Water in a canal 30 dm wide and 12 dm deep, is flowing with a velocity of 100 km every hour.

Given that,

Water in the canal forms a cuboid of Width (b) = 30 dm = 3 m

Height (h) = 12 dm = 1.2 m

Cuboid length is equal to the distance traveled in 30 min with the speed of 100 km per hour.

Therefore, Length of the cuboid = 100∗30/60 = 60 km = 50000 metres

So, volume of water to be used for irrigation $=5000 * 3 * 1.2 \mathrm{~m}^{3}$

Water accumulated in the field forms a cuboid of base area equal to the area of the field and height equal to 8/100 metres

Therefore, Area of field∗8/100 = 50000 ∗ 3 ∗ 1.2

$\Rightarrow$ Area of field $=\frac{50000 * 3 * 1.2 * 100}{8}$

⇒ 22, 50, 000 metres.