The project's potential impact on water supplies in Egypt and Sudan is causing friction, finds Rehab Abd Almohsen.
A group of Egyptian academics and experts have declared their opposition to the current plans for the US$4.8 billion Grand Ethiopian Renaissance Dam - on which work has started, and which will be Africa's largest hydroelectric power plant when completed - because they believe it will damage their country.
Egypt's Nile Basin Group was set up to assess the possible threat from the dam, which will lie close to Ethiopia's border with Sudan. Its members warn that the structure could slash the Nile's flow, especially in Egypt and Sudan, which depend on the river's waters.
Haider Yusuf Bakheit, a Sudanese hydrologist, was reported in an article in Infrastructure News as saying that the dam "will hold back nearly one-and-a-half times the average annual flow" of the Blue Nile, one of the Nile's two main tributaries, and "drastically affect the downstream nations' agriculture, electricity and water supply".
"Given the massive size of the dam, it could lose as much as three billion cubic metres of water to evaporation each year," he warned.
There was alarm in Egypt when the plan to build the dam was announced in 2011 - with some MPs talking off the record about Egypt's right to retaliate militarily - but much of the opposition now focuses on Ethiopia's decision to increase the size of the reservoir behind the dam.
"The original plan was to create a lake that would store 14 billion cubic metres of water, which is enough to generate electricity, but then the lake's capacity was increased to 74 billion cubic metres," Nader Noureddin, a member of the Nile Basin Group and professor of soil and water resources at Cairo University, tells SciDev.Net. Planned electricity output has also risen, from 5,250 to 6,000 megawatts.
Noureddin says that when Ethiopia decided to increase the height of the primary dam from the 90 metres in the original design to 170 metres, the planners were forced to include a secondary 'saddle dam' to help confine the vast reservoir created by the main dam and prevent stored water from escaping back to the Blue Nile.
"For the first time in history, we find a secondary dam that is four times as large as the original dam, which indicates the aim behind building such a huge dam is not generating electricity, but to use the dam as a way to control Egypt," argues Noureddin. In effect, he says, it would enable Ethiopia to turn off Egypt's water supply.
He favours sticking to the dam's original height and scrapping the idea for the saddle dam.
Rapid water take
Another concern is the speed at which Ethiopia plans to fill the reservoir.
Egyptian experts say that the huge proposed reservoir would normally take up to 20 years to fill, but Ethiopia intends to achieve this in just five years, consuming about a fifth of the Blue Nile's annual flow. That, argues Noureddin, would lead to "catastrophic" impacts on Egypt's agriculture.
Mohamed Mohieddin, a social policy consultant and professor of sociology at Egypt's Menoufia University, and a member of the three-country committee that is negotiating the project's next steps, suggests asking Ethiopia to extend the time allowed to fill the main dam by five or six years.
Through the committee, Egypt would be a partner in the dam's operations and have a say in how the water is released, he tells SciDev.Net.
Tensions between Egypt and Ethiopia, the source of 85 per cent of the Nile's water, rose in June, as soon as Ethiopia started work on diverting some of the river's flow as part of the project.
Both countries, as well as Sudan, see the project as affecting their national interest, which has sparked tough and aggressive comments from non-scientists.
"Egypt is always sceptical of what Ethiopia might think and do on the Nile," Tatek Kebede, the national coordinator of the Ethiopian National Youth Coalition on Climate Change, tells SciDev.Net.
He says Ethiopia is advancing economically and would not allow Egypt's diplomatic and even military pressures to deter its development ambitions, of which the dam is part.
Ethiopia's national electricity corporation has said potential buyers of electricity from the dam, scheduled for completion in 2018, include Djibouti, Kenya, Somalia, Sudan, Uganda and maybe even Egypt.
An Ethiopian ecologist, who would speak only on condition of anonymity, tells SciDev.Net that, since construction was nearly a quarter complete, "it would be good to find common ground and it would be good for the Egyptian side to deal with their concerns by working closely with the Ethiopian government and maybe even finding a way to benefit from it".
But Noureddin blames the Ethiopian government for "raising the hope of its people to a very high level", making it hard to compromise for fear of appearing weak.
Earlier this month, Ethiopia's prime minister, Hailemariam Desalegn, attempted to defuse tensions by emphasising the importance of good relations with Egypt. He described the dam as a common resource that will benefit all three countries.
But with passions still running high, Ana Elisa Cascão, a programme manager at policy organisation the Stockholm International Water Institute, believes cooperation is the only solution.
"The only hope for Egypt and Sudan is to have a share in the dam by funding it, and to cooperate with Ethiopia to jointly manage the dam," she tells SciDev.Net.
The next step in this unfolding story is a meeting of the Ethiopia-Sudan-Egypt dam committee. But even that is caught up in national and regional politics: it was due to meet on 20 October but now - due to recent rioting in Sudan over the lifting of fuel subsidies - all that has been agreed is that it will take place at some point in the next few weeks.
Rehab Abd Almohsen currently holds an IDRC/SciDev.Net science journalism internship award.