Return Period Calculation $(8$ points$)$

The graph on page $4$ provides a flood frequency diagram for the Kankakee River. The

record is divided into two time periods $1925-1967$ and $1971-2010,$ and a separate line is

shown for each time period. Use this graph to answer the following questions.

a$)$ Calculate the annual probability of occurrence from the return period and enter into

the table.

b$)$ Reading the graph, complete the table with the discharge values associated with

different return periods.c$)$ What is the percent difference in the $5$ years return period flood for the later period?

$($Percent difference $\{$:$=100\%\frac{Q_{1971-2010}-Q_{1925-1967}}{Q_{1925-1967}})$

d$)$ What is the percent difference in the $100$ year return period flood for the later period?

e$)$ Find the flow values for the $100-$year flood in the earlier period, what is the return

period associated with this magnitude flood for the later period?

f$)$ How has flood frequency changed over time for this river?