, The illustration shows a combination of steel i Among the notable masonry dams of the gravity type may be instanced the following: :,I: The Assouan Darn, across the Nile, in Egypt, largest masonry dam in the world. It is built of granite rubble, is 6,400 feet long, and has a maximum height of 112 feet. Its mass contains 1,179,000 cubic yards of solid masonry.
bents with a reinforced concrete deck, in a small dam erected at Theresa, N. Y.
High Masonry Dams.— The high masonry dam is comparatively recent, originating. in Spain some three centuries ago, but its rational design began with the Furens Dam in France less than a half century ago. The examples are not yet numerous, but the better quality of ma sonry for hydraulic construction and the greatly reduced cost, together with the more enlightened demand for the conservation of water for irri gation, water supply, xyater power, navigation and fisheries, combined with the greater security and permanence, promises an era of high ma sonry dams.
The approved cross-section has a thickneis at top of 8 to 10 per cent of the height, a curved batter down stream and a slightly curved batter up stream, the conditions being -that the locus of strain shall not pass outside the middle third, and that thg greatett pressure in the ma sonry Shall not exceed safe working limits, the latter being governed by the quality of the ma sonry. The construction is massive random rubble work with an avoidance of continuous beds and joints,' the upstream face in courses with' roughly dressed beds and joints, the down stream face of selected stone.' The top of the dam is usually finished as a roadway with pars -pet ;walls;.and the Spillway is constructed on an iiidependem location. The site is a rock gorge 'or canyon with a valley expanie'ailove for the reservoir. •, The New Croton Dam (built 1892-1906), a part of the water supply works of New York - city has a length of 1,168 feet, with spillway df L000 feet connecting at right angles. The - maxinium height Of the' dam is 297 feet, and ; the head of water 136 feet. The dam is part ',tubble and part cyclopean masonry, and has ,a , mass-of 855,000 cubic yards—by far the ler •' gest in America and second only to the great -Assouan .Dam on the Nile. (See diagram on
another page).
The of Olive Bcidge'Dain (New York city 'water suppty), across the Esopus -Creek, is 1,000 feet long, with continuing cote walls and embankment —4,800 feet in all. Its - maximum height is 251 feet. It is of cyelopean faced with concrete blocks. The :masonry mass has a content of 488,200 cubic iyards.
The Tansa Dam, in India (water supply of Bombay), is of rubble masonry, 8,800 feet long anc1.118 -feet high, with a mass of 408,500 cubic Yards.
The Waldeck Dam across the river Eder, in Germany, is of rubble-masonry. It is 900 feet long, 160 feet high and has a content of 392,400 cubic yards.
The Poona Dam, in India, is of rubble masonry, 5,136 feet long and 108 feet high, with a mass of 362,000 cubic yards, The Roosevelt Dam, in Arizona (built 1,905 11) , is of 'rubble masonry with ver tical joints. It. is feet' long and 260 feet high. It is 158 feet wide at, base and 16 feet at the top. Its content is 344,000 cubic yards.
The Mauer Dam, in Germany (built 1904 12), is of nibble masonry, 918 feet long and 208 -feet high. It has a mass of 332,000 cubic yards.
The Lake Chhesman Dam, of the Denver water supply, is one of the very high masonry dams Carrying a free head of water second only to'the Arrowrock Dam. It is 700 feet long on the crest,' with a maximam 'height' of 225 feet. It is built on a curve, the radius of which is 400 feet. it is Of granite rubble, with a mass of 103,000 cubiO yards. ' Of all-concrete dams of- the gravity type, the following are examples: 1‘ The Dami liver; the 'Boise River, iait it of;•cairerste• with as mania "plums') distributed through 'its mass - as could be conveniently placed. It is 1,160 feet long; with a maximum height of 351 feet —the highest dam in the world at the time of its completion. It is btiilt on a curve of 662 feet radius, though of gravity type, being 238 feet wide at the base, and feet at the crest. Its content is 530,000 cubic yards. The free head of water behind the dam is 248 feet-31 feet higher than at the Lake Cheesman Dam, which formerly held the record in this respect.