Question

A rectangular open channel needs to be designed carry a flow of $2.0m^3/s$ under uniform flow conditions. The Manning's roughness coefficient is 0.018. The channel should be such that the flow depth is equal to half the width. and the Froude number is equal to 0 5.

Keeping the width, flow depth and roughness the same, if the bed slope of the above channel is doubled, the average boundary shear stress under uniform flow conditions is

• A. 5.6 N/$m^2$
• B. 10.8N/$m^2$
• C. 12.3N/$m^2$
• D. 17.2N/$m^2$

Answer 1

The correct option is D 17.2N/$m^2$

The average shear stress,
${\tau }_0=\gamma R{S}_0$

Bed slope is doubled i.e

$S_0=2\times 0.0021=0.0042$

$\therefore {\tau }_0=9810\times \frac{0.836}{2}\times 0.0042$

$\therefore {\tau }_0=17.22N/m^2$