They also called for further studies on what impact the 6,000-megawatt, $4.7 billion project may have on the downstream nations of Sudan and Egypt, the International Panel of Experts said in a report e-mailed to Bloomberg News and verified by Ethiopia’s Foreign Ministry. Egypt, which relies on the Nile for almost all of its water, expressed alarm about the dam when Ethiopia in May diverted the Blue Nile as part of the construction process.

“Structural measures might be needed to stabilize the foundation to achieve the required safety against sliding” of the main dam, according to the report. There are also “weak zones” in the rock that will support an auxiliary dam that need to be studied, it said.

Construction of the Grand Ethiopian Renaissance Dam is part of a government plan to spend 569 billion birr ($30 billion) on infrastructure in the five years through mid-2015. The country, Africa’s second-most populous nation, targets becoming an industrialized middle-income nation by 2025.

Ethiopia is the source of 86 percent of the water that flows into the Nile, the world’s longest river that runs 4,160 miles through 11 countries from Burundi in the south to Egypt, where it empties into the Mediterranean Sea. Ethiopia has said it will take five to six years to fill the 74 billion cubic-meter (2.6 trillion cubic-feet) reservoir created by the dam.

Regional Specialists

The panel, which held its first meeting in May last year, was formed at the suggestion of Ethiopia’s government. It comprised two specialists each from Ethiopia, Egypt and Sudan and four from other nations. The report, which hasn’t been made public, was submitted to the three governments in June.

Ethiopia said the report found the project to be of international standard and won’t cause “significant harm” to downstream countries, while Egypt said it was inconclusive.

Ethiopia delivered a hydrological study to the panel that analyzed the downstream impact of the reservoir-filling period given low, average or high rainfall.

The project document concluded that Egypt faces a 6 percent reduction in the High Aswan Dam’s electricity-generating capacity and no water loss if the reservoir was filled during years of average or high rainfall. If the reservoir was filled in a dry year it would “significantly impact on water supply to Egypt and cause the loss of power generation at High Aswan Dam for extended periods,” according to the document.

A “comprehensive” additional study of the dam’s impact on water resources should be conducted, the panel said after reviewing the document. “The analysis presented is very basic, and not yet at a level of detail, sophistication and reliability that would befit a development of this magnitude, importance and with such regional impact.”

Ethiopia is working with Sudan and Egypt to enact the panel’s recommendations, Dina Mufti, a spokesman for the Foreign Ministry, said in an interview today in the capital, Addis Ababa.