Hec Ras Box Culvert Bug?

[schly]

In an unsteady model, I've modeled a 5.3'x5.3' (~28 sq ft flow area) concrete box culvert that conveys a maximum of 25 cfs of roughly 380 cfs at the peak of the 100-yr hydrograph. The remainder of the flow overtops a lateral structure upstream of the culvert, flows into a storage area that is also connected to the same reach at a point about 1000' downstream, thereby short circuiting a portion of the channel.

An identical channel with a 6' diameter (~29 sq ft flow area) circular corrugated metal culvert in place of the box culvert conveys a maximum of about 245 cfs of the same hydrograph.

Have any bugs been identified with box culverts in UNET?

-Brian

 

[francesca]

Have you checked your settings for entry losses at the box culvert? Also, are you sure you've entered feet and not inches? 25cfs would be about right for a 5.3" x 5.3" box culvert under pressure!

 

[schly]

I set the entrance loss coeff to 0.2 and the exit loss to 1. The coefficients are set the same for both the square and circular culverts.

My units are feet. Hec Ras won't allow for inches in this dialog.

Thanks for the response, Brian

 

[gbam]

Schly,
Try editing the cmp run to change it to a box and see if you get similar results.

 

[schly]

Thanks gbam, that worked! The peak flow through the box culvert now reasonably matches that of the cicular.

Unfortunately, now I am losing flow after the hydrograph returns to baseflow. Instead of passing 2.5 cfs as I have defined it, only 0.1 cfs makes it through. Any ideas?