Manning's equation for open channel flow is V = dfrac 1 n R^ 2/3 S^ 1/2 . The Manning's roughness coefficient n for a clean, straight natural river channel is approximately in the range:

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Civil Engineering QUESTION #2127

Question 1

Manning's equation for open channel flow is \(V = \dfrac{1}{n} R^{2/3} S^{1/2}\). The Manning's roughness coefficient \(n\) for a clean, straight natural river channel is approximately in the range:

0.008–0.010
0.011–0.014
0.025–0.035✔️
0.050–0.080

Correct Answer Explanation

Manning's \(n\) values: smooth concrete 0.011–0.013; clean, straight natural channel 0.025–0.033; winding natural channel with some pools 0.035–0.050; very weedy/brushy channels 0.075–0.150. A clean, straight natural river typically has \(n \approx 0.025–0.035\). These values are critical for flood routing, channel design, and backwater curve computations in hydraulic engineering.

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