| Applies To | |
| Product(s): | SewerGEMS, CivilStorm, StormCAD, SewerCAD |
| Version(s): | 08.11.XX.XX and higher |
| Area: | Calculations |
How do I enter a minor loss coefficient for a conduit or pressure pipe in the OpenFlows Storm and OpenFlows Sewer products?
Minor loss modeling depends on the active numerical solver used (selected in the calculation options). As of version 2024 in October, 2025:
Implicit (Bentley Dynamic)
Explicit (SWMM Dynamic)
GVF-Convex (SewerCAD)
GVF-Rational (StormCAD)
Note: by definition, minor losses typically do not account for significant head loss and are often omitted in hydraulic models.
If the solver you need to use does not support minor losses for the desired pipe type (for example pressure pipes with the SWMM solver), you can account for these minor losses by adjusting the Friction factor / Roughness Coefficient (up or down), or for conduits you can model it with a structure loss method specified in the adjacent node (manhole). For example for pressure pipes, for testing purposes, you can switch to the GVF-Convex (SewerCAD) solver (available in SewerGEMS and SewerCAD) where you can supply a Minor Loss coefficient, get the results (to see how much of an impact the losses have on the model) and then match the results by adjusting the roughness of the pressure pipes using the Explicit (SewerGEMS) solver.
In a situation where you need to account for significant minor losses in a pump station with the SWMM solver, consider compensating by adjusting the Head values in the pump definition.
Q: I have entered a value for the Exit Loss Coefficient or Entrance Loss Coefficient field in the properties of a conduit, but I do not see a drop in head at the respective pipe end.
A: For better compatibility with EPA-SWMM standards, the Implicit solver accounts for conduit entry/exit loss as part of the pipe headloss; an additional friction loss in the momentum equation. In other words, they apply across the length of the pipeline. So, you will not see a “head loss” at the end of the pipe as one might expect from the energy equation. The effect of such losses is similar to changing the pipe roughness (i.e. Manning's n) If you wish to see the minor loss localized to the pipe endpoint, then instead of using the entry/exit loss on the conduit, you can define it as a structure loss in the properties of the node (manhole) at the end of the conduit.
Q: The Notification "Conduit local losses (Entrance, Exit, Expansion, Contraction) are ignored by this solver" appears when using the GVF-Convex (SewerCAD) solver.
A: If the Entrance Loss, Exit Loss or Average Loss Coefficient was entered for a conduit when using the Implicit or SWMM solver, and then the model was later changed to use the GVF-Convex (SewerCAD) solver, this User Notification will appear, to inform the user that the values previously entered in the other solver are not used and not supported by the Convex solver. The fields will also be hidden from the properties window. This prompts the user to make a decision - either ignore this message and accept that the minor losses are ignored, or account for them in other ways (see further above) Ignoring the message may be best if there is a chance you need to use those coefficients with the Implicit or SWMM solver at a later time. Otherwise to remove the notification, temporarily switch solvers, or add the fields to your conduit flextable (see this.)
Differences between solvers: GVF-Convex vs. GVF-Rational vs. Implicit vs. Explicit (SWMM)
Structure Loss methods supported by each solver
https://www.openswmm.org/Topic/3385/modeling-minor-losses-at-structures