An in-ground swimming pool may have a leak. The 30-ft by 10-ft by 5-ft (depth) p

ID: 507 • Letter: A

Question

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

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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