Strange behavior of culverts

[tsairi]

I have a bridge with openings in the deck which I try to model as culverts. When the deck is completely blocked (i.e. no culverts), the water does not reach the lower cord at all. When I introduce the culverts, without any other modifications, the water jump up and pile above the bridge. As the blocked version is the worst case, what can cause the increase in water level?
Thanks!

[datino]

i've the same problem !!!

[MattZ]

HEC-RAS uses two different sets of equation for bridge flow problems and culvert flow problems. Check your output to see which equations are used.

Refer back to the Hydraulic Reference Manual for the details. It sounds to me like that would be why you are seeing the strange results.

[tsairi]

thanks MattZ,
i looked at the detailed output nd couldn't find a hint to what equation was used. can you give one?
Arnon

[MattZ]

Refer to page 6-13 of the Hydraulic Reference Manual. Then, you can go here:

http://www.fhwa.dot.gov/engineering/...m?pub_number=7

and find the nomographs and equations that were used to calculate flow through the culvert for each situation you are encountering. It will be a lot of detective work, but you should be able to determine what is going on.