Page 78

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Title
Page 78
Source
Colorado River problem
Is Part Of
http://digital.library.unlv.edu/u?/dig,8
Full text
DAVIS ON THE COLORADO RIVER PROBLEM 383 3.—No power head should be sacrificed unnecessarily. 4.—Agriculture should be given preference over power uses. The plan proposed by the author violates all these maxims. Importance of Storage.—The most outstanding and important feature of the Colorado River is the great fluctuation of its flow. The low-water years yield less than 9,000,000 acre-ft. below the canyons, and the high-water years yield about three times this quantity. The seasonal fluctuations are still more striking; autumn flows of 4,000 sec-ft. and less are common, and the high-water peak often reaches 150,000 and sometimes exceeds 200,000 sec-ft. The low-water flow is already appropriated and used in irrigation, and an unusually dry season produces a shortage. Without regulation, the stream will produce only about 25% as much primary power as with proper regulation, and the effect of storage on irrigation is similarly important. In addition, the great volume and long duration of the spring floods are such as to constitute an annual menace to all the valleys of the lower river, especially to the Imperial Valley, which, if entirely submerged, would be permanently destroyed, as it is largely below sea level. These conditions make indispensable a large volume of storage capacity which fortunately Nature has made possible and feasible, with proper conservation and utilization. This, however, is not all. Heavy Silt Content.—Nature sends down the river an annual average of about 100,000 acre-ft. of silt, which will fill to that amount any reservoir built within or below the canyon region. This silt clogs the channel, obstructs irrigation canals, and adds greatly to the flood menace and to the cost of irrigation operations. It makes the river unfit for municipal uses, for which it will be required extensively in the near future; all these conditions will be remedied by storage, as the silt will settle in the reservoirs, and the desilting of the river is one of the major requirements in changing it from a menace to a valuable asset. The average annual volume of this silt, however, is 160,000,000 cu. yd.—a greater amount than the total excavation performed by the Isthmian Canal Commission in digging the Panama Canal. Desilting the river by settlement in reservoirs, fills those reservoirs to the extent of the volume of the silt deposited. Obviously, the time will come when all the reservoir space will be occupied by silt, unless some means of removal is applied. Any known method of accomplishing this is troublesome and expensive—many times as expensive as constructing additional reservoir capacity, as long as other good reservoir sites are available. It thus becomes necessary to conserve reservoir space to the greatest practicable extent. The amount of storage necessary to equalize the flow of the river through all the years would be enormous, and hardly practicable. To just what extent it may pay to hold the water of extraordinary floods for use in dry years is a question about which the best engineers may differ, but all will agree that hold-over storage to a large extent is necessary if the river is to be properly used. It is necessary to retain a large amount of this storage in the Lower Basin, where most of the flow can be intercepted, in order to desilt the river and to control and utilize the floods of the lower tributaries.

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