ColoradoBasinWaterSupplyandNeedsReport

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Section 3 Physical Environment of the Colorado Basin IJ 1111 elsewhere can impact the quality of the state's waters and aquatic habitats. Habitat degradation, nutrient loading, soil erosion, and increased stormwater runoff are only a few examples of the concerns associated with rapid urbanization, particularly in the mountain recreational areas (Colorado Department of Public Health and Environment [CDPHE] 2000). Improving water quality and restoration and protection of water bodies in Colorado is occurring through programs such as the Total Maximum Daily Load (TMDL) process, Gold Medal fisheries establishment, instream flow programs, and federal and state listed threatened, endangered, and species of special concern. 3.2 Colorado Basin Physical Environment 3.2.1 Geography The Colorado Basin, as depicted in Figure 3-2, encompasses approximately 9,830 square miles (Crifasi 2000; CGS 2003). The largest cities in the basin are Grand Junction (population 45,669) and Glenwood Springs (population 8,301) (DOLA 2002). 3.2.2 Climate Because of large changes in altitude, the climate in the basin varies dramatically from alpine conditions in the east to semiarid in the west (Benci and McKee 1977; U.S. Geological Survey [USGS] 1994). Figure 3-3 shows a contour plot of the average annual precipitation throughout the basin. Average annual precipitation ranges from less than 10 inches per year in the Grand Valley to greater than 45 inches per year in the high mountains (mainly winter and early spring snowfall) (Apodaca et al. 1996; CGS 2003). 3.2.3 Topography Elevations in the basin range from greater than 13,000 feet in the headwater areas to about 4,300 feet where the Colorado River exits the state (CGS 2003). The basin's mountainous headwaters areas gradually give way to a series of canyons and gentler terrain as the river follows the Interstate 70 corridor toward Grand Junction, the Grand Mesa, and the Utah border. CDIVI 3-2 3.2.4 Land Use Land use in the Colorado Basin (USGS 1992) is shown in Figure 3-4 and Table 3-1. A substantial portion of the basin is comprised of federally owned land. Livestock grazing, recreation, and timber harvest are the predominant uses of federal lands. Active and inactive mines can be found in the basin. Coal mining occurs in the central portion of the Roaring Fork Valley and in the lower Colorado Valley (CDPHE 2002). Rangeland and forest are the predominant land uses in the Upper Colorado Basin (about 85 percent) (USGS 1994). Forested land is present throughout many parts of the basin. Table 3.1 land Cover Data for the Colorado Basin Basinwide Statewide Forest Shrubland Grassland Planted/ Cultivated Barren 224 Open Water 114 Developed 54 Orchards/ 5 Vineyards Wetland 1 TOTAL 9,830 Source: USGS 1992 NLCD 2.3 0/0 1.20/0 0.60/0 0.050/0 1.20/0 0.60/0 0.90/0 0.000/0 0.010/0 0.080/0 3.2.5 Surface Geology The underlying bedrock in the Colorado Basin area consists predominantly of crystalline and sedimentary rocks. Alluvium, consisting of stream, landslide, terrace, and glacial deposits, is present in valleys throughout the basin (Apodaca et al. 1996). 3.2.6 Surface Water The headwaters of the mainstem of the Colorado River are within Rocky Mountain National Park in eastern Grand County. The Colorado River flows southwest approximately 230 miles through Grand, Eagle, Garfield, and Mesa Counties and exits the state at the Utah border. Tributaries of the Colorado, including the Fraser, Blue, Eagle, and Roaring Fork Rivers (Figure 3-2) also drain Summit and Pitkin Counties as well as portions of Routt, Gunnison, and Rio Blanco Counties. S:\ 1177\BASI N REPORTS\COLORADO\S3_ COLORADO .DOC