Hydraulic Efficiency of Grate and Curb Inlets - Urban Drainage and ...

Efficiency for the Type R curb inlet presented in Section 5.1 was calculated from
Equation 2-11 and Equation 2-13. Calculated efficiency from these two equations can be
improved by updating the coefficient and exponents of Equation 2-13. By doing this, the
original form of the equation is preserved. Equation 5-3 illustrates the general form of this
equation, where the coefficient N and the exponents a, b, and c will be determined by regression
of the test data:
L
T
= NQ
a
S
b
L
⎛ 1
⎜
⎝ nS
e
⎞
⎟
⎠
c
Equation 5-3
where:
L T = curb opening length required to capture 100% of gutter flow;
Q = gutter flow (cfs);
S L = longitudinal street slope (ft/ft);
S e = equivalent street cross slope (ft/ft);
n = Manning’s roughness coefficient;
N = regression coefficient; and
a,b,c = regression exponents.
The improved results of using Equation 5-3 to determine efficiency are presented in
Figure 5-7. A tabular test-by-test comparison is presented in Appendix B for the Type R curb
inlet. The final form of this equation is presented as Equation 5-4:
0.51 0.058
⎛ 1 ⎞
LT
= 0.38Q SL
⎜ ⎟
⎝nSe
⎠
0.46
Equation 5-4
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