AZ vs. CA:24 California Exhibits, Vol. XXIV; Miscellaneous

page 66

66 PROBLEMS OF IMPERIAL. VALLEY AND VICINITY. 33 feet 4 inches wide, whose sills are about 13 feet lower than the crest of the dam. When these gates are raised, water from above the dam, flowing at high velocity, cuts out the sand and silt which have lodged in the desflting channel at whose lower end the gates are located. This desilting channel is separated from the river just above the dam by a rockfill spur or training wall. On the land side of this channel close above the Stoney gates is the headgate of the Yuma project canal. This is a simple structure with 35 openings, each 7.5 feet in the clear, between concrete piers which carry a concrete footbridge from which the flashboards, with which the flow of water is regulated, can readily be manipulated. The water drops into the canal over the top of these flashboards. By thus admitting water to the canal from the surface of the sluggish stream in the desilting channel much less silt is taken into the canal than would be the case if underflow gates were used. Once a week the sluice gates are opened and the sand and silt which have been deposited in the desilting channel are washed out, passing through the gates to the river below the dam. While no precise statement can be made of the amount of suspended material which is taken out of the water by this desilting process, it is generally estimated by representatives of the United States Reclamation Service to average about 50 per cent. In addition, it is /O be noted that practically none of the bed load of the river gets into iihe canal. All of this, together with the coarsest portion of the suspended load as above shown, is kept out of the canal by the desilting operation. At the present stage of development in the Yuma project, with about 45,000 acres under cultivation and with a maximum canal flow of about 1,200 second-feet, the time required per week to free the desilting channel of deposits is three to four hours. During this time the sluice gates are open and the diversion of water into the canal ceases. This is of no inconvenience, to the irrigators, who readily adjust their requirements to such a schedule. They have in fact thus far adjusted their demands to a shutdown of much longer duration than required for sluicing. The canal is being operated from early Monday morning to Saturday evening. Throughout Sunday the sluice gates are open and the canal bed is dry. Under a full development of the Yuma project the desilting operation will- have to be extended to a much larger flow of water. The maximum diversion for the irrigation of project lands will then be about 1,600 second-feet, and, on the assumption that there should be no cooperation with Imperial Valley, there would have to be added to this flow about 4,000 second-feet to be used at some point near Araz for the generation of power. The power would be necessary to lift the water to the Yuma Mesa, on which are located about 50,000 acres of project lands. The desilting channel would then be conveying from the river to the canal about five times as much water as heretofore, and there will have to be suitable enlargement of the diverting works and more frequent operation of the sluice gates. Under the cooperation with Imperial Valley the maximum diversion, as planned for the All-American Canal, will reach about 10,60C second-feet. The present desilting channel has not been dimensioned either for this amount of water nor yet for that ultimately required for the Yuma project alone. It must be enlarged and extended. But the general plan of operation will remain the same. Periodically