DALY, (JOHN) AUGUSTIN, an American dramatist and theatrical manager; born in Plymouth, N. C., July 20, 1838. Included in his original plays are : "Divorce," "Pique," "Horizon," "Under the Gaslight," and a story called "Peg Woffington, a Tribute to the Actress and the Woman." At various times during his career he managed some of the most popular and successful actors and actresses in the United States, including Fanny Davenport, Clara Morris, Ada Rehan, etc. He died in Paris, June 7, 1899.
DAM, a barrier built across a stream, valley, or other depression, for the pur pose of impounding or regulating the flow of water behind it. Dams are con structed to supply water and water power to communities, for irrigation projects, for hydroelectric development, to make streams navigable, and for sim ilar purposes. Dams may be con structed 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 over turning, 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 possibly cause its failure. To guard against this possibility flood gates, spillways, or tunnels are used.
Earth dams are made by packing suc cessive 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 hy draulic 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 some what curved. The approximately verti• cal side is placed upstream, the base is liable to be rather broad, and the to 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 develop ment in dam design is the hollow re enforced concrete dam, which consists essentially of water-tight concrete slabs supported on piers.
Rock-fill dams are constructed by pil ing largo 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 tempo rary structures.
Dams which are built to aid naviga tion, 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 hy draulic method. It is about 115 feet high and over 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 chan nel 819 feet wide. Over 20,000,000 cubic yards of material were used in its con struction.
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.