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ROY 0. WEST, SECRETARY
DAMS AND CONTROL WORKS
A Description of Representative Storage and Diversion Dams
.x. BUREAU OF RECLAMA TION
T^HE Bureau of Reclamation since it was first | organized in 1902 has constructed a total of i 125 dams. These range from simple diversion dams less than 3 feet in height to the Arrowrock storage dam with a maximum height of 348.5 feet, which for years after its completion in 1915 held the record as the highest dam in the world. Even this height will soon be surpassed by the Owyhee Dam, contract for which was recently let by the bureau. Diamond drill borings indicate that this structure will have an effective height of 405 feet at maximum section and a height above lowest concrete in foundation of 520 feet.
The Bureau of Reclamation maintains a field office at Denver, Colo., in charge of R. F. Walter, chief engineer. This office has immediate supervision of all construction work, and S. O. Harper is superintendent of construction. The design of all important structures and preparation of plans and specifications is under the supervision of J. L. Savage, chief designing engineer. Engineers of this bureau have been among the pioneers in the advances made in dam design and construction during the years since the bureau was established. Much credit is also due these engineers for pioneer work in a related field, the design of outlet works capable of regulating the discharge of the water impounded by these dams, under the high heads involved and in the large volumes required by the irrigation demand. A description of the more notable of such installations may be found in "High Pressure Reservoir Outlets," by J. M. Gaylord, formerly chief electrical engineer, and J. L. Savage, chief designing engineer, Bureau of Reclamation, published by this bureau.
Articles descriptive of many of these dams have appeared from time to time in the New Reclamation Era (formerly Reclamation Record) and detailed account of their construction has been given in the published annual reports of the bureau, especially in the ninth (1909-10) and the fifteenth (1915-16). These
last-named annual reports, however, and many of the others, are now out of print, and the stock of back numbers of the Era has in many cases been exhausted. In order to have information on typical dams readily available in published form, there are here presented reprints of a number of articles that have appeared in the New Reclamation Era, supplemented by others that have been especially prepared for this pamphlet. For more detailed and technical information relative to the dams here described and the others listed in the table at the end of the volume, reference is made to the file of published reports of the bureau which may be consulted at any depository library and to the books and periodicals listed in the accompanying bibliography.
Dam design and construction practice, as noted above, has made notable progress in the past 25 years and undoubtedly further advances will be made in the near future. As an example, the older masonry dams were built, like Roosevelt, of rubble masonry, containing from 60 to 70 per cent of stone laid up by hand with mortar and spalls. The upstream faces were cut stone with comparatively thin well-pointed joints. The more modern type is of cyclopean concrete containing a far smaller percentage of large stone (25 per cent or less) with the faces of the dam built of concrete laid against forms, while in the most recent specifications the use of "plums," or derrick stone, is frequently abandoned altogether, the entire body of the dam consisting of concrete, with the addition of cobble rock to the mix in the more massive portions of the structure. Similarly, methods of analysis and knowledge of stresses in arch dams have made great advances since the study by Wisner and Wheeler of stresses in high masonry dams of short spans, upon which the designs of Shoshone and Pathfinder Dams were based. Accounts of the earlier dams are included here, however, because of their importance as existing project works and for their historical value.—C. A. B.
TI THE Reclamation Act passed by Congress in June, 1902, was followed in October of the same year by investigations along the Colorado River, extending from about 100 miles above Needles, Calif., to the Mexican boundary some 300 miles below. In the winter of 1902-3 a possible project was found, with a dam to be located at the Yuma site, about 22 miles upstream from Yuma, Ariz. At this dam site the Colorado River passes through the first rocky gorge above the Gulf of California, the walls at this point being 1,500 feet apart. A topographic survey showed that the construction of a diversion dam 70 feet high would make feasible the reclamation of large areas in Arizona and California. Further examination of this proposition, however, disclosed the fact that there was no bedrock upon which to construct a high diversion dam, and the plan was abandoned in favor of a diversion dam of small height. Investigations led to changing the position of the structure to a point known as Laguna on the Arizona side and Potholes on the California side, 12 miles northeast of Yuma, which was the most southerly site on the river where it was feasible to locate a dam with rock abutments.
It was here proposed to build a dam or weir about one mile in length of the Indian type, diverting water through canals on either side of the river. This dam would furnish a gravity supply for irrigating about 16,000 acres on the Yuma Indian Reservation in California, the bottom lands in Arizona below Yuma containing about 55,000 acres, and 20,000 1 acres in the Gila River valley just above and east of Yuma.
DESCRIPTION OF DAM
The problem presented was to build a barrier founded on the alluvial deposits of the river, which would divert water to canals at each end, where a portion of the river's sediment could be dropped before entering
1 The GUa Valley lands were later excluded from the Yuma project, and original plans for the California and Arizona sluiceways were reversed, which prorided for the project main canal heading on the California side.
the canals. Conditions required a weir capable, if necessary, of accomodating the entire flow of the river over its crest at flood stages. Nothing of the kind had ever been built in this country, and before a decision was reached as to type of structure, a careful examination was made of foreign works, principally those of Egypt and India. The type of weir selected was one that had been in successful operation for many years in these two countries under practically identical conditions with those presented at Yuma. It followed closely in design the Okla weir across the Jumna in India, and also a later weir across the Nile below Cairo, both built by English engineers.
The structure is about 4,780 feet in length and 19 feet above the stream bed, with a maximum height of 40 feet. It raises the general surface of the river about 10 feet. The width at the base, exclusive of talus, is 166 feet. The structure is traversed longitudinally by three concrete walls extending from the top of the dam to well below the river bed, these walls being 5 feet thick. One is placed at the crest of the dam with a top elevation of 151 feet above sea level, the next one is 57Yi feet downstream from the first, and the third 933^ feet downstream from the second.
The top of the dam slopes downstream from the crest at the rate of 1 foot in 12. Between the longitudinal walls is a loose rock fill made from the ordinary run of the quarries. Below the downstream wall is an apron composed of derrick stone, the top width of which was originally 40 to 50 feet. The crest wall rests upon a row of 6-inch sheet piling, from 12 to 32 feet long, which was driven throughout the entire length of the dam for the purpose of cutting off seepage. The entire top of the dam is covered with concrete pavement about 18 inches thick, except in a very small portion near the Arizona end, which was paved with rough stone from 2 to 3^4 feet in thickness.
The lower wall of the dam is placed with its top at elevation 138, or .3 feet below ordinary low water. During the winter of 1909-10, owing to scour in the river, its low-water plane dropped until the top