To determine "I" for a given drainage area--
Calculate I adjusted to the area design TOC.
Since you already learned how to estimate the TOC in Part A of this lesson, the next step is to calculate "I"
adjusted to the TOC.
The first step is to obtain a source of rainfall data. Pinpoint data is preferable, if available (refer to Lesson 1, Part
B). Table 2-7 shows rainfall pinpoint data for Washington, D.C. It covers the ten worst storms in each time
category for 50 years. The storms are listed in descending order of magnitude. The worst five-minute rainfall
may or may not have occurred during the same rainstorm as the worst 15-minute rainfall; hence, the use of the
term storm is actually a composite of as many as six actual rainfall events over the 50 years of record.
Table 2-7. Rainfall data - Washington, D.C., 1900-1950