AquaSWMM

Migration guide

Moving an XPSWMM model to EPA SWMM 5 and AquaSWMM

XPSWMM is now sold only as an Autodesk subscription, and Autodesk presents InfoWorks ICM as its upgrade path. Some agencies are taking another route. In 2024 the Bassett Creek Watershed Management Commission (Minnesota) approved converting its model off XP-SWMM, after its engineer reported licensing changes that would “greatly increase its cost” (Barr Engineering memo, revised February 26, 2026).

If you’re weighing the same move, here is the route to a standard EPA SWMM 5 model, which AquaSWMM opens and runs on EPA’s own engine for $490 a seat per year, or $1,200 for five seats. Be clear about one thing first: this is a conversion, not a file you can simply open. Plan to check the model.

1. Know what you’re converting from

  • The 1D engine is related to SWMM, not identical to it. Innovyze’s documentation describes XPSWMM’s 1D engine as “based on the EPA SWMM engine” with “significant proprietary enhancements”, descended from the SWMM 4 line. EPA SWMM 5 is a rewrite, so results will not match to the decimal. Barr says the same about its own conversion: “the simulation results will differ.”
  • XPSWMM’s 2D runs on TUFLOW. XPSWMM links its SWMM-based 1D network to TUFLOW for the 2D calculations. That 2D model does not export to SWMM 5. In AquaSWMM you rebuild the surface from your DEM instead. Its 2D overland-flow solver keeps its settings in a separate file beside the .inp, so the .inp stays EPA’s format (manual chapter 20).

2. Export from XPSWMM

XPSWMM has a built-in export: File > Import/Export Data > Export to EPASWMM 5 (listed in Innovyze’s XPSWMM help as “Export to EPASWMM 5 model”; the menu path is from the TUFLOW wiki). Run it with XPSWMM still licensed: you need XPSWMM to write the file.

What to check afterwards:

  • Hydrology. The TUFLOW wiki warns that “XPSWMM does not write out all required hydrology information when doing a simple export to EPA SWMM 5,” and that “infiltration parameters (such as curve numbers) do not get written correctly.” Check every subcatchment’s infiltration and width against your XPSWMM data. AquaSWMM’s attribute table can set a whole column at once (manual chapter 6).
  • Special links. Users on the openswmm.org forum report that some XPSWMM-specific conduits and multi-links don’t carry over, and that # characters in object names cause trouble (thread). These are user reports, not a vendor list. Count your objects before and after.
  • Stability. Barr’s conversion included “modifying weirs lengths or converting to open channels to improve model stability.” Expect some of that.

3. Open and check the model in AquaSWMM

  • Open the exported .inp. AquaSWMM keeps the file exactly as written, including sections it has no editor for, so nothing is silently dropped on save (manual §1.6).
  • Run it on EPA’s engine. AquaSWMM runs EPA’s runswmm.exe unmodified and stamps every run with the engine version and the SHA-256 of the executable. The .inp stays EPA’s format, so the network model also runs in the free EPA SWMM program, and anyone can reproduce it without a license.
  • Compare against your XPSWMM results. Check peak flows and depths at the locations that matter: outfalls, critical structures, regulatory points. Then document the differences and why. After that, AquaSWMM’s Compare Runs tracks every change you make from the converted baseline (manual §9).

4. The cost

A Bassett Creek planning table from February 2024 listed XPSWMM at $7,500 per year (unlimited nodes, 1D) (source). An AquaSWMM seat is $490 a year, and the converted model is a standard EPA SWMM 5 file that no vendor can lock up.

Try it on your own model

The 30-day trial is the full app. If you’re converting a model and get stuck, email michael@hydrocomplete.com. I’ll send a 90-day evaluation key and look at the converted .inp with you.

XPSWMM, XPSTORM and InfoWorks ICM are trademarks of Autodesk, Inc. TUFLOW is a trademark of BMT. AquaSWMM is independent software from HydroComplete LLC and is not affiliated with or endorsed by Autodesk, BMT or the U.S. EPA. Facts about XPSWMM are quoted from the linked public sources as of October 2026. Check current terms with Autodesk.