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<br /> <br />valleys and canyons and has an average gradient of about 30 feet per <br /> <br />mile 0 <br /> <br />11. Below the South Fork confluence the Rio Grande flows through <br /> <br />'~ <br /> <br />the wide San Luis Valley. The streambed gradually changes from <br /> <br /> <br />boulders and rubble to rubble and gravel. and finally to sand and <br /> <br />gravel, as it meanders along the valley. The gradient decreases from <br /> <br />the 30 feet per mile at South Fork to about 2 feet per mile at the <br />confluence with the Conejos River. The channel oape.ci ty of' 4,500 <br /> <br />second-f'eet at Del Norte diminishes to 2,000 second-feet at A1amosa. <br />Within this stretch the banks are covered with grass and woody <br /> <br />vegetation, the latter oonsisting of' alder, willow, and cottonwood. <br /> <br />12. <br /> <br />Streamf10ws <br />During the period of record Ythe annual mean f'low of' the <br /> <br />'. <br /> <br />Rio Grande was 632 second-feet at Wason, within the Wagon Wheel Ge.p <br /> <br /> <br />Reservoir site, and computed flow at the gap was €64 second-feet. <br /> <br />Near Del Norte above the Rio Grande Canal, the annual mean f'low in- <br /> <br />oreased to 1,011 second-feet. At this point the instantaneous <br /> <br />maximum discharge was 18,000 seoond-feet on October 5, 1911, and the <br /> <br />minimum daily discharge was 88 second-feet on December 20, 1945. <br /> <br />Downstream from the Rio Grande Canal, the effect of irrigation <br /> <br /> <br />diversions on the flow of the Rio Grande is reflected in the annual <br /> <br /> <br />mean flow of' 223 second-feet at Alamosa. 51 A summary of streamflow <br /> <br />data at key points on the !lio Grande, inoluding routed flows proposed <br /> <br /> <br />by the Bureau of' Reclamation, is listed in Table 2. <br /> <br />1183 <br /> <br />y <br />gj <br /> <br />Period of record for dif'f'erent stations varies from 1902 to 19510 <br /> <br />Based on wa ter records for the period f'rom 1925 to 1948. Irri- <br />ga tion reaohed maximum deve10pnent about 1895 according to <br />decreed rights. <br /> <br />5 <br /> <br />