×
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

Post Construction Stormwater Retention

Post Construction Stormwater Retention

Post Construction Stormwater Retention

(OP)
In Wisconsin, the DNR requires post-construction peak discharge at or below the predevelopment 100-yr, 10-yr, and 2-yr, 24-hr frequency storm events. I'm currently working in a municipality that has a more restrictive ordinance, that the 100-year post-development runoff event must be stored and can be released at a maximum of the pre-development 10-year, 24-hour event.

Without knowing details of a single municipality, what would be some reasons behind restricting this? Perhaps to protect the stormwater piping system so it doesn't get to capacity as quickly? Any other thoughts? Simply just got me thinking and curious what the benefits are.

RE: Post Construction Stormwater Retention

It's about volume. Even though you're preserving the peak flows of the pre-developed conditions, the resulting volume is actually greater. This increase in volume, post-construction, is known to erode downstream channels. Hope this helps.

Terry Stringer
Hydraulics & Hydrology Software
http://www.HydrologyStudio.com

RE: Post Construction Stormwater Retention

volume is half the answer, the other half is water quality. Stormwater retention basins capture sediment and pollutants from the first flush. Storing those sediments in a small basin would result sediment being washed out downstream when you get a storm with volume greater than your retention basin. so the retention basins are often sized for the 100 year, 2 hour storm.

RE: Post Construction Stormwater Retention

(OP)
Thanks for the comments, understood HydrologyStudio & cvg. I'm still unsettled in mind why a municipality would want to be more restrictive on peak discharge than the state.

All the draft legislation the the DNR provides to municipalities, and even the extremely urban areas (this particular project is not one) are all the same as the DNR requirements.

RE: Post Construction Stormwater Retention

Wisconsin DNR seems unusual, most states do not regulate stormwater, that is generally reserved for the county or city. The only exceptions to that are generally for state owned land or right of way.

RE: Post Construction Stormwater Retention

Quote (rwcardinal)

Without knowing details of a single municipality, what would be some reasons behind restricting this?

Some variation on Robbing Peter to Pay Paul. I know some areas which require a reduction percentage beyond your predevelopment condition for your pre/post analysis. I know many which force you to pretend your site is wooded predevelopment even when it's not. I know some areas I've worked in where they had a flat discharge limit per acre for a given storm regardless of predevelopment condition, as a regional flood control measure. Any traditionally urbanized area in the US, which was developed prior to stormwater management regulations, is going to have a flooding problem that they're ill equipped to fix universally, so the hope is that it gets fixed through restrictions on redevelopment. And since the land, and land development, is so different by region, each region cooks up its own solution on how to best rob peter to pay paul.

Quote (cvg)

Wisconsin DNR seems unusual, most states do not regulate stormwater, that is generally reserved for the county or city.

This varies widely by state. I'm not sure I can think of any one thing that I'd say "most" states do, when it comes to stormwater.

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

RE: Post Construction Stormwater Retention

(OP)
Thanks beej67. That helps.

RE: Post Construction Stormwater Retention

Peak shaving using an optimized inflow weir is your friend in these cases. Design your BMP so it doesnt start filling up until you hit the peak of the target storm.

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


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