Now that the travel times for all the paths have been calculated, the TOC can be found. The TOC is the path with
the longest travel time. In our example, path 2 has the longest travel time, 26.4 minutes. The table below give the
times listed for the example problem.
Table 2-6. TOC
STEP 11. Find the rainfall intensity for the 2-year, 60-minute storm for the example on figure 1-4, page 1-7. For
this example the location is Seoul, Korea. The "I" value for this area is 2.5 in/hr.
STEP 12. Adjust the rainfall intensity "I" value to match the basin TOC using figure 1-5, page 1-9.
To read the chart, enter the graph with the basin TOC of the bottom axis. Draw a vertical line up until you
intersect with the standard curve from the isohyetal chart. Then draw a horizontal line to the left axis and obtain
the rainfall intensity adjusted Iadj in in/hr. In this example, the standard intensity is adjusted to 4.2 in/hr based on
the basin TOC of 26.4 minutes.
STEP 13. Calculate the runoff in cfs using the Rational Method equation Q = CIA.
In this example, the "C" (0.35) x "A" (48.8 acre) x "I" (4.2) in/hr = 71.7 cfs.
PART B - DETERMINE THE INTENSITY (I) WITH AND
WITHOUT PINPOINT DATA
In the formula Q = CIA, "I" equals the intensity of the rainfall. As we learned in Lesson 1, intensity is the rate at
which rain is falling. It is expressed in units of in/hr.