FROM the dawn of history through the late 19th century, no more than 7 million Egyptians populated the thin green ribbon of cultivable land created by the Nile River. With 10 times that number to provide for by the year 2000, preserving an adequate share of the Nile waters has become a matter of life or death for Egypt.
Since 1959, the status quo in the Nile Basin has been defined by an agreement between Egypt and Sudan which gives Egypt two-thirds of the average annual flow at the border, near Aswan.
So far the arrangement has worked because both Sudan and Ethiopia, which controls the source of 80 percent of the Nile water reaching Egypt, have been preoccupied by internal conflicts.
But development in either country, still considered a distant prospect, could create turmoil in the Nile Basin, where every war since the turn of the century has been fought at least partly over water.
In 1970, Egyptian President Anwar Sadat threatened to declare war on Ethiopia over the proposed construction of a dam on Lake Tana, the source of the Blue Nile. Any future plans by Ethiopia to develop the Nile's headwaters could become a new casus belli for Egypt.
``If Ethiopia constructs a dam on the Blue Nile resulting in less water for Egypt, Egypt cannot accept this,'' says Habib Ayeb, a Tunisian geographer who is writing a book in Cairo on the Nile River Basin.
A senior official in Addis Ababa says that, in principle, Ethiopia would like to build one or more dams on the upper Nile for irrigation and electric power generation. The official says the dams would also benefit downstream users like Egypt. But the foreign capital needed to make such hopes a reality is unlikely to materialize until Ethiopia's long civil war is ended and financial solvency regained.
In the meantime, Ethiopia has agreed to keep Egypt informed of future development plans on the Nile. The concession was made to win Egyptian backing for an African Development Bank loan to build irrigation canals for sugar-cane production along the river.
To ensure its long-term water security, Egypt has supported the efforts of a group of Nile riparians to cooperate in the development of the river's resources. Egypt would also like to convince Addis Ababa eventually to negotiate a river-sharing agreement that would limit Ethiopia's future use of the Nile, but without negotiating away any significant portion of its own river rights.
``Will we have a total war over the Nile? We don't know,'' says Dr. Ayeb. ``But as long as the water problem exists there may be at least limited conflict between Egypt and Ethiopia.''