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reach (river-miles 140 to 170) averaged 175 meters. The average channel width for the entire Colorado River study area was 158 meters. DISCUSSION Channel Width - Green River As expected from previous studies, average channel width for the lower monitoring reach of the Green River was substantially narrower than the upper reach (table 3), averaging about 37 percent less (lower reach = 137 meters, upper reach = 216 meters). These results are comparable with previous studies. Andrews (1986) reported the average channel width from Jensen to Ouray as 186 meters, based on only 15 cross section measurements of the Green River on large-scale aerial photographs. This number is approximately 7 percent less than the average width of about 200 meters for roughly the same reach in this study, based on 236 cross section measurements on video. The discrepancy may be related to a number of factors, but it is probably chiefly due to the dates of data collection. Andrews'photographs were acquired in 1978, and our video was acquired in 1989. The high flood years of 1983 and 1984 widened the channel width from about 1 to 5 percent on various reaches below the Jensen gauge (Pucherelli et al., 1987) and this would be reflected in the video data. Secondly, this study was based on considerably more cross sections than Andrews' which presumably produced a more accurate channel width measurement. Lastly, Andrews' measurements were derived from aerial photographs, and our data were derived from aerial video. Andrews' reported a channel width of 142 meters for a IS-mile reach below the GS Green River, Utah, gauge. This measurement was based on only 14 cross sections and is about 6 percent less than our measurement of 151 meters for a similar reach based on 99 cross sections. This difference in channel width is similar to that for the upper reach and was affected by the same study variables listed above. Pucherelli et al. (1987, 1988) determined channel width for portions of the upper and lower monitoring reaches. They reported a channel width of 205 meters for river-miles 237 to 310 (exclusive of river-miles 249 to 251), based on channel area calculations from 1986 aerial photography. Channel width in this study for river-miles 236 to 315 was approximately 206 meters. Pucherelli et al., (1988) reported a channel width of 140 meters for a portion of the lower monitoring reach from river-miles 94 to 121. The present study recorded a channel width of about 148 meters for river-miles 94 to 120, which is about 5 percent wider. Sidle et al. (1989) noted that measuring channel width by cross-sectional methods may overestimate channel width. Although our channel width measurements are within range of previous investigators, they may be slightly overestimated if the cross section is slightly off perpendicular with respect to the channel. We believe that the large number of cross sections measured in the present study should remove most of the error. Regardless, by using consistent techniques, our video monitoring data will be comparable from year to year. Channel Width - Colorado River Channel width of the Colorado River was about 13 percent narrower for the lower reach than the upper reach (table 3). Presumably, the more braided nature of the upper reach accounts for this difference. 6