The bills were introduced by Congressman Phil D. Swing and Senator Hiram W. Johnson and were known as the Swing-Johnson bills. The bills failed to come up for a vote and were subsequently reintroduced several times. In December 1928, both the House and the Senate finally approved the bill and sent it to the President for approval. On December 21, 1928, President Calvin Coolidge signed the bill approving the Boulder Canyon Project. The initial appropriation for construction was made in July 1930, by which time Herbert Hoover had become President.Early plans called for the dam to be built in Boulder Canyon, so the project was known as the Boulder Canyon Project. The dam site was eventually moved downstream eight miles to Black Canyon, but the project name remained the same.\n\nConstruction\n\n[edit] Groundworks\n \nHoover Dam Architectural PlansOverview Of Dam MechanismsTo protect the construction site from flooding, two cofferdams were constructed. Construction of the upper cofferdam began in September 1932, even though the river had not yet been diverted. A temporary horseshoe-shaped dike protected the cofferdam on the Nevada side of the river. After the Arizona tunnels were completed, and the river diverted, the work was completed much faster. Once the coffer dams were in place and the construction site dewatered, excavation for the dam foundation began. For the dam to rest on solid rock, it was necessary to remove all loose material until solid rock was reached. Work on the foundation excavations was completed in June 1933. During excavations for the foundation, approximately 1,500,000 yd³ (1,150,000 m³) of material was removed, including material removed in canyon wall stripping operations.\n\n\n[edit] River diversion\nTodivert the river\'s flow around the construction site, four diversion tunnels were driven through the canyon walls, two on the Nevada side and two on the Arizona side. These tunnels were 56 feet (17.07 m) in diameter. Their combined length was nearly 16,000 feet (4877 m, more than three miles). Tunneling began at the lower portals of the Nevada tunnels in May 1931. Shortly after, work began on two similar tunnels in the Arizona canyon wall. In March 1932, work began on lining the tunnels with concrete. First the base or invert was poured. Gantry cranes, running on rails through the entire length of each tunnel were used to place the concrete. The sidewalls were poured next. Movable sections of steel forms were used for the sidewalls. Finally, using pneumatic guns, the overheads were filled in. The concrete lining is 3 feet (914.4 mm) thick, reducing the finished tunnel diameter to 50 ft (15.24 m).Following the completion of the dam the entrances to the two outer diversion tunnels were sealed at the opening and half way through the tunnels with large concrete plugs. The downstream half of the tunnels following the inner plugs, are now the main body of the spillway tunnels. The spillways canbe seen directly above the outer diversion tunnels. They drop sharply from their entrance point and merge directly into the old diversion tunnels.\n\n \nTwo intake towers on the Arizona side.The two inner diversion tunnels have two concrete plugs in them. One is roughly half way along their length, and the other is around 75% of the way along their length. The section sandwiched between two concrete plugs is used as part of the tunnel which water travels along, to journey from the outermost intake towers and the generators. The two innermost intake towers have separate tunnels.\n\nThe large spillway tunnels have only been used three times in the history of the dam; the first was during the second half of 1941 for testing. The second was for about six weeks during the summer of 1983, when record precipitation and snow-melt in the Colorado River basin drained into Lake Mead, and the third in 1999, again with heavy precipitation that filled Lake Mead.\n\n\n\nArizona Nevada