Question

A 3 hr unit hydrograph $U_1$ of a catchment of area $235k{m}^2$ is in the form of a triangle with peak discharge $30m^3/s.$ Another 3 hr unit hydrograph $U_2$ is also triangular in shape and has the same base width as $U_1$, but has a peak flow of $90m^3/s.$
What is the catchment area of $U_2$?

• A. $117.5k{m}^2$
• B. $235k{m}^2$
• C. $470k{m}^2$
• D. $705k{m}^2$

Answer 1

The correct option is D $705k{m}^2$

Time base of both the unit hydrographs is same.
Let it be t.
$\therefore \frac{1}{2}\times 30\times t\times \frac{1}{235}=\frac{1}{2}\times 90\times t\times \frac{1}{A_2}$
$\Rightarrow A_2=235\times 3$
$\Rightarrow A_2=705k{m}^2$