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1.0 Executive Summary <br />The Consumptive Uses and Losses Summary for the Rio Grande Basin was developed <br />for the five-year period from 1991 through 1995 as part of the Rio Grande Decision <br />Support System (RGDSS). The RGDSS project was developed jointly by the State of <br />Colorado Water Conservation Board and the Division of Water Resources. The objective <br />was to account for 100 percent of the consumptive use and losses due to human <br />influence. <br />1.1 Background <br />The Rio Grande Basin is located in south-central Colorado and encompasses <br />approximately 7,500 square miles. The Rio Grande main stem rises in the San Juan <br />Mountains in the vicinity of Creede, Colorado and flows easterly where it is joined by the <br />South Fork of the Rio Grande at South Fork, Colorado. The main stem continues <br />southeast to the San Luis Valley floor until it reaches Alamosa, where it turns south and <br />flows to the state line. Major tributaries to the Rio Grande include the Conejos River, <br />Saguache Creek, Alamosa Creek, and La Jara Creek. Most stream flow originates from <br />snowmelt in the surrounding mountains. Average annual precipitation in the valley <br />ranges from 7 inches in Alamosa to 45 inches at Wolf Creek Pass. <br />The subsurface geology of the valley is generally comprised of a shallow unconfined <br />aquifer and a deeper confined aquifer. Ground water is a significant source used to meet <br />the consumptive uses and losses in the San Luis Valley. The aquifer system is in <br />hydrologic connection with the surface water system in many areas throughout the valley. <br />Agriculture is the primary industry in the basin, with irrigation accounting for 94 percent <br />of the total water use. A combination of surface water and ground water is used to supply <br />agricultural water needs. The major crops grown in the basin are potatoes, small grains, <br />meadow grasses, and alfalfa. There are several large wildlife management areas in the <br />San Luis Valley that use both surface and ground water to irrigate crops and maintain <br />wetland habitats for water fowl. <br />1.2 Approach <br />The Consumptive Uses and Losses Summary for a basin requires both historic crop <br />consumptive use other (non-agricultural) use estimates. These uses include: <br />• Reservoir Evaporation <br />• Fish/Wildlife, and Recreational Use <br />• Agricultural Use <br />- Irrigation <br />- Stockpond evaporation <br />- Livestock Use <br />• Municipal and Industrial Use <br />RGDSScusumm.doc 1 of 11 November, 2000 <br />