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OBSERVED CHANNEL CHANGES <br />Backwater Study Sites <br /> <br />The upper backwater site is formed by a moderately large bar in the 15-mile reach at RM <br />176. Sequential aerial photographs of the area show that this feature has enlarged over time as <br />several smaller bars have coalesced into one larger bar (Van Steeter et al., 1995). Figure 4 shows <br />the layout of cross sections at the site, and Figure 5 shows a sequence of changes at selected cross <br />sections. The most recent surveys at the upper end of this site (XS-1B, Fig. 5) indicate that a <br />minor amount of sediment was deposited at the entrance to the side channel (located -30 m from <br />the right endpoint), but more significant bank erosion and scour occurred in the main channel (~40 <br />m from the right endpoint). If the main channel continues to erode laterally, this will likely force <br />more flow into the side channel and possibly enlarge it. Recent measurements of cross sections at <br />the mouth of this backwater (XS-2 and XS-5, Fig. 5) indicate variable amounts of bed scour and <br />bank deposition here. The more significant changes took place at these cross sections in 1993 <br />when flows were also high, but even so this backwater was further enlarged by flows in 1995. <br />Upper Site <br />Figure 4. Layout of cross sections at the upper backwater site near RM 176. <br />7