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The Snake River basin forms the easternmost portion of the Blue River basin. It drains westerly, from Grays Peak, along the Conti- of Loveland Pass to Dillon Reservoir. The s lOll0. ano h~~ ~ drainage area of 76 square miles at Dillon Reservoir. The channel slope ranges from 5.7 percent, in the upper basin above the Town of Montezilllla, to 1.1 percent in the study area near Keystone (Refer- ence 6). The study area extends from 0.8 mile above Dillon Reser- voir, upstream for a distance of approximately 4.8 miles. Develop- ment in this area is active and is expected to continue. 2.3 Principal Flood Problems " Major floods on the streams are caused by the melting of the winter accumulation of snow. As the temperatures rise, the snowmelt runoff increases, generally reaching a peak sometime in June and receding to normal flow by mid-July or August (Reference 7). Rains that occur prior to mid-June do not increase the streamflows appreciably. However, after peak runoffs have occurred and snowmelt begins to decrease, rainfall usually increases the runoff. Rains that occur in July and August have a greater potential for causing major flood- ing (Reference 8). There has been little recorded evidence of significant flooding in sununit County, with the exception of the flood on July 23, 1965, when the Blue River left its banks. The flood was attributed to a storm of high intensity centered over a small tributary above Breck- enridge. Because of the time of year, rainfall runoff was the pre- dominant cause of flooding. During the time of this storm, the other rivers in the cormty were at their peaks (Reference 8). 2.4 Flood Protection Measures The major flood protection measures for Sununit County are Dillon Dam and D:i:llon~Reservoir,which~are located just-~upstream fromSilver-~ thorne on the Blue River. The reservoir receives flows from three of the major streams in the county: Blue River, Snake River, and Tenmile Creek. The reservoir storage significantly reduces the peak discharges of frequent floods and is also used to control discharges of Blue River through Silverthorne to Green Mountain Reservoir. The primary function of the Dillon Reservoir is collection and storage of snowmelt runoff for domestic use on the eastern slope. The structure is an earthfill dam, approximately 231 feet high at its maximum section, with a 32-foot crest width. The reservoir 1 when at the full reservoir water-surface elevation of 9,017 feet, has a total storage capacity of 261,800 acre-feet (References 7, 9, and 10). L The Goose Pasture Tarn, a small reservoir immediately upstream of Breckenridge, also serves as a flood protection measure for Blue River. The tarn has a drainage area of approximately 43.5 square 8