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<br /> <br />Section 3 <br />Physical Environment of the Dolores/ <br />San Juan/San Miguel Basin <br /> <br />3.1 Statewide Overview <br /> <br />Evaluations conducted under SWSI followed CWCB's <br />delineations of Colorado's eight major river basins, as <br />shown in Figure 3-1. The basins include the Arkansas, <br />Colorado, Dolores/San Juan/San Miguel, Gunnison, <br />North Platte, Rio Grande, South Platte, and Yampa/ <br />White/Green Basins. The purpose of this section is to <br />provide a description of the Dolores/San Juan/San <br />Miguel Basin that includes: <br /> <br />. Geography <br />. Climate <br />. Topography <br />. Land Use <br />. Surface Geology <br />. Surface Water <br />. Groundwater <br />. Water Quality <br />. Areas of Environmental Concern, Special Attention <br />Areas, and Threatened and Endangered Species <br />. Energy and Mineral Resources <br /> <br /> <br />Figure 3-1 <br />Colorado's Eight Major River Basins <br /> <br />Virtually all of these topics are interconnected or affect <br />the state's water supplies and water quality - either <br />through natural or man-made/induced factors. The <br />topography of the Continental Divide, the backbone of <br /> <br />S:\1177\Basin Reports\DSJSM\S3_DSJSM.doc <br /> <br />Colorado's Rocky Mountains, dictates the direction of <br />water flow either to the west or to the east for each of the <br />river systems in the state. The Divide is also home to the <br />headwaters of several major rivers and their tributaries <br />that run throughout Colorado, including the Colorado. <br /> <br />In contrast, over half of Colorado's land area and <br />85 percent of the state's population lies in the South <br />Platte and Arkansas Basins, which contribute only about <br />5 percent of the flows leaving the state. These two river <br />systems travel from the east side of the Continental <br />Divide to the Mississippi River and ultimately the Gulf of <br />Mexico. <br /> <br />Groundwater resources also playa pivotal role in <br />meeting Colorado's water needs. In 1995, groundwater <br />withdrawals in Colorado were slightly more than <br />2.5 million acre-feet (AF), with agricultural users <br />comprising about 90 percent of this amount. Overall, <br />groundwater withdrawals by agricultural and M&I users in <br />1995 represented slightly more than 20 percent of the <br />state's total for these uses, with the remainder coming <br />from surface water supplies. The median value for <br />groundwater use as a percentage of total use for all <br />counties in the state is 9 percent, with agricultural areas <br />in the eastern plains and in the San Luis Valley in south <br />central Colorado relying more substantially on <br />groundwater over surface water sources (Colorado <br />Geological Survey [CGS] 2003). <br /> <br />The state's unique topography and climate are clearly <br />intertwined with its water resources. Topography is an <br />important component of water resources planning, in that <br />it dictates the direction of natural flows within a <br />watershed. Much of the state's precipitation is <br />concentrated on its mountainous and western slope <br />areas. Snowpack in the state's alpine headwaters areas <br />provides the vast majority of water supplies, with spring <br />runoff causing significant flow peaking in virtually all of <br />the state's river systems. Groundwater storage and its <br />recharge are also largely affected by the topography and <br />climatological patterns that characterize the state. <br /> <br />Water quality can be affected by geography and various <br />land uses including runoff from point and non-point <br /> <br />a <br />DEPAIUMENT OF <br />NATURAL <br />RESOURCES <br /> <br />. i~"" l.~V.~/,#& <br /> <br />~.. ~~, <br />-q <br /> <br /> <br />· (~,'r .. <br /> <br />CDIVI <br /> <br />3-1 <br />