SWMM2D 6.0.0-alpha.1

The New Standard for
Urban Water Intelligence

Data-oriented, plugin-extensible next-generation computational engine for the SWMM community—reentrant design, Structure of Arrays core, and a domain-split C API. The same trusted physics, evolved for modern workflows.

Documentation & Alpha Capabilities
C++20
Modern Core
Reentrant
No Global State
C API
Domain-Split
ASCE
Sponsorship
Official resources
swmm2d.engine GitHub swmm2d.mcp Roadmap Contributing Guide
Sponsored By
ASCE
EWRI
Open Source Community
Core Capabilities

Engineered for the
Modern Water Professional

The Open-Source SWMM6 engine, a desktop GIS workspace, AI-ready MCP integration, and SWMM-nasium optimization—built for trusted physics at production scale, including container-friendly deployment for regional studies.

Open-Source SWMM6 Engine

Modern C++20 core with a data-oriented layout; reentrant API with no hidden global state; domain-split C headers; backward-compatible .inp with the legacy EPA SWMM 5.x solver.

  • 1D/2D hydrology and hydraulics with mesh generation and surface routing suited to large catchments.
  • Plugin framework for I/O, algorithms, and modules—extend water quality and green infrastructure without forking the solver.
  • Multiple simulations per process for embedding, services, and parallel batches.
2D mesh over terrain—mesh generation tied to the 1D/2D engine.
SWMM2D GUI—layers, basemaps, and simulation status in one workspace.

SWMM2D GUI

A desktop GIS environment for building and reviewing models: layer tree, map canvas, object browser, properties, message logs, and run status—aligned with real engineering workflows.

  • GIS integration with basemaps, raster layers, and coordinate reference system metadata in the status bar.
  • Visual debugging at city scale—large junction, conduit, and subcatchment counts stay navigable in the browser and map.

MCP Server AI Integration

A Model Context Protocol server connects assistants and automation to your SWMM tooling—iterate on scripts, maps, and workflows from the IDE with the same project context your model lives in.

  • Tooling-aware workflows—documented entry points for inspection, generation, and integration with external AI stacks.
  • Engineering-first—accelerates iteration without replacing professional judgment on physics and validation.
Agent-assisted modeling—chat, diffs, and maps tied to your MCP workspace.
Regional GIS context—terrain and networks at the scale optimization runs operate on.

SWMM-nasium Advanced Optimization

SWMM-nasium targets calibration, scenario search, and ensemble studies with significant runtime improvements on large networks—complementing the core engine for repetitive or optimization-heavy workloads.

  • Scenario scale—suited to city-wide and regional models where raster baselines and dense networks dominate run time.
About the Project

Beyond Legacy Code.
Built for the Next Thirty Years.

Born from a coalition of academic leaders, engineering pioneers, and the open-source community, the SWMM2D project moves the industry’s core simulation stack towards a dynamic, professional standard.

SWMM2D represents the most significant evolutionary leap in hydraulic modeling since the release of EPA SWMM 5. Sponsored by the American Society of Civil Engineers (ASCE) and the Environmental & Water Resources Institute (EWRI), SWMM2D is not just a rewrite—it is a re-imagining of critical infrastructure software.

By rebuilding the engine in modern C++20 with a data-oriented layout and reentrant API design, we have eliminated global state and opened the door to multiple independent simulations in one process. Performance and clarity go hand in hand.

The platform is designed for practical interoperability: a domain-split C API and plugin interfaces allow clean embedding from Python, .NET, and cloud services while preserving transparent, community-governed engineering standards for digital-twin and smart-city workflows.

Domain-split C API

  • Headers split by domain—engine, model, nodes, links, controls, and more
  • Plugin-based I/O: output and reports via plugins on a dedicated thread
  • Callbacks for progress, warnings, and timestep hooks
  • Backward-compatible .inp with extension options and new sections 
/* Reentrant design: global state removed; simulation state lives
   behind an opaque SWMM_Engine handle. Full symbols in:
   swmm2d_engine.h — swmm2d.engine

#include <swmm2d_engine.h>
/* Model build, step loop, plugins, hot start — see domain headers */
Strategic Roadmap

Current Development Priorities

Priorities are organized by theme, not strict release targets, because scientific software timelines depend on validation rigor and community bandwidth. A core theme is advection-dispersion transport from overland to pipe and groundwater domains, with release assignments updated as work matures through experimental branches. Read the full roadmap.

Routing

Flow Routing: Implicit 1D Saint-Venant

The current explicit solver for 1D flow routing imposes Courant-limited time steps in steep or rapidly varying flows. An implicit (or semi-implicit) full Saint-Venant formulation is planned to improve stability across subcritical, supercritical, and mixed-regime conditions while preserving compatibility with current input formats.

📋 Planned Implicit solver option Hydraulic jumps Convergence diagnostics Benchmark regression tests
Water Quality

Water Quality Transport Across Pipe, Overland, and Groundwater Domains

Focuses on advection-dispersion transport: 1D ADE in pipes, 2D or quasi-2D ADE overland, and ADE coupling into groundwater. A unified multispecies reaction framework then applies across all ADE-enabled domains once transport pathways are in place.

🔬 Exploration Pipe ADE (1D) Overland ADE (2D/quasi-2D) Groundwater ADE coupling Multispecies reactions
Transport

Sediment and Heat Transport Expansion

The public roadmap prioritizes new sediment and thermal modeling capabilities, including erosion/deposition workflows, routing in channels and pipes, and coupled heat transport from catchment to receiving waters.

📋 Planned Sediment fractions Heat exchange Field validation
Community Driven

Transparent Status Tracking

Status tracking remains public and release-updated, and users directly influence priorities through GitHub discussions, proposal feedback, and issue-level input that is reviewed during roadmap updates.

⏸ Deferred items ✅ Completed tracker Release-updated document Community-informed priorities
Read full roadmap
Get Involved

Contribute with Clear Governance

SWMM2D contributions follow an open governance model with explicit review requirements, CI gates, and documentation standards to protect scientific reproducibility.

Contribution Workflow

Start from `dev`, open or reference an issue, add tests with your change, and submit a PR with documented rationale. Bugfix and feature branch naming conventions are defined in the contributing guide.

Read Contribution Guide

Review and CI Requirements

Every PR requires Technical Manager, AI copilot, and community approvals. CI must pass build, tests, regression checks, static analysis, and documentation generation before merge.

Read Contribution Guide

Roadmap and Prioritization

Priorities are maintained in the roadmap and shaped by community discussions. Major formulation changes follow a structured proposal, feedback, and validation process.

Explore Roadmap Details

Ready to Build the Future of Water Modeling?

Read the generated API documentation online, track active development on GitHub, and join the community shaping the next generation of SWMM.

Documentation & releases GitHub
Questions

Frequently Asked Questions

Quick answers about SWMM2D, official documentation, roadmap status, and contributor workflow.

What is SWMM2D?

SWMM2D is a community-driven, open-source continuation of the EPA Storm Water Management Model (SWMM). Version 6 is a major modernization of the computational engine: data-oriented design, a reentrant SWMM_Engine API, plugin-based I/O, and a domain-split C API. The legacy SWMM 5.x solver remains available.

Where is the official documentation?

Generated documentation (overview, headers, and API reference) is published here: swmm2d.engine.

Where can I follow code changes and pull requests?

Active development is tracked on GitHub.

Where can I read the full roadmap and contribution policy?

Use the full-page readers: Roadmap and Contributing Guide. Both pages load content directly from the markdown source files so updates appear automatically on refresh.

How does SWMM2D relate to EPA SWMM 5?

The project preserves backward-compatible .inp input while extending it with new options and sections. Hydraulic and process improvements are being integrated in a way that aims to remain compatible with existing workflows; always check release notes and verification guidance for your use case.

Who sponsors the broader SWMM community effort?

The community works with organizations including ASCE’s Environmental and Water Resources Institute (EWRI) toward long-term sustainability of the SWMM codebase.