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<br />. <br /> <br />6 <br /> <br />. <br /> <br />complexity of the object being digitized. The most important features were: <br />1) river banks; 2) islands and emergent bars; and 3) side channels plus <br />backwaters (Fig. 3). <br />Without specific field data, it is very difficult to determine a true <br />backwater on a 1:20,000 scale photograph. Therefore, both backwaters and <br />side channels were digitized as one feature. This provides a measure of <br />changes in channel complexity which in turn is a surrogate for changes in <br />fish habitat. The backwater and side channel areas were defined as all areas <br />other than the main channel (Fig. 3). <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />Figure 3. Map of main channel, islands, and side channel/backwater area <br /> <br />. <br /> <br />To establish reference points for the different photo sets, four or five <br />common points were found on each photograph and on a USGS 1:24,000 <br />scale map of the area. These points commonly were road intersections, of <br />which a specific corner of the intersection was chosen. The UTM <br />coordinates of these points were determined from the USGS map to 0.01 m. <br /> <br />. <br /> <br />. <br />