Culvert error message in 6.1

[Wick]

Hello, I have a very long culvert (~7700 ft) that is fully within a 2D flow area, however I am getting the following error:

Barrel#1 on structure Long_culvert does not entirely intersect the upstream area 2D_flow_area
Geometry Writer Failed
Error Processing Geometry

Google is not helping, what does this error mean?

Thank you!

[Scott Miller]

Make sure the entire cross-section of the culvert (inlet) is at least as high as the terrain. If it is not, you can modify either the terrain or the culvert characteristics. The wording of the error message is different than I’ve see before, so this could be a different issue. An image of the geometry could be helpful.

I would be concerned with modeling such a long pipe as a culvert. It is essentially a network.

[Wick]

Thank you Scott. What do you mean it is essentially a network, do you mean I should model it as multiple separate culverts? It is a large box culvert, 13x14ft.

[Scott Miller]

I mean HEC RAS was not developed to model such a long pipe. A separate model, like EPA SWMM, may need to be used to model pipe hydraulics. I am not fully familiar with all new HEC RAS features, but to my knowledge HEC RAS still uses FHWA calculations for culverts, inlet controlled or outlet controlled. I would want to look further into the HEC RAS Hydraulic Reference Manual, or FHWA documentation, to make sure what I was doing with RAS made sense.

If the box culvert does not flow under pressure, i.e. there is always airspace at the top, I would model it as an open channel.

• This reply was modified 2 years, 10 months ago by Scott Miller.

[Wick]

Great point, I had not considered that. You are correct that HEC-RAS 6.1 still uses FHWA for inlet-controlled culverts. I’m adding the relevant info from the online manual should anyone else come across this post:

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The culvert hydraulic computations in HEC-RAS are similar to the bridge hydraulic computations, except the Federal Highway Administration’s (FHWA) standard equations for culvert hydraulics under inlet control are used to compute the losses through the structure (when a culvert is under inlet control conditions). Outlet control hydraulics are handled by balancing the energy equation from downstream to upstream.
*************

Regarding the mysterious error message, it is separate from the old “invert is lower than connected cells” error. I know this because I redrew the culvert, did not get that error message, but DID then get the “invert is lower” message (or whatever the wording is). So I am still not sure about the original error message.

[Wick]

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