×
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

Designing Overflow Weir

Designing Overflow Weir

Designing Overflow Weir

(OP)
Hey everyone,
I'm designing a ~27,000 sq-ft. wet pond which holds approx. 650,000 gal. and serves a drainage area of approximately 30 acres.

The desired pond water elevation & corresponding weir crest elevation are 465'
I'm trying to determine ideal dimensions for my sharp-crested contracted rectangular weir.
There will be a separate emergency overflow riser at a higher elevation.

I'm a bit confused on determining the Head acting on the weir. I understand H is essentially the distance between the crest height and the EGL.
However the Pressure is atmospheric, the crest elevation is the same as the surface elevation in the pond, and my reference says that for pond spillways the approach velocity is often assumed to be zero.

I'm following local design guidelines for determining my Q25 and I obtained approximately 23 cfs entering the pond over a ~5 minute storm duration.
My rationale is that 23 cfs over 5 minutes is approximately 7000 cubic feet. 7000 cf over the 27,000 pond area gives an elevation rise of ~0.26' across the pond. Is this my design Head acting on the weir?

Once I come up with some weir dimensions and results in HydroCAD, what do I compare against to see if my velocities and flows are acceptable? Or is the allowed velocity more determined by the receiving channel downstream, to prevent scouring?

Thanks in advance, I've tried to do my due diligence as this is my first project of this sort and wanted to check-in with you fine folks.

RE: Designing Overflow Weir

That's a very rough way to determine the weir head, but the head will be changing constantly with time, so you need a hydrograph routing to get an accurate answer. Since you're already using HydroCAD just adjust the weir dimensions until you achieve the desired behavior.

As for flow velocity, if you look at the device analysis (at the bottom of the pond summary) this will show the velocity for each of the outlets at the time of peak flow. If you're concerned about the velocity in the downstream channel you can model this as a reach.

Peter Smart
HydroCAD Software
www.hydrocad.net

RE: Designing Overflow Weir

(OP)
Great - thank you psmart! Always very helpful.

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


Resources

eBook - Manufacturing the Cars of Tomorrow
In this ebook, we'll explore how additive manufacturing is going to transform the way cars are made. This includes commentary from thought leaders such as Ford's CTO, Ken Washington, Customer case studies of ways 3D printing is being used today, and a variety of part examples where 3D printing is already impacting how automobiles are made. Download Now
White Paper - Smart Manufacturing for Semiconductor
New technologies and approaches present great opportunities for semiconductor manufacturers to achieve high levels of innovation, yield and improvement. This white paper explores some of these cutting-edge technologies and how they can be applied effectively in the semiconductor industry. Read about how Smart Manufacturing is transforming the semiconductor industry. Download Now
White Paper - Analysis and Simulation in Aircraft Structure Certification
Organizations using simulation and analysis tools effectively see the benefits in their ability to achieve certification faster and with drastically less total cost than those who do not maximize these tools. Read this White Paper to learn about how digital tools such as analysis and simulation help in aircraft structure certification. Download Now

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