Irrigation Water Conveyance and Application Methods
Subtopic: Surface, sprinkler and micro irrigation methods
Question Statement:
Graded furrows of 80 m length and 0.75 m spacing are used for irrigating a field with an initial furrow stream of 100 L min⁻¹. The initial furrow stream flow reaches the lower end of the field in 40 min. Thereafter, the furrow stream flow is reduced to 30 L min⁻¹ and the cutback stream flow is continued for 1 hour. The average depth of irrigation over the field in cm will be __________.
Official Answer Key:
9.65 to 9.75
Step-by-Step Solution & Explanation
• Total volume of water applied per furrow = (initial stream × advance time) + (cutback stream × cutback duration) = (100 L/min × 40 min) + (30 L/min × 60 min) = 4000 + 1800 = 5800 L = 5.8 m³.
• Irrigated area per furrow = furrow length × furrow spacing = 80 m × 0.75 m = 60 m².
• Average depth = Volume/Area = 5.8 m³ / 60 m² = 0.0967 m = 9.67 cm, inside the accepted range 9.65–9.75.
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