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

Average difference in calculated efficiency between the corrected and uncorrected data
sets was 2.3% and the R 2 value was 0.97, with the greatest differences occurring at lower
velocities. Based on that small difference, the empirical equations are not sensitive to uniformflow
conditions. In Figure 5-20, the results of repeating the analysis of Section 5.2 are presented.
The splash-over velocity coefficients were redeveloped for the corrected data set, the
calculations presented in Section 2.2 for grate inlets were repeated, and the efficiencies are
plotted against each other.
Efficiency from corrected data
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0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Efficiency from origional data
Figure 5-20: Efficiency comparison from UDFCD methods (Type 16 inlet)
Average difference in calculated efficiency between the corrected and uncorrected data
sets was 4% and the R 2 value was 0.99, with the greatest differences occurring at lower
velocities. This is due to the UDFCD methods being least accurate at low velocity. The
existence of uniform flow is more significant for the UDFCD methods than for the empirical
equations, and could be significant when the inlet efficiency is low (such as less than 10%). But
typical inlet designs are made to be highly efficient (greater than 50%). Based upon the small
differences in efficiency seen, the existence or non-existence of uniform flow in the model was
found to not significantly affect the results of predicting efficiency by the methods used in this
analysis.
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