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INSTREAM FLOWS TO ASSIST THE RECOVERY OF ENDANGERED FISHES 31 (2) increase the frequency of years with peak flows in excess of 40,000 cfs from 1 in 12 years (8%, the current condition) to 1 in 4 years (25%; i.e., flushing peaks); and (3) the rest of the time (50%) maintain peak flows equal to or exceeding 22,000 cfs (mini- mal recruitment peak). Within the 15-mile reach provide peak flows as given in the Table. Problems With the Flow Recommendations of the U.S. Fish and Wildlife Service Yampa River Recommendations made for the Yampa River specify maintenance of historical flows. This recom- mendation apparently was determined solely on the rationale that natural flows would foster con- tinued spawning success by squawfish and increase the likelihood that remaining razorback sucker and humpback chub would be protected. The Yampa River is a critical habitat for the endangered fishes. Recruitment of populations in the Green River may depend on spawning sites in Yampa Canyon. Most importantly, the Yampa River is the only reasonably pristine tributary remaining in the Upper Colorado River Basin. Hence, I view it as a "control" for evaluating the success or failure of interim flows adopted in the regulated reach which will be a critical assessment to be made in the future. Therefore, I support the recommenda- tion in principle, but the historical baseline used to derive mean monthly flows seems to be incorrect. Depletions in the Yampa River currently are about 110,000 cfs (Fig. 7; Brendecke 1993), not 68,000 cfs. Also, I do not think it is appropriate to use monthly means in such analyses because daily flow vari- ation is a very important component of river ecol- ogy. The daily flow duration curve for the period of record would more accurately reflect the real base- line. Moreover, if natural seasonal and daily flow variations are vital to the fishes, then the natural diel and daily flow variation observed in the Yampa River should provide a basis for designing more benign flows in the regulated Green River. Green River Recommendations on the Green River were based on inferences from ecological studies of the endangered fish and the backwater area to dis- charge relationship determined by Pucherelli et al. (1990). The main intent of the peak flow recommendation by the U.S. Fish and Wildlife Service apparently was to add volume to the peak flows derived from the Yampa River to create an annual spring peak sufficient to flood and main- tain connectivity of the channel to backwater en- vironments and floodplain wetlands in the allu- vial reaches near Jensen and downstream. Rationale for duration and amplitude of the spring peak was not given except with regard to constraints on releases at Flaming Gorge Dam (i.e., only 4,000 cfs can be discharged through the generators, and an additional 4,000 cfs can be passed through bypass or jet tubes without open- ing flood gates). The fact that the Yampa and Green rivers historically peaked at different times was not clearly addressed, nor were the proposed ramping rates on the rising and falling limbs of the hydrograph, in either the context of the dis- charge to backwater area relationship of Pucherelli et al. (1990) or the need to establish ecologically functional wetlands on the floodplain (e.g., flooded bottomlands at Escalante Bottom). The 1992 spring flows followed the hy- drograph recommended in the Biological Opinion (Fig. 17). Rationale for fluctuation criteria during base- flow each year was not explicit. The intent appar- ently was for the Bureau of Reclamation to select a target flow between 1,800 and 1,100 cfs and not Table. Recommendations for spring flows in the 15-mile reach (from Osmundson and Kaeding 1991) Frequency Mean monthly discharge (cfs) (percent of years) Peak day April May June 25% > 23,500 > 3,900 > 12,900 > 16,300 25% 20,500-23,500 3,200-3,900 10,800-12,900 12,800-16,200 50% 14,800-20,500 2,400-3,200 8,300-10,800 10,000-12,800 • Maintain July-September flows from 700 to 1,200 cfs in normal or wet years and 600 cfs minimum in dry years within the 15-mile reach. • Maintain current (1954-1989) base (winter) and transition (October and March) flows (1,000-2,000 cfs) in the 15-mile reach