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also uses stream cross-sections but collects less data and is less time consuming than IFIM, This _ report will not discuss the R2CROSS studies by the CDOW except to state that the results of that .. R2CROSS allowed the CDOW to select 7 cfs as tlj.e recommended in-stream flow for the CWCB. The CDOW has revised their recommendations for the in-stream flow based on work , by others and now recommends the stair-step minImum flow used by the CWCB i) The Miller (1992) report js a critique ofthe Chadwick (1992) IFIM analysis and the CDOW R2CROSS methods using their collected data sets and their analyses. Miller concludes that spawning habitat is the most limited habitat available and states that" there is a significant reduction in habitat for all life stages at a 4 cfs floyv from existing conditions where flows range from 7 to 12 cfs. This reduction is as much as 630/0 for both brown and brook trout spawning (and egg incubation) habitat (Table 3). The reducFions for other life stages range from approximately 12 to 48% (Tables 3 and 4)" (italic)s added), The Miller 1993 report represents an , IFIM analysis using data that his firm collected inpluding collection of data at low flows in April. Miller points out that IFIM analysis collected at flow regimes outside of the regime under consideration are not as reliable. Miller was hired by Pitkin County and the County was attempting to act as a broker in the disputes during the mid 1990's between the environmental groups, the SWSD, and the Ski Area, ii) Unlike the 1992 report, the Miller (19~3) report does not draw any conclusions but simply discusses how the data was collected, ho~ the model was calibrated and presents the output of the IFIM/PHABSIM model runs. The stream reach was divided into two approximately equal reaches, upper and lower, The Miller reports attempted to assess the effects .- of lowering the minimum flow from 12 cfs to 7 cfs due to the snowmaking proposal thus the .. time series analysis depicts trout habitat losses fr<)m 12 to 7 cfs. However, in Tables 6-10 the report provides habitat available for the different ~pecies and life stages at discharges ranging from 2 to 75 cfs. For this analysis, the lower ran~e of discharge is 4 cfs minimum flow in the SWSD and County agreement. For the existing oondition discharge, we have chosen 10 cfs, which represents the low flow in the 1 in 10-yearllow flow event at the end of December, On December 15 the flow is 11 cfs and it drops to 1q cfs by December 30; and 10 cfs also provides the flow that would be needed for the SWSD to ~xercise their full water right (6cfs) and reach the 4 cfs minimum flow, The 1 in 10-year low flow event is an acceptable event for assessment as there is 66% probability of it occurring in any;J O-year cycle. Late December represents a period of fairly high snowmaking withdrawals as weather conditions (temperature and humidity) are good and the need for artificial snow can be ~igh. The municipal diversions could be high to serve the peak Christmas season. Other comparirons of existing flows could be made but the real issue for this document is what happens wh~n the stream is lowered to 4 cfs. This only occurs at existing flows of 10 cfs or lower. i In Western Colorado, previous studies have used a 25 % habitat reduction threshold for significant habitat loss including the Green Mo~tain Reservoir Water Sales Contract EIS (Bur, of Reclamation 1988) and the Snowmass Ski Ar~a EIS (USFS 1994). In the EIS for the Ruedi Reservoir the Bureau of Reclarnation used a 100/;0 habitat loss as the significant impact threshold, In our permit decision for the Snowmass Ski Ar~a, we used the 25% threshold since the USFS had chosen that threshold and we were a Cooperllting Agency on the EIS, It should be noted that _ Mr. Jay Skinner (CDOW) states in his February e, 1992 memorandum that the minimum flows .. 6