Effect of Varying Recurrence Interval

The choice of recurrence interval will have a great influence on the peak rate of runoff to be expected from a watershed. This is illustrated by the following example.

Problem: Given the same watershed as the previous example, calculate the peak runoff rate for recurrence intervals of 2, 5, 10, 25, 50, and 100 years.

Solution: Table 17.5

Table 17.5. Effect of varying recurrence interval.

Recurrence

Time of

Rainfall

Runoff

Watershed

Peak runoff

interval (yr)

concentration (min)

intensity (in/hr)

coefficient (C)

area (ac)

rate (cfs)

2

33

3.0

0.40

90

108

5

33

3.8

0.40

90

137

10

33

4.5

0.40

90

162

25

33

5.5

0.40

90

198

50

33

6.3

0.40

90

227

100

33

7.0

0.40

90

252

0 0

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