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

1
0.9
Observed
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1 ft depth
0.5 ft depth
0.33 ft depth
Equal
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Predicted
R 2 Average efficiency error (%) Maximum efficiency error (%)
0.948 3.8 15.7
Figure 5-7: Predicted vs. observed efficiency for Type R curb inlet from improved UDFCD methods
Efficiency predictions by the UDFCD methods were improved slightly for each of the
inlets tested. The methods were extended to include the Type 13 and 16 combination inlets, with
efficiency over-predicted by an average of 10%. For these inlets, agreement with observed test
data is still best at low flow depth. For the Type R curb inlet, UDFCD methods were modified
slightly, and efficiency error spread evenly at 3.8%. Agreement is still best at higher flow
depths, and has been improved for the lowest depth. Efficiency predictions can be further
improved by developing new empirical relationships for each inlet.
5.3 Efficiency from Dimensional Analysis and Empirical Equations
In this section empirical equations are presented, as an alternative to the use of the
UDFCD methods, for determination of inlet efficiency for the Type 13 combination, Type 16
combination, and Type R curb inlets. Equations presented will provide a simpler and more
accurate method, than that presented in the USDCM, for determining efficiency in the on-grade
condition. Methods presented in the USDCM suffer from, in part, use of theoretical parameters
that can not be physically determined by a user (such as splash-over velocity, R f , R s , Q w , and Q s ).
61