Handbook of Civil Engineering Calculations

TABLE 4. Sanitary Sewer Design Factors

Population data

Typical population

Type of area Per acre Per km^2

Light residential 15 3,707

Closely built residential 55 13,591

Single-family residential 1OO 24,711

Six-story apartment district 500 123,555

Sewage-flow data

Sewer design basis,

per capita

City gal/day mL/s

Berkeley, California 92 4.03

Cranston, Rhode Island 167 7.32

Des Moines, Iowa 200 8.76

Las Vegas, Nevada 250 10.95

Little Rock, Arkansas 100 4.38

Shreveport, Louisiana 150 6.57

Typical sewer design practice

Design flow, per capita

Sewer type gal/day mL/s

Laterals and submains 400 17.5

Main, trunks, and outfall 250 10.95

New sewers Never 100 Never 4.38

TABLE 5. Manning Formula Conveyance Factor

Pipe Pipe cross-
diameter, sectional n
in (mm) area, ft^2 (m^2 ) 0.011 0.013 0.015 0.017

6(152) 0.196(0.02) 6.62 5.60 4.85 4.28
8(203) 0.349(0.03) 14.32 12.12 10.50 9.27
10(254) 0.545(0.05) 25.80 21.83 18.92 16.70
12(305) 0.785(0.07) 42.15 35.66 30.91 27.27
15(381) 1.227(0.11) 76.46 64.70 56.07 49.48
18(457) 1.767(0.16) 124.2 105.1 91.04 80.33
21(533) 2.405(0.22) 187.1 158.3 137.2 121.1