The “Boneyard Creek” runs about 6000 feet between 1 st Street and Lincoln Ave ju
ID: 3003938 • Letter: T
Question
The “Boneyard Creek” runs about 6000 feet between 1st Street and Lincoln Ave just north of campus, and drains about 3000 feet of land on either side. On average the creek is 20 feet wide and 25 feet deep and when full, the water flows at a rate of 10 feet per second.
A couple of years ago, the creek was blocked completely at Lincoln Avenue due to some construction. A heavy rain passed over, while the creek was blocked, and completely filled the creek!
1. Calculate how much rain (in inches) must have fallen over the drainage area to fill the creek. (Use the diagram below to help you visualize the problem.) You must show all of your work to get credit.
After the heavy rain ended, and the creek was full, a local meteorologist noticed that the radar indicated another line of heavy precipitation on its way. With the creek full and more rain on the way, local officials decided to use dynamite to blast open the blockage to let the water flow at its normal rate. They did so just in time; however, it rained so hard that the creek overran its banks anyway.
2. If the creek is full and draining properly, how much rain would have to fall over the drainage area in one hour to get the creek to overflow? You must show all of your work to get credit.
Explanation / Answer
Answer:
1)
Volume of creek = 20 ft x 25 ft x 6000 ft = 3,000,000 ft^3
Drainage area on each side of the creek = 6000 ft x 3000 ft = 18,000,000 ft^2
So total drainage area is 36,000,000 ft^2
Total amount of rain needed to fill the creek => 3,000,000 ft^3/(36,000,000 ft^2) * 12 in/ft = 1 inch.
2)
Total amount of water that flows out of creek in one hour = (10 ft/s) x (20 ft) x (25 ft) x 1 hr x 3600 s/1 hr
= 18,000,000 ft^3 of water.
So amount of water that needs to fall over the drainage area so the creek overflows is:
(18,000,000 ft^3)/(36,000,000 ft^2) * (12 in)/ft = 6 inches.
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