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2.04.7(2) <br />The Bear Lane is adjacent to the North Fork of the Gunnison <br />• River. A discussion of possible flooding at the mine site was <br />obtained with information provided from a study entitled Flood <br />Hazard Information, Nort`: Fork Gunnison River, Hotchkiss to <br />Somerset, Colorado, published by the Department of the Army, <br />Corps of Engineers in February, 1980. Additional cross-sections <br />were obtained from the ARCO Permit Application. <br />The North Fork Gunnison River is formed by the confluence of the <br />P.uddy and Anthracite Creeks near Paonia Dam. From its source <br />to its mouth near Lazear, the stream flows about 30 miles on a <br />southwesterly course. Its tributary drainage area (a part of the <br />Colorado River basin) is situated in west-central Colorado on the <br />western slope of the Rocky Mountains. At Hotchkiss and Somerset, <br />the stream drains 940 and 530 square miles respectively. Elevation <br />ranges from 5400 feet at Hotchkiss to around 13,000 feet in the <br />highest headwater regions, and stream gradients vary from about <br />• 30 feet per mile at Hotchkiss to 60 feet per mile at Somerset. <br />Terrain of the basin is mostly mountainous with some mesa and <br />tableland in the lower portion. <br />Predominant vegetation consists of pine, fir, and spruce in the <br />high portions of the drainage area, while sagebrush and other <br />low-growing shrubs are characteristic in the lower portions. <br />Thick stands of cottonwood occur alont the river. Drawing <br />2.04.7(2)(b)(i)-1 illustrates the North Fork Gunnison River <br />Drainage Basin and its tributaries within the study limits. <br />General frontal-type rainstorms approaching from the southwest <br />can occur over the North Fork Gunnison River basin from mid-June <br />through December, but records show that they occur most often <br />during September and October. Convective-type cloudburst storms <br />occur frequently during the summer in west-central Colorado. <br />Most of the annual precipitation in this region, however, occurs <br />• as snow and a deep snowpack usually accumulates in the high areas. <br />Studies show that rapidly melting snow in the spring and early <br />summer constitutes the principal source of flooding along the <br />5-49 <br />D L•t 1T CCT l.1 ~... 1C 1,101 <br />