Figure 8.21
Note: Care must be taken in treating this method of solution as a universal case. For example, if the channel slope is steep the flow may be supercritical and the plots of equations (ii) and (iii) would appear thus (see fix. 8.22).
The solution is not now the point of intersection of the two curves. The depth passes through the point of intersection of the two curves. The depth passes through the critical depth at inlet and this condition controls the discharge, given by Qc. Channel resistance no longer controls the flow and the depth of uniform flow corresponds with Qc on the curve of equation (iii)
Example 8.8
Using the data of Example 8.7 but with a channel bed slope of 1:300 calculate the discharge and depth of uniform flow.