Question

A triangle direct runoff hydrograph due to a storm has a time base of 60 hr and a peak flow of $30m^3/s$ occurring at 20 hr from the start. If the catchment area is $300k{m}^2$,what is the rainfall excess in the storm?

• A. 50 mm
• B. 20 mm
• C. 10.8 mm
• D. 8.3 mm

Answer 1

The correct option is C 10.8 mm

Area of direct runoff hydrograph
$=\text{Total volume of excess rainfall}\left(V\right)$

$\Rightarrow \frac{1}{2}\times 30\times 60\times 60\times 60$
$=\text{Total volume of excess rainfall}\left(V\right)$

$\Rightarrow \text{Depth of excess rainfall}=\frac{V}{\text{catchment area}}$

$=\frac{30\times 60\times 60\times 60\times {10}^3}{2\times 300\times {10}^6}=10.8mm$