The French firms BRL and Artelia were chosen late last year to carry out technical studies on the project following a meeting between top diplomats from Ethiopia, Sudan and Egypt.
BRL Director General Gilles Rocquelain told AFP after the contract was signed in Khartoum that the studies will begin after two months and "will take 11 months to complete".
The Egyptian, Ethiopian and Sudanese water ministers also attended today's signing ceremony.
However, the three countries have since failed to overcome their differences about sharing the water.
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Egypt, which is almost totally reliant on the Nile for agriculture and drinking water, fears that the Grand Renaissance Dam will hit supplies hard.
It draws 87 percent of its water from the Nile, which runs north from Khartoum where the Blue Nile and White Nile rivers converge.
Ethiopia had said the project would not adversely affect Egypt's share, but Cairo has maintained its "historic rights" to the Nile, which it says are guaranteed by treaties from 1929 and 1959.
Today, however, the three water ministers said they were optimistic about the project.
"We are keen to have everyone satisfied with what we are doing... We are for regional integration and prosperity," Egypt's Water Resources Minister Mohamed Abdel Aati said.
The dam is designed to feed a hydroelectric project that will produce 6,000 megawatts of power.
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