Question

Water in a canal, $5.4$ m wide and $1.8$ m deep, is flowing with a speed of $25$ km/hour. How much area can it irrigate in $40$ minutes, if $10$ cm of standing water is required for irrigation ?

Answer 1

Height of standing water required $=10$ cm
Width of canal $=5.4$ m

Depth of canal $=1.8$ m

Length of water in canal for $1$ hr $=$ $25$ km $=25000$m

Volume of water flown out from canal in $1$ hr

$=$ $l\times b\times h$

$=$ $5.4\times 1.8\times 25000$ $=$ 243000$m^3$

Volume of water for $40$ min = 243000 $\times \frac{40}{60}=162000m^3$

Area to be irrigated with $10$ cm standing water in field

= $\frac{\text{Volume}}{\text{Height}}$ $=\frac{162000}{10000}$ $[\because 10000m^2=1$ hectares]

Hence, the area irrigated $=16.2$ hectares.