A 3-hour storm on a small drainage basin produced rainfall intensities of 3.5 cm/hr, 4.2 cm/hr and 2.9 cm/hr in successive hours. If the surface runoff due to the storm is 3 cm, then the value of ϕ−index will be
A
2.212 cm/hr
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B
2.331 cm/hr
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C
2.412 cm/hr
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D
2.533 cm/hr
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Solution
The correct option is D 2.533 cm/hr Total rainfall=3.5+4.2+2.9=10.6cm Effective rainfall=3cm Infiltration=10.6−3=7.6cm
Assuming infiltration to occur for three hours. ∴te=3hrs