For a given discharge (Q), braided streams tend to have stream cross-sections wi
ID: 283806 • Letter: F
Question
For a given discharge (Q), braided streams tend to have stream cross-sections with distinctly smaller depths and greater widths than for meandering systems. a) Assuming equal channel cross-sections, what effect will shallower depths and greater widths have on hydraulic radii (recall from Lab #6: hydraulic radius = cross-sectional area/wetted perimeter)? Please explain (you may wish to use examples in your answer; e.g., a rectangular channel with dimensions 2.5 m times 10 m, versus a channel with dimensions 0.25 m vs 100 m). b) Assuming constant flow velocity and constant bed roughness along a given channel's length, what does the Manning equation (equation 3 above) imply should change in a channel's parameters if a channel transforms from a meandering to a braided system (i.e., if hydraulic radius should change in the manner predicted in "5a" above)? Please explain.Explanation / Answer
Answer:
As hydraulic radius signifies the efficiency of river flow, higher the value of hydraulic radius means more efficiency and it can be calculated as follows:
Hydraulic radius= (cross sectional area)/(wetted perimeter)
As in braided river, the width of flow are more than its depth therefore its wetted perimeter becomes more which ultimately causes decreases its hydraulic radius.
Manning formula states as follows:
V= (k/n)*Rh2/3*S1/2
Where, V= cross-sectional average velocity, k= conversion factor, n= Gauckler Manning coefficient, Rh= hydraulic radius, S= linear hydraulic loss.
As the hydraulic radius decreases, the cross sectional average velocity also decreases.
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