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<br />OC1993 <br /> <br />Pumping tests On more than 70 wells within the valley show an <br /> <br /> <br />average permeabil ity of 4,500 gallons per day per foot of cross- <br /> <br /> <br />sectional area.* Transmissibilitiesin~ of the aquifer are reported by <br /> <br /> <br />the U. S. Geological Survey to range between 0 and 700,000 gallons per <br /> <br /> <br />day per foot. Approximately 80 percent of the saturated alluvium in <br /> <br /> <br />the Arkansas Valley has a transmissibility greater than 50,000 gallons <br /> <br /> <br />per day per foot. <br /> <br /> <br />Calculations, based on information obtained from the U. S. Geolo- <br /> <br /> <br />gical Survey, indicate that approximately 1,600,000 acre-feet of water <br /> <br /> <br />are in the alluvial basin between Pueblo and the Colorado-Kansas state <br /> <br /> <br />line. If land areas which have a transmissibility of less than 50,000 <br /> <br /> <br />gallons per day per foot are excluded from the total, it is estimated <br /> <br /> <br />that approximately 460,000 acre-feet of ground water is theoretically <br /> <br /> <br />available for use within economic I imits. Approximately 300,000 acre- <br /> <br />feet of th i s tota lis be I ow John Mart i n Reservo i r. Areas in wh i ch the <br /> <br /> <br />aquifer transmissibility is less than 50,000 gallons per day per foot <br /> <br /> <br />have been excluded due to their limited capability of supplying water <br /> <br /> <br />for irrigation requirements. It must be emphasized that ground water <br /> <br /> <br />theoretically available is a measure of the quantity stored within the <br /> <br />alluvial formation of the basin. Since the alluvial and surface waters <br /> <br /> <br />are hydraulically connected and part of the same system, any removal <br /> <br />of water from the alluvial aquifer would eventually have to be replaced <br /> <br /> <br />mainly from surface water with a like reduction of flow in the surface <br /> <br /> <br />stream. In many reaches the water table gradient has been reversed <br /> <br /> <br />because of ground water withdrawal in which case water moves from the <br /> <br /> <br />river toward the wells, rather than from uplying lands toward the river <br /> <br /> <br />as would normally be expected. <br /> <br /> <br />Unconfined ground water in the Arkansas River Basin below Pueblo <br /> <br /> <br />is a valuable source of supplemental water. This ground water is <br /> <br />*Colorado Ground Water Circular No. II, U. S. G. S. Publication <br />"Pumping Test in Colorado." <br /> <br />**Rate of flow in gallons per day through a vertical section of <br />an aquifer where height is the thickness of the aquifer and <br />whose width is I foot, when the hydraul ic gradient is 1.0. <br /> <br />- 10 - <br />