Determining Which Depth the 60% Depth Rule for Mean Stream Velocity Refers To

by Elizabeth Davids

Submitted : Spring 2015

Discharge is an important consideration in both geology and engineering. It is relevant in such things as flood mitigation and water supply. A common way to find discharge is by the equation Q=Au. The components needed in this equation are the area and mean velocity. The mean velocity is the more challenging part of this equation to find since the velocity of water is different at different depths. There is a rule to help determine the mean velocity named the 0.6D rule. This can lead to confusion as to whether the rule refers to 60% of the depth from the stream bed or from the water level. Through the use of calculus, the 60% relative depth rule will be shown to refer to the depth below the water level of the stream.

[ Back ]