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RECOMMENDATIONS Flow Recommendations Based on the review of the IHA results for the Yampa River, the RIP instream flow review (Stanford 1994) and the existing biological information in this report, the Service has reevaluated the interim flow recommendations for the Yampa River (USFWS 1990). The 1990 recommendations were based on the preservation of a natural hydrograph with base flows maintained at a constant flow (Le. 50% exceedance) measured at Oeerlodge Park. During the course of the Yampa River Alternative Feasibility study (Hydrosphere Resource Consultants 1995a), the Maybell gage was identified as the reference point for flow recommendations and the depletion set above that point was updated as shown in Table 3. Based on the modeling undertaken by the Yampa River Feasibility Study this revised depletion set was still considered to be consistent with the maintenance of. a relatively natural hyprograph. Daily, seasonal and annual variation may be the responsible factor for maintaining the abundance of native fishes in Yampa Canyon. The higher gradient in the confined channel of Yampa Canyon (Miller et al. 1982) produces greater ranges in velocity, turbulence and depth than occurs in lesser gradient channel outside the canyon where wider floodplain habitats exist which may provide refuge for nonnative fishes. The harsh environment occurring in Yampa Canyon during peak flows is most likely the reason native fishes are most abundant. Annual variation should be more favorable to native fishes the closer it resembles virgin conditions,.that is, variation and magnitude around the natural hydrograph. The maintenance of constant monthly baseflows that do not vary annually.is a significant departure from a natural hydrograph and such moderation of flows may be of greater advantage to nonnative than native fish species. The baseflows for the Yampa River should therefore correspond to its largely unregulated and undepleted hydrology in any given year. However, the constant and extreme fluctuation of baseflows, such as those resulting from hydro_electric generation, should also be avoided. The recent review of the Upper Colorado River Basin flow recommendations by Stanford (1994) supported the need for the maintenance of natural variation and expressed the need for a natural hydrograph rather than a stair-stepped recommendation based on monthly averages. That report also expressed concern with the de-stabilization of daily flows by hydropower operations on the Green and Gunnison rivers, and cautioned that the daily hydropower ramping rates should not exceed pre-regulation conditions. The recommendation was to restore naturally stable summer and winter baseflows on the Green and Gunnison rivers, which would exhibit substantial daily, seasonal, and annual variation, as now occurs on the largely unregulated Yan:tpa River. Stanford (1994) suggested that natural variation during the baseflow period could be about 5% per day. The primary tenet of the interim Fish and Wildlife Service Yampa River flow recommendations, to maintain a relatively natural hydrograph, remains unchanged. High spring flows are necessary to support biological needs (initiat~s spawning 27