Detention pond volume
Detention pond volume
(OP)
Picking up a project to help an Architect we've worked with before. The project dragged out long enough that the original Engineer (also a small shop) picked up a big project and now can't set aside the time to complete. I'm completing a grading plan for the lot and trying to layout a detention pond. The project SWMP calcs are all provided, as well as storage volume.
The storage volume is 3050 cu. ft. for a 0.52 ac lot, peak inflow = 5.6 cfs, peak outflow = 3.7, storm type II. This strikes me as high, but without much familiarity in the calculations, I can't verify the numbers. The principle will be in next week (unreachable), but I would like to know if I should proceed with the work or wait until he can verify.
General opinion, if possible, would be fine. Thank you. If more data is needed, I can provide it.
The storage volume is 3050 cu. ft. for a 0.52 ac lot, peak inflow = 5.6 cfs, peak outflow = 3.7, storm type II. This strikes me as high, but without much familiarity in the calculations, I can't verify the numbers. The principle will be in next week (unreachable), but I would like to know if I should proceed with the work or wait until he can verify.
General opinion, if possible, would be fine. Thank you. If more data is needed, I can provide it.
RE: Detention pond volume
Note that the performance of a detention pond (i.e. peak reduction) is dependent on outlet configuration as well as storage capacity. A good outlet design will reduce storage requirements and resulting costs.
I've see so many projects where the designer has used lots of (expensive) storage with almost no regard for the role of the outlet control. (Not saying that's happened here, but it's worth checking.)
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Detention pond volume
As a reference point, stormwater ponds for high density development in central to northern Georgia tend to range from 9,000 cf per acre of watershed to 13,000 cf per acre of watershed, depending on the reg and the stormwater management method chosen. So by that benchmark you're low. If your site is only half buildout, maybe you're not too far off. If the site is in New Mexico, maybe you're high.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Detention pond volume
Mike McCann, PE, SE (WA)