ABSTRACT
In open channel flow an important concept is that of normal depth. This is the
depth a given flow would reach under steady-state equilibrium conditions when the
channel cross-section and slope are constant. The uniform flow which results is a
balance between the driving gravity force and the resisting friction force around the
perimeter of the channel. As an example, the expression that relates the key
variables in a rectangular channel can be written:
where Q is the flow rate, B the width of the channel, S the slope of the channel and
d
the normal depth. The friction is described using Manning’s roughness
coefficient, n, which may vary between 0.01 for very smooth surfaces and 0.1 for
rough, heavily vegetated floodplains. A typical value for a concrete channel, such
as that shown in Figure 3.1, is 0.014.
