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<br />. <br />... <br /> <br />ARKANSAS RIVER, COLORADO <br />GEOMORPHOLOGICAL ASSESSMENT <br /> <br />Purpose of Study <br /> <br />1. The purpose of this study was to identify geomorphological processes that are <br />currently affecting the long-term hydraulic conveyance changes in a 58-mile reach of the <br />Arkansas River downstream from John Martin Dam to the Kansas-Colorado state liQe. The <br />study will aid the Albuquerque District in conducting a Planning Assistance Study which is <br />currently ongoing with the State of Colorlwo.Historical documents were reviewed and a field <br />reconnaissance was conducted. Limited hydraulic and sedimentation analyses were conducted <br />using the SAM hydraulic design package. Recommendations are made for more detailed <br />studies appropriate for the Planning Assistance Study. <br /> <br />Watershed Characteristics <br /> <br />2. The Arkansas 'River originates in the central Rocky MoUntains near Leadville, <br />Colorado, and drains about 25,400 square miles in Colorado (Figure 1). There are at least 25 <br />mountain peaks in the upper watershed that exceed 14,000 ft in elevation. The Arkansas River <br />is a torrential mountain stream until it emerges from central Coloddo's Royal Gorge Canyon. <br />Downstream from the canyon, at about elevation 5,300 ft, the valley gradually widens and <br />descends through the foothills to reach elevation 4,700 ft at Pueblo, Colorado. From Pueblo <br />to the Kansas state line the river flows across the prairie of eastern Colorado thrOugh a broad <br />well-developed irrigated valley. The river then flows across the Great Plains through Kansas, <br />Oklahoma, and Arkansas to the Mississippi River. <br /> <br />3. In addition to discharge regulation at John Martin and Pueblo Dams, natural stream <br />flows are affected by trans-mountain diversions, storage reservoirs, irrigation diversion and <br />return flows, groundwater extraction, and power developments along the river. John Martin <br />Dam, which began storing water in December 1942, greatly reduced the severity and <br />frequency of flooding in the lower Arkansas River valley. However, flooding can still occur <br />from tributaries that enter the Arkansas River below the dam. Such a flood occurred in 1965. <br />About 5,570 square miles of uncontrolled contributing area e,p,sts between John Martin Dam <br /> <br />Arkansas River, Colorado <br />Geomorphological Assessment <br /> <br />1 <br /> <br />August 8, 1997 <br /> <br />I <br />I <br />