Aswan High Dam

Identification: Dam on the Nile River in Egypt

Date: Completed in 1970

The Aswan High Dam supplies electricity and has helped control seasonal flooding, but it has had several negative environmental effects, including loss of fertility on downriver floodplains, increased erosion, and increased incidence of earthquakes.

The Aswan High Dam was built with the aid of Soviet engineers on the Nile River approximately 960 kilometers (600 miles) south of Cairo, Egypt, between 1960 and 1970 at a cost of US$1 billion. The dam lies 7 kilometers (4.5 miles) south of the city of Aswan and several kilometers from a smaller dam constructed by British engineers between 1898 and 1902. The building of the High Dam followed the signing of the Nile Water Agreement between Egypt and Sudan in November of 1959.

The High Dam is a rock-fill structure with a core of impermeable clay. It measures 3,829 meters (12,562 feet) long, 111 meters (364 feet) high, 980 meters (3,215 feet) wide at the base, and 40 meters (131 feet) wide at the crest. The volume of material contained in the structure, 1.6 million cubic meters (56.5 million cubic feet), would be enough to construct seventeen Great Pyramids. The flow of the river’s waters through the dam is via six tunnels, each controlled by a 230-ton gate.

The reservoir impounded by the High Dam is Lake Nasser, named for Egyptian president Gamal Abdel Nasser, who died the year the dam was completed. The portion of the reservoir that lies within Sudan, about 30 percent, is referred to as Lake Nubia. In total, the reservoir measures 499 kilometers (310 miles) in length and has a surface area of approximately 5,996 square kilometers (2,315 square miles) and 9,053 kilometers (5,625 miles) of shoreline. It averages 9.7 kilometers (6 miles) wide, with a maximum width of 16 kilometers (10 miles). Mean water depth is 70 meters (230 feet), maximum depth is 110 meters (360 feet), and the annual vertical fluctuation is 25 meters (82 feet). The reservoir contains enough water to irrigate more than 2.8 million hectares (7 million acres).

Environmental Impacts

The filling of Lake Nasser came with a high cost. Thousands of people were displaced, and natural habitats were significantly altered. A number of ancient temples and monuments, which abound in the region, were to be submerged beneath the rising waters of the reservoir, but some of these were saved—they were cut into large blocks and reassembled at higher locations. High evaporation rates and water loss to infiltration into the underlying permeable Nubian sandstone caused the filling of the reservoir to take much longer than anticipated. A significant amount of water-storage capacity has also been lost as sediment that has been carried in occupies a part of the reservoir’s volume.

The benefits derived from the High Dam are principally hydroelectric power generation and the regulation of water flow along the lower Nile for flood control. Twelve turboelectric generators capable of producing 10 billion kilowatt-hours provide 40 percent of Egypt’s electrical power. The storage of water in Lake Nasser not only provides flood control but also allows for the irrigation of additional land and the ability to grow multiple crops over the course of a year. Since the filling of the reservoir, a fishing industry has also developed.

The yearly floods of the Nile are the result of late-summer rains that fall in the plateau region to the south in Ethiopia. At peak floods, river volume may increase by as much as sixteen times. More than 100 million tons of soil are carried with the water each year. While the impoundment of water in Lake Nasser has probably saved the lower Nile Valley from disastrous floods and alleviated the effects of regional droughts, the loss of yearly increments of silt—with its associated nutrients—on the floodplain has led to a decline in the floodplain’s fertility. Without this natural fertilization, the Egyptians have had to rely on increasing use of artificial fertilizer. The floodwaters also provided a cleansing and draining action for the soil, preventing the accumulation of salts. Further, the floodwaters reduced the numbers of rats and disease-bearing snails. With the decline in flooding, incidences of disease have been on the increase.

Historically, the influx of sediment to the Nile Delta has replenished sediment lost to wave and current erosion at the Delta’s margins. Since the construction of the Aswan High Dam, the front of the Delta is being eroded at a rate of 1.8 meters (6 feet) per year. As on the floodplain, the soil of the Delta, a region that has been farmed for more than seven thousand years, also shows evidence of declining fertility.

Since the High Dam traps 98 percent of the Nile sediment, water passing through the dam has an enhanced ability to erode. Consequently, downstream erosion has become a significant problem, scouring the riverbed and undermining riverbanks and bridge piers. In some instances, the increased erosion has also affected the delicate balance of water irrigation systems.

The effects of trapped sediment are not confined to the floodplain and the Nile Delta. Prior to construction of the dam, the river brought sediment and nutrients into the normally nutrient-poor eastern Mediterranean Sea. This provided for blooms of phytoplankton that formed the base of a food pyramid that included sardines and other commercial varieties of fish. When construction of the dam began, the sardine fishing industry in the Mediterranean declined significantly. From the late 1980’s onward, however, a resurgence occurred in sardine fishing, as the filling of Lake Nasser allowed for increased river discharge and nutrient enhancement.

One other environmental consequence of the construction of the High Dam has been the occurrence of earthquakes in the region. These are related to stress that is placed on the earth’s crust by the weight of the water impounded in Lake Nasser. A large shock of magnitude 5.6, for example, occurred on November 14, 1981. This was followed by aftershocks for a period of seven months.

Bibliography

Caputo, Robert. “Journey up the Nile.” National Geographic, May, 1985.

Collins, Robert O. The Nile. New Haven, Conn.: Yale University Press, 2002.

Johnson, Irving, and Electra Johnson.“Yankee Cruises the Storied Nile.” National Geographic, May, 1965.

Smith, Scot E. “The Aswan High Dam at Thirty: An Environmental Impact Assessment.” In Conservation, Ecology, and Management of African Fresh Waters, edited by Thomas L. Crisman et al. Gainesville: University Press of Florida, 2003.