Science of Water : Concepts and Applications

Water Hydraulics 55
Example 3.8
Problem:
The pressure gauge on the discharge line from the infl uent pump reads 72.3 psi. What is the equivalent
head in feet?
Solution:
Head (ft) = 72.3 × 2.31 ft/psi = 167 ft
HEAD/PRESSURE
If the head is known, the equivalent pressure can be calculated by
Example 3.9
head (ft)
Pressure (psi)
2.31 ft/psi
Problem:
The tank is 22 ft deep. What is the pressure in pounds per square inch at the bottom of the tank when
it is fi lled with water?
Solution:
22 ft
Pressure (psi) 9.52 psi (rounded)
2.31 ft/psi
FLOW/DISCHARGE RATE: WATER IN MOTION
(3.11)
The study of fl uid fl ow is much more complicated than that of fl uids at rest, but it is important to
have an understanding of these principles because the water in a waterworks system is nearly always
in motion.
Discharge (or fl ow) is the quantity of water passing a given point in a pipe or channel during
a given period. Stated another way for open channels: The fl ow rate through an open channel
is directly related to the velocity of the liquid and the cross-sectional area of the liquid in the
channel.
Q AV
where
Q = fl ow—discharge in cubic feet per second, cfs
A = cross-sectional area of the pipe or channel, ft 2
V = water velocity in feet per second, fps or ft/s
Example 3.10
Problem:
The channel is 6 ft wide and the water depth is 3 ft. The velocity in the channel is 4 ft/s. What is the
discharge or fl ow rate in cubic feet per second?
(3.12)