Civil Engineering MCQAE Level Civil Engineering
For a most efficient trapezoidal channel section (minimum wetted perimeter for given area), the relationship between depth y, bottom width b, and side slope z is:
Irrigation EngineeringChannel Geometry TrapezoidMEDIUM
Choose the correct answer
A
b = 2y (z=0, rectangular)
B
b = 2y (sqrt(1+z^2) - z) [best hydraulic section]
C
b = y only
D
b = 2yz
Correct Answer
B. b = 2y (sqrt(1+z^2) - z) [best hydraulic section]
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Best hydraulic trapezoidal section: b = 2y(sqrt(1+z^2) - z). For z = sqrt(3)/3 (60-degree side slopes from vertical), this gives a half-hexagon, which is the most efficient of all trapezoidal sections. For rectangular (z=0): b = 2y.
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