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<br />* CWCB Technical Manual No.1, Manual for Estimating Flood Characteristicsl'~ <br />of Natural - Flow Streams in Colorado, 1970. ~ <br /> <br />. <br /> <br />40 <br /> <br />FROM TECHNICAL MANUAL #1 * <br /> <br />Mountain Region <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 bound.ary of the Plains Region. 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 />tIe 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-New 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 regressions were attempted for eastern and western mountain 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 summe~ rainfall <br />occurs throughout the region, but, because of the elevation, the moisture <br />supply is insufficient to produce significant floods. <br /> <br />-.,. <br />.' <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 100-year flood discharge <br />and depth are depicted graphically in figures 5 and 6, respectively. <br /> <br /> Table 2.--Mountain Region regression equations for peak disaharges <br /> and depths of seleated recurrenae-interval floods with <br /> aOl'responding standard error of estimate <br /> Equat ion Standard error of estimate, in percent <br /> Average Range <br /> Q10 = 0.12AO.815pl.592 39 +46 -32 <br /> to <br /> Q50 = 0.91AO.795pl.II0 37 +44 to -30 <br /> QIOO = 1.88AO.787pO.932 38 +45 to -31 <br /> Q500 = 8.70Ao.766pO.560 45 +55 to -35 <br />I DID = 0.44Ao.196pO.347 27 +31 to -23 <br /> 050 = 1.05Ao.192pO.133 2B +32 to -24 <br />I'.. <br />I . DIDO = 1.44AO.187pO.059 28 <br /> +32 to -24 <br /> ~. 0500 = 1.94AO.184 31 +36 -26 <br /> to <br />I 37 <br />1 <br />