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The Colorado River and Hoover Dam
Facts and Figures
The river and its tributaries - the Green, the Gunnison, the San Juan, the Virgin, the Little Colorado, and the Gila Rivers - are called the "Colorado River Basin." These rivers drain 242,000 square miles in the United States, or one-twelfth of the country's continental land area, and 2,000 square miles in Mexico. Seven western states and Mexico have beneficial interests in the Colorado River Basin.
What States have beneficial interests in the Colorado River?The Colorado River Basin states are: Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming. Each state is party to the Colorado River Compact entered into in Santa Fe, New Mexico, on November 24, 1922.
How is the Colorado River Basin divided?The Colorado River Compact divided the Colorado River Basin into the Upper Basin and the Lower Basin. The division point is Lees Ferry, a point in the mainstem of the Colorado River about 30 river miles south of the Utah-Arizona boundary. The "Upper Basin" includes those parts of the States of Arizona, Colorado, New Mexico, Utah, and Wyoming within and from which waters naturally drain into the Colorado River system above Lees Ferry, and all parts of these States that are not part of the river's drainage system but may benefit from water diverted from the system above Lees Ferry.
The "Lower Basin" includes those parts of the States of Arizona, California, Nevada, New Mexico, and Utah within and from which waters naturally drain into the Colorado River system below Lees Ferry, and all parts of these States that are not part of the river's drainage system but may benefit from water diverted from the system below Lees Ferry.
How is Colorado River water apportioned?The Colorado River Compact apportioned to each basin the exclusive, beneficial consumptive use of 7,500,000 acre-feet of water per year from the Colorado River system in perpetuity. In addition, the Compact gave to the Lower Basin the right to increase its annual beneficial consumptive use of such water by 1,000,000 acre-feet.
How much water is apportioned to each State in the Colorado River Basin?The Colorado River Compact did not apportion water to any State.
On October 11, 1948, the Upper Basin States entered into the Upper Colorado River Basin Compact, which apportioned use of the Upper Basin waters among them. The compact permits Arizona to use 50,000 acre-feet of water annually from the upper Colorado River system, and apportioned the remaining water to the Upper Basin States in the following percentages: Colorado, 51.75 percent; New Mexico, 11.25 percent; Utah, 23 percent; and Wyoming, 14 percent. The Lower Basin States of Arizona, California, and Nevada were not able to reach agreement. In 1952, Arizona filed suit in the United States Supreme Court to determine how the waters of the Lower Basin should be divided. In October 1962, the Court ruled that of the first 7,500,000 acre-feet of mainstem water in the Lower Basin, California is entitled to 4,400,000 acre-feet, Arizona 2,800,000 acre-feet, and Nevada, 300,000 acre-feet. The United States has contracted with the States of Arizona and Nevada and with various agencies in Arizona and California for the delivery of Colorado River water. These contracts make delivery of the water contingent upon its availability for use in the respective States under the Colorado River Compact and the Boulder Canyon Project Act.
What are Mexico's rights to Colorado River water?The United States and Mexico entered into a treaty on February 3, 1944, which guarantees Mexico 1,500,000 acre-feet of Colorado River water annually. This entitlement is subject to increase or decrease under certain circumstances provided for in the treaty.
Where is Hoover Dam?In Black Canyon on the Colorado River, about 30 miles southeast of Las Vegas, Nevada.
How high is Hoover Dam?It is 726.4 feet from foundation rock to the roadway on the crest of the dam. The towers and ornaments on the parapet rise 40 feet above the crest.
How much does Hoover Dam weigh?More than 6,600,000 tons.
What type of dam is Hoover?A concrete arch-gravity type, in which the water load is carried by both gravity action and horizontal arch action.
What is the maximum water pressure at the base of the dam?45,000 pounds per square foot.
How much concrete is in the dam?Three and one-quarter million cubic yards. There are 4,360,000 cubic yards of concrete in the dam, powerplant, and appurtenant works. This much concrete would build a monument 100 feet square and 2-1/2 miles high; would rise higher than the Empire State Building (which is 1,250 feet) if placed on an ordinary city block; or would pave a standard highway, 16 feet wide, from San Francisco to New York City.
The first concrete for the dam was placed on June 6, 1933, and the last concrete was placed in the dam on May 29, 1935. Approximately 160,000 cubic yards of concrete were placed in the dam per month. Peak placements were 10,462 cubic yards in one day (including some concrete placed in the intake towers and powerplant), and slightly over 275,000 cubic yards in one month.
How much cement was required?More than 5 million barrels. The daily demand during construction of the dam was from 7,500 to 10,800 barrels. Reclamation had used only 5,862,000 barrels in its 27 years of construction activity preceding June 30, 1932.
How was chemical heat caused by setting cement in the dam dissipated?By embedding more than 582 miles of l-inch steel pipe in the concrete and circulating icewater through it from a refrigeration plant that could produce 1,000 tons of ice in 24 hours. Cooling was completed in March 1935.
What was an unusual feature of Hoover Dam's construction?The dam was built in blocks or vertical columns varying in size from about 60 feet square at the upstream face of the dam to about 25 feet square at the downstream face. Adjacent columns were locked together by a system of vertical keys on the radial joints and horizontal keys on the circumferential joints. Concrete placement in any one block was limited to 5 feet in 72 hours. After the concrete was cooled, a cement and water mixture called grout was forced into the spaces created between the columns by the contraction of the cooled concrete to form a monolithic (one piece) structure.
What were the principal items of work?More than 5,500,000 cubic yards of material were excavated, and another 1,000,000 cubic yards of earth and rockfill placed. By feature, this included:
Excavation for the diversion tunnels, 1,500,000 cubic yards; for the foundation of the dam, powerplant, and cofferdams 1,760,000 cubic yards; for the spillways and inclined tunnels, 750,000 cubic yards; for the valve houses and intake towers, 410,000 cubic yards; earth and rockfill for the cofferdams, 1,000,000 cubic yards. In addition, 410,000 linear feet of grout and drainage holes were drilled, and 422,000 cubic feet of grout were placed under pressure.
What were the quantities of principal materials used in the dam?The principal materials, all of which were purchased by the government, were: reinforcement steel, 45,000,000 pounds; gates and valves, 21,670,000 pounds; plate steel and outlet pipes, 88,000,000 pounds; pipe and fittings, 6,700,000 pounds or 840 miles; structural steel, 18,000,000 pounds; miscellaneous metal work, 5,300,000 pounds.
What are the geologic conditions at the damsite?The foundation and abutments are rock of volcanic origin geologically called "andesite breccia." The rock is hard and very durable.
What were the excavation depths from the river's low-water surface to foundation rock?In the upstream cutoff trench, it was 139 feet. The remaining excavation depths average 110 to 130 feet.
How long did it take to build the dam, powerplant, and appurtenant works?Five years. The contractors were allowed 7 years from April 20, 1931, but concrete placement in the dam was completed May 29, 1935, and all features were completed by March 1, 1936.
How many men were employed during the dam's construction?An average of 3,500 and a maximum of 5,218, which occurred in June 1934. The average monthly payroll was $500,000.
What construction work was necessary before operations started at the damsite?(1) Construction of Boulder City to house both Government and contractor employees; (2) construction of 7 miles of 22-foot wide, asphalt-surfaced highway from Boulder City to the damsite; (3) construction of 22.7 miles of standard-gauge railroad from the Union Pacific main line in Las Vegas to Boulder City and an additional 10 miles from Boulder City to the damsite; and (4) construction of a 222-mile-long power transmission line from San Bernardino, California, to the damsite to supply energy for construction.
What is the lake's elevation at high-water?The high-water line is at 1,229 feet above sea level. At this elevation, the water would be more than 7 feet over the top of the raised spillway gates, which are at elevation 1221.4 feet. All lands below elevation 1,250 have been retained for reservoir purposes.
What is the reservoir's area?At elevation 1221.4 feet, the reservoir covers about 157,900 acres or 247 square miles.
How long and wide is the reservoir?At elevation 1221.4, Lake Mead extends approximately 110 miles upstream toward the Grand Canyon. It also extends about 35 miles up the Virgin River. The width varies from several hundred feet in the canyons to a maximum of 8 miles.
How much water will Lake Mead hold?At elevation 1221.4, it would contain 28,945,000 acre-feet. An acre-foot is the amount of water required to cover 1 acre to a depth of 1 foot, or approximately 326,000 gallons. The reservoir will store the entire average flow of the river for 2 years. That is enough water to cover the State of Pennsylvania to a depth of one foot.
How is the reservoir capacity allotted?Below elevation 1,229, about 1,500,000 acre-feet of storage capacity is reserved exclusively for flood control; about 2,547,000 acre-feet for sedimentation control; about 18,438,000 acre-feet for joint use (flood control, municipal and industrial water supply, irrigation, and power); and 7,683,000 acre-feet for inactive storage.
Who operates the dam and reservoir?The Bureau of Reclamation operates and maintains the dam, powerplant and reservoir. The National Park Service administers Lake Mead as part of the Lake Mead National Recreation Area.
How much sediment will be deposited in the reservoir?Between 1935 and 1963, about 91,500 acre-feet of sediment was deposited in Lake Mead each year. With closure of Glen Canyon Dam, about 370 miles upstream, the life of Lake Mead is indefinite.
TUNNELS, TOWERS, PENSTOCKS AND SPILLWAYS
How was the river diverted during dam construction?The river was diverted around the damsite through four 50-foot diameter tunnels, two on each side of the river drilled through the canyon walls. The tunnels, with a total length of 15,946 feet, or about 3 miles, were excavated to 56 feet and lined with 3 feet (300,000 cubic yards) of concrete. The tunnels could carry over 200,000 cubic feet - more than 1.5 million gallons - of water per second! The river was diverted through the two Arizona tunnels on November 14, 1932.
After being used for river diversion, how were the tunnels used?The inner tunnels were plugged with concrete approximately one-third their length below the inlets, and the outer tunnels were plugged approximately halfway. The two inner tunnels contain 30-foot diameter steel pipes which connect the intake towers in the reservoir with the penstocks to the powerplant and the canyon wall outlet works. The downstream halves of the two outer tunnels are used for spillway outlets.
What gates are installed on the tunnels?The inlets of the two outer tunnels are permanently closed with 50- by 50-foot bulkhead gates. Each gate, with steel frame, weighs about 3,000,000 pounds, and required 42 railroad cars for shipment. At the outlets of the two inner tunnels, 50- by 35-foot Stoney gates are installed. These gates can be closed when the tunnels need to be emptied for inspections or repairs.
What are the intake towers?They are four reinforced-concrete structures located above the dam, two on each side of the canyon. The diameter of these towers is 82 feet at the base, 63 feet 3 inches at the top, and 29 feet 8 inches inside. Each tower is 395 feet high and each controls one-fourth the supply of water for the powerplant turbines. The four towers contain 93,674 cubic yards of concrete and 15,299,604 pounds of steel.
How are these towers connected to the powerplant and outlet valves?By 30-foot-diameter penstocks installed in 37- and 50-foot diameter concrete-lined tunnels. The upstream intake towers are connected to the inner diversion tunnels by 37-foot-diameter inclined tunnels; 37-foot-diameter tunnels also connect the downstream towers to penstocks and outlet works.
How do the intake towers control water flow?Through two cylindrical gates, each 32 feet in diameter and 11 feet high. One gate is near the bottom and the other near the middle of each tower. The gates are protected by trashracks. Total weight of the gates is 5,892,000 pounds; the trashracks weigh 7,024,000 pounds.
What pipes are installed in the tunnels for reservoir outlets?There are 4,700 feet of 30-foot-diameter pipe and 2,000 feet of 8«-foot-diameter pipe. Maximum thickness of the largest pipe is about 3 inches.
How are the 30-foot-diameter pipes connected to the powerplant turbines?By sixteen 13-foot-diameter platesteel penstocks installed in 18-foot-diameter concrete-lined tunnels. Total length of these penstocks is 5,800 feet.
What are the main characteristics of the penstock and outlet pipes?Forty-four thousand tons of steel were formed and welded into 14,800 feet of pipe varying from 8 to 30 feet in diameter. Each length of the largest pipe - 12 feet long, 30 feet in diameter, and 2 inches thick - was made from 3 steel plates, of such weight that only two plates could be shipped from the steel mill to the fabricating plant on one railroad car. Two such lengths of pipe welded together make one section weighing approximately 135 tons or, at intersections with the penstocks, as much as 186 tons.
What outlets are used?Four 72-inch needle valves in each inner diversion tunnel plug outlet; and two 84-inch needle valves each in the Arizona and Nevada canyon wall valve houses. The needle valves in the canyon walls are about 180 feet above the river. These valves are designed to bypass water around the dam under emergency or flood conditions, or to empty the penstocks for maintenance work.
What is the maximum capacity of these works?About 118,000 cubic feet per second: 32,000 cubic feet per second for power generation and 86,000 cubic feet per second of valve discharge. One cubic foot per second of water equals nearly 7 gallons passing a given point in one second.
What are the Arizona and Nevada spillways?Concrete-lined open channels about 650 feet long, 150 feet wide, and 170 feet deep on each canyon wall. More than 600,000 cubic yards of rock were excavated for the spillways. The spillway walls are lined with 18 inches of concrete and the floors with 24 inches; 127,000 cubic yards of concrete were placed for the spillways.
How is water discharged from the spillways?Into the outer diversion tunnels through inclined shafts 50 feet in diameter and 600 feet long. The discharge is controlled by four automatically or manually operated 100- by 16-foot, 500,000-pound drum gates on each spillway crest. Maximum water velocity in the spillway tunnels is about 175 feet per second, or 120 miles per hour.
What is the maximum discharge capacity of the spillways, valves, and powerplant?Five hundred and eighteen thousand ft3/s. Each spillway can discharge 200,000 ft3/s. If the spillways were operated at full capacity, the energy of the falling water would be about 25,000,000 horsepower. The flow over each spillway would be about the same as the flow over Niagara Falls, and the drop from the top of the raised spillway gates to river level would be approximately three times as great.
Where is the powerplant located?In a U-shape structure at the base of the dam. Each powerplant wing is 650 feet long, 150 feet above normal tailrace water surface, and 299 feet (nearly 20 stories) above the powerplant foundation. In all of the galleries of the plant there are 10 acres of floor space.
What is the capacity of the Hoover Powerplant?There are 17 main turbines in Hoover Powerplant. The original turbines were all replaced through an uprating program between 1986 and 1993. With a rated capacity of 2,991,000 horsepower, and two station-service units rated at 3,500 horsepower each, for a plant total of 2,998,000 horsepower, the plant has a nameplate capacity of 2,074,000 kilowatts. This includes the two station-service units, which are rated at 2,400 kilowatts each.
What is horsepower in terms of falling water?One cubic foot of water falling 8.81 feet per second equals one horsepower at 100 percent efficiency.
How does the water reach the turbines?Through four pressure penstocks, two on each side of the river. Shutoff gates control water delivery to the units.
Under what heads do the turbines operate?Maximum head (vertical distance water travels), 590 feet; minimum, 304 feet; average, 510 to 530 feet.
When were the power installations in the plant completed, and of what do they consist?Installation was completed in 1961. With the uprating completed in 1993, there are fifteen 187,000 horsepower, one 100,000 horsepower, and one 86,000 horsepower Francis-type vertical hydraulic turbines. There are thirteen 130,000 kilowatt, two 127,000 kilowatt, one 61,500 kilowatt, and one 68,500 kilowatt generators. All machines are operated at 60 cycles. There are also two 2,400 kilowatt station-service units driven by Pelton water wheels. These provide electrical energy for lights and for operating cranes, pumps, motors, compressors, and other electrical equipment within the dam and powerplant.
How was the powerplant machinery transported from the canyon rim to the powerplant?An electrically operated cableway of 150 tons rated capacity, with a 1,200-foot span across the canyon, lowered all heavy and bulky equipment. The cableway is still used when necessary.
How much energy does Hoover Powerplant produce on a yearly basis?The average annual net generation for Hoover Powerplant for operating years 1947 through 2000 is about 4 billion kilowatt-hours. The maximum annual net generation at Hoover Powerplant was 10,348,020,500 kilowatt-hours in 1984, while the minimum annual net generation since 1940 was 2,648,224,700 kilowatt-hours in 1956.
What is a kilowatt-hour?It is a unit of work or energy equal to that done by one kilowatt of power acting for one hour. A kilowatt is 1,000 watts or 1.34 horsepower.
Who operates and maintains the powerplant?The powerplant is operated and maintained by the Bureau of Reclamation.
Who are the principal contractors for energy?
The States of Arizona and Nevada; the City of Los Angeles; the Southern California Edison Co.; the Metropolitan Water District of Southern California; the California cities of Glendale, Burbank, Pasadena, Riverside, Azusa, Anaheim, Banning, Colton, and Vernon; and the city of Boulder City, Nevada.
How is the firm energy generated at Hoover Dam allocated?Arizona - 18.9527 percent; Nevada - 23.3706; Metropolitan Water District of Southern California - 28.5393 percent; Burbank - 0.5876 percent; Glendale -1.5874 percent; Pasadena - 1.3629 percent; Los Angeles - 15.4229 percent; Southern California Edison Co. - 5.5377 percent; Azusa - .1104 percent; Anaheim - 1.1487 percent; Banning - 0.0442 percent; Colton - 0.0884 percent; Riverside - 0.8615 percent; Vernon - 0.6185 percent; and Boulder City, Nevada - 1.7672 percent.
How is the income from the sale of energy used?To pay all operation and maintenance expenses and to repay the major part of the construction cost of the dam and powerplant, at interest not exceeding 3 percent. The cost of construction completed and in service by 1937 was repaid on May 31, 1987. All other costs will be repaid within 50 years of the date of installation or as established by Congress. Repayment of the $25 million construction cost allocated to flood control is deferred beyond 1987, when further action will be subject to Congressional direction. Arizona and Nevada each receive $300,000 annually, paid from revenues, and $500,000 annually is set aside from revenues for further irrigation and power development of the Colorado River Basin.
HOOVER DAM SCULPTURESOne of the highlights for many of the people who visit Hoover Dam each year is the sculpture work they find. While most people are impressed by these works, they often ask the question, "What do they mean?"
Much of the sculpture is the work of Norwegian-born, naturalized American Oskar J.W. Hansen. Mr. Hansen fielded many questions about his work while it was being installed at the dam. In response to those questions, he later wrote about his interpretation of his sculptures. Hoover Dam, said Hansen, represented for him the building genius of America, "a monument to collective genius exerting itself in community efforts around a common need or ideal." He compared the dam to such works as the great pyramids of Egypt, and said that, when viewing these man-made structures, the viewer often asks of their builders, "What manner of men were these?" The sculptor, according to Hansen, tries to answer this question objectively, by "interpreting man to other men in the terms of the man himself." In each of these monuments, he said, can be read the characteristics of these men, and on a larger scale, the community of which they are part. Thus, mankind itself is the subject of the sculptures at Hoover Dam. Hansen's principal work at Hoover Dam is the monument of dedication on the Nevada side of the dam. Here, rising from a black, polished base, is a 142-foot flagpole flanked by two winged figures, which Hansen calls the Winged Figures of the Republic. They express "the immutable calm of intellectual resolution, and the enormous power of trained physical strength, equally enthroned in placid triumph of scientific accomplishment." "The building of Hoover Dam belongs to the sagas of the daring. The winged bronzes which guard the flag therefore wear the look of eagles. To them also was given the vital upward thrust of an aspirational gesture; to symbolize the readiness for defense of our institutions and keeping of our spiritual eagles ever ready to be on the wing." The winged figures are 30 feet high. Their shells are 5/8-inch thick, and contain more than 4 tons of statuary bronze. The figures were formed from sand molds weighing 492 tons. The bronze that forms the shells was heated to 2,500 degrees Fahrenheit, and poured into the molds in one continuous, molten stream. The figures rest on a base of black diorite, an igneous rock. In order to place the blocks without marring their highly polished finish, they were centered on blocks of ice, and guided precisely into place as the ice melted. After the blocks were in place, the flagpole was dropped through a hole in the center block into a predrilled hole in the mountain. Surrounding the base is a terrazzo floor, inlaid with a star chart, or celestial map. The chart preserves for future generations the date on which President Franklin D. Roosevelt dedicated Hoover Dam September 30, 1935. The apparent magnitudes of stars on the chart are shown as they would appear to the naked eye at a distance of about 190 trillion miles from earth. In reality, the distance to most of the stars is more than 950 trillion miles. In this celestial map, the bodies of the solar system are placed so exactly that those versed in astronomy could calculate the precession (progressively earlier occurrence) of the Pole Star for approximately the next 14,000 years. Conversely, future generations could look upon this monument and determine, if no other means were available, the exact date on which Hoover Dam was completed. Near the figures and elevated above the floor is a compass, framed by the signs of the zodiac. Hansen also designed the plaque commemorating the 96 men who died during the construction of Hoover Dam, as well as the bas-relief series on both the Nevada and Arizona elevator towers. The plaque, originally set into the canyon wall on the Arizona side of the dam, is now located near the winged figures. It reads: "They died to make the desert bloom. The United States of America will continue to remember that many who toiled here found their final rest while engaged in the building of this dam. The United States of America will continue to remember the services of all who labored to clothe with substance the plans of those who first visioned the building of this dam." The five bas-reliefs on the Nevada elevator tower, done in concrete, show the multipurpose benefits of Hoover Dam flood control, navigation, irrigation, water storage, and power.
On the Arizona elevator tower is a series of five bas-reliefs, also in concrete, depicting "the visages of those Indian tribes who have inhabited mountains and plains from ages distant." Accompanying the illustrations is the inscription, "Since primordial times, American Indian tribes and Nations lifted their hands to the Great Spirit from these ranges and plains. We now with them in peace buildeth again a Nation."