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<br />I <br />I <br />-I <br />I <br />I' <br />I <br />I <br />I' <br />I.' <br />I <br />I <br />I: <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Alamosa River Watershed Project <br />Literature and Watershed Assessment <br /> <br />The Rio Grande Basin and Alamosa River Watershed <br /> <br />3.0 Introduction <br /> <br />To understand the Alamosa River Watershed it important to understand the large <br />drainage basin that contains it, the Rio Grande River Basin. The hydrologic basin <br />characteristics reflect many of the same characteristics of the watershed in terms of <br />climate, ecosystems, geology and soil characteristics. <br /> <br />The characteristics of the watershed are based upon numerous physical, chemical and <br />biological parameters that ultimately affect the water resources and production of the <br />land. This section provides an overview of the watershed in terms of basic watershed <br />parameters. <br /> <br />3.1 Rio Grande Basin <br /> <br />The Alamosa River Watershed is located within the Rio Grande Basin that comprises <br />over 7,500 square miles with elevations ranging from 7,400 to 14,000 feet. The Rio <br />Grande River is the fifth largest river in the North America. It supplies critical drinking <br />and irrigation water to major urban and rural areas in Colorado, New Mexico, Texas and <br />Mexico. The principal tributaries to the Rio Grande River in Colorado are the Conejos <br />River and the Alamosa River. The total number of stream miles in the basin is 6,875 <br />miles. Eighty-one lakes/reservoirs comprise over 5,427 acres. Less than 2 percent of <br />Colorado's population (43,000 people) live in the basin (5). <br /> <br />The San Juan Mountains form the western boundary of the basin with the Sangre de <br />Cristo Mountains forming the eastern portion. The San Luis Valley is one of the world's <br />largest high elevation alpine valleys; the valley floor receives only 7-8 inches of <br />precipitation annually, while the headwaters regions of the Rio Grande receive more <br />than 50 inches of precipitation annually. <br /> <br />Groundwater studies have been performed in the San Luis Valley (within the Rio Grande <br />Basin) to assess impacts of agricultural chemicals on groundwater. The unconfined <br />aquifer is a source of water for both agriculture and domestic drinking water. In 1993, 93 <br />wells were sampled from May to August. Thirteen wells contained nitrate levels greater <br />than the drinking water limit (10 mg/L); three pesticides were detected (2,4-D, <br />hexazinone and lindane). Lindane was detected above EPA's Maximum Concentration <br />Level of 0.2 ug/L. The USGS has initiated a groundwater quality study under the <br />NAWQA Program of 35 wells in the basin. The results of the study are due sometime in <br />2003 (5). <br /> <br />Land ownership in the basin is a mix of state, federal and private holdings. The majority <br />of the basin is privately owned and used for agricultural purposes. Federal land holdings <br /> <br />3-1 <br />