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When the cofferdams were in place and the construction site was drained of water , excavation for the dam foundation began . For the dam to rest on solid rock , it was necessary to remove accumulated erosion soils and other loose materials in the riverbed until sound bedrock was reached . Work on the foundation excava... |
The men who removed this rock were called " high scalers " . While suspended from the top of the canyon with ropes , the high @-@ scalers climbed down the canyon walls and removed the loose rock with jackhammers and dynamite . Falling objects were the most common cause of death on the dam site ; the high scalers ' wor... |
The cleared , underlying rock foundation of the dam site was reinforced with grout , called a grout curtain . Holes were driven into the walls and base of the canyon , as deep as 150 feet ( 46 m ) into the rock , and any cavities encountered were to be filled with grout . This was done to stabilize the rock , to preve... |
= = = Concrete = = =
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The first concrete was poured into the dam on June 6 , 1933 , 18 months ahead of schedule . Since concrete heats and contracts as it cures , the potential for uneven cooling and contraction of the concrete posed a serious problem . Bureau of Reclamation engineers calculated that if the dam was built in a single contin... |
The concrete was delivered in huge steel buckets 7 feet high ( 2 @.@ 1 m ) and almost 7 feet in diameter ; Crowe was awarded two patents for their design . These buckets , which weighed 20 short tons ( 18 t ) when full , were filled at two massive concrete plants on the Nevada side , and were delivered to the site in ... |
A total of 3 @,@ 250 @,@ 000 cubic yards ( 2 @,@ 480 @,@ 000 m3 ) of concrete was used in the dam before concrete pouring ceased on May 29 , 1935 . In addition , 1 @,@ 110 @,@ 000 cu yd ( 850 @,@ 000 m3 ) were used in the power plant and other works . More than 582 miles ( 937 km ) of cooling pipes were placed within ... |
= = = Dedication and completion = = =
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With most work finished on the dam itself ( the powerhouse remained uncompleted ) , a formal dedication ceremony was arranged for September 30 , 1935 , to coincide with a western tour being made by President Franklin D. Roosevelt . The morning of the dedication , it was moved forward three hours from 2 p.m. Pacific ti... |
Most work had been completed by the dedication , and Six Companies negotiated with the government through late 1935 and early 1936 to settle all claims and arrange for the formal transfer of the dam to the Federal Government . The parties came to an agreement and on March 1 , 1936 , Secretary Ickes formally accepted t... |
= = = Construction deaths = = =
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There were 112 deaths associated with the construction of the dam . The first was J. G. Tierney , a surveyor who drowned on December 20 , 1922 , while looking for an ideal spot for the dam . Ninety @-@ six of the deaths occurred during construction at the site . Of the 112 fatalities , 91 were Six Companies employees ... |
Not included in the official fatalities number were deaths that were recorded as pneumonia . Workers alleged that this diagnosis was a cover for death from carbon monoxide poisoning , brought on by the use of gasoline @-@ fueled vehicles in the diversion tunnels , and a classification used by Six Companies to avoid pa... |
= = = Architectural style = = =
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The initial plans for the facade of the dam , the power plant , the outlet tunnels and ornaments clashed with the modern look of an arch dam . The Bureau of Reclamation , more concerned with the dam 's functionality , adorned it with a Gothic @-@ inspired balustrade and eagle statues . This initial design was criticiz... |
At Kaufmann 's request , Denver artist Allen Tupper True was hired to handle the design and decoration of the walls and floors of the new dam . True 's design scheme incorporated motifs of the Navajo and Pueblo tribes of the region . Although some initially were opposed to these designs , True was given the go @-@ ahe... |
With the agreement of Kaufmann and the engineers , True also devised an innovative color @-@ coding for the pipes and machinery , which was implemented throughout all BOR projects . True 's consulting artist job lasted through 1942 ; it was extended so he could complete design work for the Parker , Shasta and Grand Co... |
Complementing Kaufmann and True 's work , the Norwegian @-@ born , naturalized American sculptor Oskar J.W. Hansen designed many of the sculptures on and around the dam . His works include the monument of dedication plaza , a plaque to memorialize the workers killed and the bas @-@ reliefs on the elevator towers . In ... |
Surrounding the base of the monument is a terrazzo floor embedded with a " star map " . The map depicts the Northern Hemisphere sky at the moment of President Roosevelt 's dedication of the dam . This is intended to help future astronomers , if necessary , calculate the exact date of dedication . The 30 @-@ foot @-@ h... |
= = Operation = =
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= = = Power plant and water demands = = =
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Excavation for the powerhouse was carried out simultaneously with the excavation for the dam foundation and abutments . A U @-@ shaped structure located at the downstream toe of the dam , its excavation was completed in late 1933 with the first concrete placed in November 1933 . Filling of Lake Mead began February 1 ,... |
In the latter half of 1936 , water levels in Lake Mead were high enough to permit power generation , and the first three Allis Chalmers built Francis turbine @-@ generators , all on the Nevada side , began operating . In March 1937 , one more Nevada generator went online and the first Arizona generator by August . By ... |
Before water from Lake Mead reaches the turbines , it enters the intake towers and then four gradually narrowing penstocks which funnel the water down towards the powerhouse . The intakes provide a maximum hydraulic head ( water pressure ) of 590 ft ( 180 m ) as the water reaches a speed of about 85 mph ( 140 km / h )... |
Control of water was the primary concern in the building of the dam . Power generation has allowed the dam project to be self @-@ sustaining : proceeds from the sale of power repaid the 50 @-@ year construction loan , and those revenues also finance the multimillion @-@ dollar yearly maintenance budget . Power is gene... |
Lake Mead and downstream releases from the dam also provide water for both municipal and irrigation uses . Water released from the Hoover Dam eventually reaches several canals . The Colorado River Aqueduct and Central Arizona Project branch off Lake Havasu while the All @-@ American Canal is supplied by the Imperial D... |
= = = = Power distribution = = = =
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Electricity from the dam 's powerhouse was originally sold pursuant to a fifty @-@ year contract , authorized by Congress in 1934 , which ran from 1937 to 1987 . In 1984 , Congress passed a new statute which set power allocations from the dam from 1987 to 2017 . The powerhouse was run under the original authorization ... |
= = = Spillways = = =
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The dam is protected against over @-@ topping by two spillways . The spillway entrances are located behind each dam abutment , running roughly parallel to the canyon walls . The spillway entrance arrangement forms a classic side @-@ flow weir with each spillway containing four 100 @-@ foot @-@ long ( 30 m ) and 16 @-@... |
The large spillway tunnels have been used only twice , for testing in 1941 and because of flooding in 1983 . During both times , when inspecting the tunnels after the spillways were used , engineers found major damage to the concrete linings and underlying rock . The 1941 damage was attributed to a slight misalignment... |
= = = Roadway and tourism = = =
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There are two lanes for automobile traffic across the top of the dam , which formerly served as the Colorado River crossing for U.S. Route 93 . In the wake of the September 11 , 2001 terrorist attacks , authorities expressed security concerns and the Hoover Dam Bypass project was expedited . Pending the completion of ... |
Hoover Dam opened for tours in 1937 after its completion , but following Japan 's attack on Pearl Harbor on December 7 , 1941 , it was closed to the public when the United States entered World War II , during which only authorized traffic , in convoys , was permitted . After the war , it reopened September 2 , 1945 , ... |
= = Environmental impact = =
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The changes in water flow and use caused by Hoover Dam 's construction and operation have had a large impact on the Colorado River Delta . The construction of the dam has been credited as causing the decline of this estuarine ecosystem . For six years after the construction of the dam , while Lake Mead filled , virtua... |
The Colorado River had experienced natural flooding before the construction of the Hoover Dam . The dam eliminated the natural flooding , which threatened many species adapted to the flooding , including both plants and animals . The construction of the dam devastated the populations of native fish in the river downst... |
= = Naming controversy = =
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During the years of lobbying leading up to the passage of legislation authorizing the dam in 1928 , the press generally referred to the dam as " Boulder Dam " or as " Boulder Canyon Dam " , even though the proposed site had shifted to Black Canyon . The Boulder Canyon Project Act of 1928 ( BCPA ) never mentioned a pro... |
When Secretary Wilbur spoke at the ceremony starting the building of the railway between Las Vegas and the dam site on September 17 , 1930 , he named the dam " Hoover Dam " , citing a tradition of naming dams after Presidents , though none had been so honored during their terms of office . Wilbur justified his choice ... |
After Hoover 's election defeat in 1932 and the accession of the Roosevelt administration , Secretary Ickes ordered on May 13 , 1933 that the dam be referred to as " Boulder Dam " . Ickes stated that Wilbur had been imprudent in naming the dam after a sitting president , that Congress had never ratified his choice , a... |
When Ickes spoke at the dedication ceremony on September 30 , 1935 , he was determined , as he recorded in his diary , " to try to nail down for good and all the name Boulder Dam . " At one point in the speech , he spoke the words " Boulder Dam " five times within thirty seconds . Further , he suggested that if the da... |
In the following years , the name " Boulder Dam " failed to fully take hold , with many Americans using both names interchangeably and mapmakers divided as to which name should be printed . Memories of the Great Depression faded , and Hoover to some extent rehabilitated himself through good works during and after Worl... |
= Tropical Storm Abby ( 1964 ) =
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Tropical Storm Abby was an exceptionally small tropical cyclone that had minor effects across Southeast Texas in early August 1964 . Forming as a tropical depression out of a trough south of Louisiana on August 5 , the system moved generally westward . It was not until August 7 that the system began to organize . That... |
Prior to Abby 's landfall in Texas , gale warnings were issued for the coast and residents on Matagorda Island were evacuated . Overall , the storm 's impacts were limited due to its small size . Only two structures sustained damage in Matagorda , one being destroyed by a possible tornado , and the remaining effects r... |
= = Meteorological history = =
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On August 5 , 1964 , a weak trough emerged from Florida over the northeastern Gulf of Mexico . According to the Atlantic hurricane database ( referred to as HURDAT ) , the system developed into a tropical depression by 18 : 00 UTC ( 1 : 00 p.m. CDT ) that day , with its center located roughly 160 mi ( 260 km ) south @... |
Abby was an unusually small storm , with its entire circulation being far less than 100 mi ( 160 km ) in diameter . Around 16 : 00 UTC ( 11 : 00 a.m. CDT ) on August 7 , reconnaissance measured a central barometric pressure of 1000 mbar ( hPa ; 29 @.@ 53 inHg ) within Abby , the lowest in relation to the system . They... |
= = Preparations and impact = =
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Owing to the abrupt nature of Abby 's development on August 7 , residents had little time to prepare for the storm . According to Irvin Velbrecht , " in the absence of aircraft reconnaissance and radar information , two reasonably new tools in storm detection , Abby could well have formed and approached the shore befo... |
Abby 's small size resulted in its effects being limited to areas within the immediate track . Sustained winds of 45 mph ( 75 km / h ) with gusts to 65 mph ( 100 km / h ) were measured by the Army Corps of Engineers in Matagorda . Near the town , a possible tornado unroofed a barn and tossed the structure 225 ft ( 69 ... |
Heavy rains accompanied the system across Texas . Most areas along the immediate track received at least 3 to 5 in ( 76 to 127 mm ) of rain , with a peak value of 6 @.@ 14 in ( 156 mm ) recorded at the Victoria International Airport . The hardest hit areas were in Jackson and Victoria counties where the heaviest rains... |
= 7 Independent Company ( Rhodesia ) =
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7 Independent Company ( 7 Indep Coy ; French : 7ème Compagnie indépendante ) was a short @-@ lived company of francophone volunteers in the Rhodesian Army during the Rhodesian Bush War . Numbering about 200 men at its peak , it was unique in the history of the Rhodesian Army as an exclusively expatriate unit . It exis... |
During the Bush War , the Rhodesian Army augmented its ranks with foreign volunteers , who were accepted into regular regiments with the same pay and conditions of service as locals . Most foreign recruits enlisted in the Rhodesian Light Infantry ( RLI ) , which launched an overseas recruitment programme in 1974 , but... |
The company 's men , a mixture of former French paratroopers , ex @-@ Foreign Legionnaires and young adventurers , had trouble from the start integrating with the Rhodesian forces , and became unsettled by the respective ranks they were given in the Rhodesian Army . In an attempt to raise their morale and create a str... |
On operations their performance was generally below par , but the Frenchmen were involved in some successful actions during February and early March 1978 . Their oppressive treatment of the black villagers they encountered made them very unpopular in the operational area . The Rhodesians quickly deemed the experiment ... |
= = Background = =
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Following a dispute with the British government regarding terms for the granting of full independence , the predominantly white minority government of the self @-@ governing colony of Rhodesia ( or Southern Rhodesia ) , led by Ian Smith , unilaterally declared independence on 11 November 1965 . Britain and the United ... |
The Rhodesian Bush War was the result , beginning in earnest on 21 December 1972 when ZANLA attacked Altena and Whistlefield Farms near Centenary in the country 's north @-@ east . The Rhodesian Security Forces launched Operation Hurricane in response and fought back strongly , reducing the number of guerrillas active... |
The Rhodesian Army , though mostly made up of local men , also included some foreign volunteers , who were integrated into regular units under the same salary and conditions of service . Almost all of the foreigners served in the Rhodesian Light Infantry ( RLI ) , a heliborne commando battalion with a glamorous intern... |
= = Formation and training = =
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The idea for a francophone unit came from a French national , François Cramer , who had business interests and connections in Rhodesia . He proposed it to Major @-@ General Sandy MacLean , then the Rhodesian Army 's second @-@ in @-@ command , while they were visiting France together . MacLean relayed the idea to the ... |
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