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<br />8.0 SAN JUAN RIVER BASIN <br /> <br />DRAFT <br /> <br />DRAFT <br /> <br />DRAFT <br /> <br />Hydrology data from detailed floodplain analyses were obtained and analyzed for the San Juan <br />River basin. The San Juan River basin was divided into two subregions, an eastern subregion and a <br />western subregion, The western subregion was determined to be an area of "No Regression" due to <br />lack of available data. A description of the San Juan River region along with the associated <br />regression equation and application criteria are presented below. Figure 1.0, which graphically <br />presents the regional and subregional boundaries for the state, is located in the map pocket at the <br />end of this report. <br /> <br />SAN-I: EASTERN SAN JUAN RIVER SUBREGION <br /> <br />This subregion includes the San Juan River mainstem and its tributaries in southwestern Colorado. <br />Streams in this subregion are located in portions of La Plata County, San Juan County, Archuleta <br />County, Hinsdale County, and Mineral County. Major tributaries in this subregion include the San <br />Juan River, Animas River, La Plata River, and Los Pinos River. The subregion is bounded as <br />follows: <br /> <br />. On the north by the San Juan River - Gunnison River basin divide; <br />. On the east by the San Juan River - Gunnison River basin divide; <br />. On the south by the Colorado - New Mexico state line; <br />. On the west by La Plata River - Mancos River basin divide; and <br />. On the northwest by the Animas River - Dolores River basin divide <br /> <br />The regression equation for this subregion is only valid for natural tributary streams that have <br />drainage areas between 1 mil and 760 mil. A detailed study or other hydrologic analysis must be <br />performed for projects involving streams with drainage areas that fall outside of the applicable <br />range. <br /> <br />The equation for subregion SAN-l is: <br /> <br />Q = 589.2(A)"512 <br /> <br />Where: <br />A = Drainage Area, square miles (1 <A <760) <br />Q = 100 year peak flow, cfs <br /> <br />SAN-2: WESTERN SAN JUAN RIVER SUBREGION <br />This subregion is an area of "No Regression" and includes the Mancos River mainstem and its <br />tributaries in extreme southwestern Colorado. Streams in this subregion are located in Montezuma <br />County and portions of Dolores County, There is insufficient data to produce a meaningful <br />regression equation at this time, <br /> <br />29 <br />