Page 128 - Water Engineering Hydraulics, Distribution and Treatment

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Chapter 4
Quantities of Water Demand
PROBLEMS/QUESTIONS
3. Assuming that you decide to supply the community at an
annual average demand of 70 gpcd, or 264 Lpcd, and that the
4.1
As shown in Table 4.3, the April census population of Detroit,
maximum daily demand is two times the annual average and
MI, was 1,028,000 in 1990 and decreased to 951,000 in 2000.
the maximum hourly demand is 1.5 times the daily demand,
Estimate the population for the following periods:
would you be able to supply this demand directly from the
1. For the fifth intercensal year in April using (a) arithmetic and
river? If not, what would you recommend in order to be able
(b) geometric progression.
to supply the peak demand?
2. For the sixth postcensal year in April using (a) arithmetic and
4.6
A small village is located near a stream that is to be used
(b) geometric progression.
as the source of water supply for the community. The minimum
3
flow in the stream is 550 m /h. The population analysis reveals that
4.2
As shown in Table 4.3, the census population of Providence,
the population is expected to increase linearly from a population of
RI, was 161,000 in 1990 and 174,000 in 2000. Estimate the 2009
10,000 in 2008 to 30,000 in 2058.
population by (a) arithmetic and (b) geometric progression.
The water consumption of the community is estimated to reach
4.3 As shown in Table 4.3, the city of Miami recorded a popu-
an annual average demand of 300 Lpcd, or 79.26 gpcd, a maximum
lation of 111,000 in its 1930 and 172,000 in its 1940 consecutive
daily demand of 1.8 times the annual average, and peak hourly
censuses. Estimate the midyear (July 1) populations for the follow-
demand of 1.5 times the daily average.
ing periods:
Would you be able to supply these demands directly from the
1. For the fifth intercensal year by (a) arithmetic increase and (b)
stream? If not, what would you recommend (1) in the year 2030
geometric increase.
and (2) in the year 2058?
2. For the ninth postcensal year by (a) arithmetic increase and 4.7 A well that is the source of water supply for a community has
(b) geometric increase. 3
a uniform production capacity of 350 m /h (79.52 gpm). Currently
Assume a census date of April 1. the community has a population of 5,000 people with an anticipated
4.4 Each of the four waterworks systems shown in Fig. 4.4 serves linear growth rate of 10% per year.
a community with an estimated future population of 100,000. Esti- If the average water consumption for the community is 400
mate the required capacities of their constituent structures for an Lpcd (105.68 gpcd), would you be able to supply the water demand
average water consumption of 150 gpcd (568 Lpcd), a fire demand (a) 5 years, (b) 10 years, and (c) 20 years from now, directly from
of 9,160 gpm (34,671 L/min), and a distributing reservoir so sized this well? If not, what would you recommend for each of the above
that it can provide enough water to care for differences between periods? Show all of your calculations and explain the reasons
hourly and daily flows and for fire demands and emergency water behind your assumptions and recommendations.
requirements. 4.8 Estimate the number of people who can be supplied with
4.5 An old town in an established agricultural area with no water from (a) 12 in. (304.8 mm) and (b) 24 in. (609.6 mm) water
prospects for extensive development is located along a river that main (1) in the absence of fire service for a maximum draft of 200
is used as the source of water supply for the community. The condi- gpcd (757 Lpcd) and (2) with a residential fire flow requirement of
tions of the river are such that it receives its water from a drainage 500 gpm (1,892.5 Lpm) and a coincident draft of 150 gpcd (567.75
3
2
2
area of 1,000 mi (2,590 km ) and its low-water flow is 0.1 ft /s/mi 2 Lpcd). Also, find the hydraulic gradient.
3
2
(0.00109 m /s/km ). The regulations are that only 10% of the river Note: Consider the most economical design velocity in the
flow can be used at any time for water supply. system piping to be 3 ft/s (0.91 m/s).
Past records reveal that the population increased as follows: 4.9 Estimate the number of people who can be supplied with
water from (a) a 300 mm water main and (b) a 600 mm water main.
Case 1: In the absence of fire service for a maximum draft of
Year Population
800 Lpcd.
1940 10,000 Case 2: With a residential fire flow requirement of 1,890 Lpm
1950 12,500 and a simultaneous domestic draft of 600 Lpcd.
1960 15,200 Note: Consider the most economical design velocity in the
1970 17,500 system piping to be 1 m/s.
1980 19,700
1990 22,000
2000 24,400
REFERENCES
Al-Dhowalia, K. H. and Shammas, N. K., Leak detection and quan-
If you are asked to design a water supply system for this tification of losses in a water network, International Journal
community, of Water Resources Development, vol. 7, no. 1, pp. 30–38,
1. What would be the expected population in the year 2040? 1991.
Justify your method of choice for estimating the future popu- American Society of Civil Engineers and Water Environment Fed-
lation. (Give the figure to the nearest 1,000.) eration, Gravity Sanitary Sewer, Design and Construction,
2. Do you think that the amount of water available in the river 2nd ed., ASC Manuals and Reports on Engineering Prac-
would be enough of a water supply and how much water can tice No. 60, WEF Manual of Practice No. FD-5, Reston, VA,
be supplied to each person in the community? 2007.