Question

A reservoir has average surface area of 20km${}^2$. Mean rate of inflow is 10 m${}^2$/S mean outflow is 15 m${}^2$/S rainfall is 10 cm and decrease in storage is 16 Mm${}^2$. Assuming surface losses to be 1.8 cm. The value of evaporation in the month of April is ___________cm.

• A. 23.4

Answer 1

The correct option is A 23.4
Total inflow in the month of April = $\frac{10\times 24\times 30\times 60\times 60}{20\times {10}^6}=1.296M$
Precipitation = 10 cm = 0.1 m
Total outflow in the month of April = $\frac{15\times 24\times 30\times 60\times 60}{20\times {10}^6}=1.944M$
Surface outflow = 1.8 cm = 0.018 m
Change in storage = $\frac{16\times {10}^6}{20\times {10}^6}=0.8m$
Using water budget equation,
Inflow + Precipitation = Outflow + Surface outflow + Change in storage + Evaporation
1.296 + 0.1 = 1.944 + 0.018 - 0.8 + E
E = 0.234 m
i.e, E = 23.4 cm