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<br />mean maximum temperaturE! varies from the mid 30s in January to <br />approximately 900F in July, while mean minimums vary from 100F in <br />January to 500F in July. Mountain regions are cooler. The growing <br />season is 136 days and extends from mid-March through late October. <br /> <br />) <br /> <br />Native vegetation in Garfield County varies from salt desert shrub <br />and associated growth in the southwest corner to alpine and tundra <br />type cover in high mountain areas. Agricultural operations and <br />urbanization have drastically modified native vegetation in the <br />main river valleys, the adjoining benchlands, and the lower portions <br />of small tributary valleys. <br /> <br />The flood plains of the streams and washes under study are not pre- <br />sently extensively developed. There are various transportation <br />facilities in the flood plains. There are some industrial and <br />rural residential land uses, but the predominant land use is agri- <br />cultural. However, continuing and probably accelerated development <br />due to increasing emphasis on tourism, winter sports, and extracting <br />and processing energy-producing minerals is expected, and pressure <br />leading to intensified flood plain use will undoubtedly accompany <br />such development. <br /> <br />2.3 Principal Flood Problems <br /> <br />As noted earlier, most 0:: the annual precipitation in the Colorado <br />River Basin upstream fror~ the areas under study occurs as snow and <br />a deep snowpack accumulates in the higher regions. General rain- <br />storms can occur in the area from late spring through late fall, <br />and convective type cloudburst storms can be expected frequently <br />during the summer. <br /> <br />~ <br /> <br />Major floodflows on the Colorado and Roaring Fork Rivers result <br />from rapid melting of thE! mountain snowpack during the period from <br />late May through early July. Snowmelt floods are characterized by <br />moderate peak flows, larsre volume and long duration, and marked <br />diurnal fluctuation in flow. Rainfall on melting snow may accel- <br />erate the rate of snowmelt and thus au~ent floodflows. Maj9r <br />floods on the dry washes, gulches, and smaller streams under study, <br />especially those with much of their drainage area below 8000 feet <br />NGVD, are generally caused by cloudburst storms. Cloudburst <br />flooding is characterized by high peak flows and short duration. <br />Due to their small areal extent and other factors, cloudburst <br />runoff would not significantly affect flooding along streams as <br />large as the Colorado and Roaring Fork Rivers. Flooding from <br />general rain does not constitute a significant problem in Garfield <br />County. Studies made for this report show that the 100- and 500- <br />year floods would result from cloudburst storms on the small washes, <br />tributary gulches, and tributary creeks; from snowmelt on the <br />Colorado River; and from snowmelt au~ented by rain on the Roaring <br />Fork River. <br /> <br />6 <br />