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Last modified
8/16/2009 4:17:36 PM
Creation date
6/15/2007 2:48:06 PM
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Basin Roundtables
Basin Roundtable
Rio Grande
Title
Water Supply & Needs Report for the Rio Grand Basin
Date
6/1/2006
Author
CDM
Basin Roundtables - Doc Type
Needs Assessment Documents
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<br />Section 3 <br />Physical Environment of the Rio Grande Basin <br /> <br />Table 3.2 Summary of Selected USGS Stream Gages for the Rio Grande Basin <br /> <br />The San Luis Valley is primarily composed of Tertiary <br />age sedimentary rocks of sand, gravel, and clay, derived <br />from the San Juan and the Sangre de Cristo Mountains <br />that border it. The sediments are nearly 30,000 feet thick <br />in portions of the basin and interbedded in part with lava <br />flows (Pearl 1980). <br /> <br />3.2.6 Surface Water <br /> <br />The Rio Grande Basin drains approximately 8,000 square <br />miles of south central Colorado. In the northern portion of <br />the basin, streams flow into the "Closed Basin," an area <br />with no natural surface water outlet, encompassing <br />approximately 3,000 square miles (Wolfe 2003). Outside <br />of the Closed Basin, the Rio Grande and its tributaries <br />collect the runoff from the western and southern portion of <br />the basin. <br /> <br />The headwaters of the Rio Grande, in the western edge of <br />the basin, are just east of the Continental Divide in <br />Hinsdale County. The Rio Grande flows east to the Rio <br />Grande Reservoir where Ute Creek enters from the south. <br />The Rio Grande continues southeast through the San Luis <br />Valley past Monte Vista and the City of Alamosa. Shortly <br />after passing Alamosa, the Rio Grande then flows straight <br />south, crossing the state line into New Mexico. <br /> <br />The Conejos River is the largest tributary of the Rio <br />Grande and drains the southwest portion of the Rio <br />Grande Basin in Colorado. See Figure 3-2 for the <br />geography of the stream system in the basin. <br /> <br />Streamflows in the Rio Grande Basin are continuously <br />measured at a number of USGS gaging stations. USGS <br />streamflow data were summarized for five sites in the Rio <br />Grande Basin. Figure 3-5 shows the location of the five <br />selected streamflow gages: one on Saguache Creek, two <br />on the Rio Grande, one on the Alamosa River, and one <br />on the Conejos River. Table 3-2 summarizes the mean <br />annual streamflow, period of record, and drainage area <br />for each of these gages. The table indicates that <br /> <br />Site Name <br /> <br />USGS Site <br />Number <br /> <br />Saguache Creek near Saguache <br />Rio Grande near Del Norte <br />Alamosa River above Terrace Reservoir <br />Rio Grande near Lobatos <br />Conejos River near Magote <br /> <br />08227000 <br />08220000 <br />08236000 <br />08251500 <br />08246500 <br /> <br />S:\1177\BASIN REPORTS\RIO GRANDE\S3_RIO GRANDE.DOC <br /> <br />streamflows vary greatly throughout the basin. Figure 3-5 <br />also shows major diversions in the basin and stream <br />segments with decreed instream flow rights. <br /> <br />3.2.7 Groundwater <br /> <br />Groundwater development in the Rio Grande Basin is <br />primarily focused in the San Luis Valley. The <br />groundwater in the San Luis Valley is considered to be <br />located in two major aquifers: <br />. Unconfined <br />. Confined <br /> <br />The average annual supply pumped from the aquifers in <br />the San Luis Valley is 380,000 AF (Wolfe 2003), or about <br />one-third of total surface water diversions. Figure 3-6 <br />shows the location of the alluvial and bedrock aquifers <br />and wells with decreed or permitted capacities greater <br />than or equal to 500 gallons per minute (gpm). <br /> <br />Throughout most of the San Luis Valley, the unconfined <br />aquifer extends 5 to 100 feet below the land surface. <br />However, in the southeast portion of the valley, along the <br />outer edges of the valley, and along the streams and <br />rivers, the unconfined aquifer can extend to depths of <br />several hundred feet below ground surface (Davis <br />Engineering 1998). In a large part of the valley, a <br />confined or artesian aquifer, which lies under an aquitard <br />called blue clay, averages from 150 to 3,000 feet in <br />depth (Wolfe 2003). <br /> <br />3.2.8 Water Quality <br /> <br />The quality of water exiting the state via the Rio Grande <br />is of very high quality and in other areas of the basin it is <br />generally good (CDPHE 2000). The major water quality <br />concerns in the Rio Grande Basin are due to the effects <br />of historic mining activities. A primary area of concern is <br />the Summitville Mine Superfund site in the Summitville <br />mining district, which operated a surface, heap-leach <br />gold mine from 1984 until December 1992. During <br />operation, the mine leaked cyanide and acidic, metal- <br /> <br />43,934 <br />596,901 <br />74,965 <br />408,655 <br />217,353 <br /> <br /> <br />595 <br />1,320 <br />107 <br />7,700 <br />282 <br /> <br />Mean Annual <br />Streamflow <br />(AFY) <br /> <br />Period of <br />Record (Years) <br /> <br />Drainage <br />(sq. miles) <br /> <br />1923-2002 <br />1890-2002 <br />1914-2002 <br />1899-2002 <br />1903-2002 <br /> <br />CDIVI <br /> <br />3-3 <br />
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