Contact US

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!

*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

no outlet velocity calculated

no outlet velocity calculated

no outlet velocity calculated

So I am working on a detention pond checking 2-yr 24-hr, 5-yr 24-hr, 10-yr 24-hr and 100-yr 24-hr storm events. I am required to list exit velocities for each storm event. Unless things have changed when you are below 5 fps vegetation is adequate erosion control. I have not being doing this lately a whole lot but I imagine things have not changed.

So my 2-yr event the output mentions 5.2 cfs of 6.9 cfs passes through the outlet culvert. It is a riser structure with a low flow orifice, mid level orifices, and the open manhole structure type inlet at the top of the riser. 18" culvert as the outlet.

The same output for the other storm events mentions barrel controls and gives a flow rate in cfs and velocity in fps in the same area where before it gave no velocity for the 2-yr event.

Why is there no velocity mentioned for the 2-yr event? It shouldn't matter since the only velocity over 5 fps is the 100-yr event but I would imagine they will be asking unless I calculate the velocity using Manning's equation myself.


RE: no outlet velocity calculated

HydroCAD only reports the velocity for the controlling device. For the devices that are "passing" less than their potential flow at a given head, the velocity is not known and will not appear in the report.

For details please see www.hydrocad.net/outlets.htm (scroll to the end of the page)

Peter Smart
HydroCAD Software

RE: no outlet velocity calculated

For a quick estimate of outlet velocity you could assume normal flow in the pipe and use Manning's.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: no outlet velocity calculated

I think FHWA's hydraulic toolbox has a circular channel that can do that calculation or flowmater. You could always revert back to the partial flow nomograph for pipes.

RE: no outlet velocity calculated

You can also do the calculation in HydroCAD. Just setup a pipe reach and examine the stage-discharge curve. No inflow is required - just an isolated reach.

Peter Smart
HydroCAD Software

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! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close