EPA SWMM solver versions used by SewerGEMS and CivilStorm

Product(s): SewerGEMS, CivilStorm
Version(s): CONNECT Edition, V8i
Area: Calculations


Which version of the EPA SWMM numerical solver is used by SewerGEMS and CivilStorm, when the active solver is set to "Explicit" in the calculation options?


As new versions of SewerGEMS and CivilStorm are released, they generally use the latest version of the underlying EPA-SWMM technology (the solver) when using the Explicit solver. There are also some Bentley-specific enhancements made to the solver. Starting with the CONNECT Edition Update 2 release of SewerGEMS and CivilStorm, you can run the SWMM engine with the Bentley extensions turned off. The default setting is to use the Bentley enhanced version. To do so, open the calculation options properties and set Solver Compatibility to “SWMM (EPA 5.1.012).” See the section below for details.

The SWMM solver version number used can be found by computing a model while using the Explicit SWMM solver. In V8i, SELECTseries 5 and earlier, a text file will appear with the SWMM version number listed at the top.

Starting with the CONNECT Edition of SewerGEMS and CivilStorm, the solver version can be seen in the SWMM output file, saved when saving the model. 

You can also refer to the below chart.

Bentley Product

EPA-SWMM Solver Version

SewerGEMS/CivilStorm CONNECT Edition Update 4 (


SewerGEMS/CivilStorm CONNECT Edition Update 3 ( and


SewerGEMS/CivilStorm CONNECT Edition Update 3 ( and


SewerGEMS/CivilStorm CONNECT Edition Update 3 (


SewerGEMS/CivilStorm CONNECT Edition Update 2 (10.02.00.XX)


SewerGEMS/CivilStorm CONNECT Edition Update 1 ( and


SewerGEMS/CivilStorm CONNECT Edition (


SewerGEMS/CivilStorm CONNECT Edition (


SewerGEMS/CivilStorm V8i SELECTseries 5 ( and


SewerGEMS/CivilStorm V8i SELECTseries 4 (


SewerGEMS/CivilStorm V8i SELECTseries 3 (


SewerGEMS/CivilStorm V8i SELECTseries 2 (08.11.02.XX)


SewerGEMS V8 XM ( and


CivilStorm V8 XM ( and


Solver Compatibility - EPA SWMM solver vs. "Bentley Enhanced"

The default EPA-SWMM solver included with SewerGEMS and CivilStorm is a "Bentley Enhanced" version, which means Bentley has added functionality so that it more seamlessly integrates with the SewerGEMS/CivilStorm data model and with other Storm-Sewer Products. 

It is important to note that as of the initial CONNECT Edition release of SewerGEMS and CivilStorm, the core SWMM hydraulic solver has not been modified by Bentley - it has simply been "enhanced" to provide more results. So, the basic hydraulic results you see when using the Explicit solver in SewerGEMS and CivilStorm should match EPA-SWMM (for the respective version - see table above) 

Note: starting with CONNECT Edition Update 2 version, you can now choose between the default "Bentley Enhanced" version of the SWMM solver, or the "standard" version of the SWMM solver, with those enhancements turned off. This can be useful if you need to ensure SWMM solver results for your model are fully compatible with EPA-SWMM itself, for example (by turning off the Bentley enhancements noted below).

These are the specific "Bentley enhancements" :

1. HEC-22 Inlet Calculations
2. Ability to compute complex pond outlet structures
3. Headloss Calculations at structures including HEC-22 and Standard Headloss methods
4. Additional detailed results
5. Integrated LID results
6. Tractive Stress Calculations
7. Hydrogen Sulfide Modelling

If the compatibility mode is set to “EPA (5.1.01X)”, these enhancements are turned off in order to match the EPA-SWMM capabilities:

  • On Grade Inlet Calculations - All on grade inlets will assumed to be full capture. (this is because EPA-SWMM itself does not have inlet elements or the ability to calculate inlet capture. See related discussion)
  • Node Headlosses - The EPA version of the SWMM engine assumes zero headloss across nodes.
  • Pond Outlet Structures - In EPA mode, composite outlet structures associated with ponds are loaded as a single outlet rating curve assuming free outfall.
  • Tractive Stress Calculations
  • Hydrogen Sulfide Analysis
  • Calculation Options - The following options were added by Bentley to improve the overall stability of simulations under certain conditions, and are not used in runs in EPA mode: “Inlet Transition Depth” and “Use Bentley Transition Equation?”

See Also

Troubleshooting unstable SewerGEMS and CivilStorm model results using the Explicit SWMM Solver