Flood Frequency Worksheet

1. View your instructor's Flood Frequency video tutorial and review Vivek Gami's (2015) Flood Frequency Analyses slideshare presentation.
2. Click the link above to open the application assignments. Read through the worksheet.
3. Answer each question in the worksheet based on the flooding readings and the instructor video tutorial.
4. You are welcome to save your individual answers as you complete the worksheet. You do not have to complete the worksheet in one sitting, however you can only submit it once.
5. Click the Submit button at the bottom of the worksheet when you have answered all of the questions.

Questions:

QUESTION 1

1. A flood-frequency curve plots the discharge of a particular stream against how often that discharge occurs. In Table 1 below, the levels of floods of a US stream were recorded each year between 1950 and 1999.

Table 1:
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According to Table 1, which size flood happens more often?
small
large
1.25 points
QUESTION 2

1. Table 2 summarizes the number of times each flood happens in 50 years (using data from Table 1). The recurrence interval indicates how often a flood of that size occurs.

Recurrence Interval = 50 years / the number of times that flood occurs in 50 years

Table 2:
Flood Discharge # of times in 50 years Recurrence Interval
100,000 ft3/sec 1
50,000 ft3/sec 6 8.3
33,000 ft3/sec 13 3.8
18,000 ft3/sec 25

2. What is the recurrence interval for the largest (100,000 ft3/sec) flood?
   2
   50
   3.8
   8.3
   1.25 points
   QUESTION 3
3. Using the data from Table 2, what is the recurrence interval for the smallest (18,000 ft3/sec) flood?
   50
   8.3
   3.8
   2
   1.25 points
   QUESTION 4
4. Does a flood with a large recurrence interval occur more or less often?
   more
   less
   1.25 points
   QUESTION 5
5. Below is the flood-frequency curve for this stream. The recurrence interval is plotted compared to the discharge (size of the flood).

Figure 1:
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Using Figure 1, how often do large floods of 75,000 ft3/sec occur? You will need to locate the discharge on the figure and then read down to the x-axis to determine the recurrence interval. Note that the x-axis is a logarithmic scale.
Once every 20 years
Once every 100 years
Once every 8 years
Once every 2 years
1.25 points
QUESTION 6

1. Using Figure 1, how often do large floods of 20,000 ft3/sec occur? You will need to locate the discharge on the figure and then read down to the x-axis to determine the recurrence interval. Note that the x-axis is a logarithmic scale.
   Once every 2 years
   Once every 8 years
   Once every 10 years
   Once every 50 years
   1.25 points
   QUESTION 7
2. Figure 1 makes it look like floods of discharge 50,000 ft3/sec occur exactly once every 8 years. Look back at Table 1. Are floods of certain sizes regularly spaced?
   Yes
   No
   1.25 points
   QUESTION 8
3. Based on your understanding of flooding events from this worksheet and your reading, answer the following question:

If there is a flood with a discharge of 50,000 ft3/sec, will that flood happen again in exactly eight years? Explain your answer.