OpenSWMM 6 from the source code up: new solvers, 2D, plugins and the GUI.
OpenSWMM 6 is the open successor to EPA SWMM5, built by Caleb Buahin and the OpenSWMM team at HydroCouple. I don’t write the engine. I build apps that open it up, run it next to SWMM5 and show what is new.
Start here
- The Road to SWMM6. SWMM 6.0 alpha, SWMM5+ at CIMM and the open lineage.
- Nesterov Gradient Optimizer for SWMM6 and SWMM5. A faster iteration, tested in both engines.
- From a SWMM5 or SWMM6 Model Set to a Finished PDF Report. One wizard for either engine.
Try a tool
- SWMM6 UX Explorer. The OpenSWMM 6 desktop workspace, recreated as one web page around a demo model.
- Inside the SWMM6 GUI. How the SWMM6 GUI (Qt6, C++20) is put together.
- OpenSWMM Finite Volume. OpenSWMM 6’s finite-volume solver, explained.
More apps on this topic
- SWMM6 Shoebox. A one-site SWMM6 desk in the style of the EnergyPlus Shoebox tools.
- SWMM6 Anderson Acceleration. Anderson acceleration of SWMM6’s fixed-point iteration.
- KW, DW and SWMM6 Finite Volume. Kinematic wave, dynamic wave and SWMM6 finite volume, side by side.
- How SWMM6 Works. A short film of how SWMM6 works, with GIF export.
- HydroCouple vs SWMM5 Architecture. The HydroCouple and SWMM5 architectures, side by side.
- Two Tables, One Pipe. Companion to Corinne Wiesner-Friedman’s article on exact cross-section geometry for OpenSWMM 6.
- SWMM6 and ANUGA 2D. ANUGA Hydro as a 2D partner for SWMM6.
Work through an example
- How to Add SWMM6 Options to a SWMM5 .inp. The new SWMM6 keywords, added to a file you already have.
- SWMM5 to SWMM6 .inp Upgrader. Upgrade a SWMM5 file to SWMM6 options, and strip it back.
Code and automation
- HydroCouple/openswmm.engine. The OpenSWMM 6 engine (upstream).
- SWMMBobSWMM6/openswmm.engine. My fork of the engine.
- SWMMBobSWMM6/openswmm.gui. My fork of the SWMM6 GUI.
- SWMMBobSWMM6/openswmm.gymnasium. My fork of the reinforcement-learning environment.
- SWMMBobSWMM6/openswmm.engine.benchmarks. My fork of the engine benchmarks.
Recently added
- SWMM6 Shoebox. October 2026.
- From a SWMM5 or SWMM6 Model Set to a Finished PDF Report. October 2026.
Explore the archive
- 2D posts. Everything tagged 2D.
- SWMM6 group on LinkedIn. The SWMM6 discussion group.
- Hydraulics (older topic page). Flow, surcharge and solver stability.
Explore the six topics
- SWMM History: SWMM1 to SWMM6
- Inside SWMM5
- SWMM5 and ICM InfoWorks
- ICM InfoWorks and SWMM6
- Inside SWMM6 (this page)
- Comparing Models with AI
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Use of AI: Claude (Anthropic) drafted this page in November 2026. It picked the entries from my swmm5.org posts, Netlify apps and GitHub repositories and wrote the one-line descriptions. I chose the six topics and the layout.