Final answer:
To plot the flood-frequency curve, calculate the recurrence interval for each flood event, plot the discharge against the recurrence interval, and draw a best-fit line. For a flood with a return period of 100 years, find the discharge associated with a recurrence interval of 100. To determine the probability of a flow of 100 cfs, find the horizontal coordinate on the graph where the vertical coordinate is 100.
Step-by-step explanation:
To plot the flood-frequency curve on lognormal probability paper, you need to calculate the recurrence interval for each flood event and plot the discharge against the recurrence interval. The recurrence interval represents the average time period within which a flood of a given magnitude will be equaled or exceeded. To calculate the recurrence interval, determine the rank of the flood event and use the equation mentioned in the instructions. Once you have all the data points, draw a best-fit line through the points on the graph. For part (a), to determine the magnitude of a flood with a return period of 100 years, find the discharge associated with a recurrence interval of 100. For part (b), to determine the probability of a flow of 100 cfs, find the horizontal coordinate on the graph where the vertical coordinate is 100.