Question

The peak discharge of the instantaneous unit hydrograph of a basin, when compared to the peak discharge of a 4-hour unit hydrograph of the basin, would be

• A. greater
• B. equal
• C. equal or lesser
• D. lesser

Answer 1

The correct option is A greater



The shape of these different unit hydrographs depends upon the value of duration of unit hydrograph (D hr)

Figure shows a typical variation of the shape of unit hydrographs for different value of D. As D is reduced, the intensity of rainfall excess being equal to 1/D increase and unit hydrograph becomes more skewed. Therefore the peak increases

Hydrograph Duration
UH D = 4 hr
IUH D $\to$ 0

Hence, peak discharge of IUH is greater than that of 4 hr UH.