OpenSWMM 6 User Guide (refactored engine)

Note

These guides cover the OpenSWMM 6 refactored engine at openswmm.engine. If you are looking for the original EPA SWMM 5.x solver — preserved verbatim for backward compatibility — see Legacy SWMM 5 — Compatibility Layer.

The User Guide is the canonical “how do I do X?” reference for the modern openswmm.engine API. Every page follows the same layout:

• Class signature — the constructor and how the class fits in.

• Key methods — grouped by purpose (geometry, state, forcing, …).

• End-to-end example — a runnable snippet covering the typical workflow.

• Common recipes — short snippets for everyday tasks.

• Bulk arrays — the numpy-friendly accessors (*_bulk).

• EngineState requirements & exceptions — what’s legal when, and what each method raises.

Newcomers, start with Installation, Quickstart, then Concepts & engine lifecycle.

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Running a simulation

• Running a simulation — Solver
• Error handling, edge cases & debugging

Domain access

The “what’s the depth of node J1 right now?” surface. One page per domain.

• Nodes
• Links
• Subcatchments
• Rain gages

Forcing & control

Inject runtime inflows, override rainfall and time-series, fire control actions.

• External inflows
• Advanced forcing
• Control rules
• Tables (time series, curves, patterns)

Water quality

Pollutants, landuse, buildup/washoff, treatment.

• Pollutants
• Water quality (landuse, buildup, washoff, treatment)

Outputs

Reading the binary .out file, hot-start save / restore, mass balance, accumulated statistics.

• Output reader (binary .out file)
• Hot start
• Mass balance
• Statistics

Specialised topics

Build a model from scratch in Python; mutate an open model in place; configure complex hydraulic infrastructure; spatial / CRS handling.

• Programmatic model construction
• Model editing (deletion + type conversion)
• Infrastructure (transects, streets, inlets, LIDs)
• Spatial (CRS, coordinates, geometry)