drainage design is based on peak runoff from a relatively small drainage area (less than a square mile). Such peak
flows are ordinarily caused by short duration, high-intensity storms such a thunderstorms.
Figure 1-2 shows three bar charts illustrating the typical intensity/duration relationships in a short rainstorm, a
medium rainstorm, and a long rainstorm. These relationships are generally consistent They are based on data
from a large number of weather stations. Notice that the shorter the storm, the greater the intensity. Stated
another way--intensity and duration are inversely proportional. Now look at the hydrography shown in figure 1-3.
Figure 1-2. Bar charts of rainstorms
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