SSA storage volume is double of Pondpack volume

[Anonymous]

I'm relatively new to SSA and want to use it as my primary hydrologic and hydraulic modeler.  It only makes sense.  Well, I got the program to work and had things linked in and was able to route a storm through the network.  But when I routed the storms, I had to model double the storage that i expected.

So I went back to the program I'm familiar with - Pondpack by Benltey - and designed the same system I routed in SSA in that program - and got the storage volume that I would expect for a site of this size - about 2 acres.

Is there possibly a setting that I'm missing that makes my outlet structures route slower or less than they should?  Or is there some other reason that a system would give this kind of inflated need for storage?

[Matt.Anderson]

RVP-Rob42-

There are a couple of possible differences.

1. Runoff ~ Are they the same?
2. Storage ~ What are you modeling?
3. Outlet Structures ~ What are you modeling?  Orifce? Weir? Both?
4. Tailwater Condition ~ Are they the same in both models? 

Can you attached a PDF of the PondPack? and a zip of the SSA?

[Anonymous]

Thanks you, I'd be glad to.



Attached is the pondpack PDF. If it's ok - I'll drop box the SSA files to
you.



Rob Painter PE

RVP Engineering

513-403-1084

rob.painter@RVPengineering.com

www.RVPengineering.com



RVP_eng_logo

[Matt.Anderson]

Rob -

I dont see the PDF or the SSA files in your message.

[Anonymous]

I am having the same problem.  The pond sizing in SSA are significantly larger than expected.  This is causeing some permitting problems and we have abandoned the use of SSA for HydroCAD. 

I would really like to continue with SSA, but cannot figure out where the problem is originating from.

[Matt.Anderson]

tmurphy -

Feel free to reach out for assistance.  Upload the model here as zip file.

One item to consider is reviewing the routing and reporting time steps.

[Anonymous]

Thank you for the response.  I have attached the file as a zip.

[Matt.Anderson]

What are you expecting for volumes that HydroCAD provides? 

Your SSA modeling appears good, the pond fails for a minor amount of time and needs a bit of freeboard to avoid a flooding warning. (0.1 feet)

The Rim elevations for the manholes are much lower your initial model starting water surface elevations. The output contains a number of warning to that effect as well.

Are your subbasin areas overriden? They look like they were imported due to shapes, but the actual sizes do not match.

[Anonymous]

HydroCAD is telling us we need a pond that is 47,589 cuft.  SSA is giving us a volume of 68,513 cuft.

Yes, my subasin areas are overwritten. 

Thank you for the feedback.

[Matt.Anderson]

Sounds a bit like apples and oranges might be going on.

Are the basin sizes / CNs the same?

Are Rainfall distributions the same?

Can you attach your HydroCAD output?

[Hidden_Brain]

if you want, attach both your hydrocad and SSA models here, I have access to both softwares (HydroCAD 10 and SSA 2013), and would be more than happy to take a look.

[Hidden_Brain]

I realized after my first reply that you had attached your SSA model previously.

i just set up a dummy HydroCAD model with your drainage area values for C1, C2, C3 and C5, ran it for Indy Huff 1Q 2-Yr (3 inches), and I get the peak flows and runoff volume results pretty comparable between HydroCAD and SSA (see attached image). I would imagine of the subbasin peak volumes are similar, the detention storage volume required should be comparable (i did not code in detention in HydroCAD).

Please check in HydroCAD>Calculation settings>Time span. I set it up to start at 0:00 and end at 24:00. i think HydroCAD 10 defaults this to stat at 5:00 and end at 20:00, which may be the source to your problem.

good luck!