Comparisons with SWMM 5.1

[Anonymous]

An engineer here is working on a SWMM model using SWMM 5.1 and also opening it in Autodesk SSA.  The comparisons between the two are not close at all.  When you run his model in SWMM 5.1, the flow in a profile view gradually goes up near the top of the pipes and goes down.  Then when you run the analysis in SSA, it looks the same until the peak flow comes through and the water all of a sudden shoots up all the manholes.  Then when he is comparing the detention pondin the two models, the SSA calculation said that he needed twice as much storage capacity as the SWMM 5.1.  He is opening the same file in both programs.  Has anyone else had this experience?  It looks like SSA calculates the peak flow a lot differently.  The water stages differently.  The SWMM model didn't seem to really peak as a typical hydrograph does, but this discrapancy is unacceptable for both these programs to be calculating things so differently.

[Matt.Anderson]

EPA SWMM 5.1 came out recently, and SSA did has not been updated to reflect these changes.

Can you forward copies of both inputs and the information?  Please also note which build of EPA SWMM 5.1 he is using ~ v001 - v006?

[Anonymous]

He is using SWMM 5.1v006.  Is there a later version of SSA that has been updated? We are using 2012, but we can probably get a later version pretty easily if that fixes the probelm. 

[Matt.Anderson]

Can you send me the files?  There are a few items that changed in EPA SWMM 5.1 that might effect the calculations, but without the files, I can't tell if if is using the pipe seepage (new to 5.1), or a dynamic wave/head tolerance value changes.

[Anonymous]

It turns out he was using SWMM 5.0.013. 

[Matt.Anderson]

Oh my!  That makes big difference and there are a number of changes to the analysis engine leading into SSA's engine.

[Anonymous]

Do you know a lot about the rainfall designer?

[Matt.Anderson]

Yes, I do.

[Anonymous]

I think I figured out my question.  I got confused when I looked up a storm event hyteograph for a kIng County WA Type 1A scs storm.  The numbers were way different than the numbers that I got in SSA storm builder.  But I imported it as an intensity based instead of cumulative.  So the units for the intensity based storm is in in/hr and the cumulative is in inches.  I get it now, but the user manual doesn't really say that.  You just have to figure it out.  It makes total sense to me now, but at first I was a little lost.  You have to be careful when creating custom storm events.  Is that right?

The other engineer dwonloaded SWMM 5.1 and is in the process of comparing it with his older version, and so far he says it seems to match up with what SSA is outputting.  If he is still getting weird solutions then I'll talk him into sending the file to you.  I think he wants to figure it out on his own.