Question

The peak magnitude of a flood hydrograph during 4 hr study duration over a catchment is $300m^3/s$. The total depth of rainfall is 6 cm, and the infiltration loss during the said 4 hr period is 2 cm. A constant uniform base flow of $20m^3/s$ is premised throughout. The peak value of the corresponding 4 hr unit hydrograph is

• A. $75m^3/s$
• B. $70m^3/s$
• C. $50m^3/s$
• D. $40m^3/s$

Answer 1

The correct option is B $70m^3/s$

Effective rainfall
= 6 - 2 = 4 cm

Peak of effective hydrograph
$=300-20=280m^3/sec$

The peak value of 4 hr unit hydrograph
$=\frac{280}{4}=70m^3/sec$.