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

Empirical
1
0.9
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
UDFCD new
Figure 5-13: Type R curb inlet efficiency comparison
A sensitivity analysis was performed on each of the variables in Equation 5-8 through
Equation 5-10 to quantify the magnitude of change in efficiency from a change in any of the
independent variables, results are presented in Figure 5-14 through Figure 5-16, respectively.
Base values for each parameter were chosen as the median values observed in testing. Each
parameter was varied throughout the range of test conditions while other parameters were held at
their base values, which produced a range of values for efficiency. Normalizing each parameter
value and corresponding efficiency by their base values then produced a curve centered about
one. Use of these figures allows for quantification of the effects from varying each parameter on
inlet efficiency. For example, when the Type 13 and 16 combination inlets are increased in
length by 50% the efficiency increases by approximately 20%. For the Type R curb inlet a 50 %
increase in length results in an efficiency increase of about 40%. A similar comparison could be
made for flow velocity, depth, or top width of flow. As expected, the equations are most
sensitive to changes in velocity and flow area (or depth in the case of the Type R curb inlet).
The Type 16 is less sensitive to changes in velocity than the Type 13 due to the directional vanes
on the grate. Type 16 and 13 equations are least sensitive to changes in inlet length due to most
flow entering the first grate for those inlets, whereas the Type R equation is least sensitive to
changes in street cross slope due to the deep local inlet depression.
68