HydroComplete is built by Michael Flynn, a practicing water-resources PE — and a lot of what gets built here is given away. A full storm sewer design app, GIS plugins, CAD libraries, and hydrology engines, all with the same rule as the paid product: real formulas, shown in full, no black boxes.
GPL / MIT licensed. Use them at work today.Draw the network over a scaled aerial, or import it from Hydraflow STM, DXF, or LandXML. Rational method hydrology, Manning capacity for circular, box, elliptical and arch sections, and a true standard-step HGL/EGL backwater profile with junction losses and tailwater. HEC-22 inlet interception with bypass carryover between structures. Auto-size to velocity and percent-full criteria, then export a submittal PDF: title block on every page, ruled pipe, structure and inlet schedules, a scaled plan, and a profile with real elevation and station axes.
No license key, no seat count, no trial clock. An open recreation of the standard public-domain methods, so every number can be checked by hand. The browser link runs the same engine compiled to WebAssembly — quick calculators and whole-network analysis from a text file, without installing anything; the drawing and profile views live in the desktop app.
Open CAD Studio is a free, open-source DWG editor written in Rust. Both plugins below are GPL, install from its Plugin Manager marketplace in one click, and keep their hydraulic data as XDATA on the drawing entities so it round-trips through DWG. Drawing and analysis are free in both; a Pro key unlocks the deliverables. Built for Open CAD Studio v2026.36 (the host refuses plugins built for another release, so the version pairing matters).
Place inlets, junctions, outfalls and pipe runs on the canvas or import LandXML, then run the Rational method, Manning capacity and the HGL backwater pass on what you drew. Free: placement, import, SS_ANALYZE, command-line report, HGL profile, design-criteria check. Pro: KaTeX HTML report, automatic pipe sizing, multi-return-period table.
Import Civil 3D sewer geometry or LandXML, Atlas 14 IDF presets, Rational + Manning HGL, network diagram, BMP/WQV, and the same KaTeX reports as HydroComplete for Civil 3D. Free: everything through the HTML report. Pro: sealable PDF export.
Draw an area of interest and get the composite curve number: SSURGO soils, NLCD land cover, DEM slope for dual hydrologic groups, and NOAA Atlas 14 design-storm runoff — all fetched automatically from federal services (CONUS). Outputs CN polygons, a per-cell CN raster, and audit-ready CSVs. Falls back to ESA WorldCover when the federal land-cover server is down.
One file per routine, named for the command it adds. No installers, no license servers.
Small AutoLISP commands for daily drafting: acreage labels, bearing-distance, slope labels, flatten, coordinate exports, and more.
Survey-first LISP for Carlson: lot bearing-distance, point renumbering, inverse, traverse, field-book reports, station labels.
Importable VBA modules for OpenRoads Designer: acreage labels, PNEZD point I/O, station-offset, level translation, Z tools.
The stormwater connector that reads pipe networks and catchments straight from your drawing. Free to use; Pro PDF export is paid.
The library behind the desktop app, standalone and dependency-light: Rational flows, Manning for four conduit shapes, standard-step HGL, HEC-22 inlets. Compiles to WebAssembly; there is a command-line build too.
Rational method, SCS runoff, Manning's equation, HGL steps — the building blocks, implemented plainly and tested.
Pip-installable dam-breach hydrograph generator for SWMM / PCSWMM. Froehlich (2008) implemented, Teton validation case included.
Reads the LandXML alignments your drawings already export — clothoid spirals and station equations included, both of which most readers get quietly wrong — and answers what is inside N feet of an alignment, or where something crosses it. No database: it writes one folder with the provenance to prove every number. Validated against Civil 3D 2023, where the clothoid agrees to 7×10⁻¹¹ ft.
Physics-based vortex particle simulation as a Manning's-equation alternative for open-channel scour screening. 109 tests.
The app's Delineate from Map tool runs watershed delineation in your browser on USGS 3DEP elevation data (public domain, U.S. Geological Survey). It is a surface-terrain screening estimate: it does not see storm pipes or culverts, and the engineer must verify the boundary. It is built on these MIT-licensed projects:
Copyright © 2026 Qiusheng Wu. The geospatial tool suite compiled to WebAssembly (WASI).
Copyright © 2021-2026 John Lindsay, Whitebox Geospatial Inc. The hydrology tools (depression breaching, D8 flow, watershed) that geolibre-wasm compiles. Used under the MIT option.
By bjorn3. Runs the WASI tools in the browser. Used under the MIT option.
Copyright © 2014 Mike Adair, Richard Greenwood, Didier Richard, Stephen Irons, Olivier Terral and Calvin Metcalf. Map projections (CONUS Albers, EPSG:5070, for equal-area measurement).
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
Want the full design suite — detention routing, water quality, sediment, sealable reports? That's the paid product that funds all of this: HydroComplete Pro.