Dam
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 DAM 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 possibly 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, DAM 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. feet wide at the base. 145 feet high, 1,025 feet long and 750 in layers, and completed in 1913. It is Irrigation project is an earth dam built 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.
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 The Shoshone Dam is a masonry dam up to the level of the river bed. The 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 1911.
Roosevelt Dam was also constructed by Idaho, construction of which was started in 1914 by the same Government agency, The Arrowrock, near is 354 feet high, and 1,060 feet long. It Boise, الله N ST 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 2½ to 1. It is a hydraulic fill dam.
The new Croton Dam of the New York City Water Supply System was The new Croton Dam of the New 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. gravity secis curved upstream, with a g tion, and is built of concrete.
Mississippi river at Keokuk, Ia., is a long, low concrete dam. Besides the spillway section, is an abutment 290 feet long, a combina- The Keokuk Dam, which crosses the of a power house, and a lock section of tion, another 1,700 feet long, in the form on, 4,278 feet long, there about 600 feet.
The Elephant Butte Dam, located a near Engle, N. M., was dedicated on ice dam of rubble concrete, with gravity section. It is 1,200 feet long and 304.5 feet high from base to top.
Oct. 19, 1916. It is a Reclamation Serv- The hydro-electric development dam of the Yadkin river, N. C., contains a dam 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, 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.
DAM 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 h االله ROOSEVELT DAM, ARIZONA 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 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, siphon spillway. It will be located in the Tuolumne river 150 miles E. of bridge supports, etc., when in May, 1889, excessive rains caused the water to go the Tuolumne San Francisco. over the entire length of the dam. The DAMAN 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.
DAMASK gardens and orchards and watered by the Barrada. The appearance of the city, as it first opens on the view, has been rapturously rapturously spoken of by all travelers; but the streets are narrow, crooked, and in parts dilapidated, and, except in the wealthy Moslem quarter, the houses are low, with flat-arched doors and accumulations of filth before the entrance. Within, however, there is often a singular contrast, in courts paved with marble and ornamented with trees and spouting fountains the rooms adorned with arabesques and filled with splendid furniture. Among the chief buildings are the Great Mosque and the Citadel. The bazaars are a notable feature of Damascus. They are simply streets or lanes covered in with high wood-work and lined with shops, stalls, cafés, etc.
DAMAN (dä-män'), or DAMÃO, a fortified post and district in India, belonging to Portugal since 1558, the Gulf of Cambay, 100 miles N. of being used as exchanges or market Bombay. The climate is generally healthy, the soil moist and fertile. The chief products are cereals, rice, tobacco, and wheat, and there are also important deep-sea fisheries and salt works.
Administratively the district belongs to GOA (q. v.). Area, 170 square miles; Pop. about 75,000.
DAMARALAND (dä-märä-), a territory in the W. of south Africa, between Namaqualand and Ovampoland proper, extending from the Atlantic to about 19° 45′ E. lon. Behind the waterless coast region (100 miles) rises a mountain district, with peaks over 8,500 feet above the sea; and farther inland stretch wide prairies. The mountains are rich in minerals, especially copper; vegetation is confined to their valleys, and to the prairie region, which in the N. enjoys a fine rainfall. The produce of the interior consists of ivory, feathers, skins, etc. The Damaras, properly Herero, a Bantu stem, number about 80,- 000, of whom 50,000 live in the mountain district; they are nomads, and own large flocks and herds. The Hawkoin, or Hill Damaras, in the N. E., however, who are a much lower type, now speak Hottentot. The only harbor in this part of the coast is Walfish Bay, which belongs to Great Britain. The rest of German colony, GERMAN SOUTHWEST Damaraland forms part of the former AFRICA (q. v.). In 1884 the desert region along the coast was made a German protectorate.
DAMASCUS, a celebrated city, formerly capital of the Turkish vilayet of Syria, now capital of the independent state of SYRIA (q. v.). It is beautifully situated on a plain which is covered with In the midst of the bazaars stands the Great Khan, it and 30 inferior khans places by the merchants. One of the most important and busiest streets is "Straight Street," mentioned in connection with the conversion of the Apostle Paul. Damascus is an important emporium of trade in European manufactures; it is also a place of considerable manufacturing industry in silk, damasks, cotton and other fabrics, tobacco, glass, soap, etc. Saddles, fine cabinet-work, and elegant jewelry are well made; but the manufacture of the famous Damascus blades no longer exists. It has railway connections with Aleppo, Beirut, and the Hejas, and is the seat of a Melchite Patriarch. It is one of the holy Moslem cities, and continues to be one of the most thoroughly Oriental in all its features of any city in existence. Of its origin nothing nothing certain is known; but it is of great antiquity, being mentioned as a place apparently of importance in Gen. xiv: 15. After passing successively under the power of Israelites, Persians, Greeks, and Romans, it fell at last in 1516 into the hands of the Turks.
Oct. 1, 1918, the city was occupied by British troops. Pop. about 250,000.
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