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

Multiple return periods in a single drainage system

Multiple return periods in a single drainage system

Multiple return periods in a single drainage system

Hello all,

As far as I know, in the design of an urban storm drainage system where drainage pipes pass through residential, local and collector roads, the whole system should be designed for a single return period (say 10-Years) and checked against a higher return period (say 50-Years) for possible flooding.

But what I'm being asked to do is to design the tertiary (residential) pipes for a 10-Year return period, the secondary (local) pipes for 25-Years and the Primary (collector) pipes for 50-Years. The logic being that flooding of residential roads can be tolerated while flooding of collector roads can not. See the attached drawing for an example.

So what is the correct approach for the design. Should the pipes be designed with different return periods based on classification? Or should I design the pipes for the larger return period, but would give me oversized pipes upstream?

Thank You.

RE: Multiple return periods in a single drainage system

It's not uncommon to see tertiary / secondary lines designed for lower return periods. Just do what they ask. If you want to be very clear about what's going on with your system, show the HGLs for all three events in your profiles.

I've seen some regulations for new residential subdivisions, for instance, that require the 25 year storm for all new lines that only carry internal runoff, but 100 year for lines that carry offsite water as well. So you'd have multiple requirements even within the same storm drain network. We usually just show both HGLs on the profile sheet, and provide two pipe charts.

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

RE: Multiple return periods in a single drainage system

Do as you are asked, and show that when the HGLs pop, the overland flow can be safely conveyed to the higher systems overland within the road network, and not flood houses.

RE: Multiple return periods in a single drainage system

Thank you beej67 and Twinkie.

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


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. 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