Environmental Engineering FOURTH EDITION

134 ENVIRONMENTAL ENGINEERING

water or enough clean water may not be available in some areas because of climate
and water use. Both groundwater and surface water supplies are available to varying
degrees over the entire earth's surface, and can be protected by sound engineering and
environmental judgment.
The next chapter addresses methods of preparing and treating water for distribution
and consumption once the supply has been provided.

PROBLEMS

6.1 A storage reservoir is needed to ensure a constant flow of 20 cfs to a city. The

monthly stream flow records are

Month JFMAMJJASOND

~~

Millionft3 ofwater 60 70 85 50 40 25 55 85 20 55 70 90

Calculate the storage requirements.

6.2 An unconfined aquifer is 10 m thick and is being pumped so that one obser-

vation well placed at a distance of 76 m shows a drawdown of 0.5 m. On the opposite

side of the extraction well is another observation well, 100 m from the extraction well,

and this well shows a drawdown of 0.3 m. Assume the coefficient of permeability is

50 m3/day-m2.

a. What is the discharge of the extraction well?

b. Suppose the well at 100 m from the extraction well is now pumped. Show with

c. Suppose the aquifer sits on an aquaclude that has a slope of 1/100. Show with

6.3 If a faucet drips at a rate of two drops per second, and it takes 25,000 drops

to make one gallon of water, how much water is lost each day? Each year? If water

costs $1.60 per. 1000 gallons, how long would the water leak until its cost equalled the

75 cents in parts needed to fix the leak (if you fix it yourself)? How long if you called

a plumber for $40.00 minimum rate plus 75 cents in parts?

6.4 A Win. pipe with centrifugally spin concrete lining carries a flow of 10 mgd.

Find the head loss per unit length and the velocity.

6.5 A 6-in. main is carrying a flow of 1.0 cfs. What head loss is produced by two

regular flanged 45O elbows and a gate valve onehalf closed?

6.6 Three pipes, each 1500 ft long, are arranged in parallel. Two have diameters

of^6 in. each, and the diameter of the third is^10 in. All three have a Hazen-Williams

C value of 100. Find the diameter of the equivalent pipe that is also 1500 ft long.

6.7 A pump delivers 900 gpm against a total head of 145 ft. Assuming a pump

efficiency of 90%, what is the BHP?

6.8 Given two identical pumps with the characteristics shown in Fig. 6-14, find

the discharge for a head of 100 ft if (a) both pumps are operated in series and (b) both

pumps are operated in parallel.

a sketch what this will do to the drawdown.

a sketch how this would change the drawdown.