Page 285 - Water Engineering Hydraulics, Distribution and Treatment

Problems/Questions
The water consumption during the maximum day demand in
Elevated
the city is as follows:
Ground tank
reservoir
P
WTP
Level
Period
C
2,000
Midnight to 4 a.m.
Pumping station
4 a.m. to 8 a.m.
4,000
8 a.m. to noon
6,000
5,000
Noon to 4 p.m.
4 p.m. to 8 p.m.
4,000
8 p.m. to midnight
3,000
Flow rate (L/s)
Period Flow rate (gpm) From Level 445.00 m A Elevation 493.00 m B 565.00 m 263
D
Midnight to 4 a.m. 126
4 a.m. to 8 a.m. 252 To distribution
8 a.m. to noon 379 network
Noon to 4 p.m. 315 Figure 8.15 Water system for Problem 8.11.
4 p.m. to 8 p.m. 252
8 p.m. to midnight 189
Period Flow rate (gpm)
Assume that the water withdrawal from the network is equally
Midnight to 6 a.m. 951
distributed among the points A, B, C, D, E, and F, which are at
6 a.m. to noon 3,804
the same elevation of 2,300 ft (701.04 m) and that all pipes are
Noon to 6 p.m. 1,902
ductile iron with C = 100. Also consider that the pump possesses
6 p.m. to midnight 1,427
the following characteristics:
The pumping station has three pumps, two of which operate
Flow (gpm) 0 2,000 4,000 6,000 8,000 12,000
in parallel and the third pump is a standby. Pumping is done at a
Head (ft) 400 390 370 345 310 225
constant rate and only for a period of 12 hours from 6 a.m. to 6 p.m.
Flow (L/s) 0 126 252 379 505 757
Each pump possesses the following characteristics:
Head (m) 121.92 118.87 112.78 105.16 94.49 68.58
Flow (gpm) 0 951 1,427 1,902 2,378 2,853
(a) Calculate the volume of the elevated reservoir needed to balance Head (ft) 54.86 50.29 46.63 41.15 32.00 19.20
supply and demand. Flow (L/s) 0 60 90 120 150 180
Head (m) 180 165 153 135 105 63
(b) Compute the maximum flow in each pipe of the network.
(c) Determine the elevation of the water tank at the treatment
plant. The Hazen–Williams coefficient C for all mains is 100. The
(d) At what rate of flow can you pump the water to the elevated total equivalent length of main AB is 8,202 ft (2,500 m) and main
reservoir if another identical pump is installed in parallel with CD is 29,527 ft (9,000 m).
the existing pump? (a) Determine the volumes needed for the ground tank and
8.11 The water supply system shown in Fig. 8.15 is planned to elevated reservoir (each separately) to balance supply and
serve a small village. Treated water from the treatment plant (WTP) demand. (Storage for firefighting and emergencies is not
flowing at a uniform rate throughout the day is collected in a ground required.)
tank. Water is then pumped to an elevated reservoir at the top of a (b) Determine the minimum standard size needed for the water
hill through the main AB. Water flows from the elevated reservoir main AB so that the two operating pumps can deliver the
into the distribution network through the main CD. required flow from the ground tank to the elevated reservoir.
Water consumption during the maximum day in the village is
8.12 A water pumping station is designed to raise water from a
as follows:
treatment plant ground reservoir at an elevation of 1,968 ft (600 m)
to an elevated reservoir located on the opposite side of town at
an elevation of 2,165 ft (660 m). The trunk line and the water
Period Flow rate (L/s)
distribution network connecting the two reservoirs is equivalent to
Midnight to 6 a.m. 60 a pipe line (C = 100) 16 in. (400 mm) in diameter and 82,020 ft
6 a.m. to noon 240 (25,000 m) long.
Noon to 6 p.m. 120 The pumping station has three pumps, two of which operate
6 p.m. to midnight 90 in series and the third pump is a standby. Each pump possesses the
following characteristics: