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Hydrology & Irrigation
Introduction and Basic Assumptions of Unit Hydrograph
The peak ordi...
Question

The peak ordinate of 4 h unit hydrograph of a basin is 60 m3/s. An isolated storm of 4 hour duration in the basin was recorded to have a total rainfall of 8 cm. If it is assumed that the base flow and the ϕ−index are 30 m3/s and 0.25 cm/hr respectively, the peak of the flood discharge due to the storm could be estimated as.

A
210 m3/s
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B
420 m3/s
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C
450 m3/s
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D
240 m3/s
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Solution

The correct option is C 450 m3/s
Peak discharge of unit hydrograph
=60 m3/s

Now, the peak of direct runoff hydrograph
=60×effective runoff
=60×(8−4×0.25)
=420 m3/s

Hence, peak of flood hydrograph
=(420+30)=450 m3/s

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