Page 114

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Page 114
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Colorado River problem
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http://digital.library.unlv.edu/u?/dig,8
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E. A. HILL ON THE COLORADO RIVER PROBLEM 419 course, will reduce the lowering, by removing the eroding and transporting agent. The effect of lowering the bed of the Colorado River, down stream from the storage dam, would be in part harmful and in part beneficial. It would lower the tail-water of the power house at the dam; this would give an increase of head, but it might destroy the effectiveness of the draft-tubes, if they were not designed for such a contingency. This effect may also occur at the proposed power dams on the Colorado. If the lowering is considerable, it will make the diversion of water for irrigation more difficult and may cause serious undermining of the existing dams founded on silt. Although it is not possible to predict how much effect this lowering will have in improving flood conditions in the lower river, it will at least be beneficial, and may become, in the course of a number of years, an important factor. It is possible that if engineers knew more of the laws governing this action, by preventing the cutting back of the tributaries, and possibly building a retarding basin on the Gila River, to remove the silt from its water also, the river might be made to excavate its own channel deep enough to carry the flood flow without endangering the surrounding country. In his discussion* of the paper entitled "Flood Problems in China", by John E. Freeman, Past-President, Am. Soc. C. E., the writer has already suggested that this method is worthy of study for the improvement of the Yellow River in China, where the conditions are particularly favorable. Raymond A. HILL,† Assoc. M. Am. Soc. C. E. (by letter).—The problem of the Colorado River is too complex for arbitrary solution at this time, as the data which are available, or which might be made available, cannot include certain important factors the determination of which is necessary to the proper solution. The extent of flood control which will be needed after storage is provided, and the quantity of water which will be required for irrigation, are two such indeterminates. The author has made use of certain curves showing the relation between the percentage of silt and the discharge of the Colorado River at Yuma, the relation between velocity and discharge, and the area-discharge relation. These curves were originally prepared by the writer in connection with certain studies to determine the relation between silt content and depth for various velocities. Fig. 24 shows the volume of silt which is transported by the Colorado River at various stages when there is no contributing flow from the Gila River. It would seem from this that the author is justified theoretically in maintaining that the Colorado River has been more stable at 80,000 sec-ft. than at 40,000 sec-ft. It must be realized, however, that during the years in which these silt measurements were made the river was constantly fluctuating in volume, particularly at the higher stages, and that even with a silt-laden river the proportion of silt would tend to decrease if the discharge were held constant. * Transactions, Am. Soc. C. E., Vol. LXXXV (1922), p. 1558. † Associate, Quinton, Code & Hill, Los Angeles, Calif.

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