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DRA,Fr Febmary 25, 1998 1993). The PRM indicate that high discharges are responsible for the construction of the spawning bar but not 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 are deposited. 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 is enhanced by reduced sediment delivery from upstream due to deposition in the upstream pool. A clean cobble substrate, with the constituent cobbles at incipient motion, and suitable for egg adhesion, is formed in the subaqueous tertiary bars that are located within the chute channels. The downstream hydraulic control for the spawning bar is formed by two coarse grained and horizontally-opposed alluvial fans that have prograded into the channel to form a constriction in a relatively wide valley segment of the Green River. Hydraulic analysis of the reach indicated that two of the three mid-channel bars located in the middle and left branch channels meet the PRM criteria for squawfish spawning habitat; gravels and cobbles that constitute the mid-channel bars attain a condition of incipient motion, and therefore, meet a criterion of the PRM. • In common with other rivers draining the Colorado Plateau (Webb and others, 1988) the vast majority of rapids (95 percent), and hence channel constrictions, are the result of tributary alluvial fans that prograde out into the channel. Although the identified site meet PRM criteria it should be recognized that other factors may also be involved in determining spawning habitat. Available data do not indicate that construction of Flaming Gorge Reservoir has caused a reduction in the alluvial fan constriction ratios at this site. The peak flow record immediately before and after construction of Flaming Gorge Reservoir has been very similar. Harvey, M.D., R.A. Mussetter, and E.J. Wick. 1993. A Physical Process-biological Response Model for Spawning Habitat Formation for the Endangered Colorado Squawfish. Rivers, v. 4, n. 2, p. 114 -131. A three-level, physical process-biological response model for spawning habitat formation was developed from field measurements, hydraulic modeling (IBC-2), and analysis of a known spawning bar at River Mile (RM) 16.5 in the Yampa River. Sediment deposition and bar formation occur at discharges greater than 10,000 W/s, a discharge at which downstream hydraulic controls cause backwater and reduced transport capacity of the flows. Spawning habitat is formed by bar dissection and erosion at a range of flows between 400 and 5,000 ft /s when the local hydraulic energy is greatest because of 23