Page 20


Page 20
Colorado River problem
Is Part Of,8
Full text
THE COLORADO RIVER PROBLEM 323 for the year of greatest run-off on record, there will be no reason for fear of disaster to the Imperial Valley. To make this practicable a maximum dis- charge of 80,000 sec-ft. in the Colorado is necessary in order to free flood storage for the succeeding flood season. If the maximum discharge is fixed at 75,000 sec-ft., the same result can be obtained by adding about 600,000 acre-ft. to the flood-storage capacity. The engineers of the U. S. Bureau of Reclamation state that, considering diversions for irrigation since 1909, the flow of 1920 may be taken to represent the largest flow of record at Yuma, They give the storage required at Boulder Canyon for flood control as shown in Table 2. TABLE 2. Required Storage, in Millions of Acre-Feet. _________________________________________________________________________________________ Permissible discharge at Yuma, Ariz. Excess flow at Yuma. Stream storage. Total. __________________________________________________________________________________________ 40,000 sec-ft............................. 6.7 0.4 7.1 50,000 sec-ft. ........................... 5.5 0.4 5.9 60,000 sec-ft............................. 4.4 0.3 4.7 75,000 sec-ft............................. 3.2 0.2 3.4 _________________________________________________________________________________________ The following conclusions seem to be justified: 1.—It is not feasible, with the quantity of water now passed by the Colorado, to relieve the Lower Basin from the expense of bank protection and levee maintenance by the construction of flood storage. 2.—Flood damage to property behind the levees will probably be avoided if the maximum discharge of the Colorado is reduced to 80,000 sec-ft, and there will be little, if any, reduction in cost of bank protection and maintenance by a greater reduction in discharge. 3.—It may be desirable, until the Gila is controlled, to reduce the flow in the Colorado during the months of December, January, and February, to that required for irrigation. This means that discharge facilities with a capacity of at least 75,000 sec-ft. should be provided. 4.—It is desirable to allay the fear of permanent inundation of the Imperial Valley by making it possible to stop completely the flow below Rockwood Heading for a period sufficiently long to permit remedial works to be carried out in the dry. This can be done by using the storage provided for flood control, if flood waters are discharged at a rate of 75,000 sec-ft. and an extra 600,000 acre-ft. of storage capacity is provided. 5.—Storage for flood control is justified to a quantity that will reduce the maximum discharge for any year of record to 75,000 sec-ft. Storage in excess of that quantity may be deferred until provided as an incident to other development on the river. 6.—The conditions mentioned will be met by 4,000,000 acre-ft. of flood stor- age. Additional storage to allow for silting of reservoirs may be advisable. The quantity of such storage necessary will depend on the shape, location, and

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