(a) Define: (i) specific energy (ii) Froude number for open-channel flow

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(a) Define:

(i) specific energy

(ii) Froude number

for open-channel flow. What is special about these quantities in critical conditions?

A long, wide channel has a slope of 1:1000, a Manning's ???? of 0.015 m-1/3 s and a discharge of 3 m3 s-1 per metre width.

(b) Calculate the normal and critical depths.

(c) In a region of the channel the bed is raised by a height of 0.8 m over a length sufficient for the flow to be parallel to the bed over this length. Determine the depths upstream, downstream and over the raised bed, ignoring frictional losses. Sketch the key features of the flow, indicating all hydraulic transitions caused by the bed rise.

(d) In the same channel, the bed is lowered by 0.8 m from its original level. Determine the depths upstream, downstream and over the lowered bed, ignoring frictional losses. Sketch the flow.