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5.0 COLORADO RIVER BASIN DRAFT DRAFT DRAFT Hydrology data from detailed floodplain analyses were obtained and analyzed for the Colorado River basin, The Colorado River basin was divided into subregions that are generally based on major watershed bmmdaries. A description of the various subregions along with the associated regression equation and application criteria are presented below. Figure 1,0, which graphically presents the regional and subregional boundaries for the state, is located in the map pocket at the end of this report. COL-l: UPPER COLORADO RIVER SUBREGION This subregion includes the Colorado River mainstem and its tributaries in the watershed areas upstream of and including Glenwood Springs, Streams in this subregion are located to the west of the Continental Divide within Grand County, Summit County, Eagle County, and Pitkin County. Major tributaries in this subregion include the Fraser River, Blue River; Eagle River, and Roaring Fork River, The subregion is bounded as follows: . On the north by the Colorado River - North Platte River basin divide; . On the east by the Colorado River - South Platte River basin divide; . On the south by the Colorado River - Arkansas River basin divide; . On the southwest by the Colorado River - Gunnison River basin divide; and . On the west/northwest by the Colorado River - Green River basin divide. The regression equation for this subregion is only valid for natural tributary streams that have drainage areas between 1 mi2 and 950 mil. A detailed study or other hydrologic analysis must be performed for projects involving streams with drainage areas that fall outside of the applicable range. The equation for subregion COL-l is: Q == 79.5(A)'714 Where: A == Drainage Area, square miles (1<A<950) Q = 100 year peak flow, cfs 22