3. Using (IDOT Rainfall IDF: IL drainage manual.pdf) (Table 1 in Bulletin 70), determine the average depth of rainfall for a 50-year, 6-hour storm over a 250 mi watershed in West Southwest Illinois. Also, compute the total storm volume in acre-ft. Table 1. Ratios of 1941-1980 to 1901-1940 24-Hour Maximum Rainfall Amounts for Selected Recurrence Intervals in NWS Climatic Sections of Illinois Recurrence interval (yrs) 5 10 25 Mean NW 1.13 1.17 1.14 NE 1.12 1.16 1.16 1.20 1.16 Average ratio for given recurrence interval W 1.07 1.07 1.07 1.01 1.06 C 1.08 1.09 1.06 1.02 1.06 1.04 1.06 1.03 1.01 1.04 WSW 1.09 1.11 111 111 1.11 ESE 0.98 0.96 0.98 1.05 0.99 SW SE 0.96 0.97 0.99 0.99 0.98 0.95 0.95 1.00 104 0.98