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DESCRIPTION OF THE BASIN o CJl ~ The Upper Arkansas River Basin is located in southeastern Colorado, ~~ western Kansas and the extreme northern part of New Mexico and includes the watersheds of' the Arkansas River and its tributaries above the mouth of Walnut River, Kansas at river mile 696.1. The basin has a length of approximately 500 miles, a maximum width of 160 miles and an area of 43,736 s~uare miles. Of the total area 7,607 s~uare miles are considered non-contributing to surface runoff because of numerous un- defined stream courses in flat terrain where stream flow is dissipated through evaporation and percolation. A map of the basin is sho'Wll on the facing page. A stream profile,Figure 1, and a detailed basin map, Figure 2, are included at the end of this report. The Arkansas River rises on the eastern slope of the Rocky Moun- tains near Leadville, Colorado (river mile 1,444) at an elevation of over 10,000 feet. Hurloff is contributed from the slopes of nearby peaks that reach an elevation of over 14,000 feet. The river drops rapidly from its headwaters until it emerges from the mountainous area at river mile 1,332 where the elevation is about 5,300 feet. The river then follows an easterly course across the flat but undulating high plains of eastern Colorado and western Kansas to the lower end of the upper basin, near the Kansas-Oklahoma border. Principal tributary streams are Purgatoire River, Big Sandy Creek, Pa'Wllee River, Walnut Creek, and Ninnescah River. The climate in the western portion of the Upper Arkansas River Basin is semi-arid to arid except for certain limited areas in the high mowltains. Average precipitation in the western portion varies with the elevation of the terrain and ranges from 13.5 inches near Trinidad, Colorado at elevation ),746 to about 21.7 inches at North Lake, which is at elevation 8,800 and about 32 miles west of Trinidad. At the higher altitudes most of the fall and winter precipitation occurs as snow. In the eastern portion of the basin the climate is subhumid and precipitation averages about 25 inches. Average annual precipitation at Dodge City, Kansas is about 20 inches and at Great Bend, Kansas about 22.5 inches. The average annual observed regu- lated stream flow is 237 cfs at ,Lamar, Colorado; 201 cfs at Garden City, Kansas, 452 cfs at Great Bend, Kansas, and 1,782 cfa at Arkansas City, Kansas. The natural flow of the stream is affected by trans- mountain diversions, storage reservoirs, ground water withdrawals and irrigation diversion and return flows. In 1945 a House Resolution granted the consent of Congress to the States of Colorado and Kansas to negotiace a compact for the division of the waters of the Arkansas River. The Arkansas River Compact was subse~uently developed between the two states and became effective in 1949. The average annual temperature for Trinidad, Colorado is )10 F. and for Dodge Ci't~', Kansas is 550 F. Temperature extremes range from 1100 F. to minus 300 F. - 3 ..