Stormwater Design Software & Calculators

Storm and foul water drainage design and 1D hydraulic modelling software for UK and Irish civil engineers.

Browser-based hydrology and hydraulics calculators for practising engineers — no install, report-ready output.

EPA's free tool for estimating site runoff reduction from green infrastructure, with climate scenarios.

The public-domain engine of urban drainage: dynamic-wave pipe networks, runoff, LID and water quality.

A free bundle of FHWA drainage calculators: channels, weirs, curb & gutter, riprap, detention and more.

Build and read EPA SWMM models as QGIS layers — free GIS-based SWMM model construction.

The US land-development standard for TR-55/TR-20 hydrographs and detention pond design.

Autodesk's integrated catchment model — the heavyweight for large sewer networks and coupled 2D flooding.

Browser-based urban stormwater and drainage modeling powered by OpenSWMM 6 compiled to WebAssembly.

eWater's stormwater-quality model — the WSUD assessment standard across Australian councils.

CDM Smith's free rainfall statistics and STORM-method screening model — IDF analysis, disaggregation, CSO planning.

Bentley's sanitary and combined sewer modelling suite, integrated with CAD and GIS environments.

CHI's commercial GIS front-end for SWMM — the most direct productivity upgrade for serious SWMM users.

Virginia DEQ's official Excel workbooks for stormwater compliance via the Runoff Reduction Method.

Hydrologic modeling software for urban and rural stormwater management, master drainage planning, and pond design.