Question

In a wide stream, a suspended load sample taken at a height of 0.30 m from the bed. The stream is 5.0 m deep and has a bed slope of 1/4000. The bed material can be of uniform size. Estimate the shear friction velocity.

(a) 0.111 m/s

(b) 0.211 m/s

(c) 0.311 m/s

(d) 0.711 m/s

This question was posed to me in an international level competition.

Question is taken from Sediment Transport in section Sediment Transport and Irrigation Channels Design of Irrigation Engineering

Answer 1

Right choice is (a) 0.111 m/s

The explanation: V*= Shear friction velocity = (S0/Dw)^1/2 where Dw is the density of water and So (Yw.R.S) is shear stress at the bottom.

V* = [(Dw. g.R.S)/Dw]^1/2 = (g.R.S)^1/2

V* = (9.81 x 5 x 1/4000)^1/2 = 0.111 m/s.