Stormwater Design Software & Calculators

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.

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.