Question

A Persian wheel with an average discharge of 230 litre/minute irrigates 1 hectare wheat crop in 50 hours. The average depth of irrigation will be nearly
1. 4 cm
2. 5 cm
3. 6 cm
4. 7 cm

Answer 1

Correct Answer - Option 4 : 7 cm

Concept:

Total discharge = Average discharge × period of discharge

Depth of irrigation = Total discharge/Area of irrigation

Calculation:

Given data, Average discharge = 230 litre/minute

Area of land irrigated = 1 hectare = 10000 m²

Time = 50 hours = 50 × 60 = 3000 minutes

Total discharge = 230 × 3000 litres = 690 m³

Average depth of irrigation = 690/10000 = 0.069m = 6.9 cm = 7 cm

Other Important Points:

Duty means the area of land that can be irrigated with unit volume of irrigation water. Quantitatively, duty is defined as the area of land expressed in hectares that can be irrigated with unit discharge, that is, 1 cumec flowing throughout the base period, expressed in days.

If the water supply is just enough to raise the crop within D hectares of the field, then a relationship may be found out amongst all the variables as:

The volume of water supplied = B × 60 × 60 × 24 m³

Area of crop irrigated = D × 10⁴ m²

Volume of water supplied per unit area = 86400B/10000D = (8.64 × B)/D