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<br />40 <br /> <br />TECHN I CAL MANUAL. <br /> <br />Moun ta in Reg ion <br /> <br />The Mountain Region comprises all areas in Colorado in which flooding is <br />predominantly caused by spring snowmelt runoff (fig. 2). The eastern bound- <br />ary coincides with the western boundary of the Plains Regiion. The western <br />boundary north of the Gunnison River corresponds to an elevation of 7,500 ft. <br />South of the Gunnison River, the boundary follows the divIde between the Lit- <br />tle Cimarron River and Big Blue Creek to the Continental Divide at Wetterhorn <br />Peak. Southward, the boundary follows the Continental Divide to the Rio <br />Grande; then it follows the Rio Grande to the Colorado-Nel" Mexico border. <br />The region includes both the steep mountain terrain and the high, relatively <br />level, mountain park areas within its boundaries. <br /> <br />The principal form of precipitation during the winter is snow derived <br />from moisture moving eastward from the Pacific Ocean. The orographic effect <br />of the high mountains generally produces more snowfall on the western slopes. <br />Separate regress ions were attempted fat eastern and western mounta in streams <br />but the two areas were combined because results did not warrant the division. <br />Infrequently, severe floods are caused by rainfall during optimum conditions <br />of snowpack depth and rate of temperature rise. During the summer rainfall <br />occurs throughout the region but, because of the elevation, the moisture <br />supply is insufficient to produce significant floods. <br /> <br />The regression equations relating flood characteristics to basin param- <br />eters for the Mountain Region are listed in table 2 with the standard error of <br />estimate for each equation. The equations for the lOO-year flood discharge <br />and depth are depicted graphically in figures 5 and 6, respectively. <br />