Open Channel Discharge by Manning
MediumManningopen channel flow
A rectangular open channel has width b = 3 m, water depth y = 1 m, Manning roughness n = 0.015, and uniform-flow energy slope S = 0.001. What is its approximate discharge in SI units?
- A1.5 m³/s
- B3.0 m³/s
- C4.5 m³/s
- D9.0 m³/s
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Answer: C. 4.5 m³/s
A = by = 3 m² and wetted perimeter P = b + 2y = 5 m, so hydraulic radius R = A/P = 0.60 m. Manning's equation gives Q = (1/n)AR^(2/3)S^(1/2) = (1/0.015)(3)(0.60)^(2/3)√0.001 ≈ 4.50 m³/s.
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