APPENDIXES TO San Carlos Water Supply and Cost Report APPENDIXES B AND C Appendix B-HYDROGRAPHY, GILA BASIN, by H. K. PALMER, Assistant Engineer, U. S. Indian Irrigation Service. REPORT ON THE HYDROGRAPHIC INVESTIGATION OF THE GILA RIVER, by C. C. JACOB, District Engineer, Water Appendix C-MAXIMUM AND MINIMUM COST OF THE SAN CARLOS 149700-19-VOL 2-15 225 HYDROGRAPHY, GILA BASIN, ARIZONA. The watershed of the Gila River has been described in detail in this report, so its essential features only need be mentioned here. The Gila River and one of its principal tributaries, the San Francisco, rise in the mountains of western New Mexico and eastern Arizona. Some water is also received from the San Carlos River, at the western end of the Solomonvile-Safford Valley, and from the San Pedro a few miles above the mining town of Kelvin, not far above the mouth of the canyon where the Gila emerges onto the desert plain of southwestern Arizona. The watershed of the Gila includes the following areas above the San Carlos Dam site: In Arizona In New Mexico_-_ Total. Square miles. 13, 455 As shown on the accompanying key map No. 1, the river traverses the Duncan, Solomonville-Safford, and Winkelman valleys above the mouth of the canyon mentioned above. In all of these valleys more or less water is diverted from the river for irrigation, a portion of which in each case returns underground. After leaving the mountains, 16 miles above Florence, the low-water flow of the river seeps away in the sand so rapidly and the Florence diversions are so great that it is only during times of moderately high water that enough reaches the Indians lands around Sacaton to permit irrigation. Except where it is confined in box canyons the river course occupies a wide sandy bed, the water saturating the sand on both sides of the stream to within a few inches of the surface. On account of the hot, dry climate a great loss is occasioned by the excessive evaporation which is a factor of vital importance especially during times of low water flow. Acting as it does over a wide sandy area whose width is not dependent upon the stage of the river, the evaporation from the ground surface depends only on climatic conditions and not on the amount of the surface flow. The evaporation from the water surface alone depends on the stage of the river. This large evaporation loss tends to amplify the fluctuations of the run-off in the lower sections. The upper Gila and San Francisco Rivers rise in forested areas and are typical mountain streams, subject to great floods resulting from the rains which occur during the winter and summer seasons. The lower sections of the Gila and its tributaries receive water also from barren lands where the run-off is large and this results in short floods of varying magnitude following every rain storm. At the dam site, in cases of drought, the river sometimes becomes entirely dry but at its highest flood it has been known to discharge more than 100,000 second feet. It is believed that in former times, water flowed past the Indian land at Sacatan at all stages of the river, but during recent years, that is, since irrigation has been carried on extensively in the upper valleys and at Florence the flow during the low water season it has entirely disappeared before reaching Sacatan. The depletion of the water supply began to be felt 20 years ago and several reports on this subject have been written between 1899 and 1914. The last of these reports, that of the Army Board, summarizes the findings of all previous investigations. In each of these reports, the need of storing the flood water is brought out and the more recent reports agree upon the site for the dam below the town of San Carlos, at the head of the box canyon, which the river enters at that point. As a result of the torrential character of the river, the hydrographic conditions are naturally divided in two well defined groups, low water and flood water. All previous reports have laid the greatest stress on the flood conditions, merely summarizing the low water conditions to show the necessity for building the dam. In this report these two groups will be considered separately and each will be fully discussed. FLOOD CONDITIONS. The torrential character of the run-off makes it impossible to use a large portion of the flow of the Gila for irrigation unless storage facilities are provided. At the same time, the annual run-off varies so greatly (from a minimum of 99,900 acre-feet in 1902 to a maximum of 1,011,000 in 1905), that sufficient storage must be provided to carry over the supply for several years. The run-off at the dam site, below the town of San Carlos, is shown by the table at the end of this appendix. The measurements of the run-off at this point have not been continuous, so it has been necessary to supply the missing observations by the use of measurements made at other points modified by a proper factor. Up to and including 1912, the run-off has been computed by the Army board. For 1913 and the first 4 months of 1914 similar computations have been made by the Geological Survey, and since the latter date the figures are based on measurements made at the dam site. This run-off has been plotted and is shown on Plate No. 65. This diagram shows that a few wet years are generally followed by a succession of dry years, and a comparison of wet and dry periods seems to indicate the existence of a cycle of about 9 years. The table shows that during the period from 1895 to 1903, inclusive, the average annual run-off amounted to 282,000 acre-feet, while during the period from 1904 to 1912, inclusive, it amounted to 413,000 acre-feet. The average annual run-off based on 21 years, 1890, and 1895 to 1914, inclusive, for which records are available, is 359,878 acre-feet. This is higher than the average of the two periods because the very wet year 1914 contributed 742,350 acre-feet amounting to 212 per cent |