The Elephant Butte Dam, across the Rio Grande in New Mexico, is of cyclopean concrete carried up in huge block sections. It is 1,310 feet long and 305 feet high, with a cubical con tent amounting to 608,000 cubic yards, making it the third largest masonry dam in the world, surpassed in bulk only by the Assouan Dam in Egypt and the New Croton Dam in New York.
The Keokuk Dam on the Mississippi is a massive concrete monolith, 4,649 feet long and 53 feet high. It is 29 feet wide at the top and 42 feet at the bottom. The spillway section is 4,278 feet in length and a height of 36 feet, allowing for a head of 11 feet over the crest. The deck of the dam above the spillway is supported on 119 arches, 36 feet from centre to centre, on 6-foot piers. From this deck are operated the steel gates (11 feet by 32 feet) which close the spillway openings. In building this dam concrete was poured 40 feet deep per day—a 15-foot lift, then 5 hours for setting, followed by the 25-foot lift.
The Barcelona (Spain) Dam, completed in 1916, the largest dam in Europe, is of concrete and was built by American engineers. Its maximum height is 330 feet and its length on the crest is 700 feet. The thickness at the base is 230-feet and at the crest 14 feet. The dam holds an artificial lake miles long and 3g miles wide, designed to irrigate 100 square miles of arid country and also furnish 20,000 electric horse power, later to be increased to 40,000 horse power. , Notable examples of the arch type of dam are the following: The/ old Bear Valley Dam (built in 1884) surpassed in boldness of design all dams pre viously built. It was of granite faces with rubble filling, set in Portland cement. It '450 feet long and arched to a 'radius' of ' 335 feet. Its maximum height was 64 feet and it was 20 feet thick at the base and 3.2 feet at the crest. Notwithstanding the severe criticism it received,, it stood unimpaired until submerged in 1915 behind the new dam.
Barossa Dam, in Australia (built 1899-1903), is of cyclopean masonry. It has a maximum height of 113 feet and is 42 feet thick at the base and feet at the crest.
An arch dam of remarkable design was re cently built across Crowley Creek, in Oregon. It is of gravel concrete, without reinforiae ment, 170 feet long with a maximum height of 65 feet. It is 5.2 feet thick at the base and 3 feet at the crest. For the upper 30 feet the
faces arelarallel, the slight batter being bekw that section on the downstream side.
The Shoshone and Pathfinder dams, Wyoming, depend in part upon their arch form for stability.
Shoshone Dam (built 1905-10) is of rubble masonry, arched to a radius of 150 feet. 200 feet long, with a maximum height of feet. It is 108 feet thick at the base and 10 feet at the crest.
Pathfinder Dam, across the North Platt River (built 1906-10), is of masonry, arched to a radius of 150 feet. It has a maximum height of 210 feet and is 94 feet thick at the base and 11 feet at the crest.
Among the more recent hollow dams are: Douglas or La Prele Dam, in Wyoming (built 1908-09), an open front dam of the Am btirsen type, 360 feet long and 135 feet maxi mum height. The deck is at an angle of 40 de grees with the horizontal and is 12 inches thick at the top and 54 inches at the bottom. The sup porting buttresses are 18 feet between centres, 12 inches thick at the top and 50 inches at the bottom, 10 feet deep at the crest and 160 feet at the base. The material is reinforced concrete. The whole batter is on the water face.
Jordan River Dam, on Vancouver's Island, is of reinforced concrete, 756 feet long and 126 feet high. The buttresses are 754 feet deep at the crest and 148 feet at the base. They are placed 18 feet between centres and are 12 inches thick at the top and 42 inches at the bottom. The deck (cast after the buttresses 16 inches thick at the top and 31 inches at the bottom. A rock foundation not being avail able, the buttresses were built on a thick mat tress of concrete.
Adjuncts.— The ordinary dam across a stream is its own spillway. For impounding dams of earth or rock-fill the necessity for independent spillway is obvious. It should be equally obvious for the high masonry dam, and this is now recognized by the best practice. Many errors have been made, especially in arid regions, through insufficient spillway. In humid regions the ((greatest flood" occurs two or three times in a century, and if these are provided for, the margin is usually sufficient for any con tingency. In the arid regions a flood as great may be possible, but the occurrence is far more erratic. Cloudbursts produce startling effects in small basins, but the results in basins of considerable area are not significant.