OCR

Though the first important reason for building was flood control, its other benefits also were epochal. Electric power and municipal water were badly needed for growing western cities and industries. Silt control was essential. The dam would also regulate the river for navigation, and its lake would supply a new recreation area and wild-life refuge. Before Hoover Dam could be built, roads and railroads were blasted over the searing desert, a model town was erected to protect 5, 000 workers and their families from the elements, factories were built to fabricate steel penstocks too large to be hauled by any railroad or truck, and the largest gravel plant then known was constructed. A year and four months of work and $25,000,000 went into the job before anything could be done on the dam itself. With its 726 foot height, Hoover is one of the highest dams in the world. Stretching 1,282 feet across the canyon, it impounds Lake Mead, which holds enough water to cover the State of New York one foot deep, and to contain the entire flow of the river for two years. Two trough-like spillways, each large enough to float a battleship, one on each side of the river, provide for discharge of any excess water. Into the dam's high bulk went 5,000,000 barrels of cement, 22, 000 tons of reinforcing steel, 9, 000 tons of structural steel, 8, 000, 000 tons of sand, gravel, and cobbles and 10,500 tons of gates and valves. Four 50-foot diversion tunnels, the largest ever opened were blasted through the cliffs nearly one mile around the dam, and two cofferdams, each larger than many permanent dams, were built to divert the river and protect the workers and machinery from the water while the dam was built. The Bureau of Reclamation also has several books available for purchase on this subject, if more information is needed. Hoover Dam Tunnels - More than 50 tunnels and shafts were required in the preliminary work and actual construction of Hoover Dam on the Colorado River. As stated above the dam creates Lake Mead which, at maximum capacity of 30,500,000 acre feet, is 115 miles long, with a maximum, width of 8 miles and a surface area of 146,500 acres. It drains an area of 167,000 square miles, with an average annual run-off of 15,000,000 acre feet. Tunnels and shafts range in size from 5 ft. x 6 ft. access drifts to 4, 000 ft. diversion tunnels and 600 it. inclined spillway tunnels excavated to 56 feet in diameter. 3 ft. concrete linings bring the completed inside diameters to 50 ft. Also included were 41 ft. penstock header tunnels, 21 ft, penstock tunnels, 26 ft. x 43 ft. construction adits and miscellaneous shafts.