Pond outfall into another pond via ditch

Question

I'm getting the following error "Engine Error Message: CalcTable.ID is 0: FRMPONDDIVERT" when I connect my pond outfall to a pond 2000' downstream via a ditch/channel. 
 
 I have a pond with two outlets (an orifice, and a weir wall), this pond outfalls into a 2000' long channel before it enters a different pond. I have the pond outfall modeled as a junction element and linked by a trapezoidal channel to the next pond. 
 Photo 1: Proposed Conditions (Error occurs)

The image below shows the existing conditions where Pond US Weir does not exist. Pond US Weir is being proposed. When I run the existing model I dont get the error message, and everything works fine. Does anyone have any ideas why I am getting this error in the proposed conditions? Basically I want to connect the two ponds in the proposed conditions by a ditch. Outfall from Pond US Weir will eventually make it downstream to Ponding US. 
 Photo 2: Existing Conditions (Error does not occur)

Scott Kampa · Answer

Hello Krystian, 
 
In the model where the error occurs, do you have an element called "FRMPONDDIVERT?" This could be a composite outlet structure as well. 
 
If not, we will need to see a copy of the model to look into this. There are two options for sharing your model on Communities, whichever you choose please be sure to zip your files first. The first option is to attach the zip file containing your model to your reply on the forum using the Advanced Reply Editor (you'll find the link below and to the right of the reply box). If your data is confidential please use the instructions in the link below to send it via Bentley Sharefile. Files uploaded to Sharefile can only be viewed by Bentley employees. Please be sure to reply on this thread with the name of the file after it has been uploaded. 
 
 communities.bentley.com/.../7079.be-communities-secure-file-upload 
 
Please post here to let us know when the file is available. 
 
Regards, 
Scott

Scott Kampa · Answer

Hello Krystian, 
 
The error may be occurring because it is having difficulty solving for the part of the system around pond "Ponding US Culvert". For instance, there are seven catchments attached to this pond. Of these, five having unusually low CN values of 0.01. If you make these five catchments inactive, the model will compute. 
 
This is a possible workaround (or making the CN values something that is more realistic, which could also help). Another is to make the three catchments and the connected elements to the right of the rest of the system inactive. These are not connected to the rest of the elements, and would have no impact on the results. However, if these are inactive, the model will compute. 
 
In addition to this, there may be an issue with the rise of the channel "Ditch/Channel". The rise in only 4 inches (compared to a span of 36 inches). This is pretty small and the channel will be prone to overtopping. 
 
Please give these a try to see if it helps at all. If these workaround are not sufficient, please let us know. 
 
Regards, 
Scott