FLOOD04282 - Laserfiche WebLink

Home Browse Search

I . northwestem Colorado (figure 4). The basin drains from the northwest in the Elkhead Mountains and flows southwesterly to its confluence with the Yampa River about 6 miles east of Craig, Elevations in the basin range from about 10,847 ft at the highest peak (Sand Mountain) of the Elkhead Mountains to about 6,200 ft at its confluence with the Yampa River. The elevation of Elkhead Reservoir is about 6,400 ft. Distinct mountains and ridges define the north (9,000 to 10,000 ft), east (-7,500 to 9,000 ft), and west (-7,500 ft) boundaries of the basin. The topography is rolling hills and valleys, except in the steeper, headwater mountain areas. Numerous tributaries and Elkhead Creek drain the mountains forming the basin dMde, Most streams have gradients of greater than 1 percent, except the lower reaches of Elkhead Creek. Cobble- and boulder-sized material cover the streambed and fine-grained sediments underlie the flood- plain. The majority of the basin has low to moderately well-drained soils (Soil Conservation Service, unpublished data, 1995), except in limited higher elevation areas having bedrock at the land surface. In lower parts of the basin below about 8,000 ft and not used for agriculture, vegetation consists primarily of sagebrush, rabbit brush, and native grasses. At higher elevations, subalpine forests consisting of apsen, lodgepole pine, Douglas fir, and Englemann spruce are common. Mean annual precipitation varies from about 16 in. at Craig to slightly more than 30 in. near the headwaters (Doesken and others, 1984). Most of the annual precipitation falls as snow in the winter months. Larger-precipitation values are limited to small parts of the basin at the highest elevations around the east and north rims of the basin. Most of the lower basin averages less than 20 in. of annual . precipitation. Frequent, localized convective rainstorms occur during the summer months, but have not produce any substantial out-of-bank flooding in most of northwestem Colorado. A few convective storms have produced localized flooding in small, steep basins with little vegetation at lower elevations in northwestem Colorado (eg" Piceance Creek Tributary, Cottonwood Gulch, and Yellow Creek). General rainstorms, which may cover large areas, are limited to several inches or less in northwestem Colorado and have not produced substantial out-of-bank flooding in historic times. This probably is because the area is so distance from the Pacific moisture source and is essentially cut off by major mountain barriers from the flow of moist Gulf air. The spring of 1995, particularly May, established new record rainfall amounts, but only minor out-of-bank flooding occurred on small tributaries subject to convective rainfall. . 14