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<br />the Colorado River basin. The agriculture people have set up a method of <br />evaluating waters for irrigation purposes. L. V. Wilcox of the Regional <br />Salinity laboratory at Riverside has given a description of the method with <br />a graph from which, with a knowledge of the concentration of dissolved solids <br />and the sodium percentage, a water can be classified for irrigation purposes, <br />as: 1) excellent to good, 2) good to permissible, 3) permissible to doubtful, <br />4) doubtful to unsuitable, and 5) unsuitable. Most of the waters in the <br />Colorado River basin are in the first two classes. Two or three are class <br />four (the.Grand Valley project drains, and the San Rafael River) and only <br />one (the Gillespie canal) class five. Waters of the basin now are in general <br />suitable. However, upstream development will change the quality, and records <br />are needed to watch for the changes and make plans for better uses of the <br />available waters. Use of more waters in the upstream areas, such as trans- <br />basin diversions and application of the waters to new uses or for further <br />irrigation, will affect the quality of the water available for downstream <br />users. Trans-basin diversions probably will cause an increase in the con- <br />centration of the water left in the basin because the water diverted is some <br />of the best in the basin. However, use of the water for irrigation and other <br />purposes in the upper basin will perhaps be responsible for a greater increase <br />in dissolved solids and for a great change in the chemical character of the <br />water available for use farther downstream. <br /> <br />*********** <br /> <br />-19- <br />