×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

HEC-RAS Culvert Model: cross-section 2 ineffective areas

HEC-RAS Culvert Model: cross-section 2 ineffective areas

HEC-RAS Culvert Model: cross-section 2 ineffective areas

(OP)
Greetings, hydrology and hydraulics engineers!

I am modelling a 6x6 reinforced concrete box culvert under a two lane highway in a rapidly urbanizing area. The original FEMA model had some errors in the location of cross-sections 1, 2, 3, and 4 of the culvert model. I have inserted new cross-sections 2 and 3 in the appropriate places, and re-termed others.

The problem I have is with the elevation of the ineffective flow areas for cross-section 2. They are supposed to be set at the top of the roadway. In my case, this is elevation 77.5; culvert invert is 69.0 and inside top 75.0.

With the elevations this high the program routes only 0.5 cfs (out of a total flow of 972 cfs) through the culvert, and puts the rest over the highway, greating an unrealistic BFE. When I drop the ineffective flow area elevations to the top of the culvert, 75.0, about 40-45 percent of the flow goes through the culvert, as you would expect.  My downstream channel sections are such I have no channel for over 30 feet, as side ditches with 4:1 sideslopes enter from both directions.

Has anyone encountered this before, where HEC-RAS refuses to route flow through the culvert when using the suggested ineffective flow elevations with the downstream culvert section?

Has anyone modelled the culvert with lower ineffective flow elevations than recommended and had FEMA accept it?

Thanks in advance,
NDG

P.S. Might come back and try to add a figure later today.

RE: HEC-RAS Culvert Model: cross-section 2 ineffective areas

Hey Norman,
I wouldn't expect to see that large of a difference from moving the inneffective flow elevations.  I generally set the inneffective flow area elevations between the top of the culvert and the bottom of the road.  My thinking is that once the water goes across the road it is then effective flow.  A diagram or just the screen capture from the HEC-RAS cross-section view would be helpful - I don't think I'm seeing the total picture from your description.

If you know where the 1,2,3,and 4 cross sections go, and if you have your ineffective flow ares moderately close, I don't think you'll have any issues with FEMA.   The signing engineer in these projects carries most of the liability.

Robert Billings
www.newrivereng.com
  

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources