Storm pipes can be a part of a regional basin? 1

[lidabc]

Whenever I design storm drain basins, I come up with a question.

Is it appropriate that storm drain pipes connected to a new basin can be included as a part of the basin capacity?

Some municipalities say "No" for conservativeness, some say "OK".

I know that conservative design of the basin is really great to prevent "flooding" in case of a big storm event, but it's hard to ignore it if the capacities of the underground pipes are huge.

I am wondering how the design criteria are in other areas….?

I am in Northern California. Thanks and have a wonderful day!

 

[gbam]

Well, I typically do not include them in my volume computation unless there is a need for volume and we are short on available space. For instance I have just submitted a retention basin design using the pipe's volumes (connected three seperated basins). In this situation there is no room to expand the basin and the depth is nearing the maximum allowble. I have never had comments regarding the use or nonuse of the pipe volum.

 

[beej67]

If you count the volume, make sure you're not counting anything below your primary control elevation (permanently wet) or anything above your peak stage (no storage).

In highly urbanized developments designers in this part of the country sometimes just upsize all their storm drain pipes and put the entire detention volume in them. This causes other issues, such as the need for good access to maintain them against sediment accumulation. Some municipalities down here (City of Atlanta) will not allow CMP stormwater detention unless it's "offline." Anything they consider to be "online" has to be RCP. That's basically an artifact of how they broke out their rules for storm drain design vs their rules for detention design. Some others don't want detention in CMP at all.

I'm not sure what sort of topography you've got to work with, but in my experience, it's best to have the last stick of pipe in your network at 1% or flatter and in the invert of your pond, for energy dissipation reasons, and keep every other stick in your pipe network as high as you can get it, both to reduce installation cost and to keep it as dry as you can for future maintenance reasons. That's presuming you've got enough fall in your system to work with.





Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[ACtrafficengr]

I recently saw a presentation that mentioned using Stormtech units between catch basins. They said they fit in enough storage to eliminate detention ponds in a new residential subdivision.

They didn't say whether or not it worked as intended or even if it had been built yet.

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

 

[beej67]

I doubt you'll see too many more of those in today's real estate market. Going underground with detention made some sense for residential when things were extremely hot, but now it really doesn't work on the balance sheet. Then again, no residential development works on the balance sheet in the current economy.

I did some masters degree work on urban stormwater infiltration, and it has fascinating potential. I have an article around here somewhere about a Japanese pilot project where they had pervious concrete, had a stone underdrain, still had catch basins that weren't really used, tied the stone underdrain in with the base course rock of the storm sewerlines, and made them perforated as well. It was one contiguous subsurface flow. They said they noticed streams that had previously dried up due to urbanization spontaneously return to base flow in the basin. There's also some French research that says infiltration through the base course acts as an aerobic bioreactor for water quality treatment.

All that said, I'd be worried about putting a stormtech chamber "on line," particularly on grade. I'm not sure the inverts of those things are designed to carry peak flows, and they only really work properly when they're flat, so using the chambers themselves as stormwater conveyance would bother me as the engineer. I've done that sort of thing with exfiltration trenches in Miami, but I wouldn't touch it in other areas.



Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[francesca]

We had a development where we considered using those swoopy chambers for underground detention. We went with 48" CMP instead. Even having to run at an incline (and losing storage by assuming the system didn't get pressurized) it was way cheaper.

 

[beej67]

Stormtech stuff starts to make more economic sense when cover gets tight and you don't have enough fall to go with a large diameter pipe. Think big boxes in coastal plains. In north/central Georgia, we do a lot of 72s and 84s for detention manifolds. Economies of scale tell you pick the biggest pipe that will fit and can still hold your traffic loading. Stormtech also makes more sense if you have an infiltration credit / requirement you're going for. I've tried them out on a couple of projects during early design development and we abandoned them for one reason or another. I do think it's a slick system, just never seemed to make the numbers work.



Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com