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SSA Junction with ponded area HGL Issue

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Message 1 of 6
Anonymous
1957 Views, 5 Replies
‎08-05-2016 07:00 AM

SSA Junction with ponded area HGL Issue

Anonymous
Not applicable
‎08-05-2016 07:00 AM

I am using SSA to analyze a storm system accounting for tailwater condition due to a submerged outfall in a flood zone, and am looking to determine the extent of flooding from inlets. I understand SSA assumes overflow is lost and does not show HGL above the rim, so I converted all the inlets to junctions and enabled overflow ponding with approx. ponding areas of 800 sf. I am currently using Rational, 1 hr storm event in this case.

 

Some "junctions" are not shown as overtopping, but when I review the profile and run through the animation, the Max. HGL is shown to meet the Rim elevation. If I increase the Rim elevation, the HGL continues to jump to match the Rim elevation. The structure shows no flooded volume or flooding time. In some cases where I have increased the rim elevation far beyond the HGL, or used an orifice/weir to another junction for overflow, the HGL drops back down below the rim elevation. I also don't see the HGL reaching the rim in the animation, it is likely a quick spike. Is this just a flaw in the program I should ignore and assume no flooding, or any way to fix this? Also, is there any difference in modeling the system with the structures as inlets versus junctions (aside from seeing the ponded area/overflow)?

 

Thank you,

Michelle

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‎08-05-2016 07:00 AM

SSA Junction with ponded area HGL Issue

I am using SSA to analyze a storm system accounting for tailwater condition due to a submerged outfall in a flood zone, and am looking to determine the extent of flooding from inlets. I understand SSA assumes overflow is lost and does not show HGL above the rim, so I converted all the inlets to junctions and enabled overflow ponding with approx. ponding areas of 800 sf. I am currently using Rational, 1 hr storm event in this case.

 

Some "junctions" are not shown as overtopping, but when I review the profile and run through the animation, the Max. HGL is shown to meet the Rim elevation. If I increase the Rim elevation, the HGL continues to jump to match the Rim elevation. The structure shows no flooded volume or flooding time. In some cases where I have increased the rim elevation far beyond the HGL, or used an orifice/weir to another junction for overflow, the HGL drops back down below the rim elevation. I also don't see the HGL reaching the rim in the animation, it is likely a quick spike. Is this just a flaw in the program I should ignore and assume no flooding, or any way to fix this? Also, is there any difference in modeling the system with the structures as inlets versus junctions (aside from seeing the ponded area/overflow)?

 

Thank you,

Michelle

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5 REPLIES 5
Message 2 of 6
Hidden_Brain
Advisor
in reply to: Anonymous
‎08-08-2016 06:28 AM

Hidden_Brain
Advisor
Advisor
‎08-08-2016 06:28 AM
are you running hydrodynamic?
Input drop down>Project Options>Hydraulic Routing
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‎08-08-2016 06:28 AM

are you running hydrodynamic?
Input drop down>Project Options>Hydraulic Routing
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Message 3 of 6
Anonymous
in reply to: Hidden_Brain
‎08-08-2016 07:24 AM

Anonymous
Not applicable
In response to Hidden_Brain
‎08-08-2016 07:24 AM

Yes, running hydrodynamic with ponding enabled.

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‎08-08-2016 07:24 AM

Yes, running hydrodynamic with ponding enabled.

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Message 4 of 6
Hidden_Brain
Advisor
in reply to: Anonymous
‎08-08-2016 09:26 AM

Hidden_Brain
Advisor
Advisor
In response to Anonymous
‎08-08-2016 09:26 AM
Convert all inlets and junctions to "functional" storage nodes and give that a shot. Can you share your model?
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‎08-08-2016 09:26 AM

Convert all inlets and junctions to "functional" storage nodes and give that a shot. Can you share your model?
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Message 5 of 6
Joe-Bouza
Mentor
in reply to: Hidden_Brain
‎09-05-2017 07:11 AM

Joe-Bouza
Mentor
Mentor
In response to Hidden_Brain
‎09-05-2017 07:11 AM

Hi @Hidden_Brain Im having a similar misunderstanding of the HGL results .  How does the functional storage node help?

 

 

https://forums.autodesk.com/t5/autocad-civil-3d-forum/trying-to-interpert-ssa-results/td-p/7342634

Joe Bouza
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Did your question get successfully answered? Then click on the ACCEPT SOLUTION button.

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‎09-05-2017 07:11 AM

Hi @Hidden_Brain Im having a similar misunderstanding of the HGL results .  How does the functional storage node help?

 

 

https://forums.autodesk.com/t5/autocad-civil-3d-forum/trying-to-interpert-ssa-results/td-p/7342634

Joe Bouza
Did you find this post helpful? Feel free to Like this post.
Did your question get successfully answered? Then click on the ACCEPT SOLUTION button.

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Message 6 of 6
fcernst
Mentor
in reply to: Anonymous
‎09-06-2017 09:29 AM

fcernst
Mentor
Mentor
‎09-06-2017 09:29 AM

...I am using SSA to analyze a storm system accounting for tailwater condition due to a submerged outfall in a flood zone, and am looking to determine the extent of flooding from inlets...

 

... Is this just a flaw in the program I should ignore and assume no flooding, or any way to fix this? ...

 

 

Yes, this is a flaw and deficiency specific to SSA. Thee SSA inlet objects do not allow upwelling flow and subsequent nodal flooding.

 

https://forums.autodesk.com/t5/autocad-civil-3d-forum/ssa-surcharged-inlet-system-losses/td-p/373259...

 

https://forums.autodesk.com/t5/autocad-civil-3d-forum/ssa-inlet-upwelling-flow/td-p/5664854

 

https://forums.autodesk.com/t5/autocad-civil-3d-ideas/ssa-provide-inlet-backflow-upwelling-flow-capa...

 

 

 

 

 

 



Fred Ernst, PE
C3D 2025
Ernst Engineering
www.ernstengineering.com
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‎09-06-2017 09:29 AM

...I am using SSA to analyze a storm system accounting for tailwater condition due to a submerged outfall in a flood zone, and am looking to determine the extent of flooding from inlets...

 

... Is this just a flaw in the program I should ignore and assume no flooding, or any way to fix this? ...

 

 

Yes, this is a flaw and deficiency specific to SSA. Thee SSA inlet objects do not allow upwelling flow and subsequent nodal flooding.

 

https://forums.autodesk.com/t5/autocad-civil-3d-forum/ssa-surcharged-inlet-system-losses/td-p/373259...

 

https://forums.autodesk.com/t5/autocad-civil-3d-forum/ssa-inlet-upwelling-flow/td-p/5664854

 

https://forums.autodesk.com/t5/autocad-civil-3d-ideas/ssa-provide-inlet-backflow-upwelling-flow-capa...

 

 

 

 

 

 



Fred Ernst, PE
C3D 2025
Ernst Engineering
www.ernstengineering.com
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