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<br />Section 3 <br />Physical Environment of the Colorado Basin <br /> <br />3.2.8 Water Quality <br /> <br />Upper Colorado River watershed water quality issues <br />largely are related to impacts due to growth, mining, and <br />the protection of threatened and endangered fish <br />species. Growth related water quality issues are <br />becoming increasingly important as the population <br />continues to grow at rates among the highest in <br />Colorado. Sediment and nutrient loading to streams in <br />the watershed have the potential to create significant <br />water quality problems. These loadings are caused <br />primarily by runoff from construction activities at new <br /> <br />Table 3.2 Summary of Selected USGS Stream Gages for the Colorado Basin <br /> <br />The Colorado River accounts for approximately <br />44 percent of the streamflow leaving the state (Colorado <br />State Engineer's Office [SEO] 2003). Interstate compacts <br />with other Colorado basin states limit development of the <br />basin yield. Between 450,000 and 600,000 AF is diverted <br />to Eastern Colorado annually. <br /> <br />Numerous USGS streamflow gages are maintained in <br />the Colorado Basin. Six of these gages were selected to <br />summarize historic flows in the basin across a broad <br />spatial scale. The locations of these gages are shown on <br />Figure 3-5 along with the location of major diversions and <br />segments with decreed instream flow rights in the basin. <br />Table 3-2 summarizes the mean annual streamflow, <br />period of record, and drainage area for each gage. As <br />the table indicates, an average of about 4.5 million AF of <br />water leaves the state annually via the Colorado River at <br />the state line. <br /> <br />3.2.7 Groundwater <br /> <br />Most of the water used within the Colorado Basin comes <br />from surface water sources. Annual groundwater <br />withdrawal data from 1995 indicate groundwater use by <br />the counties encompassing the river basin varies from <br />less than 1 percent in Grand and Mesa Counties to a <br />maximum of 9 percent in Summit County (Solley et al. <br />1998). Because of the shallow well depths and water <br />levels, alluvial groundwater is readily developed in rural <br />areas for agricultural and domestic purposes. Aquifers <br />located within the Colorado Basin are as follows <br />(CGS 2003): <br /> <br />. Alluvial Aquifer <br />. Piceance Basin <br />. Eagle Basin <br />. Dakota-Cheyenne <br />. Middle Park Basin <br /> <br /> <br />USGS Site <br />Number <br /> <br />Mean Annual <br />Streamflow <br />(AFY) <br /> <br />Blue River below Green Mountain 09057500 <br />Reservoir <br />Eagle River below Gypsum 09070000 <br />Roaring Fork at Glenwood Springs 09085000 <br />Plateau Creek near Cameo 09105000 <br />Colorado River near Kremmling 09058000 <br />I Colorado River near State Line 09163500 <br /> <br />Source: USGS NWIS web/Hydro Base database <br /> <br />S:\1177\BASIN REPORTS\COLORADO\S3_COLORADO.DOC <br /> <br />Figure 3-6 presents the aquifers broken down into two <br />groups: alluvial and bedrock (Piceance Basin, Eagle <br />Basin, Dakota-Cheyenne, and Middle Park Basin). The <br />distribution of alluvial deposits in the Colorado Basin <br />varies greatly from one reach to the next. The alluvial <br />deposits, as mapped by USGS geologic quadrangle <br />maps, are primarily located near the Towns of Eagle and <br />Gypsum, along the Roaring Fork River, Roan Creek, and <br />from the Town of Palisade to the Colorado-Utah state <br />line. Alluvium is very limited or non-existent in the canyon <br />sections of the Colorado River where the bedrock is <br />exposed (CGS 2003). The saturated thickness of the <br />alluvium in the basin is represented by the interval from <br />the water table to the underlying bedrock. Welder (1987) <br />reported that test holes in the alluvium of Roan and <br />Parachute Creeks penetrated 80 feet and 70 feet, <br />respectively, of saturated permeable sand and gravel. <br />For the Fraser River, Apodaca and Bails (1999) report <br />alluvial saturated thickness ranging from 14 to 45 feet, <br />averaging 21 feet in the spring, and ranging from 7 to <br />20 feet in the fall with an average of 15 feet. Private wells <br />used for domestic and agricultural irrigation uses are <br />common throughout the watershed (Colorado <br />Groundwater Association 1999). Major production wells <br />(those with rights that exceed 500 gpm) are also shown <br />in Figure 3-6. <br /> <br />Mean Annual <br />Streamflow <br />( cfs ) <br /> <br />Period of <br />Record (Years) <br /> <br /> <br />328,785 454 1942-2002 <br />412,586 570 1946-2002 944 <br />877,836 1,213 1906-2002 1 ,451 <br />128,999 178 1936-2002 592 <br />733,654 1,013 1962-2002 2,382 <br />4,555,526 6,292 1913-2002 17,843 <br /> CDIVI <br /> 3-3 <br />