Implementation - Inlet Capacity

The following equations are used to calculate Inlet Capacity:

On-Grade Grate Inlet Interception Efficiency:

  E = Rf*Eo + Rs*(1-Eo)
Where:
E = inlet interception efficiency
Rf = 1-0.09*(V-Vo), when (V<=Vo) then Rf=1.0
Eo = 1-(1-W/T)2.67 for case of no gutter depression
Eo = 1/((Sw*H22.67/(Sx*(H12.67-H22.67))+1) for depressed
H1 = depth of water at curb line
H2 = depth of water at intersection of depressed and normal slope.
Rs = 1/(1+0.15*V1.8/(Sx*L2.3))
W = width of the grate in ft
L = length of the grate in ft
V = mean velocity in fps
Vo = gutter velocity where splash-over first occurs, fps

Slotted Inlet and Curb Opening Inlet Interception Efficiency:

  E = 1 - (1-L/Lt)1.8
Where:
E = inlet interception efficiency
Lt = slot length or curb opening length required to intercept 100% of gutter flow, ft.
  =(0.6*Q0.42*S0.3*(1/(n*Se))0.6)
Se = equivalent cross slope, which is Sx if no gutter depression, otherwise equals Sw*Eo+(1-Eo)*Sx
L = actual length of the slot or curb opening, ft.
Q = gutter flow discharge, cfs
S = profile grade in ft/ft
Sx = cross slope in ft/ft
Sw = gutter slope
n = Manning's roughness
Eo = same as in grate inlet see above

Sump Inlet Weir Flow Capacity:

  Qi = Cw*P*d1.5
Where:
Qi = interception discharge, cfs
Cw = weir coefficient (3.0 is used)
P = perimeter of the grate not adjacent to a curb, ft
d = mean flow depth, ft

Sump Inlet Orifice Flow Capacity:

  Qi = Co*A*(2*g*d)0.5
Where:
Co = orifice flow coefficient (0.67 is used)
A = area of orifice opening, ft2 (m2)
g = gravity acceleration, ft/sec2 (m/sec2)
d = mean flow depth, ft (m)