Arkansas Basin_Water Supply and Needs

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Section 3 Physical Environment of the Arkansas Basin IJIII Range, and agriculture in the eastern plains and 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 Arkansas Basin Physical Environment 3.2.1 Geography The Arkansas Basin is spatially the largest river basin in Colorado covering an area of 28,268 square miles, or 27 percent of the surface area of the state (Wolfe 2003, CDPHE 2000). It comprises the southeast portion of the state, as shown in Figure 3-2. The largest cities in the basin are Colorado Springs (population 373,328) and Pueblo (population 103,846) (DOLA 2003). 3.2.2 Climate The climate in the Arkansas Basin is characterized by a high degree of variability with average daily temperatures ranging from 46 degrees Fahrenheit (OF) in the upper river valley to 550F in the lower valley (Smith and Hill 2000). Temperature extremes in the lower valley can range from OOF in the winter to 1 OooF in the summer (Abbott 1985). Precipitation also varies greatly within the basin. Figure 3-3 shows a contour plot of the average annual precipitation throughout the basin. Basinwide average annual precipitation ranges from less than 10 inches per year in the plains to over 30 inches per year in the high mountain regions. 3.2.3 Topography Steep slopes characterize the western part of the Arkansas Basin, while relatively flat plains characterize the eastern portion. The headwaters of the Arkansas River begin near Leadville at an elevation of more than 14,000 feet and drop to 3,340 feet at the Colorado and CDIVI 3-2 Kansas state line, representing a more than 10,000-foot change (CGS 2003). 3.2.4 Land Use Land use in the Arkansas Basin (U.S. Geological Survey [USGS] 1992) is shown in Figure 3-4 and summarized in Table 3-1. Grassland and forest are the predominant land use types in the basin covering approximately 67 percent and 13 percent of the basin, respectively. The grassland areas are concentrated in the central portion of the basin whereas the forested land is located on the western portions of the basin. Table 3.1 land Cover Data for the Arkansas Basin Basinwide Statewide Grassland Forest Planted/ Cultivated Shrubland Developed Barren Open Water Wetland TOTAL 28,268 Source: USGS 1992 NLCD 8.60/0 0.80/0 0.80/0 0.30/0 0.040/0 16,883 923 1,219 590 80 104,060 16.20/0 0.90/0 1.20/0 0.60/0 0.080/0 3.2.5 Surface Geology Geology ranging from Precambrian to Quaternary age is exposed in the Arkansas Basin. In the mountain province, Precambrian metamorphic schists and gneisses intruded by igneous rocks abound. The plains province is dominated by multiple layers of sedimentary rocks, and Quaternary alluvium fills the reaches along the lower Arkansas River. 3.2.6 Surface Water The perennial streams comprising the headwaters of the Arkansas River are supplied by the snowpack of the mountains surrounding the area of Leadville, Colorado (Abbott 1985). The Arkansas River flows out of the mountains, through the deep canyons near Canon City, and across the plains until it leaves the state and enters Kansas just east of Holly, Colorado. Along its journey to Kansas, several major tributaries enter the river. A map of the basin showing the Arkansas River and its major tributaries is provided in Figure 3-2. o :\SHAWN\ARKANSAS\S3 _ARKANSAS. DOC