The rate of runoff is not constant for any rainfall event. Depending on the characteristics of the watershed there will be some delay from the start of the rain until
runoff starts to occur. Once runoff occurs each watershed will have a different time lapse until the peak rate occurs. The effect of these differences can be seen by evaluating the hydrograph for each watershed.
The shape of the curve will be different for each rainfall event and for each watershed. For example, if the rainfall event has a longer duration, the hydrograph could look more like Figure 17.3.
FIGURE 17.2. Typical runoff hydrograph. Time (hr)
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