Great Man-Made River (GMR), a network of underground pipelines bringing high-quality fresh water from ancient underground aquifers deep in the Sahara to the coast of Libya for domestic use, agriculture, and industry. The GMR was originally conceived as having several arms, or phases, though not all have been built and some may never be. Nevertheless, since 1991 the project has supplied much-needed irrigation and drinking water to populous cities and farming areas in Libya’s north, which previously were dependent on desalination plants and on declining rain-fed aquifers near the coast.

Libya's Great Man-Made River Existing and projected pipelines of Libya's Great Man-Made River irrigation project. Encyclopædia Britannica, Inc.

Infrared satellite image of the Grand Omar Mukhtar reservoir (dark blue circle), part of Libya's Great Man-Made River water supply system, near Banghāzī, Libya. Irrigated fields display as red circles and rectangles. Jesse Allen, NASA Earth Observatory using data provided courtesy of NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team

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Water was first discovered in the Al-Kufrah area in Libya’s southeastern desert in the 1950s during exploration drilling for oil. Subsequent analysis indicated that this find was part of the Nubian Sandstone Aquifer System, a vast reservoir of “fossil water” that is anywhere from 10,000 to 1,000,000 years old, water having percolated into the sandstone before the end of the last ice age, when the Saharan region enjoyed a temperate climate. Initially, the Libyan government planned to set up large-scale agricultural projects in the desert where the water was found, but plans were changed in the early 1980s, and designs were prepared for a massive network of pipelines to the coast.

In 1983 the Great Man-Made River Authority, established by the government to manage the project, awarded a contract for construction of the first arm, known as GMR 1 or Phase I. Hundreds of water wells were drilled at two fields, Tāzirbū and Sarīr, where water was pumped up from a depth of some 500 metres (1,650 feet). From Sarīr, water from both fields was pumped underground through a double pipeline to a holding reservoir at Ajdābiyā, which received its first water in 1989. From there the water was piped in two directions, west to the coastal city of Surt and north to Banghāzī. The completion of Phase I was formally celebrated at Banghāzī in 1991. GMR 1 is capable of transporting 2 million cubic metres (70.6 million cubic feet) of water per day through some 1,600 km (1,000 miles) of double pipeline between the well fields in the south and the destination cities in the north (though not all of that capacity is used).

A second system, GMR 2 or Phase II, located in western Libya, began supplying Libya’s capital, Tripoli, with drinking water in 1996. GMR 2 draws water from three well fields in the Jabal al-Ḥasāwinah region. From Qaṣr al-Shuwayrif one pipeline pumps water to Tarhūnah in the Nafūsah Plateau region, whence it flows by gravity to the Al-Jifārah Plain. Another pipeline goes north and east to the coast, where it turns west and supplies cities such as Miṣrātah and Al-Khums before ending at Tripoli. The system’s design capacity is 2.5 million cubic metres (roughly 90 million cubic feet) of water a day, though only a fraction of that is needed for drinking water.

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When construction began on the GMR, it was described as the largest irrigation project in the world. (Indeed, the Libyan government proudly proclaimed it “the Eighth Wonder of the World.”) Some 70 percent of its capacity is intended to be used for agriculture, and from the beginning the project has included large-scale investments in irrigation infrastructure. The project also includes phases subsequent to GMR 1 and 2. These include an extension of the GMR 1 system southward to well fields in the Al-Kufrah region; a pipeline from wells near Ghadāmis in the western desert to the coastal cities of Al-Zāwiyah and Zuwārah, west of Tripoli; a pipeline connecting the GMR 1 and 2 systems; and a pipeline supplying Tobruk on the eastern coast, either from the existing reservoir at Ajdābiyā or directly from wells in the Al-Jaghbūb oasis. The total capacity of the GMR with all phases built would be some 6.5 million cubic metres (230 million cubic feet) of water per day. The complete network would include some 4,000 km (2,500 miles) of pipeline. Some Libyan officials, citing the enormous size of the underground reservoirs, have claimed that the reservoirs could continue to supply water for thousands of years. Critics have stated that such claims are greatly overstated; some insist that the GMR might not last through the 21st century.

The 250,000 sections of pipe laid in Phase I were said at the time to be the largest in the world, each having a diameter of 4 metres (13 feet) and a length of 7 metres (23 feet). Manufactured in two large factories located in Libya, the pipe was made up of layers of steel-reinforced prestressed concrete. The sections were laid in trenches 7 metres deep by specially built cranes and pushed into place by bulldozers, then the joints were sealed with giant rubber O-rings and cement grout, and the sections of trench were filled in. Open reservoirs located at distribution nodes such as Ajdābiyāh are man-made lakes excavated from the soil and rock and lined with asphalt. The largest reservoir, more than 1 km (0.6 mile) in diameter, holds as much as 24 million cubic metres (848 million cubic feet) of water. Numerous engineering companies from around the world have participated in the GMR project.