Nile River Dam in Ethiopia: how will it fill

Satellite images taken between June 27 and July 12, 2020 show a steady increase in the amount of water being held by the new mega dam, which straddles the Blue Nile in Ethiopia.

This has angered Egypt and Sudan, the two countries downstream of Ethiopia’s Great Renaissance Dam (Gerd), as the timetable for filling it has not yet been agreed in the stalled negotiations.

State media in Ethiopia have backed down after reports suggesting that the dam was being deliberately filled.

But all this gives the false impression that filling the dam will be like filling a bathroom, and that Ethiopia can turn a tap on and off at will.

Can’t stop it?

No. The reservoir behind the dam will naturally fill during Ethiopia’s rainy season, which started in June and lasts until September.

Given the stage where construction is at “there is nothing that can stop the reservoir from filling to the lowest point of the dam,” said Dr. Kevin Wheeler, who has been following the $ 4,000 Gerd project million (£ 3.2 billion) since 2012. the BBC

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Alastair Leithead and his team traveled in 2018 from the source of the Blue Nile to the sea, through Ethiopia and Sudan to Egypt.

Since the start of the process in 2011, the dam has been built around the Blue Nile as it continued to flow through the huge construction site.

Builders worked on the vast structures on both sides of the river without any problem. In between, during the dry season, the river was diverted through culverts, or pipes, to allow that section to be built.

The bottom of the center section is now complete and the river currently flows through bypass channels at the foot of the wall.

As the impact of the rainy season begins to be felt at the dam site, the amount of water that can pass through those channels will soon be less than the amount of water entering the area, meaning it will recede further and will increase lake that will sit behind the dam, says Dr. Wheeler.

Ethiopian authorities may close doors on some of the canals to increase the amount of water retained, but this may not be necessary, he says.

What is the next stage?

In the first year, the Gerd will retain 4.9 billion cubic meters (bcm) of water, bringing it to the height of the lowest point on the dam wall, allowing Ethiopia to test the first set of turbines. On average, the total annual flow of the Blue Nile is 49bcm.

In the dry season, the lake will recede a bit, allowing the dam wall to be built and in the second year another 13.5bcm will be retained.

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By then, the water level should have reached the second set of turbines, which means that the water flow can be managed more deliberately.

Ethiopia says it will take five to seven years to fill the dam to its maximum flood season capacity of 74bcm. At that point, the lake to be created could stretch about 250 km (155 miles) upstream.

Between each subsequent flood season, the reservoir will decrease to 49.3bcm.

So why is Egypt unhappy?

Egypt, which depends almost entirely on the Nile for its water needs, is concerned that in most years of filling a specific volume is not guaranteed.

And once the fill stage is complete, Ethiopia is reluctant to link to a figure for the amount of water to be released, as when fully operational, the dam will become the largest hydroelectric plant in Africa.

In normal or above-average rainy years, that shouldn’t be a problem, but Egypt is nervous about what could happen during prolonged droughts that could last for several years.