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BLM "" Bureau of Land Management DOW == Division of Wildlife (I) Predicted flow outside ofthe accuracy range of Manning's Equation. ? = Criteria never met in R2CROSS Staging Table. Biologic Flow Recommendation The summer flow recommendation, which meets 3 of 3 criteria and is within the accuracy range of the R2CROSS model is 7.3 cfs (See Table I). This recommendation was derived by averaging the results of the two data sets. The winter flow recommendation, which meets 2 of 3 criteria and is within the accuracy range of the R2CROSS model is 5.3 cfs (See Table I). It is our belief 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. Hydrologic Data After receiving the cooperating agency's biologic recommendation, the CWCB and BLM staff, conducted an evaluation of the stream hydrology to determine if water was physically available for an instream flow appropriation. Although there is a substantial amount of streamflow gage data available for the Uncompahgre Plateau and Glade Park, most of this data is severely impacted by diversions and irrigation use. This situation makes it difficult to estimate the natural flow regime for the watersheds on the Plateau. Without specific gage data to evaluate, the next best approach is a regional equation that estimates annual flow characteristics. The USGS has developed regional equations (Estimation of Natural Streamflow Characteristics in Western Colorado. Water Resources Investigations Reoort 85-4086. 1985) that apply to the Uncompahgre Plateau and Glade Park based on basin drainage area, mean annual precipitation, mean basin elevation and mean basin slope. The report "Uncompahgre Plateau and Glade Park Annual Hydrograph Estimation" in Appendix C, explains staff's water availability analysis in more detaiL Table 2 below displays the estimated stream flow of Dry Creek. For this reach, the synthetic hydrograph shows that the summer flow recommendation of 7.3 cfs is available only from April I to June 30. The summer flow recommendation was reduced to 3.0 cfs for the time period of July I through July 31 based on limited water availability. The winter flow recommendation of 5.3 cfs is not available at least 50% of the time. The winter flow recommendation was reduced to 1.2 cfs for the period of August I to February 28, and to 3.0 cfs from March I to March 31 based on limited water availability. Table 2: Estimated Stream Flow on Dry Creek: Jan Feb Mar Apr (cts) 1.2 2.6 3.8 57.3 May 208.9 Jun 95.8 JuJ 4.9 Aug 1.9 Sep 1.6 Oet 1.5 Nav 1.4 Dee 1.3 - 4- r- ~