Trouble shooting Warning Message 80. 1

[gscotchie]

I'm encountering the message, "[80] Warning: {node} Exceeded Pond x by x.x' @ x.x hrs (x.x cfs x.x af)"

More speciffically to my model, "[80] Warning: Pond 5R Exceeded Pond 6R by 0.10' @ 12.06 hrs (2.16 cfs 0.008 af)"

Ponds 5R and 6R are Catch Basins with insignificant storage. There are two nodes (1P and 6R) feeding 5R. 5R is an 18" RCP with a slope of 1.35%. The respective flows of 1P and 6R are 4.26 and 1.42 cfs for a total flow entering the 18" RCP of 5.68 cfs. 5.68 cfs doesn't seem like enough flow to cause a reverse flow or higher tailwater in an 18" RCP with a slope of 1.35%.

How concerned do I need to be about this RED label warning.

My time increment is already 0.01 hours with the Fine Routing set to 2.

One fix I've come up with is making the slope of the existing pipe steeper. Is there anything I can do in the modeling software to not have to dig up the existing pipe only to increase the slope from 1.35% to something steeper?

Thank you

gscotchie

 

[beej67]

What routing method are you using?

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[gscotchie]

Runoff Method: SCS TR-20
Reach Routing Method: Dyn-Stor-Ind
Pond Routing Method: Dyn-Stor-Ind

I attached the model.

The slope of node 5R seems to the issue. 1R through 5R are existing storm pipes. In order to remove the error message, I lowered the invert of 5R to Inlet/Outlet 522.10'/517.70' and the inverts of 4R to 517.60'/516.90'.

 

[gscotchie]

I don't want to have to adjust existing inverts elevations if I can find an alternative solution.

Thank you.

 

[psmart]

You have a momentary reverse-head situation between nodes 5R and 6R. This appears to be an accurate simulation of the actual system behavior, rather than a modeling failure. However, it means that the actual system will experience a brief reverse flow between those nodes which is not replicated in the model. Basically, the model blocks the reverse flow, hence the warning message:

[80] Warning: Pond 5R Exceeded Pond 6R by 0.10' @ 12.06 hrs (2.16 cfs 0.008 af)

Note the reverse head is only 0.10', and the potential reverse flow volume is just 0.008af.

BUT, if you reduce the time increment to 0.002 hours (and reset the finer routing to 1) this will reduce the reverse head considerably:

[80] Warning: Pond 5R Exceeded Pond 6R by 0.01' @ 12.06 hrs (0.66 cfs 0.001 af)

It pretty common for drainage systems to exhibit these brief reverse-flow conditions.


Peter Smart
HydroCAD Software

http://www.hydrocad.net