design of stormwater holding tank in nj
design of stormwater holding tank in nj
(OP)
what is the best approach to designing a stormwater holding tank below a proposed parking lot for a proposed office building in nj? in other words, what are the steps to take in designing the stormwater holding tank... and where in the nj design codes can this info be found?





RE: design of stormwater holding tank in nj
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: design of stormwater holding tank in nj
RE: design of stormwater holding tank in nj
RE: design of stormwater holding tank in nj
RE: design of stormwater holding tank in nj
So you're less interested in what happens to the "10 year storm" going into the tanks or whatever, and you're more focused on making sure the amount of water you accumulate in your tanks during the wet season carries over to match your demand in the dry season. Most times I've done it, I've used monthly rainfall averages, or if available I've used higher percentage confidence interval rainfall numbers.
So, for instance, say your owner wants to make sure that his tanks only go dry once every ten years on average. Then you go and drum up some numbers on what the 10% driest month is (if that makes sense) and you use those numbers in your water balance analysis.
Then the water balance analysis for your system will be something like this:
assumed rainfall in a given month produces
calculated runoff in a given month plus
carryover from previous month equals
total available that month, minus
whatever you use that month (irrigation demand varies, toilets typically don't) equals
carryover to the next month
Then you size your system so it can adequately carry over the stuff from the wet months to the dry months.
Then your client tells you that's too big, and actually we're just going to install whatever we can afford, regardless of whether it'll work or not, so you shrug and move on.
;)
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: design of stormwater holding tank in nj
RE: design of stormwater holding tank in nj
The lesson you're going to learn when you run this exercise, is you want to drain as much watershed to your tanks as you can. I prefer trying to limit it to impervious runoff because it's cleaner and less trash to intercept. I typically like to put some sort of pretreatment in the system as well, like an oil-grit separator or other hydrodynamic water quality device, to keep dixie cups out of your cistern.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: design of stormwater holding tank in nj
The total volume to be stored in the holding tank area is 13,369 cu.ft. From uphill, there are 2 bio-retention basins that, when combined, are a 10,700' area; and the outflow pipe is located 2' above the bottom of the basins. So therefore, there is some TSS removal, and I am not sure how to quantify the amount of total sitewide TSS, nor the amount of TSS that would be held in the 2 basins.
I've designed the holding tank system with StormTech's SC-740 system (24" dia) 60'x95' area. How would I size the width of the oil grit separator prior to flow into the StormTech holding tank area? I've attached a typical cross section.
RE: design of stormwater holding tank in nj
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Sounds like an interesting project. If you're going to be using storage in a stone reservoir as your cistern, make sure to spec washed stone. Wouldn't want sand in your toilets. I would also recommend wrapping the whole thing (stone and all) in impermeable geotextile or similar so you don't lose any water to groundwater infiltration, unless that's part of your intent.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com