Question

A 9 hour storm occured over a catchment area of $600k{m}^2$. Rainfall of 8, 2 and 12 cm occured in successive three hr unit period. Assuming average infiltration rate, $\varphi -index$ for the basin as 15 mm/m hour. The runoff volume observed would be ______ ha-m.

• A. 10200
• B. 5100
• C. 6600
• D. 10500

Answer 1

The correct option is C 6600

$\begin{array}{cccc}\text{Time}& \text{0-3}& \text{3-6}& \text{6-9}\\ \text{P, cm}& \text{8}& \text{2}& \text{12}\\ \text{i, cm/hr}& \text{2.67}& \text{0.67}& \text{4}\end{array}$

$t_e=6hours$
$P_e=8+12=20cm$

$\varphi -index=\frac{P_e-R}{t_e}$

$1.5=\frac{20-R}{6}$

$R=11cm$

Runoff volume
$=C.A\times R$

$=600\times {10}^2\times \frac{11}{100}$
$=6600ha-m$