Eagle River Inventory and Assessment (2)

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A comparison of instream flow rights with average monthly flows along the Eagle River main stem indicated that (in most locations) the instream flow rights were set more than one standard deviation below the average flow computed from post-transbasin diversion gage records for September to October and February to March. At the Gypsum and Minturn gages, it appears that instream flows are set at levels that are more than two standard deviations below recorded average flows. Thus, these rights are met the vast majority of the time, especially in the case of winter flows. Given the current administrative structure, instream flow rights generate a "call" on the Eagle River main stem when (1) flow is more than a standard deviation below average post-diversion conditions, (2) departures from instream flow levels are being monitored and reported to CWCB, (3) CWCB makes a "call" on the river, and (4) the call halts diversions that are junior to the priority date of the instream flow right. A call by the CWCB to protect an instream flow water right in the Eagle River rarely occurs. Instream flow rights are protected in changes of water rights and plans for augmentation. An organized local effort to monitor instream flows in the Eagle River watershed does not currently exist. The state instream flow monitoring program is small (one person for the entire state) and suffers from lack of resources. Most instream flow recommendations in Colorado are based on the R2CROSS methodology. Current CWCB implementation of the R2CROSS methodology seeks to satisfy three established hydraulic criteria in the summer, and two of the same three criteria in the winter based on field discharge measurement at 40- 250% of the recommended instream flow. We reviewed the original field forms describing the R2CROSS analysis used to determine minimum flow recommendations. The results of this analysis for the Eagle River main stem are summarized in Table ES.I. Table ES.1: Summary of results of reviewing instream flow field forms for the Eagle River main stem. Discharge Discharge CDOW Rec. Igo. of Meeting Meeting ISF for May- Final ISF Right Segment of eagle River Segment Transacts ~Jse~ Three Habitat Two Habitat Sept. /Oct.- for May-Sept. / Main Stem Lem th to Set ISF Criteria Criteria Aril Oct.-A ril Nfotes Homestake Creek to Cross 6 miles 1 82-85 cfs 20 cfs 25111 cfs 25/11 cfs ISF outside range of 0.4-2.SQ Creek measured, Meets one of three criteria in winter and two of three criteria in summer Cross Creek to Gore Creek 4 miles 1 290 cfs 87-107 cfs 50120 cfs SO120 cfs ISF outside range of 0.4-2.SQ measured, Meets one of three criteria in winter and one of three criteria in summer Gore Creek to Lake Creek 10.1 miles no survey ? ? 85145 cfs 85135 cfs No survey located, winter flow available reduced from recommended 45 cfs to 35 cfs Lake Creek to Brush Creek 20 miles 1 226 cfs 130 cfs 130/50 cfs 110/45 cfs Recommended summer /winter flow of 130/50 reduced to 110145 cfs, Decreed right meets one of three criteria in winter and one of three criteria in summer, Assumed Mannin n value Brush Creek to Colorado 12.8 miles 1 135 cfs 92-108 cfs 130/50 cfs 130/50 cfs Top width = 100 ft yet average top River width of 7 bankfull sections measured at Gypsum SWA = 252 ft, Meets one of three criteria in winter and two of three criteria in summer CDOW -Colorado Division of Wildlife; ISF -instream flow; cfs -cubic feet per second; Q-discharge; SWA -State Wildlife Area; ft -- feet Although the Eagle River exhibits substantial variability in morphology and hydraulic geometry, the length of river represented by a single transact (cross section) ranges from 4 to 20 miles. Excluding the Gore to Lake Creek segment (for which field records were not obtained), instream flow recommendations for the remaining 43 miles of the Eagle River main stem between Homestake Creek to Dotsero were based on measurements at 4 locations using the single-transact R2CROSS method. Two of eight instream flow quantities decreed for reviewed segments of the Eagle main stem meet recommended habitat criteria. According to a study that is widely regarded as providing the scientific basis for R2CROSS, the single- transect R2CROSS method used on the Eagle River main stem was to provide rapid and repeatable estimates Eagle River Inventory and Assessment ES-6