipes and channels.