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<br />002484 <br /> <br />shifting stage-discharge relation and we have labeled these deposits as "perched" gravel <br />bars rather than areas of deposition. <br />Similar changes have occurred at eddy deposits (Figure 22). The 1952 to 1984 <br />erosion-deposition map shows deposition of post-dam flood and fluctuating flow deposits <br />on the right bank in an area that was within the river channel in 1952. Although the 2000 <br />survey does not cover the entire cross-section, it shows the right bank to be at a lower <br />elevation (Figure 9B). These post-dam flood deposits that were within the river channel <br />in 1952 and appear on the erosion-deposition maps as deposition, are lower in elevation <br />than the pre-dam riverbed. This is further evidence that areas of apparent deposition <br />between 1952 and 1984 are the result of channel lowering rather than aggradation. <br />The channel cross-section data aided our interpretation of the erosion-deposition <br />maps. Areas where the mapping indicated erosion of channel-side sand deposits or <br />terraces are all areas where the cross-section surveys also indicated erosion, although the <br />mapping does not show the majority of the bed degradation, which occurred in the center <br />of the channel. The areas where the mapping indicates "deposition" between 1952 and <br />1984 are all perched deposits where the cross-section surveys indicate either no <br />topographic change or degradation. Included in this category are sand deposits mapped <br />as fluctuating flow deposits and post-dam flood deposits in 1984 and controlled flood <br />deposits in April 1996. Implicit in these post-dam map units is the classification of these <br />deposits as depositional features relating to preceding high flow events. Thus, these <br />features that may have experienced deposition during some of the post-dam flood events <br />have experienced net degradation or no net change since the pre-dam era. We have no <br />evidence of deposition on any of the perched gravel deposits in the post-dam era, <br />although local deposition on these deposits is possible. <br />The patterns of change in alluvial features described above are not distributed <br />uniformly throughout the study area (Plates 2 and 3). Erosion of sand bars and terraces <br />has occurred in discrete patches and the area of each of these patches varies greatly in <br />magnitude. The perched sand and gravel deposits also occur in discontinuous patches <br />throughout the study area. The reach-average magnitudes of channel adjustment are <br /> <br />34 <br />