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RESULTS <br />Historical Changes in Channel Morphology <br />Our analysis of the 1937 and 1986 aerial photographs showed that overall there was a <br />negligible (+ 1%) change in the area of the main channel, but a 20% decrease in the area of islands <br />and an 18% decrease in the area of side channels and backwaters (Table 1). However, these <br />changes were not uniform throughout the entire 32 mile reach. Figure 5 shows that although the <br />area of side channels and backwaters on average decreased between 1937 and 1986, there were <br />many reaches where side-channel area increased. Some of these reaches include sections of the <br />river that were changed dramatically in 1983 and 1984 when high flows flooded abandoned gravel <br />pits. Thus, the 1937-1986 comparison reflects both episodic changes due to recent high flow <br />events as well as long-term and potentially systematic changes in channel morphology. <br />The analysis and comparison of the 1954 and 1968 aerial photographs produced results <br />similar those described above. For the 1954-1968 time period, there was a 12% decrease in the <br />area of the main channel, a 16% decrease in the area of islands, and a 27% decrease in the area of <br />side channels and backwaters (Table 2). Compared to results for the 1937-1986 time period, <br />results for the 1954-1968 time period indicate that nearly all of the 32 reaches experienced a <br />reduction in main channel area and side channel/backwater area (Fig. 6). These results provide <br />perhaps a clearer answer to the question of whether reductions in peak discharge have caused <br />significant changes in channel morphology because they are not complicated by the effects of high <br />flows (as in the earlier analysis, which includes changes resulting from the 1983 and 1984 floods). <br />From 1954 to 1968, the mean annual flood was exceeded at the Cameo gage a total of 5 times, and <br />then only twice in the last 10 years of the period. This would suggest that when peak flows are <br />lower than average, i.e. when droughts occur several years in succession, the channel will become <br />narrower and there will be a loss of side channel and backwater habitat. We note however that <br />changes in channel morphology were not always systematic nor were they permanent; some places <br />within the study reach showed significant change in the absence of high flows, and other places <br />showed no discernible change even after very high flows. <br />8