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<br />Colorado. Initially constructed in 1883, it is the oldest major <br />irrigation project in the Grand Valley and is privately owned by the <br />Grand Valley Irrigation Company. The GVIC diversion dam is an upstream <br />barrier to endangered fish movement because of the 3 to 4 feet of head <br />differential it creates at low to moderate flow conditions. This <br />difference in upstream and downstream water surface elevations <br />functions to divert water into the GVIC canal. As flows increase, the <br />head differential across the dam decreases and the structure no longer <br />creates a barrier to upstream fish passage. <br /> <br />The GVIC Diversion structure is the most downstream of three low-head <br />structures on the Upper Colorado River which precludes the passage of <br />endangered Colorado squawfish and razorback sucker into historic <br />habitat further upstream. The two other structures are the Price-Stubb <br />and Government Highline Diversion dams. Whereas the GVIC diversion is <br />only a barrier at low and moderate flows. the other two diversion <br />structures prevent passage at all flow conditions. The Recovery <br />Implementation Program has proposed fish passage at all three of these <br />diversion dams on the Upper Colorado River to allow endangered fish <br />unimpeded movement to historic stream reaches upstream. Providing <br />passage at GVIC will only extend the range of endangered fishes <br />upstream about 3 miles to Price Stubb Dam. However, providing passage <br />at both Price-Stubb and Government Highline Diversion dams will open up <br />an additional 50 miles of historic habitat upstream. <br /> <br />The U. S. Fish and Wildlife Service documented a radio-tagged adult <br />Colorado squawfish moving upstream to the GVIC Diversion Dam in mid- <br />July 1986. The fish eventually passed the structure and moyed upstream <br />to the base of the Price-Stubb Dam. This fish either moved upstream <br />over the diversion dam or could have passed around the diversion dam <br />via the Orchard Mesa Irrigation Diversion (OMID) bypass canal. Flows <br />at this time were approximately between 5,700 and 7,600 cfs over the <br />GVIC diversion dam, therefore it is suspected this fish passed around <br />the structure via the bypass canal. This fish remained until late. <br />September when it returned downstream and passed either over or around <br />(via the OMID bypass canal or through the GVIC flood gates) the <br />diversion dam. The same fish returned to the base of the GVIC <br />Diversion in late-July 1987 and progressed upstream to the base of <br />Price-Stubb Dam. It remained there until mid-September, when it again <br />made its way downstream, passing the GVIC Diversion (Osmundson and <br />Kaeding 1989). <br /> <br />The purpose of this project is to provide upstream passage for <br />endangered fishes. The structure is being designed to provide passage <br />particularly during low flows because the structure is inundated at <br />high flows (about 15,000 cfs) and fish can pass oyer the structure at <br />these high flows. The passageway will be designed to provide passage <br />during March through October with the most important biological period <br />being Hay through mid-September (FLO Engineering, Inc. 1997). Unlike <br />the fish passageway at Redlands Diversion Dam on the Gunnison River, <br />the GVIC passage structure will not have a trapping facility to allow <br /> <br />2 <br />