Calculate the effective unit tractive force that causes bed load transportation if the unit tractive force produced by the flowing water is 3.20 N/m2. The Manning’s coefficient on an unrippled bed is 0.0108 and the actual observed value of Manning’s coefficient on ripped channels is 0.0222. Take the value of critical shear stress that is required to move the grain particle as 0.5 N/m2.

Calculate the effective unit tractive force that causes bed load transportation if the unit tractive force produced by the flowing water is 3.20 N/m2. The Manning’s coefficient on an unrippled bed is 0.0108 and the actual observed value of Manning’s coefficient on ripped channels is 0.0222. Take the value of critical shear stress that is required to move the grain particle as 0.5 N/m2. Correct Answer 0.58 N/m2

The unit tractive force causing bed load to move is reduced by ripples in the ratio of S0‘= S0 (n’/n) 3/2 = 3.2 (0.0108/0.0222)3/2 = 1.08 N/m2. The effective unit tractive force = S0’ – Sc = 1.08 – 0.5 = 0.58 N/m2.
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