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3. On a mesoscale level, the maximum shear stress at the cross sections between the bend (XS 5) and the base of the upstream riffle (XS 10) occurs in the right chute channel because of scour along the base of the rock outcrop and this provides the pool that meets the resting- staging phase of spawning. The riffle/tertiary bar provides the location for the deposition- fertUization stage. 4. The reported presence of large numbers of ripe and tuberculated squawfish at this site at a discharge of about 600 cfs can be correlated to the results of the hydraulic analyses which indicate that the riffle/tertiary bar that is most likely to be utUized for spawning meets the microscale requirement for incipient motion conditions at a discharge of about 600 cfs. 5. Although the data are stUllimited it appears that there may be a reasonable correlation between the observed locations of squawfish in the lower Yampa Canyon and the physical conditions at the spawning bars during the spawning period. Combined fish capture and hydraulic data indicate that different locations around the same bar are utUized at different discharges as well as different bars. For example, at a discharge of 1200 cfs two of the three identified tertiary bars at the RM 16.5 spawning bar met the PRM requirements and fish captures were reported at these locations. Hydraulic analysis indicated that the third tertiary bar would meet the PRM requirements at a discharge of about 600 cfs and fish captures were reported at this location in,. J 992. The hydraulic data indicate that the Mathers Hole bar should meet the PRM requirements at the range of discharges when fish captures were reported in 1992. 6. The physical conditions that determine the hydraulic controls at the three known spawning bars in the lower Yampa Canyon are dissimilar. However, this range of physical settings produces very similar hydraulic, sedimentologic, and geomorphic responses that meet the basic requirements of the PRM. Within the limits of the avaUable data it appears that the PRM provides a means of physically identifying other potential Colorado squawfish spawning sites. 7. Water chemistry data within the lower Yampa Canyon are extremely limited, but a preliminary analysis of conductivity data collected by the USFWS in 1981 indicates that there may be differences in water chemistry at the known spawning sites and these may be related to either chemoreceptive imprinting or spawning cues. The reasons for the different chemistry may be local tributary contribution of carbonates or gypsum derived from erosion of the Park City or Moenkopi Formations during eariy summer thunderstorms, and or geologic structure control of groundwater. 8. Resurveys of previously established cross sections at C1eopatras Couch, and resampling of bar sediments at the same locations as in 1991, suggest that rejuvenation of the spawning bar, as expressed by deposition of finer sediments, occurred at a discharge of about 17,600 cfs. Topographic data did not indicate that significant change had occurred on the bar between 1991 and 1993. The sediment data suggest that moderate size flood events can counteract the sediment coarsening and chute channel widening trends that are responsible for loss of spawning habitat. However, without further investigation of sediment supply, storage and subsequent remobilization in reaches upstream of the backwater-affected spawning bars, it is not possible to define a lower limit for effective floods. 4.2 Resource Consultants & Engineers, Inc.