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1A) (3 points) The total precipitation for the month of August (PAUG) in Groton for a 10 year period was as follows. What is the highest volume (inches) of precipitation in August to be expected in a 20 year period? (Use the arithmetic/probability graph paper or modify the Excel spreadsheet, both available at http://environmentalet.org/env245.) ANSWER: 4.01 inches.

Rank

p

z-value

PAUG (in)

1

0.05

-1.64485

3.92

2

0.15

-1.03643

3.49

3

0.25

-0.67449

3.27

4

0.35

-0.38532

3.07

5

0.45

-0.12566

2.71

6

0.55

0.125661

2.52

7

0.65

0.38532

2.43

8

0.75

0.67449

1.85

9

0.85

1.036433

1.46

10

0.95

1.644854

1.38

2) A storm contributes 2.5 inches of runoff to a 5 acre parking lot.

  1. (1 point) How many cubic feet of water is this?
    2.

  2. (1 point) The runoff drains into a square detention basin, which is 165 ft along each side with vertical walls. If the basin is empty before the storm, how deep would it need to be to hold all of the runoff?
    3.

    Depth = volume/area:

  3. (1 point) The basin drains into a channel that is 4.0 feet wide. When the basin is full, you observe that the water in the channel is 1.0 feet deep. You drop a stick in the water and see that it travels 8.0 feet in 60.0 seconds. Assume that the velocity of the stick is the velocity of the water in the channel. What is the flow rate (in ft3/s) in the channel?
    4.

  4. (1 point) If the channel continues to flow at this rate, how long will it take for the basin to empty?
    5.

  5. (1 bonus point) Would the channel continue to drain at that rate? Why or why not?

The flow rate would probably decrease as the depth of water in the basin decreased.

3) (2 points) What is the maximum intensity of rainfall (in inches per hour) lasting 50 minutes, expected in Harford, CT, once during a ten year period? (Use an IDF curve for Hartford).

2.0 inches per hour. See IDF curve.