a water resource engineer is in charge of designing a trapezoidal open channel for flood control. Typically, these types of channels are made of concrete. Use Manning’s Equation. Flowrate (Qb), channel slope (S0), bottom width (Bw), channel sidewall angle (θ), actual depth (y), and Manning’s coefficient (n) are tabulated below. State all assumptions. * z is the sidewall ratio: for every 1 unit increase in depth, the top width increases by z on each side of the channel, or 2z total. A) Given the actual depth, y = 1.25 ft, find the discharge Qa. B) Find the Critical Depth, yc, for the discharge Qa found in (a). For a trapezoid, dA/dy =Bw +2 yz . Is the flow sub- or super-critical? C) Determine the uniform flow normal depth (yn) at Qb = 209 cfs.

Structural Analysis
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Author:KASSIMALI, Aslam.
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Chapter2: Loads On Structures
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a water resource engineer is in charge of designing a
trapezoidal open channel for flood control. Typically, these types of channels are made of
concrete. Use Manning’s Equation.
Flowrate (Qb), channel slope (S0), bottom width (Bw), channel sidewall angle (θ), actual depth
(y), and Manning’s coefficient (n) are tabulated below. State all assumptions.

* z is the sidewall ratio: for every 1 unit increase in depth, the top width increases by z on each
side of the channel, or 2z total.
A) Given the actual depth, y = 1.25 ft, find the discharge Qa.
B) Find the Critical Depth, yc, for the discharge Qa found in (a). For a trapezoid,
dA/dy =Bw +2 yz .
Is the flow sub- or super-critical?
C) Determine the uniform flow normal depth (yn) at Qb = 209 cfs.
D) If the slope is increased to 0.001, what roughness coefficient would be needed to
maintain the same discharge Qa? What about for Qb? Would it be the same value?

 
 
Variable
y
Qb
So
Bw
Z*
n
Units
ft
cfs
ft/ft
ft
ft
Value
1.25
209
0.0007
12.5
1.1
0.012
Transcribed Image Text:Variable y Qb So Bw Z* n Units ft cfs ft/ft ft ft Value 1.25 209 0.0007 12.5 1.1 0.012
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Solution is done neatly, using same solution what would happen If the slope is increased to 0.001, what roughness coefficient would be needed to
maintain the same discharge Qa? What about for Qb? Would it be the same value?

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