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Routt County is divided into the Northern Plateau Region and the Mountain Region. The two regions separate at the 7,5oo-foot elevation. The Northern Plateau Region comprises the Yampa River Basin below an elevation of 7,500 feet. The annual precipitation ranges from approximately 10 inches at areas below the 7,500-foot elevation to about 20 inches at areas above 7,500 feet, of which approximately 60 percent occurs as snowfall from October through April. Summer thunderstorms produce high-intensity rainfall in the region but usually are limited in areal extent. Floods are primarily caused by snowmelt runoff from April through June. The Mountain Region comprises approximately two-thirds of Routt County and consists of land at an elevation of 7,500 feet or higher. The principal form of precipitation in the Mountain Region during winter is snow derived from moisture moving eastward from the Pacific Ocean. The orographic effect of the high mountains generally produces more snowfall on the western slopes. Infrequently, severe floods are caused by rainfall during optimum conditions of snowpack depth and rate of temperature rise. During the summer, rainfall occurs throughout the region, but because of the elevation, the moisture supply is insufficient to produce significant floods (Reference 3). The climate in Routt County is characterized by cool summers and severe winters. The monthly average temperature in January is 15.00F and 61.90P in July. The mean maximum temperature in January is 29.40P and 83.0oF in July, and the mean minimum temperature in January is 0.60P and 4O.80P in July (Reference 8). 2.3 Principal Flood Problems Town of Hayden Low-lying areas in the western part of Hayden are subject to periodic flooding caused by the overflow of Dry Creek. Flooding caused by ponding of runoff and overflow from two irrigation ditches that intercept runoff from a small watershed southeast of the town occur in low-lying areas in the eastern and central parts of the town. The flooding generally occurs in early spring as a result of snowmelt or a combination of snowmelt and rain. The effect of historical floodflows from the Yampa River has been essentially negligible as a result of the protection provided by the railroad earth embankment that parallels the town's northern corporate limits. Town of Oak Creek Significant flooding occurred in 1914, 1939, 1950, and 1984, as well as other years (Reference 9). The streamflow that occurred during the May 1984 snowmelt flood was estimated by Dismuke and Dismuke Consultants, Inc., at approximately 650 cubic feet per second (cfs) at CR 27 at the northern end of town. Local residents have stated that the May 1984 flood was the "flood of record." Streamflows for the other flood events are not known. In terms of recurrence interval, the 1984 flood was approximately a 41-year flood event. Typical flooding along Oak Creek is caused by snowmelt runoff. However, at frequencies as rare as the l00-year event, flooding can occur from rainfall runoff. A 17