Water in a canal, 6 m wide and 1.5 m deep, is flowing with a speed of 10 km/h. How much area will it irrigate in 30 minutes, if 8 cm of standing water is needed?

Consider an area of cross-section of canal as ABCD.
Area of cross-section = 6 × 1.5 = 9 m²
Speed of water = 10 km/h = 10000/60 meter/minute.
Volume of water that flows in 1 minute from canal = 9 × 10000/60 = 1500 m³
Volume of water that flows in 30 minutes from canal = 30 × 1500 = 45000 m³
From figure 2: Assume the irrigated area be A. Volume of water irrigating the required area will be equal to the volume of water that flowed in 30 minutes from the canal.
Volume of water flowing in 30 minutes from canal = Volume of water irrigating the required area
⇒ 45000 = A × 8/100
⇒ A = 562500 m²
So, area irrigated in 30 minutes is 562500 m².