AutoCAD Civil 3D - Stormwater

AutoCAD Civil 3D - Stormwater

17 Posts
3 Kudos
Registered: ‎06-08-2012
Post 1 of 2

HGL Issues

435 Views, 1 Replies
07-09-2012 08:11 AM

After searching through the stormwater forums, I am still having issues figuring out why the reported HGL in the summary table does not match the HGL as computed at the junction. I have attached an image that shows the HGL at (approx.) 741.5', yet the table shows the max HGL occuring at 743.70'. I have also included the zipped file with the SPF file inside. If you open the model (We have been using SSA 2011), the junction in question is labeled "SD-H 0+97.41". This issue occurs at a handful of junctions, this was just an example I wanted to post for feedback.


Information about the way we modeled the system:

  • Rational Method - therefore can't change the reporting/routing time steps to match
  • Kirpich TOC method
  • Hydrodynamic Routing
  • Hazen-Williams

We also opted to model all the inlets as sags despite there being a significant amount of bypass due to the issue I had asked previously re: overflow over the crown of a roadway. We ran the drainage calcs in excel and ended up using the excel table to create profiles in Civil 3D, but would like to see how we could fix this for future projects, if possible.




Clayton Farrow

Clayton Farrow
Civil 3D 2014
Windows 7 Professional
Intel Xeon E31270 @ 3.4 GHz
8 GB, 64-bit
Valued Contributor
55 Posts
5 Kudos
Registered: ‎04-21-2008
Post 2 of 2

Re: HGL Issues

10-02-2012 08:27 PM in reply to: cfarrow

I'm not certain of the reason, maybe someone can confirm, but I have been able to replicate what you are talking about and have found that that peak when clicking on nodes is the same, while changing the reporting interval results in changes on the profiles and results graphs.  Try changing your reporting interval to a very small number (such as 1 second) and see if the results start to converge. 


IF this is the case, then you have to look at the reporting interval and determine whether or not there should be such a significant increase in HGL.  Sometimes reporting at very small intervals will pick up anomalies in the model that may not be reflective of actual conditions.  For large basins, larger time intervals are appropriate, and for very small basins, very short intervals are appropriate. 

Alan Neal, P.E.
Autodesk Infrastructure Suite Premium 2012/2013
Windows 7, x64
Xeon E31225 w/ Quadro 600
Post to the Community

Have questions about Autodesk products? Ask the community.

New Post