Energy and momentum under critical flow conditions

Abstract

The definitions of the critical flow condition in open channel hydraulics, based on the momentum and the energy equations, differ from each other if non-hydrostatic pressure and non-uniform velocity distributions are considered. The concept of minimum energy and minimum momentum yields two distinct critical flow conditions, both in terms of their magnitude and their position. Consequently, for a given discharge, there are two singular points in the water surface profile, derived from the momentum and the energy principles, respectively. Extended momentum and energy equations for non-uniform velocity and non-hydrostatic pressure distributions are presented and the critical flow condition is generalized in relation to those conservation laws.