Science: Dammed to destruction: For thousands of years the Nile fertilised Egypt. No longer. Fred Pearce on a catastrophe in the making

THE NILE delta, granary of ancient Egypt and still Africa's most productive farmland, is being eaten by the oceans and invaded by the desert. The Aswan dam, hailed in the 1960s as a triumph of engineering and water management, is now seen as a major cause of the region's impending devastation.

The delta is a wedge of highly fertile land the size of Northern Ireland where the Nile reaches the Mediterranean. It is composed of layer upon layer of silt, most of it eroded from the highlands of Ethiopia over tens of thousands of years. Each year, 100 million tons of soil slips from the parched lands of Wollo and Tigre, and flows north in a muddy gush as the Blue Nile floods.

What was Ethiopia's loss was Egypt's gain. The silt raised the Nile delta by about one millimetre each year, fertilising it and counteracting natural subsidence and erosion by the sea. Until 1964, that is. That was the year when Colonel Gamal Abdel Nasser completed the Aswan dam. As planned, it trapped the Nile's fierce annual flood which rushed downstream each summer, and replaced it with near-constant flows designed to provide water all year round for irrigation canals. But the dam also trapped 98 per cent of the Nile silt, which now drops uselessly to the bed of Lake Nasser, the reservoir which formed behind the dam.

For Nasser, 'the largest lake ever shaped by human hand' would be 'a source of ever-lasting prosperity' for Egypt. But the prosperity looks set to be anything but everlasting.

Denied the fertile silt that has sustained farms on the delta for more than 7,000 years (longer than anywhere else on Earth), Egypt already uses more fertiliser per hectare than any other nation.

And fertiliser won't protect the delta from the sea. Without a constant supply of silt, it faces eventual destruction as surely as a sandcastle meeting an incoming tide. As Egypt's population of 58 million grows by a further million every nine months, what future is there for this, Africa's second most

populous state?

The bleakest prognosis yet for Egypt and the delta came in April in the journal Science, in a paper written by Daniel Stanley and Andrew Warne of the Smithsonian Institution in Washington DC. This 'vulnerable oasis in the vast inhospitable eastern Sahara desert', they wrote, is at risk from sea erosion. The coastal village of Borg-el-Borellos is now beneath the waves, two kilometres out to sea.

As the sea advances, the desert is also invading. Here again, mankind is to blame. Modern irrigation canals no longer bring silt to the fields with the waters of the Nile, but they do bring natural salts eroded upstream and dissolved in the water. In ancient times, when the river flooded fields, the ebbing flood flushed the salts away each year. But modern canal irrigation leaves the salt behind. It is gradually poisoning the soil of this, one of the world's leading cotton-producing regions, and turning it to desert.

Each year, one ton of salt accumulates on each hectare of delta fields. The country is spending tens of millions of dollars each year, laying the largest drainage network the world in an attempt to flush out the salt. Even so, salt is already reducing crop yields on more than a third of the fields.

Once, much of the delta was composed of marshes and brackish lagoons, protected from the sea by sand bars. Today the lagoons have been reduced by drainage, and are increasingly poisoned by sewage and pesticides. Lake Maryut, once a haven for wildlife depicted in Lawrence Durrell's Alexandria Quartet, is now a cesspit for the metropolis of Alexandria. Fish catches there dropped by 85 per cent during the 1970s. The sewers of Cairo, a city of 10 million people, now empty into the equally fetid Manzala lagoon.

Even so, the four surviving lagoons supply 100,000 tons of fish (two-thirds of Egypt's catch) and employ 100,000 people. But soon the lagoons may disappear altogether. Deprived of silt, the sand bars are fast eroding and will collapse. They and the lagoons form the main defence against the sea for the entire delta. With them gone, the tides will rush inwards ever faster.

Another exacerbating factor is the greenhouse effect. Rising sea levels can only hasten the destruction of the delta. A rise of one metre over the next century could inundate the northern third of it, affecting 15 per cent of Egypt's farmland and 8 million of its people. Long before then, seawater would penetrate deep into the groundwaters beneath the delta, adding to the salt build-up.

But what of the flow of the Nile itself? In the fifth century BC, the Greek historian Herodotus called Egypt 'the gift of the Nile'; without the annual flood, there would be only desert. The river's capricious flow has been measured for more than 5,000 years, since before the construction of the Great Pyramid. But in recent years 'the gift' has faltered. Average flows have fallen by a third in the past 30 years, as the rains have failed repeatedly in Ethiopia.

Is this a random fluctuation one of the legendary 'seven years' of low flows that could bring famine, or could it be something even more serious? Blame has been placed on everything from sunspots to lunar cycles and El Nino, an oscillation of ocean currents and winds in the far-off Pacific. Many climate models predict a long-term fall in Nile flows as the greenhouse effect takes hold.

In recent years, there has often been less water in the river than Egypt is allowed to abstract for its own use under the Nile Water Agreement, signed with Sudan in 1959. It is a rare year when any water at all is allowed to pass naturally into the sea.

Ethiopia, the source of more than 80 per cent of the Nile's flow, currently uses less than 1 per cent of it. This drought-ridden country now wants to take water from the Blue Nile, perhaps by damming its source, Lake Tana. But Ethiopia is not party to the Nile Agreement, and its downstream neighbours acknowledge no right for it to dam the river's waters. If it ever does, the prophecy of Egypt's former foreign minister (and now UN Secretary-

General), Boutros Boutros-Ghali, may well come true: 'The next war in our region will be over the waters of the Nile.'

The Aswan dam can protect Egypt against a few years of low river flow, as it did in the mid-1980s, but not against a long-term cut in the Nile's gift - whether caused by declining rainfall or an Ethiopian dam. The prognosis for the Nile, its delta and Egyptian agriculture is bleak. Declining agricultural production will devastate this desert country, already unable to feed itself and expecting a doubled population within 30 years.

Drought and famine threaten to wrack Egypt as severely as they have its upstream neighbours, Sudan and Ethiopia. -

(Photograph omitted)