Question

A 4 hr storm had 4 cm of rainfall and the resulting direct runoff was 2.0 cm. If the $\varphi -index$ remains at the same value, the runoff due to 10 cm of rainfall in 8 hr in the catchment is

• A. 6.0 cm
• B. 7.5 cm
• C. 2.3 cm
• D. 2.8 cm

Answer 1

The correct option is A 6.0 cm

$(\varphi -index{)}_4=\frac{P-R}{t_e}=\frac{4-2}{4}=0.5cm/hr$
But,
$(\varphi -index{)}_4=(\varphi -index{)}_8$
$\Rightarrow 0.5=\frac{10-R}{8}$

$\Rightarrow R=10-4$
$\Rightarrow R=6cm$