Storm and Sanitary Analysis - Weir Link for flow across roadway at sag

[ben.scholtz]

While using Storm & Sanitary Analysis 2014, I'm having trouble understanding how to properly link two inlets opposite each other at the low point (sag) in a roadway so that if one structure surcharges, the remaining flow will overtop the crest in the road and flow to the opposite inlet.

The help section (Spillways and Weirs, p.331-332) shows an illustration that this is possible, but does not explain how to manipulate the weir link to function properly.

How do I design a link (weir or otherwise) to permit excess water to flow across the road with a crown?

Also, some additional information (or an illustration) on the Crest Invert, and Total Weir Height would be useful to understand how it might apply in the surface flow application, as opposed to a weir installed inside a structure...

Notes on these conditions:

Both inlets are receiving runoff directly from 2 nearby sub-basins (catchments)

Both inlets are in sag

One (surcharged) inlet also receives surface runoff from only one direction (south) from gutter bypass (user-defined open channel surface) link

Both inlets discharge to a common junction (manhole) in the center of the road

Surcharged (flooded w/blue dot) inlet invert = Elev. 1498.45, Rim = Elev. 1501.00

Roadway centerline elevation = 1501.69

Opposite inlet (not surcharged) invert = Elev. 1498.74, Rim = Elev. 1501.06

Roadway is approximately 40' wide w/ crown centered

Thanks in advance for any help,

[Hidden_Brain]

i do not have access to the user manual at the moment, but how about you model the two sag inlets as storage nodes (functional type, not storage curve), and then add a rectangular weir connecting them that would represent the road crown?

[ben.scholtz]

Thank you for the response - I will attempt to adjust my model as you suggest.

Ideally, it would be great to understand how to properly link these two inlets as the (2014) Help manual describes (and illustrates).

If you or others can provide further insight/input on how to connect these structrues to mimic the illustration and brief description provided in the Help manual titled "Roadway Overflow Routing" under the section for Spillways and Weirs on pages 331 and 332, it would be greatly appreciated. 

[fcernst · Accepted solution]

I just confirmed with Support that SSA does not have this capability with Sag Inlets as stated in the manual.

This isn’t the first time we have caught the SSA manual asserting and proclaiming to potential Users capabilities that SSA cannot deliver. Hope you didn't burn too much billable time trying to get this to work as portrayed in the manual.

[fcernst]

[ben.scholtz]

Thanks Fred,

Unfortunately that doesn't really solve the problem, but at least I know the program doesn't currently support that method.

Hopefully they'll get around to fixing that sometime soon.

For now, i've allowed ponding above the sag inlets to prevent excess flow from getting lost from the system - sort of fixes the flooding problem, but doesn't truly represent what's happening as the water would actually crest over the road to the other inlet.

I'll figure something out, but for now, it's working ok.

I appreciate your efforts,

[fcernst]

I found the SSA inlet objects to have very limited functionality. They can't handle upwelling flows from the sewer lines (they were showing in the manual they could and we had them correct that in the manual too awhile back).

Overflow from Sag inlet locations cannot be rotued anywhere.

Without these capabilities you can't do dual drainage analysis for street systems. Using the Inlet objects you can't model where inlets may be flooding from upwelling sewer flow. SSA and its inlet objects are really thus only applicable and capable to model the Minor Storm event (no curb overtopping, no surcharged flow). 

Area Inlets:

The manual states to use a Sag inlet to model an area inlet and just fill in some dummy values for the gutter variables. This doesn't work because a Sag inlet located in a gutter only has three sides accounted for when computing weir length for the grate. Again, they can't model upwelling flow which is problematic for many modeling scenarios such as analyzing parking lot detention.

[Hidden_Brain]

Fred is right, its a shame that the software has this drawback.

[cstringer-ns]

Is this possible with an on grade inlet? How would you set up the link?