Page 45


Page 45
Colorado River problem
Is Part Of,8
Full text
ALLISON ON THE COLORADO RIVER PROBLEM 349 Flood Control.—-The lower irrigation projects of the Colorado River, including the Imperial Valley, the Yuma Valley, and the Palo Verde Valley, must continue their levee maintenance work until regulation of the river is complete. With the tremendous variation in the annual discharge from a low point of 9,110,000 acre-ft. in 1902, to as high as 25,400,000 acre-ft. in 1909, it must be evident that one dam can never perfectly perform the triple functions of providing maximum flood control, maximum conservation of water for irrigation, and maximum power development. The provision neces-sary for silting space alone should bar this unattainable feat from further consideration. A dam in or below the Canyon Section having a storage capacity of 4,000,000 acre-ft. and discharge facilities of 75,000 sec-ft., should be sufficient to care for the immediate problem, this dam to be utilized later for re-regu-lation of the flow for irrigation when other dams for storage and power purposes are built above it. Such a dam meets all the requirements for imme-diate flood control noted by Colonel Kelly, with the possible exception of regulation to provide entirely for the Gila River floods. Unless the dam itself is located within a reasonable distance from Laguna Dam, above Yuma, Ariz., it is impractical to attempt any substantial regulation of the Colorado River supply to offset the flash discharges entering the river from the Gila at Yuma. Inasmuch as it is necessary to continue the maintenance of the levee system of the lower valleys, the floods of the Gila are automatically cared for until such time as its complete regulation is justifiable. The very fact that the duration of the Gila floods is so extremely limited, justifies the assumption that only local damage can be done to the lands in Yuma and Imperial Valleys in case of levee failure. The reasons for continuing the maintenance of the levee system in the lower valleys, as enumerated by the author, are conclusive. Irrigation.—In the speaker's opinion the conclusion drawn by Colonel Kelly and by the engineers of the U. S. Reclamation Service, as well as by many of the State engineers interested in the project, that there are more lands to irrigate eventually than can be served by the water available, is erroneous. Only experience will determine this issue. If the speaker's judgment is correct, as the facts herewith indicate, a great many of the most serious problems involved in the regulation of the Colorado River disappear completely. Table 20 illustrates the progress of irrigation and the net usage of water on the lands of Imperial Valley. For a period of 5 years the average duty was 2.8 acre-ft. per annum, which can be safely applied to the other valleys below the Canyon Section. It has taken 22 years to reclaim and irrigate 731,893 acres below the Canyon Sec-tion, distributed as indicated in Table 21. This relatively small total area represents the lands most easily irrigated during a period in which agriculture has had a great stimulant through the necessities of war.

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