6 minute problem 37

In Six minute solutions for water resources #37, they find the velocity of the flow in the channel by the equation v=SQRT2gh. The head was given as 42 ft and the depth of flow was not given. The equation for energy (head) of the flow is H = d +v^2/2g (Eq19.62 CERM). Based on the solution, it appears they neglected the depth of flow. Is this assumption that d is negligible made because the flow condition is supercritical flow, and thus the depth is likely to add negligible head/energy? Later we will find that the depth was only 1.3 ft, which indeed provides little energy compared to the 52 fps velocity. However I would like to be clear why this assumption is made.

The depth of flow is not needed. The difference between EGL and HGL is V^2/2g ... since they gave you the head, just solve for V.

Without seeing the text of the problem I dont know exactly how they phrased it.