Ordinary high water mark
Ordinary high water mark
(OP)
I am working on project which bound by a swale on one side (which cannot be used to drain this site) and a river. My problem is that I can only drain the site to the river which is located 45 feet from the nearest catchbasin. The ordinary high water mark (OHWM) for the river is 7.42', the top of my catchbasin is 11.5'. With 2' cover at the catchbasin for the lead and an 18" dia. lead at 1% I will be approx. 6" above the OHWM. In addition I also have to install a stormceptor before discharging in the the river. Does anybody have comments or suggestions?





RE: Ordinary high water mark
RE: Ordinary high water mark
RE: Ordinary high water mark
RE: Ordinary high water mark
RE: Ordinary high water mark
RE: Ordinary high water mark
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RE: Ordinary high water mark
If it's a parking lot (C=0.95), half that size.
So are you sure about that 100-year flow? Because I believe you now about not having enough room for a detention basin. :)
RE: Ordinary high water mark
In my area i=6.6in/hr, area of grass=.4ac, roof=0.34ac, parking lot/driveway=0.312ac, therefore total = 1.05ac, C=0.6....Q=4cfs. In the parking lot I have maximum elevation diff of 1 foot...very level.
RE: Ordinary high water mark
volume of runoff is approximated by V = C * (I/12) * A
assuming total storm is 6.6 inches, then
V = 0.6 * 6.6/12 * 1.05 = .35 ac-ft
depress your grass by 1 foot and you have room to retain the entire thing