Ethiopia and Egypt “urgently” need to agree on the coordinated operation of their two large dams in the Nile River basin to ensure water is shared fairly during periods of reduced flows, a group of international experts said.

Ethiopia is planning to complete the $4 billion state-funded Grand Ethiopian Renaissance Dam, known as GERD, in mid-2017 on the Blue Nile River, the main tributary of the Nile. Downstream Egypt, which finished its High Aswan Dam in 1968, has expressed concern that the hydropower plant will reduce its water supply while the reservoir is being filled.

Coordination is needed so “Egypt and Sudan are not harmed during the filling period or during periods of prolonged drought,” according to a report by the International, Non-Partisan Eastern Nile Working Group, brought together by the Massachusetts Institute of Technology. The experts also warned of dam-safety issues.

Ethiopia, Egypt and Sudan, another downstream nation, last month agreed on principles governing the 6,000-megawatt GERD, including that it shouldn’t cause “significant harm” to the other two countries. The three will discuss how to manage what will be Africa’s largest power plant in about a year, after international consultants have assessed its regional impact.

Ethiopia has said it may take as long as six years to fill GERD’s 74 billion cubic-meter reservoir, which is more than 1.5 times the volume of the annual flow of the Blue Nile at the dam site. The plan must be “flexible” enough to respond to varying rainfall, the experts said in the report, posted on MIT’s website Thursday.

‘Weak Zones’

If dam levels are low in Egypt and Sudan during filling, then Ethiopia could release more water downstream, they said. Egypt’s Aswan dam can store 132 billion cubic meters.

Egypt, which relies on the Nile for almost all of its water, criticized the MIT study and said it ignored the finding of a previous international report on the dam. Most of the recent experts’ analysis “probably relied on the politicians announcement rather than accurate information,” a group advising the Egyptian Water and Irrigation Ministry said in its response posted on MIT’s website.

The 17 mainly U.S. scientists expressed concern at aspects of the dam’s design, including the likelihood of “weak zones” in a 5-kilometer (3-mile) long rock-filled auxiliary dam.

“We are concerned that the risks posed by the GERD’s extensive saddle dam may not have been fully appreciated or analyzed,” they said. Problems would mean significant extra costs for Ethiopia, while a “significant rupture” would be an “economic and humanitarian disaster for Sudan,” it said. Sudan supports the GERD project.

Global Practice

“The design and construction of the saddle dam has followed international standards and is informed by the practices on the ground around the globe,” an Ethiopian panel of government and non-government experts said in a response to the study posted on MIT’s website.

Building transmission lines and agreeing on power deals as soon as possible for electricity produced by the GERD is “essential,” the group said. The dam will generate an amount of power approximately equal to Ethiopia’s domestic consumption, it said.

Ethiopia’s export plans include sending 1,200 megawatts of power to Sudan and 2,000 megawatts to Egypt. Revenue from exporting the GERD’s electricity could be at least $1 billion a year, although any delay in power trading would be at a “major” cost to Ethiopia, the group said.

Salt Buildup

“Also, if there is no power trade agreement in place and transmission lines are not ready when it becomes possible for the GERD to generate hydropower, then water cannot be released through the GERD’s turbines,” the study shows. “This has significant implications for a joint operating agreement.”

Reduced flows to Egypt during GERD filling and because of other upstream developments may lead to increasing salinization of farming land and needs “immediate” attention, according to the report. “A rapid buildup of salts in Egyptian agricultural lands in the Nile Delta could create a political crisis in the basin if Egyptian farmers and policymakers blame their problems on Ethiopia,” it said.

The group said it believes that Blue Nile hydro-projects are “economically and financially attractive investments” and some of its concerns may be “assuaged” as Ethiopia makes more information available about GERD.