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Evaluation of Flow Records Streamflow data were obtained from USGS Water Supply Papers and from a commercially available CD-ROM and software package that contains peak- and daily-flow data from the USGS WATSTORE files. These data were used to quantify changes in flow regime due to reservoir regulation and water withdrawals. We have made no attempt at this point to evaluate the quality of these records, particularly the peak flow data from early in the century. We raise this point because it appears that peak flows on the Colorado River were anamolously high in the early 1900s (Graf, 1985) and because other researchers have questioned estimates of peak discharge made early in the century on streams elsewhere in Colorado (Jarrett et al., 1993). In any event, it was not until the middle of this century that water development in the upper basin began to have much of an effect on streamflows of the upper Colorado River (Liebermann et al., 1989), and thus our analysis focuses on the changes in flow regime that occurred after 1930. Field Studies Field measurements were made at four sites in spring and summer 1993; three of these sites were chosen to study changes in backwater habitats (Sites 1-3, Fig. 1) and the fourth site (Site 4, Fig. 1) was chosen to evaluate thresholds for bed-material transport. The backwater study sites are all formed by lateral bar that forces flow down a side channel. These side channels are in all cases much smaller than the main channel. Field work at these sites consisted of repeated surveys to determine erosion and deposition in the side channels. A series of cross-sections were established across these channels prior to the 1993 spring runoff, and they were surveyed subsequently through the summer. Measurements of the bed material substrate were also made at each site. The site chosen for studying bed-material transport is located in a single thread alluvial reach of the Colorado River near Fruita (Site 4, Fig. 1). In this reach, the river has an average slope of 0.0015 and the bed material consists of cobbles and gravel. Survey measurements of channel cross sections and water surface slopes were taken through the reach at several different 6