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Uniform unsteady flow would require that the velocity vary, and the flow depth would have to vary too to keep discharge a constant.
If the flow depth varies, then the flow is no longer uniform.
Or, if the velocity varies at constant depth, the friction would have to vary along the channel, and the flow would change in flow depth.
b.
Energy is a scalar; momentum is a vector.
Energy is the integral of the force over distance; momentum is the integral of the force over time.
c.
W/D ≥ 10.
d. Because in natural channels, where the Manning equation is used, the Manning roughnees coefficient varies with the stage.
e. Because β - 1 is directly related to the ratio of Vedernikov and Froude numbers, two very important concepts in open-channel hydraulics.
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