Quick Inlet Capacity Eq??

[Xbxaddict]

Anyone know of a good, general equation determining the capacity of an inlet? My basin in question is in a parking lot low point; Given dimensions and open area of the casting, what Q can it take before it ponds a given depth?
I found one that says Q(cfs)=3.0(grate permimeter)(depth of ponding)^(3/2) but this doesnt take into account open area.

 

[Xbxaddict]

The equation needs to take into account basin dimensions and slope of approaching pavement as well as desired depth of ponding.

 

[gbam]

You can use the standard weir and orifice equations for sag conditions or a nomograph for splash over velocity from HEC-22/12.

Weir:
Qw = Cf x Cw x Pw x Y^1.5
Cf = clogging factor
Cw = weir coefficient, typically 3.0
Pw = weir perimeter
Y = Ponding Depth

Orifice:
Qo = Cf x Co x Ag x (2gY)^0.5
Cf = Clogging Factor
Co = orifice coefficient, 0.67
Ag = Clear open Area of Grate or?
g = gravity 32.2
Y = Ponding Depth

You originally found the weir equation but i reproduced anyway. Clogging is a safety factor. I typically use 50% or 0.5 for sag conditions. You can graph flows vs depths for various catch basin configurations and keep them handy for quick reference. I them for 6 or 7 different cbs. Graph both weir and orifice on same chart to see where each control the head. Good luck and have fun with it!

 

[Xbxaddict]

Thank you! Much appreciated.