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and velocity measurements were not taken at high flows during the study, impressions of biologists experienced with the Upper Colorado River Basin were that the hydrology over the diversion structure was less extreme than that of many natural or manmade features found within the migrational range of the Colorado squawfish. Easy downstream navigation of the structure in a motorized Jon boat during Trip 1 and 2 was reflective of the hydrology. Depth and velocity measurements taken in various features of the structure during low flows indicate that these parameters were suitable for passage of fish in either direction over the structure. Radiotagged Colorado squawflSh have been observed utilizing velocities of up to 1.93 mls in the Colorado River and velocities in suspected egg depositional areas for Colorado squawflSh in the Green and the Yampa Rivers have been measured as high as 1.49 mls (Valdez et al. 1987). Average velocities measured in the structure during low flows of 1.4 mls appear to be well within a suitable range for the species. Depths measured in the structure are also within the range utilized by the species. BIOIWEST's measurements of depth and velocities associated with the grade control structures were within the range of those projected for the structure by FLO Engineering Inc (Pers. Comm., J. O'Brien, FLO Engineering). Based on results of HEC-2 analysis, at a flow of 200 cfs, mean velocity through the structure was estimated at 1.22 mls. Mean velocities though the structure (measurement locations 1,3 and 5) measured by BIOIWEST were 1.5 mls. The water velocity at the base of the vertical overfall was estimated at 2.13 mls for a flow of 200 cfs. This compares to a mean velocity of 2.23 mls measured by BIOIWEST (measurement locations 2,4 and 6 on Figure 2). Depth measured in the center of the fISh passage notch was 0.43 meters as compared to 0.6 meters projected by FLO. It must be noted again that flow used by BIOIWEST for this study was based on gaging information taken from the USGS gage at near Craig, Colorado and does not reflect the true discharge through the structure at the time of the measurements. Additionally, assumptions made by FLO Engineering in the formulation of projected depth and velocities regarding flow configurations through the structure and design conditions need to be considered for a detailed evaluation of real versus projected parameters in the structure. BIOIWEST presents this information only for the purpose of indicating that the structure appears to be reasonably conforming to projected performance. BIOIWEST believes that the overall design and construction of the City of Craig's Yampa River control structure is suitable to provide unimpeded fish passage at all flows observed during this study. It is speculated that at times when flows in the Yampa River reach a critical low, fish passage is likely to be inhibited by numerous natural features, i.e. "critical riffles", and several manmade features below Craig. The impact of the Craig diversion on overall movement of large migratory fISh, although possibly significant on a local level, would not likely significantly affect movement system wide. Since the structure is designed to concentrate or funnel all the flow through a narrow opening, it is speculated that fish passage would be easier though the structure than through other natural barriers created by shallow cobble bars within the study area. Velocities through the fish passage notch are projected to decrease at lower flows. Documentation of fish movement over the structure at velocities associated with higher flows suggests that velocities through the structure at lower flows would not prevent fish passage. Two other diversion structures on the Yampa River were visited by BIOIWEST biologists for purposes of comparison. These included a temporary dike structure located approximately 5 miles upstream of Craig, Colorado and a larger, semi-permanent rock control structure located at the head 26