SWMM Technical Reference

The SWMM Reference Manual Volume I (Hydrology) describes how SWMM simulates rainfall–runoff processes across urban catchments. It covers key components such as precipitation input, evaporation, interception, infiltration, surface runoff generation, and groundwater interactions. This volume explains how subcatchments respond to rainfall and generate both runoff and pollutant loads under single-event and continuous simulation conditions. It provides the theoretical basis and parameter definitions needed for accurate hydrologic modeling, calibration, and interpretation of results.

"The revised SWMM Reference Manual Volume I (Hydrology) updates the original SWMM hydrology framework with enhanced methods for simulating urban runoff processes. It includes refinements to infiltration modeling, improved rainfall data handling, and more accurate representation of surface runoff and subcatchment response. This revision also improves integration with hydraulic components of SWMM, enabling more consistent and reliable simulation of both single-event and continuous conditions. These enhancements support greater accuracy in runoff estimation and overall model performance for modern stormwater applications."

"The SWMM Reference Manual Volume II (Hydraulics) explains how SWMM models flow routing through urban drainage systems, including pipes, channels, storage units, and hydraulic control structures. It details both kinematic and dynamic wave routing methods, including the simulation of backwater effects, pressurized flow, and surcharging conditions. The manual also covers hydraulic elements such as weirs, orifices, pumps, and regulators, providing the theoretical and numerical foundation for accurate system-wide hydraulic analysis."

"The SWMM Reference Manual Volume II (Hydraulics) Addendum (2022) introduces important enhancements to SWMM’s hydraulic modeling capabilities for urban drainage systems. It includes advanced methods such as the Preissmann Slot approach for simulating pressurized flow in closed conduits, improving accuracy under surcharged conditions. Additional updates include refined street runoff capture modeling and the introduction of a variable-speed Type 5 pump, expanding the flexibility of system representation. These enhancements strengthen SWMM’s ability to model complex hydraulic behavior and provide more robust analysis for modern stormwater systems."

"SWMM Reference Manual Volume III - Water Quality focuses on the simulation of pollutant generation, transport, and treatment within urban drainage systems. It describes buildup and washoff processes, pollutant routing through the network, and the impact of treatment devices on water quality. This volume also introduces Low Impact Development (LID) controls, including green infrastructure practices such as bioretention, infiltration systems, and permeable surfaces. It provides the modeling framework needed to evaluate water quality performance and sustainable stormwater management strategies."

"The SWMM Reference Manual Errata provides corrections and updates to Volumes I (Hydrology) and II (Hydraulics) of the SWMM Reference Manuals. It includes revisions to table headings, parameter definitions, equations, and numerical values to improve the accuracy and clarity of the original documentation. This document serves as an important companion resource, ensuring that users apply the most accurate formulations and interpretations when working with SWMM’s hydrologic and hydraulic models."