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Effects of Direct Withdrawal from the Colorado River: Impingement/Entraitvnent of fish at intake Remnant populations of Colorado pikeminnow and razorback sucker between Rifle and Palisade were cited in BLM's Programmatic Biological Assessment for Minor Water Depletions in 1994, though, according to various people involved with the Colorado River recovery program, it seems probable that no fish and certainly no reproduction is occurring in the stretch of river between Rifle and the mouth of DeBeque Canyon at present. However, in recent conversations with Tom Nesler (CDOW) and Terry Ireland, we have learned that the Rifle to Palisade teach is slated for razorback and pikeminnow recovery activities (stocking) this yeaz or next. Two size classes aze to be released (4-6" and 10-12"), with an objective of building an adult population as rapidly as possible. With recovery activities imminent, particulazly those that involve subadult fish with a presumed future goal of reestablishing reproducing populations, we consider it appropriate to discuss possible direct impacts to razorback and piketninnow forms that may inhabit this reach in the neaz future. The ultimate effect of this intake structure on these fish depends on fish size, the future reproductive activity of ftsh, where such spawning activity occurs relative to the intake, and when water is to be taken from the river. We have little information with which to assess the potential for entrainment of free- swimming fish at this intake, but based on the information presented below, fmd no reasonable likelihood of impingement. Based on a maximum pumping capacity of 2100 gallons per minute (2 pumps rated at 1050 gpm) under static conditions, we calculated an average inflow velocity of 0.19 fps at the mouth of the 48-inch diameter standpipes and 0.013 fps on the perimeter of the screens. USGS Water Resources provided us with mid-channel velocities measured during relatively low flow periods (about 2200 cfs Q Colorado River at DeBeque, about 11 river miles downstream of intake) of about 3.5 fps. This information seems to indicate that water entering the intake would exert little draw for lateral impingement against stronger river flows parallelling the trash racks. The 2-inch by 6-inch screen openings comprising the trash racks may not prevent smaller stocked fish from entering the crib and entering the mouths of the standpipes. Although we aze not familiaz with the behavior of subadult pikeminnow or razorback in seeking cover, we would expect that even if entering a standpipe mouth, they would not only remain capable of overcoming intake velocities, but would not be prone to progress the 100 yazds or so through the horizontal section of pipe beneath the river bed. Once adult populations aze established in this stretch of river, the potential for smaller subadult forms being exposed to this structure in the future may be less likely. Tyus and Karp ("Habitat Use and Streamflow Needs of Rare and Endangered Fishes, Yampa River, Colorado", USFWS Biological Report 89(14)) found that upper reaches of the Yampa • and Green rivets aze generally occupied by adult and, to a lesser extent, lazger juvenile fish. If this trend were to follow on the Colorado, the upper 17 miles of historically occupied habitat