Page 19


Page 19
Colorado River problem
Is Part Of,8
Full text
322 THE COLORADO RIVER PROBLEM will be 200 miles or more above Yuma, it will take at least three days for a change in discharge at the storage dam to be felt at Yuma and accurate regulation will not be possible. If the Colorado is regulated to a discharge of 40,000 sec-ft. as proposed by the U. S. Bureau of Reclamation, the flood waters will not be discharged before the middle of February in years like 1909. That means there will be a discharge of 40,000 sec-ft. in the Colorado through the period of Gila floods. It is impossible to predict what the effect of such a condition will be, but there is certainly a chance that damage from Gila floods may be increased, or that the irrigation supply may be interfered with, if an attempt is made to shut off the Colorado to conform to floods in the Gila, as proposed by the U. S. Bureau of Reclamation. It would seem wise to plan on reducing the discharge of the Colorado to the irrigation demand during the three months of probable Gila flood. In order to do this, it will be necessary for the outlet works at the dam to be capable of passing a maximum discharge in the Colorado of at least 75,000 sec-ft. so as to insure emptying, the flood storage for the summer flood of the next year. [Fig. 11. MAXIMUM AND MINIMUM CROSS SECTIONS - COLORADO RIVER, YUMA, ARIZONA, FOR 1916] The most positive benefit that may be obtained by flood storage is that it will give insurance against permanent inundation of the Imperial Valley, provided it is great enough to permit releasing no more water than necessary to meet the irrigation demand over a period of low-water flow sufficient to enable any break into the Valley to be closed in the dry. Such a break can doubtless be closed in less than three weeks with the railroad and quarry equipment available. If storage is provided to hold the low-water flow for two months

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