Final Programmatic Biological Opinion for Bureau of Reclamation's

The explanation for low razorback sucker reproduction was that, currently, flows often do notreach levels high enough to inundate low-lying floodplain features where spawning takes place.The Service also reported that in the absence of high spring flows, important backwater habitatsfilled with silt and sand, tamarisk colonized sand and cobble bars, and nonnative minnows capableof preying on or competing with larval endangered fishes greatly increased in numbers.The Service's earlier flow recommendations for spring identified the magnitude and frequency of arange of minimum peak flows and the mean monthly flows capable of producing these peaks andof maintaining the natural shape of the hydrograph. Refinement of these earlier flowrecommendations for spring was based on the results of new streambed monitoring studies. Theresults of one study showed that the spring runoff in 1993, which peaked at 25,900 cfs, wascapable of moving coarse bed materials thereby winnowing accumulated fines from the channelsubstrate. Based on preliminary results from hydrologic modeling (Pitlick and Van Steeter 1994),Osmundson et al. (1995) assumed that the earlier recommended peak of 23,500 cfs would also becapable of moving bed materials. The results of another study (Pitlick et al.1996) showed that aspring runoff with a peak of about 12,900 was capable of flushing accumulated fine sedimentsfrom the bottoms of backwaters thereby restoring their depth. Based on this information, theService refined the earlier recommendations for spring peak day flows as follows:Target Peak Day Spring Flows in the 15-Mile Reach:>23,500 cfs (5 in 20 years)21,750 cfs (10 in 20 years)16,700 cfs (16 in 20 years)12,900 cfs (20 in 20 years)The Service's 1995 year-round flow recommendations are summarized in Table 2 as meanmonthly discharges. Spring (April-July) recommendations are further subdivided into 10-dayincrements and are reported in Table 3 as volumes of water needed for each of twelve 10-daytime periods. The mainstem Colorado River above the 15-Mile Reach does not have a largereservoir that controls flows. Therefore, variation in precipitation levels from year to year istaken into account and recommendations are provided for years of high, above-average,below-average, and low snow fall. With the exception of winter, recommendations are for flowsconsiderably lower than historic levels (1902-1942) but somewhat higher than recent levels.ENVIRONMENTAL BASELINERegulations provide that the environmental baseline includes the past and present impacts of allFederal, State, and private actions and other human activities in the action area; the anticipatedimpacts of all proposed Federal projects in the action area that have already undergone formalsection 7 consultation; and the impact of State or private actions contemporaneous with theconsultation process. Environmental baselines do not include the effects of the Federal actionunder review in the consultation.39