Armfield C4-MKII, Инструкция по эксплуатации

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Theory
The depth and velocity of a given flow at any section of an open channel adapt
themselves to the energy available at that section. For a constant discharge this energy
reaches a minimum value at the ‘critical’ depth. This parameter is fundamental to a
complete understanding of free flow behaviour because the response of a stream to
energy (and force) depends on whether the actual depth is greater than or less than the
critical depth.
In an open channel it is convenient to use the bed as the datum and to compare the
specific energy at different sections where the specific energy is defined as the sum of the
potential energy (the depth of flow) and the kinetic energy (the velocity head):