User notification: The peak inflow to inlet (xxx.xx cfs) is in excess of the In Sag operating range (40.00 cfs)

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

Problem

After computing a model, there are user notifications that say:

"The peak inflow to inlet (100.00 ft³/s) is in excess of the Curb In Sag operating range (40.00 ft³/s)."
"The peak inflow to inlet (100.00 ft³/s) is in excess of the Curb On Grade operating range (50.00 ft³/s)."

What does this message mean?

Solution

The values listed for the different inlet types (40 cfs for catch basins that are In Sag, 50 cfs for catch basins that are On Grade) are when the HEC-22 equations start to extrapolate data. If you look in the HEC-22 manual at Chart 9B located in the appendix, note that there are no flows listed in the chart after about 40 cfs. This is the source of the value from the user notification.

This user notification is generated to provide the user a warning that the FWHA equations were regression fit and valid within their operating ranges. The results here may be valid, but they were extrapolated from existing data and there may be some inaccuracies possible as a result.

Note that the user notification is a warning not so much that the inlet is beyond the flow it is designed for than that it is a warning that you have reached a point where the solver has started needing to extrapolate results.

This is basically a warning that your flows may be higher than expected. A yellow, or warning level, user notification shouldn't result in the model stopping calculation or even that the results are incorrect. What they indicate is there is a condition that the solver doesn't anticipate (in this case, a higher than expected inflow) so that you can review the data to make sure it is correct.

See Also

HEC-22 Manual

  • Created by Bentley Colleague
  • When: Mon, May 14 2018 11:56 AM
  • Revisions: 1
  • Comments: 0
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