Stream: Willow Creek Executive Summary

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Biological Data This segment of Willow Creek is a moderate gradient stream, with moderate to large substrate size, punctuated by large boulders. The proposed reach is confined by a canyon, and some portions of the creek are further confined by the construction and maintenance of a county road. The riparian community is in good condition and composed of willow, alders, and cottonwood. The creek supports a good diversity and biomass of aquatic macroinvertebrates, including mayfly, caddisfly, and stonefly. The creek provides a good mix of pools, riffles, and runs for fish habitat, and some of the deeper pools are critical for year -round survival of the fish population. The fish population appears to change in response to hydrologic conditions. Historical surveys have documented speckled dace in the creek system. Recent surveys have documented white suckers. It is likely that the creek is repopulated from stocks in Blue Mesa Reservoir after dry periods. There are also numerous wildlife species that depend on the creek. There have been numerous sightings of chorus frog and salamanders. In addition, bird inventories have documented Audubon's warbler, yellow warbler, Wilson's warbler, green towhee, warbling vireo, broad - tailed hummingbird, red- tailed hawk, common nighthawk, and brown -head cowbird. Finally, the riparian habitat along the creek is considered critical brood - rearing habitat for the Gunnison sage grouse, because the stream is close to leks (display areas) and nesting areas in adjacent uplands. Field Survey Data BLM staff used the R2Cross methodology to quantify the amount of water required to preserve the natural environment to a reasonable degree. The R2Cross method requires that stream discharge and channel profile data be collected in a riffle stream habitat type. Riffles are most easily visualized, as the stream habitat types that would dry up first should streamflow cease. This type of hydraulic data collection consists of setting up a transect, surveying the stream channel geometry, and measuring the stream discharge. Biological Flow Recommendation The CWCB staff relied upon the biological expertise of the cooperating agencies to interpret output from the R2Cross data collected to develop the initial, biologic instream flow recommendation. This initial recommendation is designed to address the unique biologic requirements of each stream without regard to water availability. Three instream flow hydraulic parameters, average depth, percent wetted perimeter, and average velocity are used to develop biologic instream flow recommendations. The CDOW has determined that maintaining these three hydraulic parameters at adequate levels across riffle habitat types, aquatic habitat in pools and runs will also be maintained for most life stages of fish and aquatic invertebrates (Nehring 1979; Espegren 1996). For this segment of stream, four data sets were collected with the results shown in Table 1 below. Table 1 shows who collected the data (Party), the date the data was collected (Date), the measured discharge at the time of the survey (Q), the accuracy range of the predicted flows based on Manning's Equation (240% and 40% of Q), the summer flow recommendation based on meeting 3 of 3 hydraulic criteria and the winter flow recommendation based upon 2 of 3 hydraulic criteria. It is believed that recommendations that fall outside of the accuracy range of -3-