AutoCAD Civil 3D - Stormwater

AutoCAD Civil 3D - Stormwater

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Distinguished Contributor bf
Distinguished Contributor
bf
Posts: 221
Registered: ‎08-27-2003
Message 1 of 10 (635 Views)

Hydraflow vs SSA results

635 Views, 9 Replies
04-16-2012 11:42 AM

Ran a drainage design through SSA, then exported to Hydraflow and ran.  The results were markedly different.  So I exported the Hydraflow to XML, imported to SSA, configured necessary parameters.  Reran.  Same problem.  Anyone have this happen?

 

Employee
Matt.Anderson
Posts: 2,909
Registered: ‎05-13-2005
Message 2 of 10 (635 Views)

Re: Hydraflow vs SSA results

04-16-2012 12:16 PM in reply to: bf

That is to be expected.

 

Hydraflow performs a standard step method using the Peak Q. 

 

SSA performs a hydrograph routing conserving mass and momentum. 

Matthew Anderson, PE
Product Manager
Distinguished Contributor bf
Distinguished Contributor
bf
Posts: 221
Registered: ‎08-27-2003
Message 3 of 10 (628 Views)

Re: Hydraflow vs SSA results

04-16-2012 01:33 PM in reply to: Matt.Anderson

Thank you Matt.  I may have other replies following.

Member
Paulns2
Posts: 4
Registered: ‎03-26-2012
Message 4 of 10 (420 Views)

Re: Hydraflow vs SSA results

11-03-2013 06:29 AM in reply to: Matt.Anderson

Please explain in more detail. run ana analysis in hydraflow and ssa using the same idf curves and i find that my system floods in hydraflow and i end up having to use larger pipe sizes. However the same system analysed in ssa indicates that the now larger pipe sizes are too big since there is extra capacity. I am trying to optimise my network and the difference between the two software is befuddling.

 

Regards,

 

Paul

Employee
Matt.Anderson
Posts: 2,909
Registered: ‎05-13-2005
Message 5 of 10 (408 Views)

Re: Hydraflow vs SSA results

11-04-2013 05:45 AM in reply to: Paulns2

Paul -

 

Hydraflow Storm Sewers follows the procedures outlines in HEC-22 for storm sewer systems.  The process starts at the downstream outlet to a system, stepping iteratively up a network in search of a balance of the HGL and time.  The rainfall intensity for the each system is overall system intensity for the upstream area.  This results in a peak Q for a pipe.  It is a very conservative design method.

 

SSA uses the EPA SWMM hydraulic calculation engine which uses the Saint Venant equations to balance continuity and momentum in the system.   This is a time-dependant system and is typically startes from the upstream moving downstream, however, the solutions do allow reverse flow, attenuated system storage, and pumps - items that Hydraflow and the Standard Step method does not support.

 

 

Matthew Anderson, PE
Product Manager
Member
Paulns2
Posts: 4
Registered: ‎03-26-2012
Message 6 of 10 (393 Views)

Re: Hydraflow vs SSA results

11-04-2013 11:28 AM in reply to: bf
Then what's the use of hydra flow if the results cannot be trusted. In that case it's better to start and finish the design in SSA even though SSA does not have the automatic design capability. Is the auto design capability in the pipeline for future SSA iterations?

Regards

Paul
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Matt.Anderson
Posts: 2,909
Registered: ‎05-13-2005
Message 7 of 10 (387 Views)

Re: Hydraflow vs SSA results

11-04-2013 11:36 AM in reply to: Paulns2

Paul -

 

The methods using by Hydraflow are still valid, and are simple to the point that many still utilize Excel spreadsheets to accomplish these calculations.  In many jurisdictions, this is all that is required.

 

 

Matthew Anderson, PE
Product Manager
Valued Mentor
Hidden_Brain
Posts: 701
Registered: ‎03-24-2009
Message 8 of 10 (354 Views)

Re: Hydraflow vs SSA results

11-08-2013 10:45 AM in reply to: Matt.Anderson

Matt,

you may have already answered my question below before, but would like to ask again to get your thoughts:

"if SSA is set to a link routing method of Steady Flow, is that not the same as the standard step method?"

Avishek Chhibber, P.E., CFM
Civil 3D 2013 SP2, Win 7-64 bit
8GB RAM
Employee
Matt.Anderson
Posts: 2,909
Registered: ‎05-13-2005
Message 9 of 10 (350 Views)

Re: Hydraflow vs SSA results

11-08-2013 11:05 AM in reply to: bf

SSA's Steady Flow Routing is Q in = Q out hydrograph routing.

 

It is NOT Standard Step Backwater calculations.

Matthew Anderson, PE
Product Manager
Valued Mentor
fcernst
Posts: 1,131
Registered: ‎01-07-2011
Message 10 of 10 (334 Views)

Re: Hydraflow vs SSA results

11-08-2013 02:34 PM in reply to: bf

It sounds like you are trying to size pipes using Rational Method hydrographs in a dynamic routing simulation model like SSA. This violates the assumption the Rational Method is based on (rainfall intensity constant over the storm duration, rainfall uniformly distributed over the watershed, etc)..

 

To size pipes from multiple upstream catchments using the Rational Method, you need to implement a system tc and weighted CA methodology  (McCuen) . This is what a storm sewer analysis program like Hydraflow does. 

Fred Ernst, PE
C3D 2015
Ernst Engineering
www.ernstengineering.com
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