Question

A direct runoff hydrograph due to an isolated storm with an effective rainfall of 2 cm was trapezoidal in shape as shown in the figure. The hydrograph corresponds to a catchment area (in sq-km) of

• A. 790.2
• B. 599.4
• C. 689.5
• D. 435.3

Answer 1

The correct option is B 599.4

$(\frac{\text{Area of runoff}}{\text{hydrograph}})=(\frac{\text{Area of}}{\text{catchment}})\times (\frac{\text{Effective rainfall}}{\text{depth}})$

$\left(\frac{4+70}{2}\right)\times 3600\times 90=A\times \frac{2}{100}$

$A=599.4k{m}^2$