Problem 1: An in-ground swimming pool may have a leak. The 30-ft by 10-ft by 5-f
ID: 1829076 • Letter: P
Question
Problem 1:
An in-ground swimming pool may have a leak. The 30-ft by 10-ft by 5-ft (depth) pool is filled
on June 1. On June 13, a hose, flowing at a rate of 10 gallons per minute, is used to add water to
the pool. The hose is turned off after 1 hour. Four inches of rain fell during the month.
Evaporation from a nearby lake was 8 in. during June. It is estimated that 25 percent more will
evaporate from the pool than the lake. On July 1, the pool is 5 inches below the top. Does the
pool have a leak? If so, what is the rate of leakage in gallons per day?
Problem 2: A dry detention basin is to be designed for a 70 ha residential development. The
runoff coefficient for the area is 0.3 and the average rainfall during the year is 4 cm. What is the
necessary volume for the basin?
Problem 3:
What is the peak discharge for an area with the following characteristics? The rainfall intensity
is 120 mm/hour.
Land use Area, m2
Forest 10,000
Single family residential 9,000
Parking lots 5,000
Explanation / Answer
Total volume of Pool = 30*10*5 = 1500 ft3
Initial depth of water on pool = 5*12 = 60 inches
1gallon = 0.1337 ft3
Water inflow rate through hose = 10gallons/minute
Water pooled in after 1 hour = 10*60*0.1337 ft3 = 80.22 ft3
Depth of water pooled in = 80.22/(30*10) = 0.2674ft = 3.2088 inches
Rainfall - 4inches
Total depth of water in pool now = 7.2088 inches
Evaporation from pool = 8 + 0.25*8 = 10 inches
No-leak scenario water depth = 60+7.2088-10 = 57.2088 inches
Measured depth of water = 60-5 = 55inches
Water leakage in the month = 57.2088- 55 = 2.2088 inches
Volume of water lost in the month = 300*2.2088/12= 55.22ft3 = 413 gallons
Water leakage per day = 413/30 = 13.77 gallons/day
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Area of basin = 70*10^(4) = 7*10^(5) m2
run off coefficient = 0.3
Rainfall = 4cm
Water retained in the area = 0.7*4cm = 2.8cm = 0.028m
Volume of basin = 7*10^(5)*0.028 =19600m3
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