Stormwater Detention 1

[martin888888]

Hello,

We have a jurisdiction with a detention requirement that you only need to detain the 100yr storm. Their conveyance design storm is the 25 year storm. Has anyone ever ran into such a requirement? If your conveyance system is only going to handle the 25year storm you would need a secondary system to collect the 100year storm in order to convey it into a detention system.
Thanks

 

[jasonpc]

You know I've never really understood the requirements in South Florida. I guess maybe it is an admission that there is not way to be able to route a 100-year storm through a detention system that won't cause negative effects (nuisance flooding but not catastrophic property damage). People in Texas and Louisiana sure know that it doesn't take a Cat 5 to exceed a 100-year rain event. Some of the worst flooding disasters caught people off guard subtropical systems, stalled cold fronts, etc. In many cases the worst flooding usually occurred with no evacuation.

 

[beej67]

The SFWMD 100 year requirements are predicated on an understanding that when the 100 year storm happens, there literally is no where for the water to go. Routing it through your outlet works is scientifically disingenuous, since there will never be a case where a 100 year storm falls on your property, but the receiving watercourse isn't also staging up to the same level your property is also staging. Think of it in terms of tailwater. How do you route your storm when the tailwater is the 100 year elevation, and your own pond is at the same elevation?

They might do things differently down there, but the proof is in the pudding. It works for them, and they've been doing it that way for a long time, after putting a lot more thought in to their regs than anyone else at the time did. Only now are some portions of the rest of the southeast catching up to SFWMD's level of rigour.

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