Page 117


Page 117
Colorado River problem
Is Part Of,8
Full text
422 DEBLER ON THE COLORADO RIVER PROBLEM irrigable acre of a fully developed area will be almost equal to the net duty on each cropped acre, as the transmission losses are generally counterbalanced by the difference between the irrigable and cropped areas. Even without further improvement in irrigation and farm methods, at least 1.5 acre-ft. per acre, or about 5,000,000 acre-ft., should be deducted from the estimated total requirement. Projects comprising several million acres in the San Joaquin Valley of California are being carried forward on the basis of 2.0 acre-ft. per acre, and this quantity is considered sufficient in Southern California. As the character of development progresses, the economic advantages arising from the minimum use of water will force a similar procedure in the Colorado River Basin. Therefore, it is the writer's firm opinion that future experience will disprove the contention that the water supply from the Colorado River will be insufficient for much of the lands, because he believes that the water supply has been under-estimated, that the economically feasible area has been overestimated, and, finally, that the available supply can serve a far greater area than that claimed by the author. E. B. Debler, Esq.* (by letter).—According to the paper, little, if any, saving in the cost of bank protection and maintenance will result from reducing the flood discharge of the Colorado to less than 80,000 sec-ft. Porter J. Preston, M. Am. Soc. C. E., Project Manager and Superintendent of the Yuma Project since 1920, and R. N. Priest, Assoc. M. Am. Soc. C. E., Construction Superintendent since 1903, most of the time in charge of river control work through the Yuma Project, advise that the levees begin to undercut at discharges of 50,000 sec-ft. and that overflow of the natural banks below Yuma begins at discharges of 30,000 to 50,000 sec.-ft., depending on river conditions. Colonel Kelly states on the authority of the Engineer of the Palo Verde Project that flooding without levees would begin in the Palo Verde Valley with discharges of 50,000 sec-ft. and that bank protection is required for flows exceeding 35,000 sec-ft. These conditions are typical of all the valleys below the canyon region. Mr. Preston further states that the channel capacity is increased by 10,000 to 20,000 sec-ft. by scouring of the river bed with continuation of the flood. Until the Gila River is controlled, levees will have to be maintained to the present levels, but the Gila floods are of such short duration that they do not require bank protection for the levees. The expenditures on levees have largely been for purposes of revetment and this is required by reason of the continued persistent undermining of levees by extended floods originating along the Colorado. In 1913, a levee was cut entirely through with a maximum flood discharge of 62,000 sec-ft. The advantages of reducing all ordinary floods to less than 50,000 sec-ft. are obvious. Colonel Kelly recommends a flood-storage capacity of 4,000,000 acre-ft. to reduce recorded floods to 75,000 sec-ft. and to permit the interruption of flow for repairs in case of breaks in levees. His floods refer, however, only to the period since 1902. Reliable records indicate a flood in 1884 far in * Engr., U. S. Bureau of Reclamation, Denver, Colo.

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