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were cQnstructed to evaluate the impact of well pumping on streamflows and surface diversions. The study reported well growth was slow until 1950 and increased very rapidly during the period 1950-1965. The average growth rate was eight wells per year during the period 1940-1945, nineteen wells per year in 1946-1950, seventy-eight wells per year in 1951-65, and eight wells per year in 1965-1972. Id., p. 17. Based upon information from the Colorado State Engineer's Water Data Bank, there were 1,477 registered irrigation wells pumping from the Arkansas River alluvium between Canon City and the state line as of 1972. The study found that: "With the development of wells, ground water withdrawals have increased rapidly since the early 1950's. The average annual withdrawal during the period 1940-1945 was 6,600 acrefeet. This increased to 19,900 acreLeet d'ring 1946-1950, and 112,300 acre feet " during 1951-1965. The ~verage annual withdrawal further increased to 154,700 acre feet during the period 1966-1972." Id., p. 21. The study further determined that: In order to observe the effects of ground water withdrawals on stream flows, mass diagrams of Arkansas River flows at Granite, Canon City, Pueblo Nepesta, La Junta, Las Animas, and the stateline were constructed. It can be observed from the mass diagrams that the Arkansas River flows at Granite and Canon City have remained unchanged and there is no significant deviation from the historic trend during the study period. Conditions below Canon City become quite different as evidenced by the mass diagrams. The annual flows at Pueblo, Nepesta, La Junta, Las Animas, and the state line show a declining trend as indicated by the deviation of the data points from the straight line which represents essentially the -5- ~. ~ ~d