Dam
2 of the 7 encyclopedias on this shelf carry an entry for Dam. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
a barrier built across a stream, valley, or other depression, for the purpose of impounding or regulating the flow of water behind it. Dams are constructed to supply water and water power to communities, for irrigation projects, for hydroelectric development, to make streams navigable, and for similar purposes. Dams may be constructed of earth, timber and loose stone, stone masonry, steel, or, as has been the most general practice of recent years, re-enforced concrete. A dam must be designed to prevent failure by overturning, by sliding at the base or at horizontal joint, by crushing (in the case of masonry dams), by fracture caused by tension, and by erosion. The head or height of the water behind the dam determines the pressure that the dam has to withstand, not the volume of water behind it. Every well-designed dam has ample provision for the easy passage of flood waters, because force exerted by an extremely large volume of water passing over the crest of the dam would possibl ibly cause its failure. To guard against against this possibility flood gates, spillways, or tunnels are used. Earth dams are made by packing successive layers of earth. The earth may be drawn in carts or buckets, and packed by rolling, or by water, or the earth may be both transported and packed by hydraulic means. Usually, in an earth dam, the upstream face of the dam is paved with some material more resistant to seepage than earth, or the dam is provided with a waterproof lining or corewall. Earth dams vary in height from a few feet to over 100 ft., and in length from a few feet to miles. Masonry dams are constructed either of stone set with cement mortar, or of re-enforced concrete. The cross section of a modern masonry dam of the gravity type resembles in general a right-angle triangle, except that the sides are somewhat curved. The approximately vertical side is placed upstream, the base is liable to be rather broad, and the top rounded. Some engineers favor the use of the arch principle, either single or multiple, to resist the force of the water, and it is said that a considerable saving of material may be gained with no loss of strength. Another recent development in dam design is the hollow reenforced concrete dam, which consists essentially of water-tight concrete slabs supported on piers. Rock-fill dams are constructed by piling large stones together, and facing the upstream side with planks, concrete, or other waterproof material. Steel dams never had a great vogue, and timber dams are seldom constructed by modern engineers, except as temporary structures. Dams which are built to aid navigation, are usually so constructed that they may be raised or lowered. The Gatun Dam across the Chagres river, Panama canal, is an earth dam. It was partly constructed by the hydraulic method. It is about 115 feet high and over 1½ miles long. The base of the dam, which is about sea-level, is 2,020 feet wide. At the water line, which is located 85 feet above the base, the dam is 390 feet thick, and it is 100 feet thick at its top. The dam is built with very flat slopes to provide unusual stability. The dam has a spillway channel 819 feet wide. Over 20,000,000 cubic yards of material were used in its construction. The San Leandro Dam of the San Francisco waterworks is an earth dam with no core-wall, and is 158 feet high. The Goose Creek Dam of the Oakley Irrigation project is an earth dam built in layers, and completed in 1913. It is 145 feet high, 1,025 feet long and 750 feet wide at the base. الله NEW CROTON DAM, NEW YORK The highest earth dam ever attempted is the Calaveras Dam of the Spring Valley Water Company of San Francisco. This dam is 240 feet high, the crest length is 1,300 feet, the base is 1,300 feet wide, the upstream slope is 3 to 1, and the down stream slope is 21½ to 1. It is a hydraulic fill dam. The new Croton Dam of the New York City Water Supply System was completed in 1907, and provides a storage capacity of 32,000,000,000 gallons of water. It is a masonry dam with a erest length of 2,168 feet, and a height of almost 300 feet. There is a roadway on the top of the dam. The spillway is 1,000 feet long, and varies in width from 50 to 125 feet. The Shoshone Dam is a masonry dam built by the United States Reclamation Service in Wyoming near Cody. It is 324 feet high, curved upstream, 10 feet thick at the crest, and 108 feet thick at its base, which thickness is continued up to the level of the river bed. The Roosevelt Dam was also constructed by the United States Reclamation Service. It is located in Arizona, has a maximum height of 284 feet, a storage capacity of 420,000,000,000, and was completed in The Arrowrock, near Boise, 1911. Idaho, construction of which was started in 1914 by the same Government agency, is 354 feet high, and 1,060 feet long. It N ST gravity secis curved upstream, with a g tion, and is built of concrete. The Keokuk Dam, which crosses the Mississippi river at Keokuk, Ia., is a long, low concrete dam. Besides the 4,278 feet long, there spillway section, on, is an abutment 290 feet long, a combination, another 1,700 feet long, in the form of a power house, and a lock section of about 600 feet. The Elephant Butte Dam, located near Engle, N. M., was dedicated on Oct. 19, 1916. It is a Reclamation Service dam of rubble concrete, with a gravity section. It is 1,200 feet long and 304.5 feet high from base to top. The hydro-electric development dam of the Yadkin river, N. C., contains a dam built of concrete, 1,400 feet long, and 217 feet in height. The Noguera Pallaresa River Dam in Spain was built and designed by American engineers. It is 330 feet high, hig 700 feet long, has a base width of 230 feet, and is built of concrete. The deep water plans for the Mississippi river include the construction of numerous dams, and in 1917 Dam No. 1, located near St. Paul, was placed in operation. It made the river available for navigation for 13 miles. h The Hetch Hetchy Dam of the San Francisco water system will be one of the largest masonry dams in the world. The height from foundation base to crest will be 311 feet. It will be a masonry dam with a straight gravity section of 600 feet, and will have a siphon spillway. It' It the Tuolumne San Francisco. In New South Wales the Murray River Dam has been planned as part of an irrigation project. It will be 3,600 feet long, long, and have both earth and concrete sections. In 1864 a poorly constructed earth' dam at Sheffield, England, went out the first time it was put to use, and caused a flood which cost 238 lives. No engineer was employed to design the Mill River Dam at Williamsburg, Mass., which went out in 1874, with a loss of 143 lives, and $1,000,000 in property. The االله ROOSEVELT DAM, ARIZONA South Fork Dam, owned by the South Fork Hunting and Fishing Club of Pittsburgh, Pa., was an earth dam of 70 feet height. It was designed to have a spillway of 150 feet, but this was not carried out, and the existing spillway was partially blocked with screens, honuspillway.rivit will be located in bridge supports, etc., when in May, 1889, over the entire length of the dam. The dam itself was carried away, and flooded the town of Johnstown, Pa., with a loss of over 2,000 lives and about $4,000,000 in property. The Walnut Grove Dam in Arizona failed on Feb. 22, 1890. This dam was a rock-fill structure, and the failure was caused by inadequate spillway. The Colorado River Dam at Austin, Tex., failed in 1900 because of poor foundations; and because of faulty construction, the concrete dam at Austin, Pa., failed on Sept. 30, 1911, and cost 35 lives. Because of structural weakness caused by improper drying of the materials, the Lyman Dam across the Little Colorado river in Arizona, failed in 1915. In 1916 an old dam near Gablonz, Bohemia, failed, with a loss of over 300 lives.
The Encyclopedia of Founding (1892)
A reservoir or tank used for collecting or gathering a large quantity of metal to cast heavy castings. Whilst constructed in various ways, the main features consist in making it strong to maintain the metal, and of such materials as will conduce to its preservation in a good condition for casting with. A thoroughly well-dried loam and brick construction within suitable curbs is the best, taking care to have it as hot as possible when the metal enters, and keeping from 4 to 5 inches of dry charcoal on the surface. The mode of emptying the dam is usually by a shutter, which hermetically closes the outlet whilst it is being filled, and is raised by means of a controlling lever, so that the metal may be delivered at any desired speed. See GATHERING METAL; CURBS; SHUTTER.