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Figure Captions: ,.i.'!:" Figure 1. The study site is located on the Green River, near Ouray, Utah. The river is partially controlled by Flaming Gorge Dam (closed in 1963), with approximately half the river's flow coming from the unregulated Yampa River. Green cross hatching indicates reaches of known spawning area. Blue hatching indicates known Colorado squawfish nursery habitat. Figure 2 (on color copy) Figure 3. Green River peak flow is highly variable. The average peak flow decreased from about 600 m3/s to about 500 m3/s after dam closure; the annual variability in peak flow also decreased. Figure 4. Post-dam peak flows occur in response to snowmelt in the Yampa River basin. Baseflow at other times is typically less than 80 m3/s. The 1993 instantaneous peak discharge of 574 m3/s has a 1.5-yr recurrence on the annual flood series for unregulated flows (prior to 1963), but has a 3-yr recurrence using only the post-dam annual flood series. The 1993 peak was the highest in 7 years. Arrows note the times of four of the channel cross-section measurements (data are unavailable for water year 1994). Figure 5a-b. Repeated cross section surveys on the descending limb. The discharges were 402, 328, 45 and -45 m3/s, respectively. The 6a cross section is near the downstream end of the upstream river right bar complex shown on Fig. 8, 6b is located across the middle of this bar. These cross section show the adjustment of the bar during the descending limb and low flow regime of 1993. On June 10, the bar was completely submerged, on June 22, the tops of the bar was emergent. By August 15, the bar had emerged as a single, higher elevation unit than had been measured in November, 1992. Figure 6a-b. The cross section in 6 a-b were measured in previous years (during low flows) and compared with our data. 1986 was the last year of three years of high peak discharges. The bar aggradation from this year's high flows was greater at the head of the bar (B - B') than previously measured. Near the downstream end of the bar (A - A'), aggradation occurred to the same levels with and without high peak discharges. Figure 7a-c. Modeled topography. During the passage of the spring flood, the bar aggraded -1m, the thalweg scoured up to 3 meters. During the low flow regime, the bar aggraded to approximately the pre-flood condition. Figure 8. This graph shows the time series of minimum bed elevation at the time of each stream discharge measurement at the U. S. Geological Survey gaging station Green River near Ouray, located about 17 Ian downstream from the study reach. These data show the annual bed scour associated with spring runoff water stage rise. Annual bed scour was between 3 and 4 meters, and this cross-section refilled each summer. These data show that the type of bed behavior measured in our study reach in 1993 (and inferred from the Andrews and Nelson measurements in 1986) occurred annually at the Ouray gage between 1951 and 1968. Further analysis of these data will indicate the hydraulic conditions that initiated bed scour at this site.