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/ <:::) c~ ~ N en CJl CHAPTER 2 Basin Descriptions ARKANSAS RIVER Main Stem - Colorado, Kansas, Oklahoma The Arkansas River rises in the Rockies near Leadville, Colorado, and flows in an easterly direction 1,450 miles to the Mississippi River near Arkansas City, Arkansas. The total drainage area, including tributaries, is 160,375 ~ square miles. Above Canon City, Colorado, the Arkansas River is a typical moun- tain stream, with steep slopes and a narrow valley. The mean annual precipitation in this area is more than 20 inches, and the mean flow at Canon City, 107ith a drainage area of 3,117 square miles, is more than 500,000 acre-feet per year, on the basis of 61 years of record. Near Pueblo, Colorado, where the annual precipitation is about 12 inches, the river enters the Piedmont section underlain largely by shale. With- in a relatively short distance the flow becomes highly mineralized, and there is considerable sediment load. The shale beds are relatively im- permeable, and there is little ground-water inflow. The mean annual flow past the Colorado-Kansas State line near Holly, Colorado, for the period 1908-42, where the drainage area is about 25,300 square miles, \l8S about 281,000 acre-feet. Since the completion of John Martin Reservoir in 1942, the distribution of flow at Holly has been radically altered. The res- ervoir is now operated in accordance with the provisions of the Arkansas River Compact, which allocates the division of water between the states. Near the Colorado-Kansas State line the Arkansas ,(iver enters the High Plains. Here there are extensive gravel and sand beds, in places as much as 500 feet thick. In the area of sand hills that borders the valley to the south the rainfall is rapidly absorbed and recharges the underlying and adjacent ground-water bodies. There are also many shallow depressions in the flat plains, some of them quite extensive, that hold local runoff until it is evaporated or absorbed by the ground-water reservoir. Flows of tributary streams are intermittent, and some large areas seldom, if ever, contribute to the flow of the Arkansas River. Inflow that does occur in the High Plains region is not highly mineral- ized and tends to reduce the concentration of the mineralized water from Colorado. From Canon City, is a "losing" stream. for irrigation to the Colorado, to Garden City, Kansas, the Arkansas River In this reach there are diversions of stream flow extent that often all of the stream flov is diverted. !I 'Ihe drainage areas stated herein correapoud with values on which eeveral AWR asenc1ea o.gree. The AWRBlAC 18 expected to adopt these :t'1gtU'e8, aubJoct to rev1l!11OD., which adopted .t1gure8 V1Il then become the only o:N'1c1al source tor vaterebed ft.luea .tar purposes or that COZlllll1ttee. 2-1