FIGURE 5.11 Longitudinal valley profiles of streams crossing the Monroe Uplift, and Macon Ridge, which is a remnant of a Pleistocene Mississippi River terrace. From Burnett and Schumm (1983).

the position of the uplift axis (Figure 5.12). In each case sinuosity increases as the axis is approached or crossed. Where sinuosity is high above the axis, there is a decrease of sinuosity as the axis is approached (Bayou Bartholomew). The results are as suggested by Figures 5.2 and 5.3.

To examine the variability of the channel-bed elevation and also changes in the bank height along the streams that cross the Monroe Uplift, channel thalweg elevations were plotted in relation to the valley distance along Boeuf River and Big Colewa Creek (Figure 5.13). These projected channel profiles are not affected by changes in sinuosity because the thalweg elevation (or low water elevation) at a given location is plotted with reference to valley distance rather than channel distance (Burnett, 1982).

In Figure 5.13, the difference in the elevation of the projected channel profile and that of the valley profile at a given location represents the depth of the channel below the valley surface at that location. The reaches with large differences in elevation between the valley surface and channel (high banks) are those where the channel has downcut or degraded. Also, where average bank height is small the channel has not degraded, or it has, in fact, aggraded. The projected channel profiles do not parallel the valley profiles, indicating that varying amounts of degradation or aggradation have occurred along the channel. The Boeuf River has apparently com

FIGURE 5.12 Variations of sinuosity along six streams crossing the Monroe Uplift. Distance above and below uplift axis is shown. Downstream is to the right. Arrows indicate axis of uplift, and cross hatching shows zones of modern uplift. From Burnett (1982).

pensated for the uplift, but the Big Colewa Creek profile contains a major convexity (Figure 5.13). At the axis of the uplift and in the downvalley zone of the uplift, the average bank heights are, in general, high (11 to 13 m for the Boeuf River and 6 m for Big Colewa Creek). These observations indicate that degradation has occurred at and below the uplift axis, but above the axis

FIGURE 5.13 Valley and projected-channel profiles of Boeuf River and Big Colewa Creek. From Burnett (1982).

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