CIVIL ENGINEERING FORMULAS

STORMWATER, WASTEWATER, AND ENVIRONMENTAL PROTECTION 363

When a grate inlet is used to collect the storm water, an opening of 18 in, or
more, is recommended. With a flow depth of up to 4.8 in, the inlet capacity is

(13.7)

wherePperimeter, ft, of grate opening over which water may flow, ignoring
the bars.
If the flow depth exceeds 1 ft 5 in, the capacity is

(13.8)

whereAtotal area of clear opening, ft^2
gacceleration due to gravity, 32 ft/s^2

Controlling Sewer-Water Flow

Controls used to regulate sewer-water flow include side weirs, siphon spill-
ways, and leaping weirs (Fig. 13.2). Flow diversion for a side weir is, in cu ft/s:

Q3.32l0.83h1.67 (13.9)

Q0.6A 22 gy

Q 3 Py3/2

Manhole cover

Joint

filler Curb

Normal gutter line

Depressed

gutter

5' 3' wide

Opening

Minimum

inside

width 2'-6"

Rungs-14"

C. to C.

Pipe

12 1

6"

6"

Invert shaped with

concrete fill

6"

FIGURE 13.1 Storm-water inlet with opening in a curb. (Merritt—Standard Handbook for
Civil Engineering, McGraw-Hill.)