GATE 2022 AG – Question 55
Twelve100 m lateral drains are spaced50 m and connected to a collector. Water table falls50 cm in 4 days while mean collector discharge is 12 L/s. Find drainable porosity in percent, to two decimals.
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Correct answer: 13.75 to 13.85
Explanation
Drained area is 12(100)(50)=60000 m² using one tributary strip per lateral. Discharge volume=.012(4)(86400)=4147.2 m³. Released storage is porosity×area×water-table decline; hence $n_d=4147.2/(60000(.5))=.13824$, or **13.82%**.