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<br />O~1957 <br /> <br />their proportionate share of surface water and have in addition a supple- <br /> <br /> <br />mental ground water supply which reduces the surface water available for <br /> <br /> <br />other users under the canal. The inequities to those who do not have <br /> <br /> <br />wells and/or who cannot develop ground water on their lands are apparent. <br /> <br /> <br />Detailed investigations and analyses were not made of individual <br /> <br /> <br />water rights and ditch diversions upstream from Pueblo. It is believed <br /> <br /> <br />that these rights can be adequately protected in any conjunctive use that <br /> <br /> <br />may be adopted in the lower basin by use of the Canon City gage as an <br /> <br /> <br />index station. A formula or formulae could be developed for the index <br /> <br /> <br />station which would permit upstream water rights to"divert out of <br /> <br /> <br />priority" when conjunctive use in the lower basin would result in priority <br /> <br />demands which would not have occurred under pre-pumping conditions. The <br /> <br /> <br />development of such a formula will require either detailed mathematical <br /> <br /> <br />or computer studies. The U.S. Geological Survey is conducting studies <br /> <br />with analog and digital computers in which the use of the index station <br /> <br /> <br />could be incorporated. <br /> <br /> <br />Any plan for the maximum utilization of the water resource of the <br /> <br /> <br />Arkansas River basin should include the relationship between plant <br /> <br />growth and salt concentration in the water solution. It is known that <br /> <br /> <br />some salts are more toxic than others and that certain plants are able <br /> <br /> <br />to tolerate high concentration of salts, whereas others are sensitive to <br /> <br /> <br />low concentrations. In this regard, the Arkansas Valley is fortunate to <br /> <br />have a water supply that is primarily sal ine in character rather than <br /> <br />alkaline. A saline soil is generally loose and friable and permits <br /> <br /> <br />percolation and the leaching of salts applied in the irrigation water. <br /> <br />Water at Pueblo averages about 250 ppm dissolved solids and is <br /> <br /> <br />excellent for agricultural use. The quality deteriorates progressively <br /> <br /> <br />downstream and at the state line averages about 1,800 ppm. During periods <br /> <br /> <br />of low flow at the state line, the concentration may exceed 3,900 ppm. <br /> <br />At Lamar during the 1964 irrigation season, the Arkansas River averaged <br /> <br /> <br />five tons of dissolved solids per acre-foot. Increased depletions or use <br /> <br /> <br />of the basin water supply would result in a further quality deterioration <br /> <br /> <br />throughout the basin. High irrigation efficiencies cause salts in the <br /> <br />12 <br />