Bridge Weir Flow

[Anonymous]

In the Deck/Roadway Editor, you input an upstream and a downstream roadway profile. They don’t have to be the same but the stationing origin for he Road Elevation (high chord) must be he same as the bounding stream cross section. The upstream (Bridge XS 3) and downstream XS (Bridge XS 2) do not have to be the same. My question is which roadway profile does HEC-RAS use to calculate weir flow- the upstream, downstream, or a combination based on which is higher? I don’t think it can be a combination because the stationing for Bridge XSs 2 and 3 does not have to be the same. I have assumed that it was the upstream road profile, but I have a situation where the downstream road profile is higher than the upstream road profile.
David Preusch, PE, PH, CFM, D.WRE
Senior Supervising Water Resource Engineer
WSP USA Water & Environment
Direct: (410) 246-3849
Cell: (240) 701-9922
[email protected]
WSP USA
1 East Pratt Street
Suite 300
Baltimore, Maryland 21202
WSP.com

[Anonymous]

My assumption is that it uses which ever one causes the highest energy grade for a given flow. Or another way of stating it: it uses whichever one allows the smallest flow for a given energy grade.

You could run a series of tests to determine whether that is correct or not.

[Author]

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