Example 2

A trapezoidal channel with base width 2m and side slope of 1:2 carries water with a depth of 1m. The bed slope is 1 in 625. Calculate the discharge and average shear stress at the channel boundary. Take Manning coefficient as .

Solution :

Given that,
; ; Side slope,
The area of the flow and wetted perimeter for a trapezoidal section is given by,
                      
By definition of hydraulic radius,
                      
Using Manning's formula,
                      
Discharge,
Average shear stress at the channel boundary,