Question

Calculate the runoff (cm) from a rainfall of 3 hours. The intensity of the rainfall is 2 cm/hr. The evaporation and infiltration losses are 8 mm and 16 mm.

• A. 1.2
• B. 2.8
• C. 3.6
• D. 6.8

Answer 1

The correct option is C 3.6

Given that: Intensity of rainfall = 2 cm/hr.
Duration = 3 hours
Evaporation = 8 mm = 0.8 cm.
Infiltraton loss = 1.6 cm.
Water budget equation ;
$P-R-E-T-G=\Delta S$
$\text{where,}P=\text{Precipitation.}$
$R=\text{Net runoff.}$
$E=\text{Net evaporation.}$
$T=\text{Net transpiration.}$
$G=\text{Net groundwater flow.}$
$\Delta S=\text{Net storage.}$
$\text{Precipitation}\left(P\right)=2\times 3=6\text{cm}$
$\text{Hence,}6-R-0.8-0-1.6=0$
$\text{Runoff}\left(R\right)=(6-2.4)\text{cm}=3.6\text{cm}$