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<br />o <br />o <br />o <br />i...) <br />Ul <br />~ <br /> <br />DR p),F T <br /> <br />While large numbers of either the Colorado squawfish or razorback sucker have <br />not been collected in the San Juan River. the historical distribution and <br />abundance of the species have never been intensively studied. The <br />construction and impoundment of Lake Powell obviously limited the movement of <br />the highly migratory squawfish. Further the development of water resources in <br />the San Juan basin. including the construction of Navajo Dam. changed. in <br />large part, the natural hydrograph that was part of the environment in which <br />native fishes evolved. <br /> <br />2,2 WATER DEVELOPMENT <br /> <br />2.2.1 Historic flows <br /> <br />Historic flows in the San. Juan River were highly variable. however flows below <br />Navajo Reservoir are now largely controlled and stabilized by Navajo Dam. <br />From Navajo Dam to Lake Powell. the river is supplemented by perennial and <br />ephemeral tributary rivers. arroyos and washes. and diverted for use by <br />industry. municipalities and agricultural irrigation. Mean annual discharge <br />of the San Juan River from 1914 to 1986 was 2.574 cubic feet/second (cfs) at <br />Bluff. Hi9h flows of 69,986 cfs and low flows of 1 cfs have been recorded at <br />the Bluff gage. In addition to moderating natural flows. hypolimnetic <br />releases from Navajo Reservoir have decreased mean annual water temperature <br />and diminished temperature fluctuations of the San Juan River downstream to <br />near the confluence of the Animas River. Overall. the San Juan River below <br />Farmington exhibits a fairly natural discharge regime. although reduced in <br />magnitude, having peak flows during spring runoff and low flow periods in <br />summer and fall. <br /> <br />2.2.2 OeveloDment and deDletions <br /> <br />There are many points of water diversion including numerous pumps on the San <br />Juan River between Navajo Dam and its confluence with Lake Powell, Downstream <br />from Farmington. water is diverted for the Farmers Mutual Ditch. Fruitland <br />Irrigation Canal. San Juan Power Plant. Jewett Valley Ditch, Four Corners <br />Power. Hogback Canal, Cudei Ditch and a few small water users. A small amount <br /> <br />7 <br />