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<br />ARK-S: SOUTHERN MOUNTAINS SUBREGION (No Regression) <br /> <br />At the time of this publication, there was insufficient data to obtain a meaningful regression <br />equation within the southern mountains subregion. The streams in the southern mountains <br />subregion have 100% of their drainage basins above an elevation of about 7500' MSL. The <br />southern mountains subregion is bounded as follows: <br /> <br />. On the south by the Colorado-New Mexico state line; <br />. On the east by an elevation line of generally 7500'; <br />. On the north by the Grape Creek-Huerfano River basin divide; and <br />. On the west by the Arkansas River-Rio Grande basin divide. <br /> <br />Studies within the southern mountains subregion should be perfonned using detailed methods or <br />appropriate USGS methodologies. <br /> <br />ARK-6: NORTHERN MOUNTAINS SUBREGION <br /> <br />This subregion includes streams within the northern mountains area. These streams have 100% of <br />their drainage basins above an elevation of 7500' MSL. Chaffee County was included in its <br />entirety within this subregion, despite the fact that portions of the county lie below the 7500' <br />elevation limit. The subregion is bounded as follows: <br /> <br />. On the south by the Grape Creek-Huerfano River basin divide; <br />. On the east by an elevation line of generally 7500'; <br />. And on the east by the Fourmile Creek-Currant Creek basin divide; <br />. On the north by the Arkansas River-South Platte River basin divide; <br />. On the northwest by the Continental Divide; and <br />. On the southwest by the Arkansas River-Rio Grande basin divide <br /> <br />The regression equation for this subregion is only valid for tributary streams that have drainage <br />areas between 4 mi2 and 330 mi2. This equation is also valid for the Arkonsas River mainstem <br />upstream of the Lake Creek confluence only. The remainder of the Arkonsas River mainstem <br />(downstream of the Lake Creek confluence) is exempt from this subregion. A detailed study or <br />other hydrologic analysis must be performed for projects involving most of the Arkonsas River <br />mainstem or streams with drainage areas thatfall outside of the applicable range. <br /> <br />The equation for subregion ARK-6 is: <br /> <br />Q = 46.0(A)"-717 <br /> <br />Where: <br />A = Drainage Area, square miles (4<A<330) <br />Q = 100 year peak flow, cfs <br /> <br />14 <br />