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I I I I I I I I I I I I I I I I I I I 60 SUMMARY Changes in the physical habitats of the Colorado squawfish and razorback sucker may affect both the adults' ability to reproduce, and the survival of larval fish (Osmundson and Kaeding, 1991). In this study we have documented historic changes in channel morphology, recent effects of discharge on backwater habitats, and we have determined the range of flows which are needed to maintain and create channel complexity. Aerial Photograph/GIS Analysis Our GIS analysis shows that there has been a general decrease in the area of most channel features throughout the Grand Valley and Ruby- Horsethief Canyon (Figures 3,6,7). Changes are consistent for both comparisons of 1954-1968 and 1937-1993. The 1954-1968 analysis documents channel change during a period of below average peak flows, and the 1937- 1993 analysis shows channel change over a longer period which includes the extremely high flows of 1983 and 1984. In either case, there was a decrease in water, island, and side channel/backwater area in the Grand Valley, and a decrease in water and side channel/backwater area in Ruby-Horsethief Canyon. The analysis of Ruby-Horsethief Canyon showed an increase in island area through time which could be due to the accretion of sediment to islands, but these islands have not become part of the floodplain as in the Grand Valley reach. In summary, there has been a general decrease in channel complexity through time, which indicates a decrease in available low velocity habitats. Field Studies Studies of side channel/backwater sites showed some changes in channel morphology from the relatively high flows of 1993, but very little change in 1994. These effects are consistent with our flow modeling results