If the natural range of patterns along a river can be identified, then within that range it should
be possible to identify the most appropriate channel pattern and sinuosity. If so, the
engineer can work with the river to produce its most efficient or most stable channel.
Obviously, a river can be forced into a straight configuration or it can be made more sinuous,
but there is a limit to the changes that can be induced beyond which the channel cannot
function without a radical morphologic adjustment as suggested by Figure 5.4. Identification
of rivers that are near the pattern threshold would be useful, because a braided river near
the threshold might be converted to a more stable, meandering, single-thalweg stream. On
the other hand, a meandering stream near the threshold should be identified in order that
steps could be taken to prevent braiding due, perhaps, to changes of land use.
Perhaps the best qualitative guide to river stability is a comparison of the morphology of
numerous reaches, and the determination of whether or not there has been a change in the
position and morphology of the channel in the past. Another approach might be to
determine the position of the river on the Leopold-Wolman (1957) or Lane (1957) gradient-
discharge graphs (Figure 5.18). If a braided river plots among the meandering channels or
vice versa, it is a likely candidate for change because it is incipiently unstable.
An example of the way that this could be done is provided by the Chippewa River of
Wisconsin, a major tributary to the Mississippi River (Schumm and Beathard 1976). The
Chippewa River rises in northern Wisconsin and flows 320 km (200 mi) to the Mississippi
River, entering it 120 km (75 mi) below St. Paul (Figure 5.23). It is the second largest river in
Wisconsin, with a drainage basin area of 24 600 km (9,500 sq mi).
From its confluence with the Mississippi to the town of Durand 26.5 km (16.5 mi) up the
valley, the Chippewa is braided (Table 5.6). The main channel is characteristically broad
and shallow, and it contains shifting sand bars. The bankfull width as measured from U.S.
Geological Survey topographic maps is 333 m (1,092 ft). The sinuosity of this reach is very
low, being only 1.06. However, in the 68 km (42 mi) reach from Durand to Eau Claire, the
Chippewa River has a meandering configuration with a bankfull width of 194 m (636 ft) and a
sinuosity of 1.49. The valley slope and channel gradient are different for each reach of the
river. The braided section has a gentler valley slope than the meandering reach upstream,
0.00035 as opposed to 0.00040, contrary to what is expected from Figure 5.18, but the
situation is reversed for channel slope. The braided reach has a channel gradient of
0.00033, whereas the meandering reach has a gradient of 0.00028.
Table 5.6. Chippewa River Morphology.