| Product(s): | StormCAD, CivilStorm, SewerGEMS, OpenRoads Designer |
| Version(s): | CONNECT Edition |
| Area: | Layout and Data Input |
When attempting to compute a model, the following User Notification appears and the calculation does not complete:
"The outlet structure's entered minimum headwater elevation X ft is greater than or equal to the entered maximum headwater elevation X ft. The minimum headwater elevation must be less than the maximum headwater elevation."
The "outlet structure" in this case could refer to a pond outlet structure or a headwall rating curve.
For a pond outlet structure, open the Composite Outlet Structure dialog, click on the composite outlet structure in question and examine the input, notably the minimum and maximum headwater elevation.
For a conduit attached to a Headwall node element, this message refers to the invert and ground elevation settings in the headwall. Internally the program constructs a culvert rating curve and takes the "Elevation (invert)" as the minimum elevation of that rating curve, and takes the "Elevation (Ground)" as the maximum. The error in question can occur if both are set to the same value, as this prevents the program from creating the rating curve. To resolve this you will need to set the ground elevation higher than the invert. The ground elevation should be set to at least the top of the culvert barrel, or higher if you want the headwater elevation to surcharge the pipe (since the ground elevation defines the maximum headwater elevation of the culvert rating curve). If you have multiple headwalls in the model, you may want to add the invert and ground elevation to the Headwall Flextable to make the process of fixing this easier.
Note that if you are seeing this issue in OpenRoads Designer (which has the OpenFlows storm/sewer drainage functionality built in), you may need to check which node you are using to represent the headwall. If you have a point in the cell for elevation and the cell only has the one point, this will cause both the ground and the invert to match so you will not be able to set the ground to be higher than the invert. In this case you can consider using another type of node which will pull a cell that has two elevation points, so that you can set them as needed. Also note that starting with version 10.11 of OpenRoads Designer, you should be able to compute drainage if a headwall ground and invert elevation are set equal.