PySWMM: The Python Interface to Stormwater Management Model (SWMM)

Abstract

Stormwater management seeks to reduce runoff from rain or melted snow and improve water quality. Where it can absorb into soil, runoff is filtered and returns to streams, rivers, and aquifers, but in developed areas, precipitation often cannot soak into the ground because impervious surfaces (e.g., pavement, buildings), and already saturated soils can create excess runoff. This water, which can contain pollutants, then runs across urban surfaces and into storm drains, drainage ditches, and sewer systems. Stormwater runoff can cause flooding, erosion, infrastructure and habitat damage, and contamination (including combined and sanitary sewer overflows). In urban and developed areas, effective stormwater management that routes and detains stormwater helps to mitigate these impacts and improve water quality. The U.S. Environmental Protection Agency's (EPA) Stormwater Management Model (SWMM) is a dynamic rainfall-runoff model that has been used for decades to conduct single event or long-term hydrologic, hydraulic, and water quality simulations. It has been used widely throughout the world for planning, analysis, and design of drainage systems (Rossman, 2015). SWMM models the hydrologic processes that generate runoff including rainfall, snowmelt, evaporation, infiltration, and groundwater dynamics, and it routes water through a hydraulic network that includes channels, pipes, storage units, and pumps. The EPA distribution of SWMM does not, however, allow the modeler to interact with the SWMM model during simulation time nor access all of the simulated values and results. Over the last decade, several libraries have been developed to read, parse, and run SWMM models (*.inp). These tools have been developed in several programming languages including, but not limited to, Python, R, MATLAB, and Visual Basic. Beyond simple SWMM interfacing utilities, many libraries include a collection of specific features for different applications.