A watershed of 4.8 km2 generates 4.3 cm runoff from a rainstorm of 4 – hour duration. The measured rainfall intensities for this storm in successive 30-min duration are given below: -
|
Time Interval (min) |
0 - 30 |
30 - 60 |
60 - 90 |
90 - 120 |
120 - 150 |
150 - 180 |
180 - 210 |
210 - 240 |
|
Rainfall intensity (cm/hr) |
1.6 |
4.8 |
3.2 |
3.4 |
2.2 |
5.0 |
4.2 |
1.2 |
The value of ϕ -index for the watershed in cm/hr will be
1
6.5
2
5.3
3
2.4
4
2.1