Negative Sloped Culvert Outlet

[TerryScan]

Peter,

I am modeling an exiting culvert in a ditch which is acting as a pond. The culvert has a negative slope.

The original modeler had set up the culvert with a flat slope using the downstream elevation at both ends.

36.0" Round Culvert
L= 100.0' RCP, sq.cut end projecting, Ke= 0.500
Inlet / Outlet Invert= 45.08' / 45.08' S= 0.0000 '/' Cc= 0.900
n= 0.025 Corrugated metal

When I "correct" the upstream invert to the actual value (44.94), producing a negative slope, an increase in flow results (from 9.73cfs on a 2yr event to 10.48cfs).

This does not appear to be appropriate, can you explain?

Thank you,
Terry

 

[psmart]

First, be sure there are no warning messages that could indicate routing problems. These need to be resolved before you have meaningful results that are suitable for comparison.

Next, I would compare the stage-dischrage curves for the two situations, which should show no discharge until the WSE exceeds the higher of the inlet and outlet.

If you still have questions, please send both files to HydroCAD support or post them here.


Peter Smart
HydroCAD Software

http://www.hydrocad.net