	Applies To
	Product(s):	SewerGEMS, StormCAD, SewerCAD
	Version(s):	08.11.XX.XX and higher
	Area:	Calculations, Results and Output
	Original Author:	Terry Foster, Bentley Technical Support Group

Problem

When attempting to compute a model with the GVF-Rational (StormCAD) solver,it fails with the following red User Notification:

"The scenario failed to compute. Review your data and try again."

Solution

This is a generic error that could occur for multiple reasons, if the program encounters an unexpected situation during calculations.

General

Validate - First, use the Validate option to check for any obvious issues. Also, take a close look at the setup of the model and check for missing data or other problems.

Upgrade - Next, it's generally a good idea to have the most up to date version of the software. You can check for new versions in the Fulfilment Center. You can read more on that here:

How do I download the Water and Storm-Sewer hydraulics and hydrology products?

How can I find out when a new version or patch is available?

Narrow down - If the specific solutions below do not apply or do not resolve the issue, the next step would be to try to narrow down the problem by incrementally removing parts of the model. Save a copy of the model, then delete roughly half of it, in such a way that does not cause a network disconnection. Try computing again and if the error still occurs, continue removing more of the model. Once you get to the point where the error not longer occurs, use Undo to get back to the last state, and focus on the elements that were removed. Try deleting other sections of the model to further narrow it down, then take a close look at the connectivity and properties of the element(s) that you've narrowed it down to.

Check for Missing Information

Use the element Flextatbles and/or properties to check for:

Catchbasin Road Cross Slope set to zero or an unreasonably large value (check units)
Catchment roughness coefficient set to zero
Cross section roughness (such as Mannings n) set to zero
Pipes missing nodes: Run the query "pipes missing nodes" under the Network Trace section of Network Navigator. A pipe missing an end node could potentially cause this issue in some cases. Delete any identified pipes and re-draw. If using the AutoCAD platform, try opening the model in Standalone first before running the query.

Fix the irregular cross section input

This has been known to occur in a case where the user mistakenly set a conduit section type to "Irregular Closed Section" with the data input for the section in the format of Station vs. Elevation, when this section type expects Elevation (Relative) vs. Width. The conduit was supposed to be set to a section type of "Irregular Channel".

Go to Components > Inlet Catalog. Click each inlet and click the "design" tab. Make sure you do not have a length of zero in the table of
available design lengths.

or
Open the properties for the conduits that are setup incorrectly by double clicking on the conduit link in the drawing pane. Adjust the input data accordingly

This has also been known to generally occur if the flow exceeds the capacity of the irregular closed section. Ensure that the data is input correctly and that the conduit is large enough to handle the flow for the particular scenario / storm event (this can explain why a larger return event fails to compute while smaller ones compute, due to the flow difference).

Create user defined IDF Table from IDF Curve Equation data

Another instance of this was fixed by creating a user defined IDF Table from the duration and intensity values provided by the IDF Curve Equation.

Check for combination of 3D length and headwall as outfall

If this occurs and you're using a headwall node as an outfall (Boundary Condition Type set to Free outfall or user defined tailwater) with the "3D length" option enabled in Tools > Tools > Options, you may be encountering known issue # 624509. To resolve this, either change the end node to an outfall, disable the 3D length option, or upgrade to CONNECT Edition SELECTseries 1 or greater, when available.

Check for user defined conduits using the "Modified Basket Handle" section type

If the rise of conduit is less than one-half of the span use a different conduit shape or change the values for the conduit. The equation specifically states the rise be greater than or equal to one-half of the span. The conduit shapes are listed in the help document that comes with the software. The user notification for this conduit shape will be fixed in a future version of the software.

Check for combination of the use of gutter depth vs. captured flow inlet type with the trapezoidal gutter shape.

In version 08.11.05.58 of StormCAD, SewerGEMS and CivilStorm and in Subsurface Utilities/SUDA V8i SELECTseries 4, the above combination can cause the error in question (reference defect # 694565). This has been resolved in the latest cumulative patch set for 08.11.05.58 (and SUDA V8i SS4). It is also resolved in later versions of these products. Please contact technical support for help with the patch, or use a different type of inlet of gutter shape if possible.

Note that a similar but separate issue is known to occur as of version 10.03.04.53 with the combination of in-sag inlet location along with the gutter depth vs. captured flow catalog inlet type and trapezoidal gutter shape. In such cases the inlet type should be set to "full capture". Related bug # 706687.

Check for a combination of using the "As Flow" Carryover Modeling Method calculation option, with a catch basin whose attached catchment has zero rational flow.

For example compute with "As CA" selected for this calculation option, check the calculated Rational Flow at all catchments (use the catchment flextable), and check the input for any that show a rational flow of zero. For example a mistake could be made with the Tc units and the value entered in hours when it was intended to be minutes.

Running constraint-based design run in with the GVF-Rational (StormCAD) solver with cross sections

There is an issue in the GVF-Rational solver in StormCAD, SewerGEMS, and CivilStorm version 10.04.00.158 where the program cannot minimum cover constraint for cross section elements. This as been resolved in a patch for version 10.04.00.158 and will be resolved in future versions of the products (reference #1333230). Please contact Global Technical Support for assistance.