Applies To
	Product(s):	CulvertMaster
	Version:	CONNECT Edition and earlier
	Area:	Modeling
	Original Author:	Jesse Dringoli, Bentley Technical Support Group

Problem

Can Culvertmaster analyze culverts with adverse (uphill) slopes?

Solution

Yes, backwater profiles can be performed for culverts for which uniform flows are undefined. The headwater elevation needs to be greater than the tailwater.

Adverse Downstream Tailwater

It should be noted that if you are modeling a case where there is an adverse sloped downstream channel used for the tailwater, you may run into an issue with the results. See the screenshot below.

Entering a negative value for the "Channel Slope" field in the Tailwater tab is not supported and the absolute value will be used instead (effectively modeling a downhill-sloped channel). 

As seen in the diagram above, the culvert itself has a downhill slope but there is an adverse slope in the channel downstream of the culvert. Since CulvertMaster is looking only at a single culvert, with no length consideration for the downstream channel, the tailwater at the downstream end cannot be properly calculated. This is because an adverse slope does not make sense for a normal depth calculation (which is what the channel options for tailwater do) where the channel length is not considered. If it is an upward slope, then it would not be possible to have any flow, because water would need to pond up infinitely (as the length is essentially infinite). Imagine the tailwater channel (brown) slope on the right side of the diagram above extending to the right.

A workaround would be to somehow develop the tailwater rating curve externally and use it with the “tailwater rating” option in the tailwater tab. You could also model this in another product, like StormCAD or SewerGEMS, where you will be able to us a Headwall element to model the culvert and model the actual length of the downstream channel. The network hydraulics would be calculated (instead of a simple normal depth) and the resulting tailwater elevation would impact the culvert hydraulics.

Or, if there is a downward-sloping channel after the uphill channel, you could assume the high point as the invert of the channel and model that next downhill-sloping channel as the tailwater condition.