GATE 2022 AR — Planning – Question 27
The rectangular open drain shown has internal width 600 mm, total depth 400 mm and water depth 250 mm. Find hydraulic radius in mm, to two decimal places.
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Show answer and explanation
Correct answer: 135.00 to 138.00
Explanation
Flow area is 600×250=150000 mm². Wetted perimeter includes the bottom and two submerged sides:600+2×250=1100 mm; the free surface is excluded. Hydraulic radius A/P=150000/1100=136.36 mm. Use water depth 250 mm rather than the full 400 mm drain depth.