Question

A 4 h unit hydrograph of a catchment is triangular in shape with base of 80 h. The area of the catchment is $720k{m}^2$ . The base flow and $\varphi -index$ are $30m^3/s$ and 1 mm/h, respectively. A storm of 4 cm occurs uniformly in 4 h over the catchment.

The peak discharge of 4 h unit hydrograph is

• A. 40 $m^3/s$
• B. 50 $m^3/s$
• C. 60 $m^3/s$
• D. 70 $m^3/s$

Answer 1

The correct option is B 50 $m^3/s$

Catchment area,
$A=720k{m}^2=720\times {10}^6{m}^2$



Excess rainfall = 1 cm
$\text{Peak discharge}=Q_p$
Run off volume = Area under UH
$A\times 0.01=\frac{1}{2}(80\times 3600)\times Q_p$

$\Rightarrow 720\times {10}^6\times 0.01=\frac{1}{2}(80\times 3600)Q_p$

$\Rightarrow Q_p=50m^3/s$