Rillwork: Engineering Disclaimer

DRAFT — not legal advice. Plain English. Have it reviewed before it is published or relied on. A short version should also appear in the app's About box and at the foot of every printed drainage report.

Last updated: 24 October 2026

The engineer is responsible for the design

Rillwork is software that helps a qualified engineer build, run and report a stormwater or sewer model. It does not design anything, and it does not certify anything.

You, the engineer, are responsible for your work and its results. That means you must:

• check your inputs: geometry, inverts, roughness, losses, rainfall, infiltration, boundary conditions and units;
• check your results for reasonableness: continuity errors, flooding, surcharge, instability warnings and any messages in the EPA report;
• confirm the method suits the project, and that it meets the standards of the reviewing agency and jurisdiction;
• seal, sign or stamp your own work where the law requires it, and only after your own review.

Producing a report in Rillwork is not a check, an approval or a certification of the design.

About the engine

• Rillwork runs the EPA Storm Water Management Model (SWMM) 5.2.4 engine, compiled to WebAssembly from EPA's public-domain C source with no changes to the engine.
• Every drainage report states the engine version that produced it.
• EPA SWMM is public domain. The EPA did not make, review or endorse Rillwork, and it is not responsible for Rillwork or for your results.
• We tested the compiled engine against EPA's example and regression models (see the app's documentation). Testing reduces risk; it does not remove it.

What Rillwork adds, and its limits

These parts are Rillwork's own work, not EPA's. Check what they produce before you rely on it:

• The editor, the results viewer and the report layout.
• Design storms. NRCS (SCS) Type I, IA, II and III 24-hour distributions, written as SWMM time series. The source tables and their verification status are documented in the app.
• Optional NOAA rainfall lookup. Fetches depths from NOAA's public server when you turn it on. Confirm the values against NOAA's own site before using them in a design.
• Import of files exported from Civil 3D Storm and Sanitary Analysis, SewerGEMS and CivilStorm. This import is new and has not been tested against real exports. It lists every change it makes. Compare the imported model with the original before relying on it.
• Optional map background. Map tiles from OpenFreeMap are for orientation only, not for survey or design.

It is a beta

Rillwork is in a free public beta. It may contain errors. It is provided with no warranty of any kind (see TERMS.md and EULA.md).

Short form (for the app and the foot of each report)

Produced with Rillwork (beta), using the unmodified EPA SWMM 5.2.4 engine. Results are the responsibility of the engineer of record, who must check them and seal their own work. Rillwork is not affiliated with or endorsed by the US EPA. No warranty.