What is the delta for a crop when its duty is 864 hectares/cumec on the field (the base period of this crop is 120 days)?
- A100 cm
- B110 cm
- C120 cmCorrect
- D130 cm
Solution
Concept
Relation between duty and delta
Formula
Δ = 8.64 B / D (Δ in m, B in days, D in ha/cumec)
Step-by-step solution
1. Δ = 8.64 × 120 / 864 = 1.2 m = 120 cm.
Explanation
Delta is the total depth of water required by a crop during its base period. It is related to the duty and base period by Δ = 8.64B/D.
Why the other options are wrong
100, 110 and 130 cm do not satisfy Δ = 8.64B/D.
Shortcut
864 = 8.64 × 100, so Δ = B/100 m = 1.2 m.
Common mistake
Forgetting to convert metres to centimetres.
Correct answer: C) 120 cm