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SSA - Surcharged Inlet System Losses

13 REPLIES 13
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Message 1 of 14
fcernst
2748 Views, 13 Replies

SSA - Surcharged Inlet System Losses

I am investigating SSA's capability for my company's use in modeling dual street drainage systems utlizing SSA's Inlet objects.

 

I created a surcharged flooding condition at an Inlet node location with no surface flows coming into the inlet for the testing. I tested Inlets in both the Sag and OnGrade conditions. The model was ran for 24 hours to allow the system to drain and pass all upstream surcharge events.

 

I found that SSA lost the surcharged flooding water from the system, generating hydraulic routing continuity errors of greater than 96%.

 

I have included the two SSA models for your review. There are also 5 screen captures below with numbered descriptions.  I would appreciate any comments.

 

Sag Inlet Condition:

 

I provided a large area for the Ponded Area property of the Sag Inlet. The Ponded Area is a constant-area volume mechanism used to store water that has surcharged up through the inlet, to be conveyed back into the inlet node when the system is no longer surcharging at that location. SSA calls the surcharge flooding "upwelling" flow in the Help.

 

I also conneted a trapezoidal channel link to the Sag Inlet at the Rim elevation to see if SSA would convey the surcharged flows  through this overflow channel. This is a typical model setup in dual street drainage system analysis.

 

Result: SSA failed to convey any Ponded surcharged or "upwelling" flow back into the system after all surcharging events had passed, and  SSA failed to convey any surcharged flooding flow to the Overflow link, and the flooding flow volume was lost from the system.

 

OnGrade Inlet Condition:

 

In SSA there is no Ponded Area property available for an OnGrade inlet. There is a Roadway/Gutter bypass link option available to convey surface flows leaving the OnGrade inlet location.

 

I chose the same trapezoidal Overflow channel used in the Sag Inlet test that is connected with its invert at the Rim elevation of the inlet, as the Bypass link.

 

Result: SSA was not able to convey any surcharged or "upwelling" flow into the Bypass link, and it was lost from the system.

 

Conclusions:

To model the Major Storm in dual street drainage analysis, the modeler is required to convey and track the surcharged flow from the storm sewer system on the ground surface. The storm sewer becomes surcharged during the Major Event analysis due to the fact the storm sewer pipe system is typically sized only to accomodate the Minor Storm sewer system without surcharged nodal flooding. 

 

To model an Existing storm sewer system, the modeler is also required to be able to model surcharged nodal flooding to determine where the system is undersized and problematic.

 

  • SSA utilizing the Inlet object in its present form, can not be used to analyze either the Major Storm event for a dual drainage storm sewer system or used for an Exisitng sewer system study.

 

  • SSA utilizing the Inlet object in its present form would be only appropriate to analyze the Minor Storm sewer system events, where there is no nodal flooding.

 

 

1. From the SSA Help showing "upwelling" flow or nodal flooding.

jjCapture7.JPG

 

2. Plan view of test model.Capture5.JPG

 

3. Profile of surcharged model with Inlet location circled.

Capture6.JPG

 

4.  Time series of the links going into "Inlet In" and out: "Inlet Out" and "Overflow". This shows the flow being lost at the Inlet.Capture.JPG

 

 

5. Hydraulic routing continuity error.

 

Capture2.JPG

 

 

 

 

 

 

 

 



Fred Ernst, PE
C3D 2024
Ernst Engineering
www.ernstengineering.com
13 REPLIES 13
Message 2 of 14
fcernst
in reply to: fcernst

I received confirmation from Autodesk support that the Inlet objects in SSA can not support surcharged nodal flooding ("upwelling") as they show it can in the Help.

 

Therefore I can not use the Inlet objects to model dual drainage storm sewer systems for the Major Storm event, or use them to analyze an Existing storm sewer system.

 

Capture.JPG



Fred Ernst, PE
C3D 2024
Ernst Engineering
www.ernstengineering.com
Message 3 of 14
FRANKSANTELLI2314
in reply to: fcernst

My office is having a similar issue modeling an existing storm sewer drainage system. 

 

'Inlets’ in the model appear to only calculate 'bypass' surface flows in excess of the grate capacity, which are accounted for using ‘bypass links’ to downstream ‘inlets’.   This however does not account for ‘surcharge’ flows from the storm sewer system, or what I would term ‘outflow’ or what is termed ‘upwelling’ in this thread.

 

'Junctions' in the model do report volumes and peak rates at 'surcharged' flow, but these flows typically simply disappear or are unaccounted for in the model.  The software can account for these flows by inputting ponding volumes at the junctions, but that is not representative of what is physically occurring on the site.  It appears there is no way to input a ‘bypass link’ from a 'junction' to a downstream ‘inlet’ to account for the 'surcharged/outflow/upwell' flows out of the storm sewer system. 

 

Has Autodesk ever addressed this issue or has anyone come up with a workaround for either accounting for the ‘upwelling/surcharging/outflowing’ in ‘inlets’, or routing ‘bypass links’ from ‘junctions’ to downstream ‘inlets’? 

 

Message 4 of 14
matt_anderson_pe
in reply to: fcernst

@fcernst, this isn't new... we've had this conversation on the old stormwater forum.  SSA inlets are calculated rating curves for capture.   The team in India (BOSS) never completed reverse flow calculations before Autodesk bought the software.

 

I would suggest InfoWorks ICM is you want to model 1D major/minor systems.

Matthew Anderson, PE
Message 5 of 14
fcernst
in reply to: matt_anderson_pe

EPA SWMM 5 now has HEC-22 inlets with flow reversal capability 



Fred Ernst, PE
C3D 2024
Ernst Engineering
www.ernstengineering.com
Message 6 of 14
matt_anderson_pe
in reply to: fcernst

SSA is based on the 5.0 version of the SWMM engine.   (non-multithreaded)

EPASWMM 5.2 has HEC-22 inlets with the reversal.

Even the Innovyze tools haven't adopted the 5.2 version code yet.  (Mind you - they had inlets for years before EPA added them and there are some untangling as they are done differently)

Matthew Anderson, PE
Message 7 of 14
fcernst
in reply to: matt_anderson_pe

and that was almost three years ago now



Fred Ernst, PE
C3D 2024
Ernst Engineering
www.ernstengineering.com
Message 8 of 14
matt_anderson_pe
in reply to: fcernst

and you expect them to update SSA after purchasing Innovyze?

Matthew Anderson, PE
Message 9 of 14
fcernst
in reply to: fcernst

 on engine version 5.2.4 and there have been so many enhancements and bug fixes the past three years to the engine



Fred Ernst, PE
C3D 2024
Ernst Engineering
www.ernstengineering.com
Message 10 of 14
fcernst
in reply to: matt_anderson_pe

don't expect anything



Fred Ernst, PE
C3D 2024
Ernst Engineering
www.ernstengineering.com
Message 11 of 14
fcernst
in reply to: FRANKSANTELLI2314

Version 5.0 is 20 years old now..

 

Screenshot 2024-02-01 071407.png



Fred Ernst, PE
C3D 2024
Ernst Engineering
www.ernstengineering.com
Message 12 of 14
matt_anderson_pe
in reply to: fcernst

SSA contains engine version 5.0.14 when I picked it up as QA Contractor.   I was only able to get approval for the bug fixes up to 5.0.22.

Matthew Anderson, PE
Message 13 of 14

Lol @ Autodesk updating SSA to fix major issues

 

I told my boss we can't ever trust SSA enough to use it for design which is too bad as it has the potential to be a great program but I don't feel like taking the time to research all the other bugs it probably has and the necessary work arounds.

 

For large drainage systems we use PCSWMM now.

 

Message 14 of 14
FRANKSANTELLI2314
in reply to: fcernst

I very much appreciate all the feedback, and thanks to Fred Ernst for his posts.  I've used the SSA software to assist with the design of storm sewer networks on previous projects and believe it works quite well for that purpose. When analyzing existing storm networks, where there may be significant surcharge conditions at certain points in the sewer network, I believe the software is less effective.

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