Aswan High Dam
Aswan High Dam
A heroic symbol and an environmental liability , this dam on the Nile River was built as a central part of modern Egypt's nationalist efforts toward modernization and industrial growth. Begun in 1960 and completed by 1970, the High Dam lies near the town of Aswan, which sits at the Nile's first cataract, or waterfall, 200 river mi (322 km) from Egypt's southern border. The dam generates urban and industrial power, controls the Nile's annual flooding , ensures year-round, reliable irrigation , and has boosted the country's economic development as its population climbed from 20 million in 1947 to 58 million in 1990. The Aswan High Dam is one of a generation of huge dams built on the world's major rivers between 1930 and 1970 as both functional and symbolic monuments to progress and development. It also represents the hazards of large-scale efforts to control nature . Altered flooding, irrigation, and sediment deposition patterns have led to the displacement of villagers and farmers, a costly dependence on imported fertilizer , water quality problems and health hazards, and erosion of the Nile Delta.
Aswan attracted international attention in 1956, when planners pointed out that flooding behind the new dam would drown a number of ancient Egyptian tombs and monuments. A worldwide plea went out for assistance in saving the 4000-year old monuments, including the tombs and colossi of Abu Simbel and the temple at Philae. The United Nations Educational and Scientific Organization (UNESCO ) headed the epic project, and over the next several years the monuments were cut into pieces, moved to higher ground, and reassembled above the water line.
The High Dam, built with international technical assistance and substantial funding from the former Soviet Union, was the second to be built near Aswan. English and Egyptian engineers built the first Aswan dam between 1898 and 1902. Justification for the first dam was much the same as that for the second, larger dam, namely flood control and irrigation. Under natural conditions the Nile experienced annual floods of tremendous volume. Fed by summer rains on the Ethiopian Plateau, the Nile's floods could reach 16 times normal low season flow. These floods carried terrific silt loads, which became a rich fertilizer when flood waters overtopped the river's natural banks and sediments settled in the lower surrounding fields. This annual soaking and fertilizing kept Egypt's agriculture prosperous for thousands of years. But annual floods could be wildly inconsistent. Unusually high peaks could drown villages. Lower than usual floods might not provide enough water for crops. The dams at Aswan were designed to eliminate the threat of high water and ensure a gradual release of irrigation water through the year.
Flood control and regulation of irrigation water supplies became especially important with the introduction of commercial cotton production. Cotton was introduced to Egypt by 1835, and within 50 years it became one of the country's primary economic assets. Cotton required dependable water supplies, but with reliable irrigation up to three crops could be raised in a year. Full-year commercial cropping was an important economic innovation, vastly different from traditional seasonal agriculture. By holding back most of the Nile's annual flood, the first dam at Aswan captured 65.4 billion cubic yd (50 billion cubic m) of water each year. Irrigation canals distributed this water gradually, supplying a much greater acreage for a much longer period than did natural flood irrigation and small, village-built water works. But the original Aswan dam allowed 39.2 billion cubic yd (30 billion cubic m) of annual flood waters to escape into the Mediterranean. As Egypt's population, agribusiness, and development needs grew, planners decided this was a loss that the country could not afford.
The High Dam at Aswan was proposed in 1954 to capture escaping floods and to store enough water for long-term drought , something Egypt had seen repeatedly in history. Three times as high and nearly twice as long as the original dam, the High Dam increased the reservoir's storage capacity from an original 6.5 billion cubic yd (5 billion cubic m) to 205 billion cubic y (157 billion cubic m). The new dam lies 4.3 mi (7 km) upstream of the previous dam, stretches 2.2 mi (3.6 km) across the Nile and is nearly 0.6 mi (1 km) wide at the base. Because the dam sits on sandstone, gravel, and comparatively soft sediments, an impermeable screen of concrete was injected 590 ft (180 m) into the rock, down to a buried layer of granite. In addition to increased storage and flood control, the new project incorporates a hydropower generator. The dam's turbines, with a capacity of 8 billion kilowatt hours per year, doubled Egypt's electricity supply when they began operation in 1970.
Lake Nasser, the reservoir behind the High Dam, now stretches 311 mi (500 km) south to the Dal cataract in Sudan. Averaging 6.2 mi (10 km) wide, this reservoir holds the Nile's water at 558 ft (170 m) above sea level. Because this reservoir lies in one of the world's hottest and driest regions, planners anticipated evaporation at the rate of 13 cubic yd (10 billion cubic m) per year. Dam engineers also planned for siltation , since the dam would trap nearly all the sediments previously deposited on downstream flood plains. Expecting that Lake Nasser would lose about 5% of its volume to siltation in 100 years, designers anticipated a volume loss of 39.2 billion cubic yd (30 billion cubic m) over the course of five centuries.
An ambitious project, the Aswan High Dam has not turned out exactly according to sanguine projections. Actual evaporation rates today stand at approximately 19 billion cubic yd (15 billion cubic m) per year, or half of the water gained by constructing the new dam. Another 1.3–2.6 cubic yd (1–2 billion cubic m) are lost each year through seepage from unlined irrigation canals. Siltation is also more severe than expected. With 60–180 million tons of silt deposited in the lake each year, current projections suggest that the reservoir will be completely filled in 300 years. The dam's effectiveness in flood control, water storage, and power generation will decrease much sooner. With the river's silt load trapped behind the dam, Egyptian farmers have had to turn to chemical fertilizer, much of it imported at substantial cost. While this strains commercial cash crop producers, a need for fertilizer application seriously troubles local food growers who have less financial backing than agribusiness ventures.
A further unplanned consequence of silt storage is the gradual disappearance of the Nile Delta. The Delta has been a site of urban and agricultural settlement for millennia, and a strong local fishing industry exploited the large schools of sardines that gathered near the river's outlets to feed. Longshore currents sweep across the Delta, but annual sediment deposits counteracted the erosive effect of these currents and gradually extended the delta's area. Now that the Nile's sediment load is negligible, coastal erosion is causing the Delta to shrink. The sardine fishery has collapsed, since river discharge and nutrient loads have been so severely depleted. Decreased fresh water flow has also cut off water supply to a string of fresh water lakes and underground aquifers near the coast. Salt water infiltration and soil salinization have become serious threats.
Water quality in the river and in Lake Nasser have suffered as well. The warm, still waters of the reservoir support increasing concentrations of phytoplankton , or floating water plants. These plants, most of them microscopic, clog water intakes in the dam and decrease water quality downstream. Salt concentrations in the river are also increasing as a higher percentage of the river's water evaporates from the reservoir.
While the High Dam has improved the quality of life for many urban Egyptians, it has brought hardship to much of Egypt's rural population. Most notably, severe health risks have developed in and around irrigation canal networks. These canals used to flow only during and after flood season; once the floods dissipated the canals would again become dry. Now that they are full year round, irrigation canals have become home to a common tropical snail that carries schistosomiasis ,a debilitating disease that severely weakens its victims. Malaria may also be spreading, since moist mosquito breeding spots have multiplied. Farm fields, no longer washed clean each year, are showing high salt concentrations in the soil. Perhaps most tragic is the displacement of villagers, especially Nubians, who are ethnically distinct from their northern Egyptian neighbors and who lost most of their villages to Lake Nasser. Resettled in apartment blocks and forced to find work in the cities, Nubians are losing their traditional culture.
The Aswan High Dam was built as a symbol of national strength and modernity. By increasing industrial and agricultural output the dam generates foreign exchange for Egypt, raises the national standard of living, and helps ensure the country's high status and profile in international affairs. For all its problems, Lake Nasser now supports a fishing industry that partially replaces jobs lost in the delta fishery, and tourists contribute to the national income when they hire cruise boats on the lake. Most important, the country's expanded population needs a great deal of water. The Egyptian population is currently at 68 million but projected at 90 million by the year 2035, and neither the people nor their necessary industrial activity could survive on the Nile's natural meager water supply in the dry season. The Aswan dam was built during an era when dams of epic scale were appearing on many of the world's major rivers. Such projects were a cornerstone of development theory at the time, and if most rivers were not already dammed today, huge dams might still be central to development theory. Like other countries, including the United States, Egypt experiences serious problems and threats of future problems in its dam, but the Aswan dam is a central part of life and planning in modern Egypt.
[Mary Ann Cunningham Ph.D. ]
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