Page 532 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

JWCL344_ch13_457-499.qxd 8/7/10 8:49 PM Page 490

490 Chapter 13 Hydraulics of Sewer Systems

2. From Eq. 13.40,
L 1.8
E = 1 - a1 - b
L T
0.9 = 1 - (1 - L>4) 1.8
L = 2.87 m
The length of curb inlet required to capture 90% of the flow 2.87 m.

13.10.4 Combination Inlets on Grade
Combination inlets, shown in Fig. 13.16, consist of both grate and curb openings. The
curb inlet functions as a sweep, removing debris from the runoff before it can clog the
grate inlet. If the curb inlet length is equal to the grate inlet length, the flow intercepted
by the combination inlet is assumed to be equivalent to that intercepted by the grate
inlet alone.
The curb inlet is often extended upstream of the grate for more efficient removal of de-
bris than when the curb opening length equals the grate length. The total flow intercepted
by this configuration is calculated as the sum of:

1. The flow intercepted by the portion of the curb opening located upstream of the
grate
2. The flow that bypassed the upstream curb opening and is intercepted by the grate
alone (the flow intercepted by the portion of the curb opening adjacent to the grate
is neglected).

L c

Discharge W g L g

L c

L g
W g
Discharge

Figure 13.16 Typical Combination Inlets.