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OJOllb SECTION I I ARKANSAS RIVER STUDY REACH The study reach of the Arkansas River, which is the subject of this assign- ment, is a subsystem of the total river system and Its basin. Furthermore, administration of the water and distribution of its losses can sometimes be better understood with the overview picture of the river In mind. ThIs Section presents a few of the physical facts and characteristics of the river needed to realize the complexity of the river administration. GENERAL DESCRIPTION OF ARKANSAS RIVER BASIN The Arkansas River from Its source in Colorado to Its junction with the Mississippi River flows 1500 miles and drains an area of 177,500 square miles. It starts Its 1940-mile journey to the Gulf of Mexico at over 11,000 feet ele- vation and joins the Mississippi at about 100 feet elevation. Most of this drop occurs within 200 miles of its source. For the remainder of its journey, the river flow is tranquil and meandering, traveling over a bed of fine sand and silt. The channel profile of the Arkansas River has a continuously decreasing gradient from its source to its mouth. It is unique among streams Issuing from the east side of the Rocky Mountains in having no sharp irregularities in its long profile -- that is, its stream gradient over long segments. The river provides a substantial part of the economic wealth of its basin, and inhabitants in this area are subject to its vagaries. The Arkansas River within Colorado is 350 miles long and drains 25,000 square miles, 24 percent of the entire state (See Map I I-I). It crosses into Kansas at an elevation of 3400 feet. It provides irrigation for 490,000 acres of Colorado land and Is a great economic force in this semi-arid land. The grip the river has on people is evidenced by the location of most of the towns and transportation routes along its banks or main tributaries. Table I I-I I ists the average annual river flows, drainage areas, period of record, irri- gated areas, and elevations for 14 gaging stations maintained on the maIn stem of the river in Colorado. The table brings out the fact that the drainage basin of the Arkansas RIver in Colorado is composed of two entirely different terrains. First of all, there is the mountainous upper reaches of the river which produce much of the runoff but use little of the water for agricultural or domestic use because of the 1 imlted arable land and low population density. Below Canon City, however. the'quantity of Industrial and irrigation use Increases with major diversions. The quantity of water flowing in the river is seen to decrease after passing Avondale in Pueblo County as It proceeds toward the Colorado-Kansas state line. The quality of water also experIences a drastic change from Its clear mountain state. Below Canon City, It has higher suspended and dissolved sol ids because of domestic, industrial, and irrigation return flow and natural processes of sediment transport. At present, the main stem of the Arkansas River In Colorado has only one major reservoir on it. This Is John Martin Reservoir with a maximum of 384,000 5