[Wick]

edit

[Wick]

I’ve gotten an error once, but bypassed it and it didn’t seem to affect the results.

[Wick]

Look at the error codes, do they tell you how far off your elevation is? If it is close, you can just adjust the culvert inverts to match. A fraction of a foot here and there in your model is not going to drastically change your results for a dam breach.

The elevation is taken from the cell faces at the location, not necessarily the lowest point in the terrain. You can try adjusting your 2D flow area grid size smaller in that area to see if you can pick up the lower elevations you checked off the GIS contours.

Another option is to use RASMapper to make very small terrain modifications in the areas of the culverts to match the elevations you want (you would not have to adjust your culvert geometry data). By nature, terrain files tend to miss high and low spots depending on their resolution.

[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:

*************
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]

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.

[Author]

Posts