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RESOUll.CE USE For FISH HABITAT Description of Area: Virltin Valley Subevaluation Unit, Arizona, Nevada, Utah Water quality (Virgin River) Future Conditions Plaunin Alternatives Present Future Unit Conditions Without 1 2 rating!.! 2 2 2 2 See Nevada Department of Fish and Game letter which follows. 3 3 3 3 Parameters Rare or endangered species 1/ Summary rating Impact on Threatened and Endanltered Species No measurable impact on woundfin, round tail chub and spinedace is based on minor changes in flow and salinity of surface water of the Virgin River. These changes are slight when compared to variations in flow and salinity occurring with present, and future without program conditions. Alternative 1 total annual surface flow at Riverside, Nevada is estimated to increase from 192,600 acre-feet to 195,600 acre-feet. This increase of 3,000 acre-feet is a two percent increase in total flow volume or about four cubic-feet-per-second increase in daily flow. However, most of the increased flow will occur during the irrigation season, March through November. Alternative 2 surface flow at Riverside, Nevada is estimated to increase from 192,600 acre-feet to 201,700 acre-feet. This increase of five percent is about 12.5 cubic-feet-per-second increase in the daily flow. The Setting section of the text describes water quality and variations with flow. Flows and salinity concen~rations vary considerably between Little- field, Arizona and Riverside, Nevada. Littlefield, Arizona October 20, 1978 - 83 cfs, 2,610 mg/l May 20, 1979 - 1,570 cfs 460 mg/1 Riverside, Nevsda October 10, 1978 - 10 cfs, 3,770 mg/l May 21, 1979 - 1,310 cfs, 580 mg/l ~/ The rating scale is from I to 5: I, unsuited; 2, poor; 3, fair or neutral; 4, good; and 5, excellent. A-13 OUCJ34