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<br />I'~, ~, \l r.: '1 <br />ti..,: '..' .'" '.) 'J '",oj <br /> <br />. <br /> <br />PART II--GENERAL DESCRIPrION <br /> <br />PHYSICAL CHARACTERISTICS <br /> <br />The St. Vrain Unit is located principally in Boulder and Weld <br />Counties in north-central Colorado within the drainage basin of <br />St. Vrain Creek, as shown on exhibit 1. The other major stream <br />in the basin is Boulder Creek, which traverses the southern portion <br />of the unit and joins St. Vrain Creek east of Longmont. The basin <br />drains about 1,000 square miles. Most of the upper portion of the <br />basin lies within the boundary of the Roosevelt National Forest, <br />with the uppermost part bordering the Continental Divide. The <br />higher peaks of the area have elevations above 14,000 feet, and the <br />streams are entrenched in narrow, steep-walled canyons and valleys. <br />The mountainous area provides most of the water supply of the basin. <br />The basin slopes to the east and the mountainous sector merges into <br />the Colorado Piedmont (plains area) through which the St. Vrain Creek <br />extends to its confluence with the South Platte River. The Colorado, <br />Piedmont is a part of the Great Plains Province. <br /> <br />. <br /> <br />CLIMATE <br /> <br />The climate of the St. Vrain Creek basin is as diversified as <br />its topography. The mountainous region has a rigorous climate with <br />heavy snowfall and a short growing season. Precipitation varies <br />with the altitude and exposure and generally increases toward the <br />higher elevations. The greatest precipitation--in excess of <br />50 inches annually--falls in the Continental Divide area. <br /> <br />Summer temperatures in the mountainous region seldom exCeed <br />900 F., and killing frosts occur throughout the summer in the highest <br />elevations. <br /> <br />The lower portion of the basin, including the foothills and <br />adjacent plains, is semiarid. The average annual precipitation, as <br />measured at Longmont, is 13.25 inches (63 years of record between <br />1887 and 1965). Large variations in precipitation occur year to <br />year, however, and extremes have ranged from 6.42 inches in 1939 <br />to 22.67 inches in 1915. The frost-free period averages 142 days <br />annually and extends from May 10 to September 29, as recorded at <br />Longmont for the period of record between It\t\7 and 1960. The <br />mean annual temperature is 48.30F. (59 years of record between <br />1887 and 1965), and has ranged from a high of 1050F. in July 1954 <br />to a low of -3BoF. in January 1930. <br /> <br />. <br /> <br />4 <br /> <br />,.~ ,',--;' -i., <br /> <br />,''. ';.',;,'-_....--:,- ,'ii::' <br /> <br /> <br />U: <br /> <br />!!' <br /> <br />ii <br /> <br />V' <br />" <br />