Glen Canyon Dam

Glen Canyon Dam
	The Glen Canyon Dam
Location:	Arizona , USA
Tributaries:	Colorado River
Drain:	Colorado River
Larger places nearby:	page
	Arizona , United States
Coordinates	36 ° 56 ′ 0 ″ N , 111 ° 29 ′ 0 ″ W Coordinates: 36 ° 56 ′ 0 ″ N , 111 ° 29 ′ 0 ″ W.
	Data on the structure
Construction time:	1956–1964 and 1966, respectively
Height above valley floor:	178 m
Height above foundation level :	216 m
Building volume:	3,750,000 m³
Crown length:	475 m
Crown width:	7.6 m
Power plant output:	1296 MW
	Data on the reservoir
Altitude (at congestion destination )	1131 m
Water surface	658 (1627?) Km²
Storage space	33,304 million m³
Catchment area	280,586 km²
Design flood :	7250 m³ / s

The Glen Canyon Dam (Glen Canyon Dam) is a dam that dams the Colorado River in Arizona by means of an arch weight dam. Based on the content of the reservoir, the resulting reservoir , Lake Powell , is the second largest reservoir in the USA after Lake Mead .

Dam wall

The dam was planned by the Bureau of Reclamation and built from 1956 to 1964; the cost was $ 187 million. With a construction height of 216 meters (above the natural rock) it is the fifth-highest dam in the USA. The height above the former river bed is 178 m. The top of the wall is 475 m long and 7.6 m wide. The wall is 91 m wide at the deepest construction point, the greatest width is reached at the right abutment with 106 m. The wall has a concrete volume of 3,750,000 m³. Because of this thickness, it can no longer be called a pure arch dam . It also carries part of the water load as a gravity dam; therefore, like the Hoover Dam , it is also a "bow-weight (dam) wall".

4,212,551 m³ of sand and stone had to be moved during the construction work.

Directly at the foot of the dam on the underwater side is the power house , which is arranged across the river and houses eight machine sets for generating electrical energy from hydropower.

Relief and withdrawal systems

The wall has a bottom outlet four pipes (outlet pipes) can flow of 2 m diameter, through which 420 cubic meters of water per second. These flow out to the left of the power house above the underwater level.

Eight penstocks with a diameter of 4.6 to 4.3 m conduct a total of 940 m³ of water per second to the eight Francis turbines with vertical machine shafts with 155,550 hp each , which drive eight generators with a total electrical output of 1320 MW . The power station on the Glen Canyon dam supplies the states of Wyoming , Colorado , Utah , New Mexico and Arizona with electricity .

A spillway tunnel , which tapers in diameter from 15 m to 12 m, leads through the rock on both sides of the dam . Both together can drain up to 5,890 m³ of water per second. The flood relief systems (spillways) are only needed when large amounts of water have to be removed in order to lower the water level of the reservoir or to prevent the wall from flooding . When the flood reliefs were used, it was found that the emerging water, in contrast to the water of Lake Powell, was clearly red in color. An investigation after the overflows had been closed revealed that the water had caused considerable erosion in the red sandstone as a result of cavitation inside the tunnels. In order to prevent further leaching during the next use, both tunnels were lined with concrete and ventilation was installed.

The added maximum discharge capacity of the relief and extraction systems is 5890 m³ / s + 420 m³ / s + 940 m³ / s = 7250 m³ / s.

History of the dam

View from the sea side

The Glen Canyon Dam was designed and constructed as part of the Colorado River Storage Project . The purpose of this structure was to build a water reservoir for the arid states of the southwest. At the same time, electricity should be generated for the ever-increasing demand . In addition, the construction of the dam made it possible to prevent the recurring flooding in the regions downstream.

From 1946 to 1948, engineers and geologists from the Bureau of Reclamation surveyed Glen Canyon to find the right location for the barrier . The place they finally chose had several advantages:

The area covered by the reservoir forms a basin that can hold a large amount of water.

The walls of the gorge are very steep at this point and are very close together.

The rock of the canyon walls and the subsoil are firm enough to give the dam wall the necessary support.

There was enough sand and rock nearby for the enormous amount of concrete required to build it.

On October 15, 1956, construction work on the dam officially began. To divert the waters of the Colorado River during construction , a tunnel was blasted through the red sandstone on each side of the canyon . This drained the actual river bed in the area of the construction site. Since the road for vehicles from one side of the gorge to the other was more than 200 miles, the Glen Canyon Bridge was built in the immediate vicinity and was completed in 1959. On June 17, 1960, the concreting work for the dam began, which was not interrupted day and night for three years and ended on September 13, 1963. In 1957, a camp was built in the immediate vicinity for the workers involved in the construction and their families, from which the town of Page later developed. 17 construction workers died during the ten-year construction period. In 1963, the river began to be dammed. From 1963 the turbines and generators were installed. The last two generators were put into operation in 1966. Ladybird Johnson, wife of American President Lyndon B. Johnson , opened the dam on October 22, 1966 . It took 17 years, from March 13, 1963 to June 22, 1980, to completely fill the reservoir. With a maximum depth of around 171 m at the dam, Lake Powell contains 33.3 billion m³ (= 33.3 km³) of water and is therefore the second largest reservoir in the USA after Lake Mead . According to various sources, the area of the reservoir is either 640 km², 658 km² or 627 km².

In 1964 the construction project received the Outstanding Civil Engineering Achievement Award from the American Society of Civil Engineers (ASCE).

Impact on the environment

The construction of the Glen Canyon dam has far-reaching consequences for nature. The regulation of the river changed the amount of transported sediment and the seasonal fluctuations of the water temperature. As a result, the water quality of the Colorado River below the dam and in the reservoir has improved significantly. Since most of the sediments in Lake Powell settles, the water is now blue-green and clear instead of red and muddy. This made it possible to settle different species of perch in the lake. Rainbow trout now live below the dam in the Colorado River .

On the other hand, the damming of the Colorado River has also had significant disadvantages for the further course of the river, especially in the Grand Canyon area .

The reduced number of floods since regulation has also reduced the size of the sandbanks on the banks and allowed vegetation to encroach on the river bed. Piles of debris, which could be deposited laterally in the mouths of the tributaries due to the low water speed, narrow the river more and more and the backwater areas, in which native fish species live, gradually silted up. As an indicator species for the changes in fish applies Gila cypha , who species protection is the federal government. Experiments were carried out with the water level to protect it.

Since the construction of the dam, more water has only been drained from the reservoir on a few occasions than the 930 m³ / s that flow through the pressure pipes:

In 1965, a large amount of water was drained off during a flood in order not to endanger the equilibrium of the reservoir.
In 1980, when Lake Powell reached its target height, a flood was used to test the spillways.
In 1983 the water level of Lake Powell had risen so much by a spring flood that a provisional elevation of the dam wall by almost 2.50 m had to be made. At the same time, as much water as possible was drained for about a month to prevent the wall from flooding. The drainage capacity of the system could not be fully used, as the Spillway tunnels were damaged so severely by cavitation that the dam itself could have been washed under. After the floods, meter-long gaps were found in the concrete lining in the tunnels that had to be repaired; the spillways as a whole had proven to be poorly constructed and had to be reworked in order to be better prepared for future floods.
In 1984, 1985 and 1986 the floods were still so powerful that up to 1,415 m³ / s had to be discharged for a month. As with the spring floods before the dam was built, the tidal waves washed sand into the river bed. Small sandbanks were removed by the flood and higher sandbanks were left behind when the water level dropped. The backwater areas were cleared of fine sediment deposits and vegetation. This cleaning process improved the habitat for the native fish species.
In 1990 and 1991, individual tidal waves were released in order to investigate the above-mentioned effects more closely and to obtain data for an environmental study.
In 1996, on behalf of the Bureau of Reclamation , a controlled tidal wave was released for 7 days with a discharge rate of 1,275 m³ / s. This was hoped to have an effect similar to that of the 1983-1986 floods. This action should help researchers decide whether regular large drains would help restore the natural habitats that have been at risk since the waters of the Colorado River is dammed.
On March 5, 2008, another controlled tidal wave was released for the purpose of studying the effects on nature, which lasted 60 hours.
In May 2012, after evaluating the results of previous attempts, the plan was presented to increase the water runoff through the dam at irregular intervals for periods of between a few hours and up to four days to up to 1275 m³ / s. This drainage pattern will be sustained through 2020.
Flooding according to the new pattern has been taking place in November since 2012. Shortly after the flooding, sandbanks form, but they are quickly removed in the following weeks, as only 6% of the total bed load passes the dam. Long-term success cannot therefore be achieved with these measures.

Panorama of the south side

Carl T. Hayden Visitor Center

At the western end of the dam is the "Carl T. Hayden Visitor Center". The owner is the Bureau of Reclamation (USBR) and the Visitor Center is operated by the National Park Service .

In the large rotunda, which towers above the dam wall, you have a unique view of the reservoir, the wall, the bridge and the further course of the Colorado River through the huge panorama windows . An exhibition documents the construction of the Glen Canyon Dam and the Glen Canyon Bridge with the help of pictures, texts and video films . Other exhibitions show pictures of the surrounding area or provide information about the arts and crafts of the indigenous people. You can register for a tour of the dam at reception. The Visitor Center is open every day except Thanksgiving , December 25th and January 1st.