The result of increasing any or several of these variables (Figure 5.18 and Table 5.4) is to
promote braiding of this channel. When locating this stream on Lane's diagram (Figure 5.18) it
0.25
0.25
is shown that with SQ
= 0.002 (SI = .00082), this river is very close to the line SQ
=
0.0017 (.0007 for SI) for meandering streams. Hence an increase in discharge or slope would
be required to change the planform to a braided stream.
(c) Determine the effect of increased discharge of bed sediment size, bed sediment load and
washload on channel stability, resistance to flow, energy slope and stage of the same river.
The Table 5.4 can be used to provide a qualitative response to these changes.
Increase in discharge results in an increase in stage and a decrease in energy slope and
channel stability.
Increase in sediment size results in an increase in stage, energy slope and resistance to
flow. The channel stability might not be changed.
Increase in bed sediment load should increase the channel stability through a decreased
resistance to flow, slope and stage.
Effect of increasing washload is similar to that of increasing bed sediment load except for
channel stability, which is uncertain.
5.9.2 PROBLEM 2 Classification of Alluvial Reaches
Identify the three types of alluvial river reaches sketched below. Discuss the relative stability of
each channel.
Figure 5.32. River channels (After Petersen 1986).
5.68
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