Page 524 - 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 482

482 Chapter 13 Hydraulics of Sewer Systems
Table 13.3 Suggested Minimum Design Frequencies and Spreads for Gutter Sections on Grade

Road Classification Design Return Period Design Spreads
High volume or 6 70 km/h (45 mph) 10-year Shoulder + 1 m (3 ft)
Bidirectional 7 70 km/h (45 mph) 10-year Shoulder
Sag point 50-year Shoulder + 1 m (3 ft)
Low volume 10-year 1 2 Driving lane
Collector High volume 10-year Shoulder
Sag point 10-year 1 2 Driving lane
1
Low volume 5-year 2 Driving lane
Local Streets High volumes 10-year 1 2 Driving lane
1
Sag point 10-year 2 Driving lane

openings. Debris accumulating on the gratings will then deflect water into the curb in-
lets. Gratings for gutter inlets are most efficient when their bars parallel the curb. If
crossbars are added for structural reasons, they should be kept near the bottom of the
longitudinal bars. Depression of inlets, especially curb inlets, enhances their capacity.
Long shallow depressions are as effective as short deep ones. If a small flow is allowed
to outrun the inlet, the relative intake of water is greatly magnified. Significant
economies are effected, therefore, by small carryover flows and their acceptance by
downgrade inlets.

13.10.1 Gutter Sections on Grade

The main curb and gutter section types are the uniform section and the composite sec-
tion, as illustrated in Fig. 13.12 with their defining variables. Uniform gutter sections
have a constant slope across the section. Composite gutter sections are defined by a

T
Q w Q s
T

S x
d
S x a S w
Uniform road section Composite road section

3
3
Q w flow in depressed section (m /s, ft /s)
3
3
Q s side flow (m /s, ft /s)
S w gutter cross-slope (m/m, ft/ft)
S x road cross-slope (m/m, ft/ft)
T total width of flow or spread (m, ft)
W width of flow in depressed section
d depth of flow at the curb (mm, in.)
a continuous gutter depression (mm, in.)
Figure 13.12 Uniform and Composite Gutter Sections.