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Show PROBLEMS OF IMPERIAL VALLEY AND VICINITY. 5 It is believed to be possible to develop on the above streams approximately 3,000,000 continuous horsepower below the reservoirs after they are built without interfering with irrigation in the. upper basin or entering the Grand Canyon Park if these reservoirs are not used for irrigation in the lower basin. Anv construction of reservoirs for irrigation above those mentioned in the above table would affect other additional power resources, but those mentioned are believed to be the most feasible, in an economic sense, upon their respective streams. The Dewey Reservoir on the Grand is below any considerable feasible irrigation development on that river, but all the other reservoirs listed are above proposed irrigation projects and might, to some extent, affect them either beneficially or adversely in accordance with the plans under which the storage was developed and used. URGENCY OF RELIEF. In the valleys of the lower Colorado, and especially the Imperial Valley, storage is needed for the extension of irrigation and for safety against drouth of the areas already irrigated when the cycle of low years rolls around. The need is also vital for protection from floods of the Colorado which threaten the levees along the river valley and which are a constant menace to the Imperial Valley, threatening a repetition of the experience of 1906. Both of these problems are urgent and vital. The years 1902, 1903, 1915, and 1919 were years of low-water flow, the first two being shortly after the beginning of irrigation in the lower valleys and when the area irrigated was so small that no shortage occurred. In the year 1915 irrigation had proceeded to a substantial degree. The records of the Imperial irrigation system show that for a considerable period in 1915 the waters of the Colorado River were all, or practically all, diverted at the intake of that canal and applied in irrigation of Imperial Valley, with the result that an actual shortage existed there part of the time. The shortage was not severe nor disastrous, but it had a value as indicating the actual state of the water supply in relation to use. The shortage would have been still greater had a period as low as that of 1902 and 1903 occurred at that time. This relation appears in the following table showing the annual discharge of the Colorado River at the Laguna Dam. It will be noted that 1915, when the first shortage occurred, was by no means the lowest year of record. A shortage also occurred in 1919, and the years 1902, 1903, and 1904 all show a less discharge than 1915. Table No. fi.-Discharge of Colorado at Laguna Dam. Year. Acre-feet. Per cent of mean. Year. Acre-feet. Per cent of mean. 1899 21,700,000 16,800,000 15,200,000 9,110,000 11,300,000 9 890 000 132 102 93 56 69 60 1911....... ...... 17,600,000 1 18,200,0001 11,800,000 i 20,200,000 12,900,000 18,900,000 20,000,000 13,100,000 11,000,000 21,100,000^ " 107 ~* 111 72 123 79 115 122 80 67 - 129 1900 1912... 1901 1913........ 1902____ 1914...................,..... 1903 1915 1904 1916..... 1905... 16,000,000 98 17,700,000 108 24,800,000 151 12,600,000 77 25,400,000 155 14 200 000 1917......... 1906 1918...... 1907____ 1919.............. 1908 1920...... 1909 Mean................. 1910. 16,400,000 |