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152 Chapter 4 Quantities of Water and Wastewater Flows
PROBLEMS/QUESTIONS

4.1 As shown in Table 4.3, the April census population of 1. What would be the expected population in the year
Detroit, Michigan, was 1,028,000 in 1990 and decreased to 2040? Justify your method of choice for estimating the
951,000 in 2000. Estimate the population for the following future population. (Give the figure to the nearest 1,000.)
periods: 2. Do you think that the amount of water available in the
1. For the fifth intercensal year in April using (a) arith- river would be enough of a water supply and how much
metic and (b) geometric progression. water can be supplied to each person in the community?
2. For the sixth postcensal year in April using (a) arith- 3. Assuming that you decide to supply the community at an
metic and (b) geometric progression. annual average demand of 70 gpcd, or 264 Lpcd, and
that the maximum daily demand is two times the annual
4.2 As shown in Table 4.3, the census population of
average and the maximum hourly demand is 1.5 times
Providence, Rhode Island, was 161,000 in 1990 and 174,000 in
the daily demand, would you be able to supply this de-
2000. Estimate the 2009 population by (a) arithmetic and (b)
mand directly from the river? If not, what would you rec-
geometric progression.
ommend in order to be able to supply the peak demand?
4.3 As shown in Table 4.3, the city of Miami recorded a pop-
4.6 A small village is located near a stream that is to be used
ulation of 111,000 in its 1930 and 172,000 in its 1940 consecu-
as the source of water supply for the community. The minimum
tive censuses. Estimate the midyear (1 July) populations for the 3
flow in the stream is 550 m /h. The population analysis reveals
following periods:
that the population is expected to increase linearly from a popu-
1. For the fifth intercensal year by (a) arithmetic increase lation of 10,000 in 2008 to 30,000 in 2058.
and (b) geometric increase. The water consumption of the community is estimated to
2. For the ninth postcensal year by (a) arithmetic increase reach an annual average demand of 300 Lpcd, or 79.26 gpcd, a
and (b) geometric increase. maximum daily demand of 1.8 times the annual average, and
peak hourly demand of 1.5 times the daily average.
Assume a census date of 1 April.
Would you be able to supply these demands directly from
4.4 Each of the four waterworks systems shown in Fig. 4.4
the stream? If not, what would you recommend (1) in the year
serves a community with an estimated future population of
2030 and (2) in the year 2058?
100,000. Estimate the required capacities of their constituent
4.7 A well that is the source of water supply for a community
structures for an average water consumption of 150 gpcd (568 3
Lpcd), a fire demand of 9,160 gpm (34,671 L/min), and a dis- has a uniform production capacity of 350 m /h (79.52 gpm).
tributing reservoir so sized that it can provide enough water to Currently the community has a population of 5,000 people with
care for differences between hourly and daily flows and for fire an anticipated linear growth rate of 10% per year.
demands and emergency water requirements. If the average water consumption for the community is
400 Lpcd (105.68 gpcd), would you be able to supply the water
4.5 An old town in an established agricultural area with no demand (a) 5 years, (b) 10 years, (c) 20 years from now, directly
prospects for extensive development is located along a river from this well? If not, what would you recommend for each of
that is used as the source of water supply for the community. the above periods? Show all of your calculations and explain
The conditions of the river are such that it receives its water the reasons behind your assumptions and recommendations.
2 2
from a drainage area of 1,000 mi (2,590 km ) and its low-water
3 2 3 2 4.8 Estimate the number of people who can be supplied with
flow is 0.1 ft /s/mi (0.00109 m /s/km ). The regulations are
water from (a) 12-in. (304.8-mm), and (b) 24-in. (609.6-mm)
that only 10% of the river flow can be used at any time for
water main (1) in the absence of fire service for a maximum
water supply.
draft of 200 gpcd (757 Lpcd), (2) with a residential fire-flow
Past records reveal that the population increased as follows: requirement of 500 gpm (1,892.5 Lpm) and a coincident draft
of 150 gpcd (567.75 Lpcd). Also, find the hydraulic gradient.
Year Population
Note: Consider the most economical design velocity in the sys-
1940 10,000 tem piping to be 3 ft/s (0.91 m/s).
1950 12,500 4.9 Estimate the number of people who can be supplied with
1960 15,200 water from (a) a 300-mm water main and (b) a 600-mm water main.
1970 17,500
Case 1: In the absence of fire service for a maximum draft of
1980 19,700
800 Lpcd
1990 22,000
Case 2: With a residential fire-flow requirement of 1,890 Lpm
2000 24,400
and a simultaneous domestic draft of 600 Lpcd.
If you are asked to design a water supply system for this Note: Consider the most economical design velocity in the sys-
community, tem piping to be 1 m/s.