Hi Chris,

The culvert output table shows that the 500-year flow has Inlet Control at the culvert, while the rest of the profiles have Outlet Control. As a result, the 500-year profile experiences a supercritical flow regime through the culvert, which results in the crossing profiles. I don’t believe there is anything intrinsically wrong with it hydraulically.

Please see page 6-9 of the HEC-RAS Hydraulic Reference Manual for more details about RAS and inlet vs. outlet control.

Good luck!

– Jake Gusman

p.s. While I didn’t look at the model in detail, the cross sections, especially adjacent to the culvert seems to have too many right angles and/or “doglegs” in them. You may want to reassess those.

Some doglegs are fine, but you don’t want an excessive number of doglegs and typically no 90-degree angles in your cross sections. Unless you’re just modeling low flows, think about overall flow direction during a large flood event rather than being focused on localized contour changes that won’t affect the overall flow. Along a bridge roadway, the bounding cross sections should typically be based on the overall flow direction during a large event rather than localized changes along the bridge/roadway.

Here’s a screenshot from an HEC publication (TD-39) that shows a good example of overall cross section layout.