Stream: Cebolla Creek (Lower Segement) Executive Summary

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Biological Data This segment of Cebolla Creek is a moderate to high gradient stream, with large substrate size. Boulders ranging from one to three feet in diameter in the stream channel are common. Throughout much of the reach, the creek is confined to a narrow canyon. The riparian community is in good condition, but is occasionally impacted by the close proximity of the county road in the canyon. The riparian community is similar to the upper reach, but the willow component of the community is less prominent. The combination of large woody debris and frequent large boulders in the creek channel provide good pool habitat for velocity cover and overwintering. In this reach, riffle habitat appears to be more limited, but it does not appear to be affecting the success of the fish population. Fishery surveys indicate that the creek supports a self - sustaining population of brown trout. The survey revealed a variety of age classes and individual specimens up to 14 inches in length. The Colorado Division of Wildlife has implemented trout habitat improvement projects within this reach. 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, three 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 the model, over 250% of the measured discharge or under 40% of the measured discharge may not give an accurate estimate of the necessary instream flow required. Table 1: Data Party Date Q 250 % -40% Summer 3/3 Winter (2/3) BLM 10/8/2008 39.80 99.5-15.9 31.73 Out of range BLM 10/8/2008 41.85 104.6-16.7 28.72 Out of range -3-