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2.2 Community Description Rio Blanco County, Colorado, is located in the northwestern quarter of Colorado. It is bordered to the north by Moffat County, to the east by Routt County, to the south by Garfield County, and to the west by Uintah County, Utah. According to the 1980 U.S. Census, Rio Blanco County has a population of 6,255, an increase of 29 percent from the 1970 population of 4,842 (Reference 2). The climate of the study area is classified as semiarid, with relatively warm summers and cold winters. The mean annual tempera- ture near Rangely in the western part of the county is 460F, with extremes of -370F and 1060F. In the eastern portion of the county near Meeker, the county seat, the mean annual temperature is 44oF, with extremes of -430F and l030F. The average annual precipitation varies from less than 10 inches near Rangely to 16.5 inches around Meeker. Normally, approximately 60 percent of the annual precipi- tation occurs during the winter months, mostly in the form of snow. The majority of the rainfall occurs during the late spring and summer months. This rainfall generally results from convective type thunderstorms, which cause short-duration runoff that is character- ized by high-peak, low-volume flows. The topography 10 the area is extremely diverse, and includes dissected plateaus, sharp ridges, abrupt cliffs, and rugged badlands that are interspersed wi th open valleys, meadows, and basins. The presence of underlying rock layers with wide differences in resist- ance to erosion has been the principal factor in the evolution of these varied land forms. Deep and extensive gullying along drainageways and narrow valleys is of considerable agricultural significance. In many locations, dissection by gullies severely limits use of the land. The ground cover consists primarily of sage brush at lower elevations and forests of aspen, pine, juniper, and scrub oak at high elevations (Reference 1). 2.3 Principal Flood Problems Rio Blanco County near the Town of Meeker 1S subject to periodic flooding from the White River and Sulphur Creek. The climate of the study area and the differing nature of the watersheds and streams subject the area to floods of three basic types: snowmelt, ice jams, and convective thunderstorms. In the past, spring runoff due to mel ting snow in the high mountain watershed above Meeker has caused the highest water levels in the White River for the longest periods of time. Ice jams, caused by Chinook winds melting snow at higher elevations, and temperature inversions freezing the water at obstacles in the river have also occurred in the White River in and near Meeker. Periodic floods on Sulphur Creek occur from melting snow, but convective thunderstorms also cause frequent and high runoff flows of short duration. A U.S. Ceological Survey (USGS) 4