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<br />In the 1940's the average ground-water pumpage was
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<br />1,200 acre-feet per year, in the 1950's, 11,000 acre-feet
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<br />pe~ year, and in the first half of the 1960's, 25,000 acre-
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<br />feet per year. The year of greatest pumpage was this year,
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<br />when 29,700 acre-feet was withdrawn. On the other hand,
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<br />the return flow to the Arkansas River was reduced by
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<br />20,000 acre-feet from 1940 to 1963. The similarity of
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<br />the trends is apparent. A significant cause of the reductions
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<br />of return flow is the increased pumpage of water from wells.
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<br />Phreatophyte growth has increased over this same period
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<br />and has caused a part of the reduction in return flow.
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<br />The irrigation-well development in the Arkansas Valley has
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<br />been beneficial in that the wells provide water to crops
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<br />during times of def~cient surface-watersupply.
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<br />However,
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<br />these wells were drilled and were used with little evaluation
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<br />of their effect on the surface-water supply.
<br />To minimize adverse effects and to achieve maximum
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<br />use of the available water supply, ground water and surface
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<br />water must be developed and managed as a single supply, but
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<br />development and management cannot be planned properly until
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<br />the operation of the hydrologic system is quantitatively
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<br />described.
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<br />The U.S. Geological Survey in cooperation with the
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<br />Colorado Water Conservation Board and the Southeastern
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<br />Colorado Conservancy District is studying the Arkansas
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<br />Valley in order to evaluate the hydrologic system so that
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<br />the effects of selected changes in water management can be
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