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<br />nrJ~: <::"8 <br />v'.... _........v: <br /> <br />Affected Environment & Consequences <br /> <br />3-26 <br /> <br />concentration of dissolved solids in the Uncompahgre at Delta is about 1,000 to 1,300 <br />ppm (USGS, 1994), <br /> <br />Iorns (1965) estimated that the annual suspended sediment load in the Gunnison River at <br />Grand Junction was approximately 2.1 million tons during the period 1914 to 1957. <br />Using data published by the US Geological Survey (USGS) for the period 1959 through <br />1993, MEI estimated the post-Aspinall annual sediment yield to be about 1.0 million tons, <br />or 740,000 cubic yards,4 Considering the generally accepted estimate that bed material <br />load in rivers similar to the Gunnison River is about 10 percent of the total sediment load <br />(Gregory and Walling, 1973), the total annual load of the Gunnison River is about 1.1 million <br />tons, or 810,000 cubic yards. The increased loading from the Uncompahgre River <br />(15,000 to 76,000 tons/year), therefore, represents about 3 to 3.5 percent of the existing <br />total load during the initial period when the channel adjustment rate is highest, and <br />diminishes to less than one percent after 10 years of project operation. This is still far <br />less than the natural annual pre-Aspinall sediment load. Because this is such a small <br />increase compared to background sediment loads, significant aggradation in the Gunnison <br />Ri ver is not expected. <br /> <br />Wetlands within the Uncompahgre flood plain tend to filter return flows from drains and <br />agricultural land, and thereby improve local water quality. Although some land within <br />the lower terraces will be converted to stream bottom with river widening, the total <br />amount of filtering wetlands within the floodplain (after project mitigation) will remain <br />stable or increase. As such, the project should not adversely affect such filtering benefits, <br />and may improve them. <br /> <br />3.6.4 <br /> <br />Potential Effects Due to Seleium <br /> <br />Another indirect effect of reduced hydrologic regimes is the potential to increase <br />selenium concentrations in the Gunnison River downstream of the Gunnison River <br />Tunnel. The FWS has indicated that selenium is a potential problem to survival of the <br />Colorado pikeminnow,5 a federally listed endangered species. Due to the effects of <br />bioaccumulation, selenium levels in pikeminnow tissue can exceed concentrations in <br />water around them. In a briefing statement released on February 9, 1995, the FWS cited 8 <br />/-lglg6 dry weight selenium in pikeminnow muscle tissue as a biological effect threshold. <br />The same memo also cited a concentration in occupied flow of 5 /-lglg as a goal for <br />protection of aquatic life. In meetings with the Sponsors, the FWS expressed concerns <br />that reductions in-Gunnison River flows may reduce the dilution of polluted runoff <br />downstream of the North Fork confluence, thereby increasing selenium concentrations in <br />the Hartland reach upstream from Delta. <br /> <br />4 <br />S <br />6 <br /> <br />Assumes a bulk unit weight of 100 pounds per cubic foot of material. <br />Formerly referred to as the Colorado squawfish, <br />One microgram per gram (J.lglg) is equivalent to one part per billion (ppb). The J.lglg unit is used here <br />because it is used in the original source. <br /> <br />AS Lateral Hydropower Project <br /> <br />July 2000 <br /> <br />.. <br /> <br />:41 <br />1,:TI <br />{:, ;,~ <br />~,-~,"i <br /> <br />'1.~ <br /> <br />..;-:\.i,':.<i;.';}< <br />