Assgn10-Rivers

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Geology

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Jan 9, 2024

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GEOL 111G Learning Assignment 10 Streams, Flooding & Recurrence Intervals 1. By reading the trendline on the graph, determine the peak discharge expected in a flood with a recurrence interval of 50 and 100 years. Go to 50 on the x-axis, follow the line until it intersects the trendline, then to to that point on the y-axis to read the streamflow. Do the same for the 100-year peak discharge. These are the discharges expected in a 50-year flood and a 100-year flood. 50-year peak discharge: 31500ft3/sec 100-year peak discharge: 37500 ft3/sec 2. The annual exceedance probability, P, is the probability that a given discharge will occur in a given year. It is calculated as the inverse of the recurrence interval, R: P = 1 / R Thus, the probability that a flood with a 10-year occurrence interval will occur in any year is 1/10 = 0.1 or 10% (0.1 x 100). Using the graph, determine the probabilities that a 50- year flood and a 100-year flood will occur in any given year. 50-year flood probability (%): 2% 100-year flood probability (%): 1% 3. The mean annual discharge can be calculated by summing the peak annual discharges and dividing by the number of years. What is the mean annual discharge for the San Francisco River? Please show all your work. If doing this within Excel, mark the mean annual discharge on your spreadsheet in BOLD GREEN , to 1 decimal place. On your spreadsheet select the data in the streamflow column to the first blank at the bottom of the column. You can either pick out the average from the Sum symbol on Excel or use the formula bar: =AVERAGE(B3:B32) Average is 5545.7
GEOL 111G Learning Assignment 10 Streams, Flooding & Recurrence Intervals 4. Flood stage, or bankfull stage on the San Francisco river occurs at a discharge of 15000 ft 3 /sec. Looking at your graph, find the flood stage on the y-axis, go to the trendline and then down to the x-axis and read the number. What is the recurrence interval of such a discharge according to your graph? A. 7 5. Someone has offered to sell you a 4-bedroom, 2-story house with a 2 car garage and swimming pool on a 1 acre lot on a relatively flat piece of land on the banks of the San Francisco river for what seems like a great price of $175,000. The last time the house was flooded it cost $150,000 to repair the flood damage. a. Using the data from the graph and the recurrence interval determine how often this land will flood in a 25-year period. i. The recurrence interval will be 2.2 b. What is the probability that the land and house will be flooded in the first year that you own it? i. P=1/1.5= .66 x 100= 66% ii. There is a probability that the land and house will be flooded 66% within the first year of buying it.
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