Proceed downstream to subarea Y and repeat Steps 1, 2, and 3.
Sum the accumulated runoff to get the total runoff at the outlet of subarea Y: Qoutlet Y = Qx + Qy
Continue working downstream until the runoff at the lowest outlet in the series is calculated.
Remember that there is a limitation of 1,000 acres when using the Rational Method.
Always check the
accumulated acreage to ensure it does not exceed 1,000 acres.
As you can see from the summary above, the method of calculating runoff for successive areas differs from the
Rational Method in that each subarea must be delineated separately and the TOC must be obtained for each
The schematic example (see figure 3-1) used every step outlined in the successive areas summary. Numerical
values must of course, be found for each variable Cx, Ix, and Ax, using the procedures in Lessons 1 and 2.
Figure 3-1. Schematic example of successive areas