Tributaries of the upper course converge
by the middle course. Water flow increases, as do the
river's erosive and carrying capacity, resulting in
geomorphology unique to the middle course, with features
such as meanders and bluffs. A meander is a deep curve
in the channel created by the erosion being strong along
the inner margin of the curve, while deposition dominates
along the outer margin. A bluff is a steep slope along
the riverside, formed by lateral erosion of interlocking
spurs along the stream.
In addition, lateral erosion
becomes severe because of the increased water flow.
The valleys are V-shaped - albeit the "Vs"
are mostly irregular, and broader than along the upper
course. In Hong Kong, there is often no obvious middle
course between the steep upstream and gentle downstream