Thanx for ANY help.

MINN. drainage Manual recommends putting pipe inlet invert to pond AT NWL or perm pool level.

FDOT drainage manual says the tailwater for inlet pipe must be HIGHEST or max level pond will reach.


Fl and county just 4 laned road by me.

If permanent pool of wet detention pond extends way back into the inlet pipe..... inlet pipe of Pond 1 for SR 415 is 2.2 ft submerged always. It's top elev is 5.5 ft (invert is at 6 inches and pipe is 5 ft diam) and permanent pool elev is 8.7. Max level of pond is predicted to be 10.5 ft or a full 10 ft ABOVE invert of inlet pipe.

I believe a backwater is created in the inlet pipe up to the 8.7 ft elevation... way upstream in the pipes feeding this pond.

I think, this is HUGE problem cause flat inlet drain on SR 415 S side has 54 in or 4.5 ft inlet pipe whose invert is ONLY 3 ft, thus top of pipe is 7.5.

This pipe is thus ALWAYS full due to perm pool elevation of pond 1. When design storm of 8.6 in in 24 hrs hits.... this pipe will not be able to handle all the inflows due to high tailwater induced by pond perm pool. Max elev of 10.5 and thus VERY high tailwater.

Issues: water stagnates in inlet pipe, breeds mosquitoes (zika and other dangers); drainage from SR 415 will NOT work properly due to high tailwater behind curb inlets..... pipes close to pond are 100% full for quite a distance BACK from pond (due to backwater of the perm pool.)

And the design calculations reports did NOT state that they addressed a high tailwater condition for the pipes close to pond 1 or inlet pipe of same pond.

I think there will be slow/little drainage in some curb inlets and high risk of hydroplaning.

They reused a borrow pit for pond 1 should have put it further N at higher elevation and used exfiltration trenches in low spots near Reed Ellis rd like they did in flood plain of river.

I suspect under 25yr/24 hr storm water may bubble up out of some flat inlets on side of sr 415.

Plans say some inlets are < 10ft.

FDOT dropped install of manhole closest to pond... only 112 ft away. I think because it would have been bubbling up water DURING DESIGN STORM due to top elev of under 10.5 ft.

Am I off mark...... what other issues are there..... scour on pond bottom and turbidity? thanx, john