Figure 5.23. Map of lower Chippewa River. The river is braided below Durand, Wisconsin.
Buffalo Slough is an old course of Chippewa River (Schumm and Beathard
1976).
There is no evidence to suggest that the Chippewa River is either progressively eroding or
aggrading its channel at present. In fact, the river below Durand has remained braided
during historic time. It has maintained its channel position and its pattern, but a significant
narrowing as the result of the attachment of islands and the filling of chute channels has
occurred downstream of Durand, which resulted in a recent decrease in channel width of
over 40 percent. The only other change in the lower river is a noticeable growth of the
Chippewa delta into the Mississippi valley. The delta deposits show increased vegetational
cover as well as extension into the Mississippi River valley.
The relations described by Leopold and Wolman (1957) and Lane (1957), which are
combined in Figure 5.18, provide a means of evaluating the relative stability of the modern
channel patterns of the Chippewa River. The bankfull discharge was plotted against channel
slope on Figure 5.24 (the Leopold and Wolman relationship) for both the braided and the
meandering reaches of the Chippewa. The value used for the bankfull discharge is 1,503
3
m /s (53,082 cfs), which is the flood discharge having a return period of 2.33 years. The
braided reach plots higher than the meandering reach, but both are well within the
meandering zone, as defined by Leopold and Wolman. This suggests that the braided reach
is anomalous; that is, according to this relation the lower Chippewa would be expected to
display a meandering pattern rather than a braided one. Even when the 25-year flood of
3
2,787 m /s (98,416 cfs) is used, the braided reach still plots within the meandering region of
Figure 5.24.
When the Chippewa data are plotted on Lane's graph (Figure 5.25) the same relation exists.
The Chippewa River falls in the intermediate region, but within the range of scatter about the
regression line for meandering streams. Again the braided reach is seen to be anomalous
because it should plot much closer to or above the braided stream regression line. The
position of the braided reach as plotted on both figures indicates that this reach should be
meandering.
5.36
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