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Filial Report 3-44 September 2000 submerge these bars and substantially increase the amount of inundated vegetation along shorelines. The amount of talus shorelines in eddies peaked near 198 m3/s and declined at higher flows. Flooded side canyons also provide low-velocity habitats used by fish; the relationship between the area of flooded side-canyon habitat and flow in Reach 3 was examined by FLO Engineering, Inc. (1996). Flooding of side canyons begins at a discharge of approximately 198 m3/s. At flows greater than 198 m3/s, a linear increase in the area of flooded side-canyon habitat occurs until bankfull discharge (1,104 m3/s) is reached; only 2 ha of flooded side-canyon area is available at this study site at bankfull discharge. There is no optimum flow for the area of inundation of side-canyon habitat; a higher discharge results in a larger amount of flooded area. 3.6.3 Sediment Dynamics and Spawning Substrates Cobble and gravel deposits free of silt and sand are preferred spawning areas of the endangered fishes (Chapter 4), and the suitability of these areas for spawning are affected by sediment-transport and depositional patterns. The morphologic characteristics and sediment-transport regime at a known spawning site for razorback suckers were described by Wick (1997). This spawning site on the Green River is in Reach 2 upstream of Jensen, Utah, about 156 km downstream from Flaming Gorge Dam. It was studied between 1992 and 1996. Sediment-deposition and scour patterns were described by using mathematical models of hydraulics and sediment transport calibrated to observed field data. This modeling indicated that a downstream constriction in the river created a "backwater effect" at discharges above 340 m3/s and resulted in sediment deposition on portions of the bar. Measured sedimentation of the bar began at flows of 200 m3/s, and flows resulted in deposition of about 0.6 m of sand as they approached 650 m3/s (Wick 1997). At lower flows, the backwater effect did not occur, the channel became narrower, and higher velocities scoured sand from the bar, making it suitable for spawning. The timing of peak flow was found to be important in maintaining this spawning bar. Wick (1997) suggested that the magnitude and timing of releases from Flaming Gorge Dam could affect the suitability of the bar and could be manipulated to ensure that the bar substrate is clean. Harvey and Mussetter (1994) reported on the hydraulics at a potential spawning area for Colorado pikeminnow located at the head of Gray Canyon in Reach 3. They used field data from this site to test a proposed physical process-biological response model for spawning-habitat formation. This model was initially developed from data and analyses conducted about 27 km upstream from the Yampa and Green River confluence in lower Yampa Canyon (Harvey et al. 1993). The model indicated that high discharges are responsible for the construction of the spawning bar but not for the actual formation of the spawning habitat. Downstream hydraulic controls cause a backwater condition that results in the formation of the bar as a heterogenous mass of sediments is deposited during high flows. Reduced tailwater during recessional flows causes a steepening of the local hydraulic gradient, which in turn leads to bar dissection and erosion of chute channels. Dissection of the bar causes the fines to be flushed, and this process is enhanced by reduced sediment delivery