Modeling Culvert with Junction and Angle Change

[huesmann]

How would one go about modeling a box culvert with a 45º bend at a junction box about halfway down its length? Lidded sections (if so, how frequent?)? Some other way? Thanks in advance.

[Chris G.]

Are you trying to capture the head loss from the bend? If the culvert is long enough, the loss from the 45 degree bend is probably fairly minor compared to the friction loss and the entrance and exit losses. Plus, RAS does not explicitely calculate minor losses in pipes (other than the entrance and exit losses). You would have to put in some forced energy loss. Unless there is a particular reason you have so show the 45 degree bend, I’d ignore the bend altogether. If you really want to include some loss, bump up the mannings n value slightly in the culvert to simulate the minor loss from the 45 degree bend.

If you have to show the 45 degree bend, lidded cross sections would work, but again RAS will not caluculate losses due to this 45 degree bend-it will purely be a visual thing.

Keep in mind that RAS is not designed to be a pipe network model. The culvert routines were designed for typical highway culverts. That being said, if you understand the limitations, you can simulate long tunnels and pipes to some degree. Lids do provide flexibility to do that.

[huesmann]

The culvert is about 360′ long; the junction box is at about the mid-point. I know I could bump up the Manning’s, but have no idea how much would be appropriate.

As far as the bend losses with lidded cross sections, can’t one input minor losses into HEC-RAS (Geometric Data–>Tables–>Minor Losses–>Minor Loss Coefficient), into the section immediately upstream (or downstream?) of the junction?

[Chris G.]

Yes! I forgot about the Minor Loss Table. If you go with lids, definately use that.

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