Civil Engineering MCQAE Level Civil Engineering
In gradually varied flow analysis in open channels, the governing differential equation dy/dx = (S0 - Sf) / (1 - Fr^2) shows that for a mild slope (S0 < Sc) with subcritical flow (Fr < 1) and Sf > S0:
Fluid MechanicsGradually Varied FlowMEDIUM
Choose the correct answer
A
dy/dx is positive (depth increases downstream)
B
dy/dx is negative (depth decreases, M2 drawdown)
C
dy/dx is zero
D
Flow is impossible
Correct Answer
B. dy/dx is negative (depth decreases, M2 drawdown)
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For mild slope (S0 < Sc) subcritical flow: Fr < 1, so (1 - Fr^2) > 0. If Sf > S0, then (S0 - Sf) < 0, giving dy/dx < 0 = M2 drawdown curve (depth decreasing downstream, approaching critical depth).
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