Glen Canyon Dam: Difference between revisions

Glen Canyon Dam
The dam and Glen Canyon Bridge viewed from the front
Location of Glen Canyon Dam in USA West
Construction began	1956
Construction cost	$135 million
Owner(s)	U.S. Bureau of Reclamation
Dam and spillways
Spillway type	Twin concrete tunnels, controlled by double radial gates
Spillway capacity	276,000 cu ft/s (7,800 m3/s)
Power Station
Commission date	1964

Glen Canyon Dam is a concrete arch dam on the Colorado River in northern Arizona in the United States, near the town of Page. The dam was built to provide hydroelectricity and flow regulation from the upper Colorado River Basin to the lower. Its reservoir is called Lake Powell, and is the second largest artificial lake in the country, extending upriver well into Utah. The dam is named for Glen Canyon, a colorful series of gorges, most of which now lies under the reservoir.

The dam was proposed in the 1950s as part of the Colorado River Storage Project, a U.S. Bureau of Reclamation (USBR) federal water project that would develop reservoir storage on the upper Colorado River and several of its major tributaries. The project's main purpose was to allow the upper basin to better utilize its allocation of river flow as designated in the 1922 Colorado River Compact, and a second purpose was to provide water storage to ensure the delivery of sufficient water to the lower basin during years of drought. However, problems arose when the USBR proposed to build dams in the federally protected Echo Park canyon in Utah. After a long series of legal battles with environmentalist organizations such as the Sierra Club, they settled for a high dam at Glen Canyon.

Construction of Glen Canyon Dam started in 1956 and was not finished until 1966. When the reservoir filled, the dam began to deliver a steady, regulated flow of water downstream and a supply of electricity to the region. In 1983, major floods nearly led to the dam's collapse, but disaster was averted by a close margin. By taming floods and other factors that once characterized the Colorado, the dam has led to major physical and ecological changes in the lower river. Controversy continues over the effects both positive and negative of the dam, which has also been antagonized in many literary works.

Background

In 1922, six U.S. states signed the Colorado River Compact to officially allocate the flow of the Colorado River and its tributaries. Each half of the Colorado River Basin – the upper basin, comprising Colorado, New Mexico, Utah and Wyoming – and the lower basin, with California and Nevada – was allotted 7,500,000 acre-feet (9.3 km³) of water annually, and a treaty between the U.S. and Mexico was signed in 1944 allocating 1,500,000 acre-feet (1.9 km³) to the latter country. The third lower basin state, Arizona, did not ratify the Compact until 1944 because it was concerned that California might seek to appropriate a portion of its share before it could be put to use. The total, 16,500,000 acre-feet (20.4 km³) annually, was believed to represent the river's flow at the time as measured at Lee's Ferry, Arizona (the official dividing point of the upper and lower basins), 16 miles (26 km) downstream of present-day Glen Canyon Dam, while in fact it turned out to be the result of one of the Southwest's climatic shifts during the past 800 years. The actual annual flow past Lee's Ferry is now believed to be about 13,500,000 acre-feet (16.7 km³).

Annual discharge from the Colorado River and its tributaries ranges from 4,000,000 to 22,000,000 acre-feet (4.9 to 27.1 km³), and 10-year averages may fluctuate as much as 1,000,000 acre-feet (1.2 km³). In addition, the Colorado carries a heavy silt load that led to difficulties for the irrigation interests in the lower Colorado River Valley that were a primary benefactor of the treaties. The general consensus among inhabitants of the Colorado River basin and government officials was that a high dam had to be built on the Colorado to provide flood control and carry-over water storage for times of drought. Possible locations for this dam were debated for years, and in fact the Bureau of Reclamation's first study for a dam at Glen Canyon was made in 1924, in addition to studies for locations at Black and Boulder Canyons lower on the Colorado, below Grand Canyon. However, these studies found that the lower Colorado sites had stronger foundation rock, might result in less reservoir seepage and were easier to access.

The initial need for a reservoir was realized in 1936 with the completion of Hoover Dam in Black Canyon, marking the first time man held control of the Colorado. However, even with Lake Mead's mammoth storage capacity, it was not able to handle the worst floods or droughts, and was filling with sediment at a rate that would render it useless in a few hundred years. But most importantly, Hoover only controlled the lower portion of the river, and the upper basin, whose rivers flowed wild and free, had no way to ensure it could utilize its water allotment in dry years because of the lack of sufficient storage. Arizona also had qualms over the chosen site of Hoover Dam, because it was located in a relatively inaccessible northwestern corner of the state and was too far to provide water to the Gila River Valley, its major population center. A dam at Glen Canyon, just upstream of Lee's Ferry, would both be located entirely within that state and provide much of the power needed to pump water from the Colorado River to Phoenix and Tucson. Finally, the Glen Canyon dam would provide flow regulation between Lee's Ferry and Lake Mead which would make it more economically feasible for the USBR to go ahead with even more ambitious plans to construct hydroelectric generating facilities in the Grand Canyon as part of the Pacific Southwest Water Plan (see Bridge Canyon Dam).

Lee's Ferry, the official dividing point between the upper and lower Colorado River

This lack of water surcharge or insurance for the upper Colorado River basin led to a demand for what would later become the Colorado River Storage Project. The general outline of this project was for a dam on the Colorado River at Glen Canyon, several other dams on the Gunnison and San Juan tributaries of the Colorado, and a pair of dams to be built on the Green River, the Colorado's major upper tributary, at Echo Park and Split Mountain. The two Green River dams would have submerged more than 110 miles (180 km) of canyons in the federally protected Dinosaur National Monument, a move abhorred by environmentalists who did not want to see a repeat of the 1924 O'Shaughnessy Dam controversy, when a dam was built in a scenic valley in Yosemite National Park.

Led by David Brower, the environmentalist organization Sierra Club fought a protracted battle against the Bureau of Reclamation, on the basis that "building the dam would not only destroy a unique wilderness area, but would set a terrible precedent for exploiting resources in America's national parks and monuments". In the mid-1950s, the USBR agreed not to build the two dams – an act widely hailed as a major victory for the American environmentalist movement – but only if they could go ahead without opposition with other proposed dams at Flaming Gorge and Glen Canyon. In fact, Brower and the Sierra Club supported the expansion of the proposed dam at Glen Canyon to replace the storage that would have been provided by the Echo Park dam on the Green River. The only qualm that the environmentalists had about the proposed Glen Canyon Dam was that high elevations of its reservoir would extend into Rainbow Bridge National Monument, and a proposal to build a barrier to keep water out of the monument was fought over and litigated for years until it was permanently shelved in 1973. The Colorado River Storage Project was authorized in April 1956, and groundbreaking of Glen Canyon Dam began in October of the same year. A common misconception is that the environmentalists were given a choice between damming Echo Park and damming Glen Canyon, but the USBR "had always planned to build a dam at Glen Canyon, regardless of the outcome of the Echo Park debate".

In 1963, when construction on the dam was well underway, the Sierra Club published a book on Glen Canyon, The Place No One Knew, lamenting the loss of the scenic gorge before most of the American public had a chance to visit, or indeed know it. Brower had visited Glen Canyon shortly after the decision to build the dam, and "realized once he arrived that this was not a place for a reservoir". This was not strictly true as a handful of hikers and boaters (John Wesley Powell for whom the reservoir is named, leader of the Powell Geographic Expedition of 1869, among them) had explored the canyon pre-dam, and some had even been interviewed by Brower. As said to Brower by writer Wallace Stegner, who had been to the canyon in 1947, "Echo doesn't hold a candle to Glen."

Construction

Site preparations

Glen Canyon's design was overall based on that of Hoover Dam, a massive concrete arch-gravity structure anchored in solid bedrock, with several changes. The engineers wanted the dam to rely predominantly on its arch shape to carry the tremendous pressure of the impounded water into the canyon walls instead of depending on the sheer weight of the structure to hold the reservoir back, as had been done at Hoover. However, most of the rock in the region consists of porous and relatively weak Navajo sandstone in contrast to the stronger rock at the Hoover Dam site, forcing the Glen Canyon design to follow more conservative lines by greatly thickening the abutments, thus increasing the surface area through which the weight of dam and reservoir would be transmitted to the rock and relieving the pressure per square inch on the highly breakable cliffs. The primary designer and overseer of construction was veteran Reclamation engineer Lem F. Wylie, who had worked on the Hoover Dam project and had been chief engineer of six other USBR dams.

Before building the dam, Reclamation identified two possible sites, both located in the narrow lower reaches of Glen Canyon shortly upstream of Lee's Ferry. One, just 4 miles (6.4 km) upstream, was originally considered the superior site, but the final decision was to build the dam 16.5 miles (26.6 km) upstream because of stronger rock and easier access to the gravel mining area at the confluence of Wahweap Creek with the Colorado. The dam site lay in a remote, rugged area of the Colorado Plateau, more than 30 miles (48 km) from the closest paved road, U.S. Highway 89, and a whole new road had to be constructed, branching off from Highway 89 north of Flagstaff, Arizona, and running through the dam site to its terminus at Kanab, Utah. Because of the isolated location, acquiring the land at the dam and reservoir sites was not incredibly difficult, but still conflicts arose with the ranchers and miners in the area (many of the Navajo tribe). Much of the land acquired for the dam was through an exchange with the Navajo, in which the tribe ceded Manson Mesa south of the dam site for a similar-sized chunk of land in New Mexico, which the Navajo had long coveted.

Glen Canyon damsite from the air in November 1957, prior to construction of the Glen Canyon Bridge

As a road link was obviously needed for transport across the canyon from one end of the dam site to the other, a bridge had to be built, several hundred feet downstream of the dam and capable of carrying not only workers but heavy construction material. An earlier footbridge built of chicken wire and metal grates certainly did not fit the bill. The contract for building the bridge was awarded to Peter Kiewit Sons and the Judson Pacific Murphy Co. for $4 million and construction began in late 1956, reaching completion on August 11, 1957. When finished, the Glen Canyon Bridge was in itself a marvel of engineering: 1,271 feet (387 m) long and rising 700 feet (210 m) above the river, it was the highest bridge of its kind in the United States and one of the highest in the world. By 1959, the bridge itself was a major tourist attraction and it was said that "motorists [were] driving miles out of their way just to be thrilled by its dizzying height".

Workers flooded into the dam site beginning in the mid-late 1950s, and the construction camp started out as a haphazardly organized trailer park that grew with the workforce. During the construction of the Glen Canyon Bridge, Reclamation also began planning a company town to house the workers. This resulted in the town of Page, Arizona, named for former Reclamation commissioner John C. Page. By 1959, Page had a host of temporary buildings, electricity, and a small school serving the workers' children. As the city grew, it gathered additional features, including numerous stores and a hospital, even a jeweler's. It was intended to serve a maximum population of eight thousand, accounting for the workers' families; the peak workforce would eventually exceed 2,500 in the busiest phases of construction.

River diversion

In 1956, work began on the two diversion tunnels that would carry the Colorado River around the dam site during construction. Each of the tunnels was 2,700 feet (820 m) long and 41 feet (12 m) in diameter, and had a combined capacity of 200,000 cubic feet per second (5,700 m³/s). The diversion tunnel at river right would be used for carrying the river's normal flow around the dam site, while the left tunnel, 33 feet (10 m) above the water, would only be used during floods. The lower reaches of the tunnels would later be used to form the lower ends of the dam's spillways. On October 15, 1956, President Dwight D. Eisenhower pressed a button on his desk in the capital of Washington D.C., sending a telegraph signal that set off the first blast of dynamite at the portal of the right diversion tunnel. Drilling the tunnels through the porous Navajo sandstone abutting the dam site posed major problems for the excavation crews of the Mountain States Construction Company, which won the contract for the diversion tunnels in 1956.

First, transporting workers and equipment to the bottom of the canyon was extremely difficult. Initially, transport was done by barge from the Wahweap Creek gravel deposits shortly upstream, but this was dangerous and was replaced by a vertical cable system when a barge capsized, spilling tons of machinery into the river. The geology of the area also posed problems. During excavation, the rock frequently broke apart or "slabbed" and collapsed into the tunnels, and metal bolts had to be drilled into the rock to secure it. The largest such event, on August 5, 1958, sent 5,200 cubic yards (4,000 m³) crashing down onto the upper portal of the left diversion tunnel. Material excavated out of the tunnels and excavations for the dam abutments on the canyon walls was used to build the two cofferdams that would keep the damsite dry during construction of the dam itself, the last of which was finished in February 1960. The upstream cofferdam was 168 feet (51 m) high, and it alone could store several million acre-feet of water to protect the dam site from flooding in the event that inflows exceeded the capacity of the diversion tunnels. On February 11, 1959, the right diversion tunnel was completed and began to carry the flow of the Colorado. The left tunnel was finished over three months later on May 19, 1959, slightly behind schedule.

Concrete placement and completion

With the Colorado River safely out of the dam site, construction could begin on the actual main body of the dam. The contract was given to the Merritt-Chapman & Scott Corporation for an astonishingly low $107,955,552. Unfortunately, right before construction could start, about 750 workers organized a strike because of a wage reduction due to the completion of public facilities at Page. In late 1959, salaries were raised by $4 a day, quelling the strikers. Concrete placement started on June 16, 1960, and started at a sluggish but growing pace. In 1962 the workforce topped out at nearly 2,500 employees laboring on the dam. Construction would ultimately claim eighteen lives and injure numerous other workers, but contrary to popular myth, no workers were buried alive in the concrete. Cement needed to make concrete for the dam came from the Phoenix Cement Company plant constructed for the purpose in Clarkdale, south of Flagstaff.

Architectural plans for the Glen Canyon Dam and ancillary structures

A huge concrete plant capable of putting out 1,450 tons per hour was installed, and a pair of cableways with movable towers with capacities of 50 and 25 tons each spanned the canyon, carrying the 12-ton concrete buckets to their final destinations on the steadily rising crest of the dam. The concrete was poured into modular 7.5-foot (2.3 m) high wooden blocks or "forms", the largest measuring up to 60 feet (18 m) by 210 feet (64 m); more than 3,000 of these blocks made up the main structure of the dam. Once the concrete dried, the wooden scaffolding was removed and shifted upwards to accommodate the next load of concrete. As construction efficiency increased, the workforce slowly decreased, as new methods of transportation and placement were implemented including conveyors and remotely controlled buckets. By late 1962, concrete was being poured into the dam at a rate of 8,000 cubic yards (6,100 m³) per day even as the workforce was scaled down to about 1,500.

At the beginning of 1963, the dam was high enough to begin impounding water; huge steel gates were closed over the diversion tunnels on January 2, and Lake Powell began to rise. On that day, Sierra Club leader David Brower entered the Oval Office in a last-ditch effort to save Glen Canyon from inundation – but failed to convince the president. Construction continued and on September 13, 1963, the dam was topped out. Work on the power plant and spillways began directly after the dam wall was complete. The spillway tunnels were excavated around both abutments of the dam and drop steeply from their control gates on Lake Powell to merge with the lower ends of the diversion tunnels. This measure saved cost, but introduced a weak point in the spillways – the point where the spillways met the diversion tunnels now had an abrupt directional change of 55 degrees. The upper ends of the diversion tunnels were then sealed with solid concrete. The first electricity was generated on September 4, 1964, with the power sent into the regional electric grid through a pair of long-distance transmission lines as far as Phoenix, Arizona and Farmington, New Mexico.

Later history

1983 floods and legacy

Further information: Risks to the Glen Canyon Dam

During the first half of 1983, a deep snowpack in the Colorado River headwaters, heavy spring rain and a rapid rise in temperatures that precipitated swift snowmelt combined to create perfect conditions for maximum runoff on the Colorado River. Faulty weather forecasts delayed emergency releases from the dam to prepare for the coming high water, and by June water was pouring into the reservoir at over 120,000 cubic feet per second (3,400 m³/s). Even with the power plant and river outlet works running at full capacity, Lake Powell continued to rise to the point to which the spillways had to be opened. Other than brief tests in 1980, this was the only time the spillways had ever been used.

At the beginning of June dam operators opened the gates on the left spillway, sending 10,000 cubic feet per second (280 m³/s), just 7.2% of capacity, down the tunnel into the river below. After a few days, the entire dam suddenly began to shake violently. The spillway was closed down for inspections and workers discovered that the flow of water was causing heavy cavitation – the explosive collapse of air bubbles in water moving at high speed – which was damaging the concrete lining and eroding away at the rock below. Additionally, the spillway tunnels were designed to feed into the lower ends of the diversion tunnels used during construction as an economic measure. Concrete plugs separate the spillway tunnels from the upper ends of the diversion tunnels, which connect to the bottom of the reservoir. This was rapidly being destroyed by the cavitation and it was feared that a connection would be made to the bottom of Lake Powell, causing it to catastrophically burst through the dam abutment.

Right spillway gates during 1983 flood, showing flashboards that were installed to increase the water level

Meanwhile, snow continued melting in the Rockies and Lake Powell continued to rise rapidly. To delay having to use the spillways, Reclamation installed plywood flashboards (later replaced by steel) atop the gates to increase the lake level. Even this additional capacity was exhausted; discharges through the left spillway reached 32,000 cubic feet per second (910 m³/s) and the right spillway gates were also opened. Flows downstream at Lee's Ferry peaked at 97,300 cubic feet per second (2,760 m³/s), which was and still is the highest water flow recorded there since early construction work at the dam site in 1958. On July 15, Lake Powell reached its highest recorded level in history. Just as it seemed inevitable that the dam would fail, inflows fell and the dam was saved. Upon inspection, it was found that cavitation had caused massive gouging damage to both spillways, carrying away thousands of tons of concrete, steel rebar and huge chunks of rock.

Repairs to the spillways commenced as soon as possible and continued well into 1984. Aeration slots were installed at the bottom of each spillway to break up and absorb the shock of the bubbles formed by cavitation. In 1984, the Colorado River basin produced even more runoff than 1983, but fortunately Reclamation had drawn down the reservoir enough that it absorbed most of the early high flows. Nevertheless, Lake Powell rapidly approached the top of the spillway gates and construction efforts were subsequently focused on the left spillway in order to get it in operation in time. On August 12, the left spillway gates were opened, releasing water at a rate of 50,000 cubic feet per second (1,400 m³/s). The spillway was undamaged, proving the worth of the re-engineering and ensuring that Glen Canyon Dam will also be able to hold against future floods with the magnitude of 1983.

Continuing debates

Long after the Glen Canyon Dam was built and continuing to the present day, heated debate continues between those who believe the dam should remain in place and those who think it should be removed. "Without Glen Canyon Dam, the big sponge of Lake Powell to absorb the flood years, there's no way that the upper basin states could put their seven and a half million acre feet of water to use. They say now of course that Glen Canyon isn't needed, you don't divert any water out of Lake Powell, well, you do divert water out of Lake Powell by transfer. When you divert water through the mountains in the Utah and Colorado into other uses, it's really out of Lake Powell because it's the big storage that's possible there-- makes possible the upper basin a development," said Former Bureau of Reclamation Commissioner Floyd Dominy, a figure heavily associated with the building of Glen Canyon Dam and many of the other big dams built by Reclamation. On the other end of the line, David Brower called the dam his worst mistake and "the biggest sin I ever committed" because of the compromise his organization made to build it instead of Echo Park.

On March 21, 1981, one of the more interesting anti-dam protests against Glen Canyon Dam occurred. Four members of the environmental group Earth First! made the then-emerging organization's debut by unfurling a 300-foot (91 m) tapered black sheet of plastic down the face of the dam, making it appear as if a gigantic crack had appeared in the structure, as more than a hundred people looked on. However, authorities were unable to find the individuals responsible.

Design

Structure and storage

The Glen Canyon Dam impounds the Colorado River about 1 mi (1.6 km) northwest of Page in the narrow lower reach of Glen Canyon and 16.4 miles (26.4 km) upstream of Lee's Ferry. The dam is 710 feet (220 m) high from the crest to the foundations and has a crest length of 1,560 feet (480 m). The maximum height above the river is about 583 feet (178 m). Overall, the dam relies on its arched design to carry the reservoir's weight into the canyon walls, but because of the sheer scale of the structure and the relatively weak surrounding rock, the dam has medium thickness of about 300 feet (91 m) at the widest point. The crest is 3,715 feet (1,132 m) above sea level and the river immediately downstream sits at 3,132 feet (955 m).

Two spillways and four high pressure outlet works protect the dam against floods. Located on both sides of the dam shortly upstream, the spillways are concrete-lined tunnels that drop sharply through the canyon walls abutting the dam, emptying into the lower ends of the diversion tunnels to save the expense of digging new tunnels. Each spillway is controlled by two 40-foot (12 m) long, 52.5-foot (16.0 m) high radial gates and is capable of carrying 138,000 cubic feet per second (3,900 m³/s) for a combined capacity of 276,000 cubic feet per second (7,800 m³/s). The river outlets consist of four 8-foot (2.4 m) diameter pipes each controlled by a follower gate and hollow-jet valve with a capacity of 15,000 cubic feet per second (420 m³/s). Glen Canyon's spillways were used for flood purposes only once in 1983, which caused severe damage that nearly led to dam failure (see section above).

The interior of Glen Canyon Dam's power plant, showing six of the eight generators

The power plant at Glen Canyon Dam is located at the foot of the structure and contains eight 155,500 horsepower generators with a combined capacity of 1,296 megawatts (MW). Each generator is driven by a turbine which is in turn fed by a penstock with a starting diameter of 15 feet (4.6 m), narrowing to 14 feet (4.3 m) as it enters the turbines. Five generators are rated at 165 MW and the remaining three have a capacity of 157 MW each. Before an uprating project in the late 20th century, each of the generators were rated at 118.75 MW for a total of 950 MW. The maximum hydraulic head for the power plant is 510 feet (160 m). Power generated at Glen Canyon is distributed by the Western Area Power Administration.

Lake Powell is the second-largest reservoir in the United States, with a full storage capacity of some 26,214,900 acre-feet (32.3356 km³). The original design storage capacity of Powell was some 27,000,000 acre-feet (33 km³), but some of it has been compromised by sedimentation. At maximum pool, the reservoir reaches 186 miles (299 km) upstream to the mouth of Cataract Canyon, covering 252 square miles (650 km²) with a twisting, winding shoreline of over 2,000 miles (3,200 km). The active capacity is 20,876,000 acre-feet (25.750 km³) and the inactive capacity is 4,000,000 acre-feet (4.9 km³) (the lowest point where electricity can still be generated). The dead pool volume is 1,900,000 acre-feet (2.3 km³), marking the lowest point where water can be released through the dam. Although the dam lies in northern Arizona, the vast majority of the reservoir is actually in southern Utah. Many arms branch off the lake, the longest being those formed by Wahweap Creek, Navajo Creek, Last Chance Creek, the San Juan River, the Escalante River, Halls Creek, and Bullfrog Creek. The reservoir lies mainly in the Glen Canyon National Recreation Area.

Operations

By and large, the Glen Canyon Dam's main purpose is to fulfill the agreement in the Colorado River Compact made by the upper basin states to allow at least 7,500,000 acre-feet (9.3 km³) of water to flow annually past Lee's Ferry for use by Arizona, Nevada and California. The dam is operated to maintain a minimum annual release volume of 8,230,000 acre-feet (10.15 km³) or about 11,350 cubic feet per second (321 m³/s), which is well over the amount stipulated by the compact but not enough to deliver enough water to Mexico as written in the 1944 Treaty for the Utilization of Waters of the Colorado and Tijuana Rivers and of the Rio Grande. Water for delivery to Mexico is provided by the additional amount released from Glen Canyon – about 730,000 acre-feet (0.90 km³) in the average year – as well as tributaries entering the Colorado between Glen Canyon and Hoover Dam, as well as tributaries below Hoover, although many of those have been diverted for irrigation in central Arizona.

The lower end of Lake Powell, with Glen Canyon Dam in the foreground

When the dam was first built, the set annual release volume was believed to be the minimum sustainable flow of the Colorado River past the dam site minus the Upper Basin's allocation of 7.5 million acre feet. Reclamation's studies suggested that the Colorado and other tributaries that feed into the reservoir, such as the San Juan and Escalante, would dump more water into the reservoir during spring runoff than could be efficiently released to maximize power generation on an average of one out of every four years, so the reservoir is operated to reach a peak annual volume of 90% of capacity during July, with power plant releases scheduled based on runoff forecasts. The 1983 and 1984 floods dramatically noted that runoff could not be predicted accurately enough all the time. Since then, even though Glen Canyon was never built for the purpose of flood control, Reclamation has maintained a minimum of 2,400,000 acre-feet (3.0 km³) of flood-storage space in the reservoir (approximately 9% of Lake Powell's capacity) to be available on January 1 of any year. In the 21st century, protracted drought caused Lake Powell to drop significantly, reaching a record low of 33% full in 2005, with 2011 being the first year of relief after eight straight years of low water.

The dam's powerplant is operated as a "cash register" power station, meaning that sales of the electricity it generates was used to pay for the original construction cost and is used for maintenance needs as well as a source of revenue for the Bureau of Reclamation. In fact, the primary function of the dam is power production; it wields more than 75% of the hydroelectric capacity of the entire Colorado River Storage Project. The dam also serves as a primary peaking power plant and black start power source for the electrical grid of much of the southern Intermountain West. Colorado River flows fluctuate daily below the dam, as much as 15,000 to 22,000 cubic feet per second (420 to 620 m³/s) every 24 hours, depending on power demand. Minimums may drop as low as 1,000 cubic feet per second (28 m³/s) in December and highs as much as 31,500 cubic feet per second (890 m³/s) in June and July (the full discharge capacity of the turbines). In an average year, the power plant uses only about one-fourth of its full capacity, producing 3.454 billion kilowatt hours (KWh) annually. Annual power output has ranged from a high of nearly 10.4 billion KWh in 1984 to less than 2.0 billion KWh in 2002.

Environmental impact

View of the Colorado immediately downstream of Glen Canyon Dam (right). The green, clear water is caused by the dam trapping sediment, which would naturally cause the river to have a reddish-brown color.

Because of its tremendous ecological effect on the Colorado River, the Glen Canyon Dam has inspired heavy controversy from environmentalists. Because of its location in the desert amid porous geology, Lake Powell causes huge evaporation and seepage losses. It is estimated that between 675,000 acre-feet (0.833 km³) and 1,000,000 acre-feet (1.2 km³), with an average of 860,000 acre-feet (1.06 km³), is lost from the reservoir each year. This amounts to 6-8% of the Colorado River's flow, an increasingly valuable amount of water in an arid land for both humans and the animals and plants that live along the river.

Like all dams, Glen Canyon traps silt, but because the Colorado is an especially high-sediment river, the dam has posed even worse consequences for the river between it and Lake Mead (essentially, the Grand Canyon). About 100 million tons of sediment are trapped behind the dam annually, equal to about 30,000 dump truck loads daily. Because of the dam, sediment deposited by the Colorado and its tributaries is slowly filling up the canyon, and the most optimistic projections put the useful life of the reservoir at 300–700 years. If no action is taken such as dredging, in a few hundred years, sediment deposits will begin to build up at the foot of the dam and will gradually block the different outlets used to release water. Thus, if drought intervenes during the same period, the dam may not be able to release water due to the blockage of the river outlets and penstocks. The Colorado below the dam would be reduced to a trickle, causing unprecedented loss of riverine life.

The Colorado through Grand Canyon now lacks the source of sediment it needs to build sandbars and islands, and these natural fluvial formations within the canyon have now suffered severe erosion damage. The floods that once scoured the river yearly are now contained behind the dam except in the worst cases; the elimination of this periodic scouring has promoted vegetation encroachment which not only has considerably changed the riparian zone environment but has created problems for tourism, wherein hikers and rafters often cannot find good spots to camp due to overgrowth. Flow control has also caused an inability of the river to carry away the rockslides that are common along the canyons, leading to the creation of incrementally dangerous rapids that pose a hazard to fish and boaters alike. Before the dam, the Colorado commonly reached flows of more than 90,000 cubic feet per second (2,500 m³/s) during the spring; this has been limited to less than 35,000 cubic feet per second (990 m³/s) most years with few exceptions.

Glen Canyon, which Lake Powell flooded, was really more of a narrow and steep sided valley than a canyon and was once described as the "biological heart" of the Colorado because of its abundant riparian growth and streamside habitat on the numerous low river terraces. The canyon once supported 79 plant species, 189 bird species and 34 kinds of mammals. Below the dam, the Colorado has turned into a "death zone for native fish" such as the endangered humpback chub as said by Nikolai Ramsey of the Grand Canyon Trust. Throughout most of the year, water released by Glen Canyon is a consistent 47 °F (8 °C) due to a thermal mass effect in Lake Powell where the water typically released from hundreds of feet below the lake surface through the penstocks is insulated from temperature fluctuations by the thick layer of water above it. Pre-dam, the river ranged from over 80 °F (27 °C) in the heat of summer to just above 32 °F (0 °C) in winter.

In addition to the effect this has on native fish species, biologist and veteran river guide Michael P. Ghiglieri proposed many drowning deaths by boaters in the Grand Canyon Colorado have been caused or exacerbated by rapid hypothermia and hypothermic shock caused by entering the cold water. He further noted during the record post-dam high-flow season of 1983 (mentioned above), there was only one boating fatality in the canyon, providing a strong challenge to views that the dam, by reducing and mediating river flows, increases the safety of canyon river users. The river water temperature in 1983 was significantly higher than normal, due to a large portion of the water having come from overflows of warmer surface water over the spillways of Glen Canyon Dam, rather than the colder lower levels which feed the penstocks.

Restoration efforts

On March 26, 1996, the penstocks and two of the outlet works' bypass tubes at Glen Canyon Dam were opened to maximum capacity, producing a flood crest of about 45,000 cubic feet per second (1,300 m³/s) on the Colorado River. This was not due to any flood or mechanical failure, but rather was a controlled effort to assist the recovery of the damaged riverine ecosystem by mimicking the spring freshets that once swept through the canyons yearly. The flow appeared to have scoured clean numerous pockets of encroaching vegetation, carried away rockslides that had become dangerous to boaters, and rearranged sand and gravel bars along the river, and was considered an environmental success.

Contrary to the initial results, the following years revealed that the offensive vegetation had not been carried away as previously thought – only buried, and had mostly recovered within six months. The surface area of sandbars had been increased, but much of the material had been eroded from the submerged portions of the bars and deposited on top, making them unstable, rather than scoured from the riverbed as hoped. Reclamation has repeated the floods periodically, another time in 2004, 2008, and again in 2012.

Nevertheless, some continue to believe that the dam has too large and severe of an effect on the river's ecology to make restoration efforts worthwhile.

Recreation

Lake Powell is one of the most popular houseboating and water-skiing areas in the United States; the Glen Canyon National Recreation Area, which surrounds the reservoir, receives more than 1.9 million visitors annually.

About 300,000 of these tourists travel via boat to Rainbow Bridge in Utah, a large natural arch once very hard to access, but now easily reachable because one of the arms of the reservoir extends near it.

Glen Canyon National Recreation Area draws more than two million visitors annually. Recreational activities include boating, fishing, waterskiing, jet-skiing, and hiking. Prepared campgrounds can be found at each marina, but many visitors choose to rent a houseboat or bring their own camping equipment, find a secluded spot somewhere in the canyons, and make their own camp (there are no restrictions on where visitors can stay).

Currently most Marinas on the lake don't have Automatic Identification System monitoring stations that transmit boat positions to the AIS websites for the boating community. A substantial number of vessels on the lake do not have AIS transponders, so extra precautions must be taken with respect to boating safety. The telemetry system used to monitor the hydrologic activity of the lake by the federal government agencies in charge of the dam does not at this point support AIS monitoring, creating an additional safety gap.

Because most of the lake is surrounded by steep sandstone walls, access to the lake is limited to developed marinas:

1. Lee's Ferry Subdistrict
2. Page/Wahweap Marina
3. Antelope Point Marina
4. Halls Crossing, Utah Marina
5. Bullfrog Marina
6. Hite Marina

The following marinas are accessible only by boat:

1. Dangling Rope Marina
2. Rainbow Bridge National Monument
3. Escalante Subdistrict

In popular culture

• Edward Abbey's novel The Monkey Wrench Gang describes the fictional efforts of a group of environmentalists who fantasize about blowing up the dam.
• In detective novel Wet Desert by Gary Hansen, the Glen Canyon Dam is destroyed by environmental terrorists.
• The dam was used as a shooting location for the 2011 Doctor Who episode "Day of the Moon."
• The dam was used as a location in the television cult classic, Route 66 . "Layout at Glen Canyon" (episode 9, season 1) was broadcast December 2, 1960.

See also

• List of dams and reservoirs in the United States
• Navajo Generating Station

Works cited

• Adler, Robert W. (2007). Restoring Colorado River ecosystems: a troubled sense of immensity. Island Press. ISBN 1-59726-057-6. {{cite book}}: |access-date= requires |url= (help)
• Big dams of the New Deal era: a confluence of engineering and politics. University of Oklahoma Press. 2006. ISBN 0-8061-3795-9. {{cite book}}: |access-date= requires |url= (help); Unknown parameter |authors= ignored (help)
• The History of Large Federal Dams: Planning, Design, and Construction. Government Printing Office. 2005. ISBN 0-16-072823-1. {{cite book}}: |access-date= requires |url= (help); Unknown parameter |authors= ignored (help)
• Ghiglieri, Michael P. (2001). Over the Edge: Death in Grand Canyon (Revised and Updated) (1st, tenth revision ed.). Flagstaff: Puma Press. pp. 211–215. ISBN 0-9700973-1-X. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
• Martin, Russell (1990). A Story That Stands Like A Dam: Glen Canyon and the Struggle for the Soul of the West (1 ed.). Henry Holt and Company. ISBN 0-8050-0822-5.
• National Research Council, Committee to Review the Glen Canyon Environmental Studies (1996). River resource management in the Grand Canyon. National Academies Press. ISBN 0-309-05448-6. {{cite book}}: |access-date= requires |url= (help)
• Nersesian, Roy L. (2010). Energy for the 21st Century: A Comprehensive Guide to Conventional and Alternative Services. M.E. Sharpe. ISBN 0-7656-2413-3. {{cite book}}: |access-date= requires |url= (help)
• Parks, Timothy L. Glen Canyon Dam. Images of America. Arcadia Publishing. ISBN 0-7385-2875-7. {{cite book}}: |access-date= requires |url= (help)
• Powell, James Lawrence (2008). Dead pool: Lake Powell, global warming, and the future of water in the West. University of California Press. ISBN 0-520-25477-5. {{cite book}}: |access-date= requires |url= (help)
• Rogers, Jedediah (2006). "Glen Canyon Unit" (PDF). U.S. Bureau of Reclamation. Retrieved 2011-05-22.
• Schneiderman, Jill S. (2003). The earth around us: maintaining a livable planet. Westview Press. ISBN 0-8133-4091-8. {{cite book}}: |access-date= requires |url= (help)
• Stevens, Joseph E. (1990). Hoover Dam: An American Adventure. University of Oklahoma Press. ISBN 0-8061-2283-8. {{cite book}}: |access-date= requires |url= (help)
• Hoover Dam 75th Anniversary History Symposium: Proceedings of The Hoover Dam 75th Anniversary History Symposium October 21–22, 2010 Las Vegas, Nevada. ASCE Publications. 2010. ISBN 0-7844-1141-7. {{cite book}}: |access-date= requires |url= (help); Unknown parameter |editors= ignored (|editor= suggested) (help)

External links

• 1995 Glen Canyon EIS
• Glen Canyon Before Flooding – 1962
• Glen Canyon Institute
• Glen Canyon National Recreation Area
• Glen Canyon Natural History Association
• USBR Lake Powell daily water levels