Irrigation Water Conveyance and Application Methods
Subtopic: Design of irrigation channels and underground pipelines
Question Statement:
A sprinkler irrigation system has been designed for a crop with the water application rate of 1.17 cm h⁻¹ and sprinkler discharge of 1.3 L s⁻¹. The coefficient of discharge and uniformity coefficient are 0.9 and 0.8, respectively. If the sprinkler spacing along the lateral is 20 m, the lateral spacing in m is
Options:
(A) 14.4
(B) 16.0
(C) 18.0
(D) 20.0
Official Answer Key:
D
Step-by-Step Solution & Explanation
The application rate for a rectangular sprinkler spacing pattern is: I(cm/h) = 360×q(L/s) / [S_e × S_l], where S_e = sprinkler spacing along the lateral (m), S_l = lateral spacing (m).
Rearranging for lateral spacing: S_l = 360×q/(I×S_e) = 360×1.3/(1.17×20) = 468/23.4 = 20.0 m.
(Note: the given coefficient of discharge (0.9) and uniformity coefficient (0.8) are not required for this direct application-rate/spacing relationship — they are extra data testing whether the correct governing parameters are identified.) Answer: (D) 20.0.
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