Question

In one fortnight of a given month, there was a rainfall of 10 cm in a river valley. If the area of the valley is 7280 ${km}^2$, show that the total rainfall was approximately equivalent to the addition to the normal water of three rivers each 1072 km long. 75 m wide and 3 m deep.

Answer 1

For each of three rivers.
length(I) = 1072 km = 1072 \times 1000 m
= 1072000 m.
Breadth = b = 75 m and depth = h = 3 m
volume of water in river = Ibh
= 1072000 x 75 x 3
= 241200000 m${}^3$
Volume of water in 3 rivers
= 3 x 241200000
= 723600000
= \frac{723600000}{1000 \times 1000 \times 1000}
= 0.7236 km${}^3$ (1)
Area of the valley = 7280 km${}^2$
Rainfall in the valley
$=10cm=\frac{10}{100}m=\frac{1}{10}$ m
$=\frac{1}{10}\times \frac{1}{1000}=\frac{1}{10000}$ km
Volume of rainfall = Area of the valley x height of rainfall
$=7280\times \frac{1}{10\times 1000}$
$=0.7280k{m}^3$........(2)
From (1) and (2) total rainfall is approximately equivalent