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<br />BACKGROUND INFORMATION <br /> <br /> <br />3. DRAINAGE BASIN FEATURES.- The Arkansas River originates in <br /> <br /> <br />the central part of the Rocky Mountains near Leadville, Colorado. Its <br /> <br /> <br />waters enter the Mississippi River, approximately 20 miles north of <br /> <br /> <br />McGehee, Arkansas, after following a 1,460 mile course through the <br /> <br /> <br />States of Colorado, Kansas, Oklahoma and Arkansas. Runoff is received <br /> <br /> <br />from one of the highest regions in North America. At least 25 Colo- <br /> <br /> <br />rado peaks in the upper watershed exceed 14,000 feet in elevation. <br /> <br /> <br />These include Mount Elbert, the highest point in Colorado, at an ele- <br /> <br /> <br />vation of 14,431 feet. Above Great Bend, Kansas, the total watershed <br /> <br /> <br />area comprises 34,356 square miles, with 6,002 square miles classified <br /> <br /> <br />as noncontributing. The major contributing subbasin area, consisting <br /> <br /> <br />of 18,130 square miles, is controlled 286 miles upstream from Great <br /> <br /> <br />Bend by John Martin Darn near Las Animas, Colorado. <br /> <br /> <br />4. The Arkansas River is a typical torrential mountain stream <br /> <br /> <br />until it emerges from central Colorado's Royal Gorge Canyon, a nation- <br /> <br /> <br />ally famous scenic attraction with steep walls over 1,000 feet high. <br /> <br /> <br />Below the canyon, at about 5,300 feet elevation, the valley gradually <br /> <br /> <br />grows wider and descends through the foothills to reach 4,700 feet at <br /> <br /> <br />Pueblo, Colorado. From Pueblo through the fertile Great Plains region <br /> <br /> <br />to Great Bend, the river is characterized by a wide streambed with <br /> <br /> <br />low banks that occasionally shifts across a broad, well developed, <br /> <br /> <br />irrigated valley. <br /> <br /> <br />5. STREAMFLOW CHARACTERISTICS.- Stream slopes vary from a maxi- <br /> <br /> <br />mum of about 110 feet per mile in the mountain reaches to 7.5 feet per <br /> <br /> <br />mile immediately below John Martin Darn; then gradually decrease to <br /> <br /> <br />less than 6 feet per mile near Great Bend. In addition to regulation <br /> <br /> <br />by John Martin Dam, natural streamflows are affected by transmountain <br /> <br /> <br />diversions, storage reservoirs, irrigation diversions and return flows, <br /> <br /> <br />groundwater withdrawals, and power developments along the river <br /> <br />channel. Pertinent drainage areas and maximum known discharges for <br /> <br /> <br />the Arkansas River and its tributaries are given in Table I. <br /> <br /> <br />6. Past historic floods originating on the Purgatoire River, <br /> <br /> <br />Fountain Creek, and other major tributaries in the upper Arkansas <br /> <br />, <br /> <br />. <br /> <br />. <br /> <br />A-2 <br />