Eagle River Inventory and Assessment

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to 1986. We analyzed data from USGS flow gages in stream and river segments with decreed instream flow rights to (1) examine the frequency of flows below the instream flow rights, and (2) compare the instream flow rights to the average and deviation of actual flows at different times of year. Of 6~ s~~m~n~s i~ ~h~ Ea~l~ ~iv~r w~~~rsh~d with i~str~am £~ow r~~~ts, 47 ar~ u~~a~~d, a~d ~h~ ~~pnaini~~ s~~m~n~s ~av~ ~nstr~am flows ~~a~ ~r~ ~ot ~~t at wi~~ly vary~n~ f~~qu~r~c~~s. Nine of the 19 segments that have been gaged for at least 10 years have instream flow rights that have not been met at least one time per year in each year of the record since appropriation. 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 ~ow field forms for the Eagle River main stem. Dis~har~~ Discfl~arge CDOW Rec. l~oo ~f 1VI~~tin~ Meeting ~SF for IVIay- Firnal ~SF IZight Se~~ent o~ ~a~le River Se~ment Trams~cts ~1s~~ ~'fl~ree Ha~itat Two Habitat Sept, I Oct.- ~or May-Se~t. I Main S~en~ Let~ ~h to Set ISF Criteria Criteria A ril Oc~.-A r~l l~o~es Homestake Creek to Cross 6 miles 1 82-85 cfs 20 cfs 2S111 cfs 2S111 cfs ISF outside range of 0.4-2.5Q 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 50I20 cfs 50I20 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 101 miles no survey ? ? 8S145 cfs 8S135 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 c~s 110145 cfs Recommended summer 1 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 Manlun n value Brush Creek to Colorado 12.8 miles 1 135 cfs 92-108 cfs 130150 cfs 130150 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 vi Eagle River Inventory and Assessment