Hydraflow Free Outfall Condition?

[pbradburyYWE5N]

Hello, 

I am new to using Hydraflow in Civil 3d. I previously used Bentley's StormCAD to model pipe system hydraulics. When using StormCAD there was an option to set an outfall to a free outfall condition, meaning the starting HGL was essentially at the invert of the pipe at the outfall. In my short review of the Hydraflow software I have been unable to figure out how to model this type of condition. Anyone can advise how this can be accomplished or how I could trick the software into modeling this would be greatly appreciated! 

Thanks very much for any help!

[fcernst · Accepted solution]

If you set the tailwater elevation below critical depth, it will use critical depth.

You can choose an elevation, crown, critical depth, normal depth  or (dc+D)/2.

[pbradburyYWE5N]

This is what the help menu says regarding the min starting depth: 

Min. Starting Depth

Specifies how to choose the starting water surface elevation at the downstream end of any line, except outfalls. The choices are: Normal, Crown, (dc + D)/2, and Critical depth. If the starting hydraulic grade line (HGL) at any line, other than an outfall line, is below the Minimum Starting Depth, Hydraflow Storm Sewers Extension automatically sets the starting HGL to this specified depth. This value refers to all lines upstream, not the beginning HGL.

All of this says "except outfalls", if this setting doesn't apply to outfalls, then how does the software calc the starting HGL at the outfall? Or does this indeed apply to outfalls and the help menu is just poorly written?

[fcernst]

That setting is for the junctions... You set the tailwater elevation when you hit Run.

[pbradburyYWE5N]

Yes I see the option to set the Tailwater elevation but it is already populated by an elevation and any elevation I try to put in that is lower than the one that is in there it just reverts back to the one it has in there.. The question is, where does this elevation even come from, how does the software know to start at this elevation? Is it critical depth?

[fcernst]

Click on the cell above that one... A little tricky there.

[lynn_zhang]

Hello @pbradburyYWE5N ,

Just checking to see if your problem has been solved. Did you follow the suggestion above and did it work for you? Let us know if you still need help.

[rmeeksRQ6VC]

I'm trying to figure out this issue in Hydraflow 2021. I would like to set the HGL below the critical elevation because the pond elevation at the outfall will be below critical elevation. When I set the elevation below critical in the Compute System menu, it reverts to the critical elevation when it does the calculations. Is there a way to make a keep a lower HGL elevation?