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Damming the tides of history

Perhaps the most controversial civil engineering project of the 20th Century is Egypt's Sadd el-Aali, or Aswan High Dam.

Only in Egypt could a dam assume such national significance. The Nile is the only river in the country. From south to north the 1,600km of the Egyptian Nile has no tributary, and a 5km wide strip each side of the river was the only fertile land available for agriculture amid millions of hectares of desert.

This fertility came from the annual Nile floods. Every year rain water from the Ethiopian mountains, 5,000km away to the south, spilled out from the river and deposited rich silt over the surrounding lands. In favourable periods the land could support around 7M people, despite a growing season of only three or four months.

For thousands of years man tried to spread the river's bounty further from the banks, and extend the growing season. Canals were dug, barrages attempted and reservoirs constructed, with mixed success. It was not until Egypt introduced cotton as a cash crop in 1805 that pressure to act over seasonal variations became irresistible.

The agriculture-dependent Egyptian population was booming but available arable land had hardly increased for several centuries. In addition the cotton needed irrigating for six months. The obvious solution was a dam, creating a reservoir which would release stored flood water in the dry season.

Winston Churchill attended the opening of the first Aswan dam in 1902. It was British-designed and built, with the help of an army of Egyptian, Greek and Italian workers. This masonry dam was a major civil engineering triumph. It stretched more than 3km across the valley, reached a height of 27m and held back more than 1km3 of water, releasing it when needed, complete with silt, through 180 mighty sluices.

Aswan was chosen because it was the site of the first cataract, which blocked river transport. A dam and ship locks would open up the southern Nile all the way to the Sudan. The cataract was also in a place where hard, durable granite came to the surface. This would provide a firm foundation and raw material for the dam's construction.

The boost to agriculture from this first dam generated enough wealth to pay for the tricky job of heightening the structure twice - in 1912 and 1933. This took the volume stored up to 5km3 and increased arable land by thousands of hectares.

But it was not enough to keep up with the population boom, and both the shortage of suitable land and lack of hydroelectric generating capacity were still undermining the country's future. In the late 1930s the British administration began to plan a third heightening and the diversion of some sluices to power a hydroelectric plant.

War and politics overtook these proposals. In 1952 the Egyptian government threw its weight behind plans for a monstrous new dam, 6km south of the first one. Originally part of a visionary management scheme for the entire Nile basin involving six countries, it would store a huge amount of water and enable Egypt to be totally independent of natural variations in the river's flow.

But relations between the Egyptians and the West soured and promised funding was withdrawn.

Egypt responded by nationalising the Franco-British Suez Canal, provoking an invasion by France, Britain and Israel in a doomed attempt to regain control.

After the dust had settled, Egypt's new ally, the Soviet Union, stepped in. Soviet engineers modified the original German design for a massive earth and rockfill dam, and work started in 1960.

The challenge was enormous. The volume was to be 16 times that of the Great Pyramid. Underlying sediments had to be stabilised and a vast grout curtain installed down to bedrock.

All this had to be done in extreme desert conditions. The Soviet Union insisted on using only Soviet plant on site, but earth moving fell way behind schedule until 54 British Aveling-Barford dump trucks were discreetly added to the fleet.

Environmentalists were criticising the whole rationale of the project even before it opened in 1968.

The threat to a number of ancient monuments, not least the awesome Abu Simbel temples, also aroused archaeologists' ire. They were dismantled after much dispute and reassembled above the final water level.

Environmentalists' objections centred on the water which would flow from the new reservoir being silt-free. This meant power from the dam would be needed to run an artificial fertiliser plant whose products would have to replace the silt's beneficial effects.

There were also fearsthat the absence of silt would accelerate erosion of the riverbed downstream of the dam, and the reservoir itself would gradually silt up, reducing its effectiveness.

There was concern that, further north, the coastal waters of the Mediterranean would lose the annual influx of nutrients from the Nile and fish catches would drop. This has happened, but supporters of the dam point to the creation of a significant new fishery in the reservoir itself. Erosion of the riverbed, as measured in 1990, was 250mm, rather than the 8.5m predicted by some.

Soil salinity has increased, as has incidence of certain waterborne diseases. But a 20% increase in agricultural land area, and protection against the severe 1988 floods and the preceding nine years of drought, can be set against that.

Hydroelectric power from the project has also brought undoubted benefits. Debate about its merits will continue for a long time, but the Sadd el- Aali's place in history is assured.

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