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1.9 Distribution Works 19

EXAMPLE 1.5 ESTIMATION OF THE SIZE OF A WATER CONDUIT
Estimate roughly the size of a supply conduit leading to an adequate distributing reservoir serving
(i) relatively small residential community of 10,000 people, and (ii) a relatively large industrial
community of 400,000 people.
The following are the design conditions specifically for a North America region:
a. The average daily water consumption for small communities with populations of 10,000 or
less 100 gpcd (378.5 Lpcd).
b. Average daily water consumption for communities with populations of greater than 10,000
150 gpcd (567.8 Lpcd).
c. Maximum daily water consumption is about 50% greater than average daily water
consumption.
d. The design water velocity in the circular conduit when flowing full 4 ft/s 1.22 m/s.
Solution 1 (U.S. Customary System):
1. Average daily water consumption at (a) 100 gpcd and (b) 150 gpcd for the 10,000 people
community and the 400,000 people community, respectively:
(i) 10,000 100>1,000,000 1.0 MGD.
(ii) 400,000 150>1,000,000 60 MGD.
2. Maximum daily water consumption is 50% greater than the average:
3
(i) 1.0 1.5 1.5 MGD 1.5 1,000,000>(7.5 24 60 60) 2.32 ft /s.
3
(ii) 60 1.5 90 MGD 90 1,000,000>(7.5 24 60 60) 139 ft /s.
3. Diameter of circular conduit flowing at 4 ft/s:
2
2
(i) Cross-sectional area A Q>v 2.32>4 D >4 0.785 D .
Diameter D 0.833 ft 10 in. for the small 10,000 people community.
2
2
(ii) Cross-sectional area A Q>v 139>4 D >4 0.785 D .
Diameter D 6.667 ft 80 in. for the large 400,000 people community.
Solution 2 (SI System):
1. Average daily water consumption 378.5 Lpcd for the 10,000 people community and aver-
age daily water consumption 567.8 Lpcd for the 400,000 people community.
(i) 10,000 378.5>1,000,000 3.785 MLD.
(ii) 400,000 567.8>1,000,000 227.1 MLD.
2. Maximum daily water consumption is 50% greater than the average:
3
3
(i) (3.785 MLD) 1.5 5.6775 MLD 5,677.5 m /d (5,677.5 m )>(1,440 60)
3
s 0.066 m /s 66 L/s.
3
3
(ii) (227.1 MLD) 1.5 340.65 MLD 340,650 m /d (340,650 m )>(1,440 60)
3
s 3.94 m /s.
3. Diameter of circular conduit flowing at 1.22 m/s:
3
2
2
(i) Cross-sectional area A Q>v (0.066 m /s)>(1.22 m/s) 0.054 m 0.785 D .
Diameter D 0.26 m 260 mm for the small 10,000 people community.
2
3
2
(ii) Cross-sectional area A Q>v (3.94 m /s)>(1.22 m/s) 3.23 m 0.785 D .
Diameter D 2.03 m 2030 mm for the large 400,000 people community.
1.9 DISTRIBUTION WORKS
Supply conduits (Fig. 1.8) feed their waters into the distribution system that eventually
serves each individual property—household, mercantile establishment, public build-
ing, or factory (Fig. 1.1). Street plan, topography, and location of supply works and