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<br />12 <br /> <br /> <br />001230 <br /> <br />their proportionate share .of surface water and have in addition a supple- <br />mental ground water supply which reduces the surface water available for <br />other users under the canal. The inequities to those who do not have <br />wells and/or who cannot develop ground water on their lands are apparent. <br />Detailed investigations and analyses were not made of individual <br />water rights and ditch diversions upstream from Pueblo. It is believed <br />that these rights can be adequately protected in any conjunctive use that <br />may be adopted in the lower basin by use of the Canon City gage as an <br />index station. A formula or formulae could be developed for the index <br />station which would permit upstream water rights to"divert out of <br />priority" when conjunctive use in the lower basin would result in priority <br />demands which would not have occurred under pre-pumping conditions. The <br />development of such a formula will require either detailed mathematical <br />or computer studies. The U.S. Geological Survey is conducting studies <br />with analog and digital computers in which the use of the index station <br />could be incorporated. <br />Any plan for the maximum utilization of the water resource of the <br />Arkansas River basin should include the relationship between plant <br />growth and salt concentration in the water solution. It is known that <br />some salts are more toxic than others and that certain plants are able <br />to tolerate high concentration of salts, whereas others are sensitive to <br />low concentrations. In this regard, the Arkansas Valley is fortunate to <br />have a water supply that is primarily saline in character rather than <br />alkaline. A saline soil is generally loose and friable and permits <br />percolation and the leaching of salts applied in the irrigation water. <br />Water at Pueblo averages about 25D ppm dissolved solids and is <br />excellent for agricultural use. The quality deteriorates progressively <br />downstream and at the state line averages about 1,800 ppm. During periods <br />of low flow at the state line, the concentration may exceed 3,900 ppm. <br />At Lamar during the 1964 irrigation season, the Arkansas River averaged <br />five tons of di ssolved solids per acre-foot. Increased depletions or use <br />of the basin water supply would result in a further quality deterioration <br />throughout the basin. High irrigation efficiencies cause salts in the <br />