Page 195 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

JWCL344_ch05_154-193.qxd 8/2/10 9:44 PM Page 157

5.1 Fluid Mechanics, Hydraulics, and Water Transmission 157

c. The pressure, p, on the bottom BC:
p h
3
2
(62.4 lb/ft )(6 ft 12 ft)>144 in /ft 2
7.8 psi
d. The total weight, W, of the water:
W V
3
62.4 lb/ft (20 6 8 12 1) ft 3
60,700 lb

Solution 2 (SI System):
3
3
a. Specific weight for water at 39 F (4 C) is 62.4 lb/ft (9.81 kN/m ). Specific weight in
SI unit can be calculated like
2
3
g = (r)(g) = (1,000 kg>m )(9.81 mN>s )
3
= 9,810 N>m = 9.81 kN>m 3
The resultant force, P f , acting on area AB:
P f = (g)(hcg)(A)
3
= (9.81 kN>m )(3.7 m + 1.8 m>2)(1.8 m * 2.44 m)
198.2 kN
b. The location of the resultant force acting on area AB:
y cp = [I cg >y cg A] + y cg
I cg = (1>12)bh 3
3
y cp = [(bh >12)>y cg A] + y cg
3
= [(2.44 * 1.8 >12)>(4.56)(1.8 * 2.44)] + 4.56
4.62 m
c. The pressure, p, on the bottom BC:
3
p = gh = (9.81 kN/m )(1.8 m + 3.7 m) = 53.9 kN>m 2
53.9 kPa
d. The total weight, W, of the water:
W = rV
2
3
= (1,000 kg>m )(6.1 m * 1.8 m * 2.44 m + 3.7 m * 0.093 m )
26,865 kg

5.1.2 Transmission Systems

Supply conduits, or aqueducts, transport water from the source of supply to the commu-
nity and, hence, form the connecting link between collection works and distribution sys-
tems. The location of the source determines whether conduits are short or long, and
whether transport is by gravity or pumping. Depending on topography and available
materials, conduits are designed for open-channel or pressure flow. They may follow
the hydraulic grade line (HGL) as canals dug through the ground, flumes elevated above
the ground, grade aqueducts laid in balanced cut and cover at the ground surface, and
grade tunnels penetrating hills; or they may depart from the hydraulic grade line as pressure