Question

A 4-hour rainfall in a catchment of $250k{m}^2$ produces rainfall depths of 6.2 cm and 5 cm in successive 2-hour unit periods. Assuming the $\varphi$ index of the soil to be 1.2 cm/hour, the runoff volume is

• A. 1.6 ha-m
• B. 16 ha-m
• C. 160 ha-m
• D. 1600 ha-m

Answer 1

The correct option is D 1600 ha-m

Net runoff depth
$=(6.2-2\times 1.2)+(5-2\times 1.2)$
= 6.4 cm = 0.064 m
Runoff volume of catchment
$=Runoffdepth\times Area$
$=0.064\times 250\times {10}^6\times {10}^{-4}ha-m$
= 1600 ha-m