Dam Watch: Egypt/Sudan/Ethiopia
Below is a collection of satellite images from the ESA’s Sentinel satellite showing the major dams on the Nile over time. You can view the images directly and browse the dates (a photo every 5 days) using Sentinel Hub. Here’s links for Ethiopia/Sudan and Egypt.
At this scale and for these landscapes, viewing the images as ‘natural colour’ can make it a bit hard to see. Instead I’ll use ‘Normalized Difference Water Index’.
For each selected date, I’ll show two images (at the same scale). First is the Grand Ethiopian Renaissance Dam (GERD) and Sudan’s Roseires reservoir. The second is Egypt’s Aswan dam (Lake Nasser) and the Toshka Lakes that take excess water when Aswan is full.
Of course, these images are two-dimensional and so depict area, not volume; Roseires and the Toshka Lakes are relatively shallow compared to GERD and Lake Nasser, and a reservoir’s area doesn’t increase linearly as it fills.
Despite this, the volume of the Aswan dam system really is enormous, so looks aren’t too deceiving. (Reports of the GERD being the largest dam in Africa are patently incorrect. Maybe the Washington Post doesn’t have access to maps.)
I’ll start with a few years before the GERD started filling to give you a feel for the ebb and flow of the whole system. When looking at the dates, keep in mind that the monsoon runs from about May to August in Ethiopia, and the four dams along the Blue Nile respond with varying delays. And remember that only 55% of the Aswan dam’s water comes from the Blue Nile (where the first two dams are).
In 2017, there was little left of the Toshka Lakes (Egypt’s overflow lakes) which had peaked in the early 2000s. But you’ll soon see them making a comeback.
This is close to the low point for the year, Roseires (Sudan’s first of two dams) is just a few ponds by this point.
Middle of the wet season, Roseires is filling up.
By October Roseires is full. The GERD is holding back some water, but it will be a few years before it begins to fill in earnest.
By May, the GERD has almost completely emptied and Roseires is drying up.
By early September the rains have just started. The GERD is filling up, but barely visible. Roseires is empty.
One month later, Roseires is full to the brim. One month!
10 months later, we’re back near the lowest water levels.
In October 2019 something interesting happened: a new lake appeared in Egypt. This is a result of a canal that essentially takes overflow from Lake Nasser. It’s an indication that the Aswan dam is ‘full’.
A friendly reminder that we’re only looking at surface area here, these new lakes are huge (big enough to fit a few Manhattan Islands and still have water views), but they don’t have a particularly high volume (and as far as I’m aware, can’t flow back through Egypt).
By the new year, the Toshka lakes were filling up nicely.
This is the end of the last dry season before the GERD starts seriously filling. In this image, Roseires fails to show up as blue, but it’s there.
A few months later, filling of the GERD has kicked in, Roseires is very low, but it didn’t get as low as either 2018 or 2019.
One month later, it appears the GERD has stopped filling and water is flowing through to Roseires.
Meanwhile in Egypt, the canal that connects Lake Nasser to the Toshka Lakes is flowing again (yes, the GERD filled up some and Aswan still overflowed).
Three weeks later, Roseires is full, the GERD looks much the same, and Egypt’s overflow lakes are filling out nicely.
Remember in prior years, Roseires is beginning to dry up by May, so it’s pleasing to see that both it and the GERD have levels similar to October.
Egypt’s new lakes have grown ever larger, but note that the canal is no longer flowing (that stopped at the end of December).
I’ll update this page in a few months when the rains pick up.
What it all means
So far this is good news. It means that the GERD was able to grow to this size…
…while letting enough water through to fill Sudan’s and Egypt’s dams to the brim. There’s a lot of filling left to do, but the reality so far certainly is a long way from the doomsday scenarios many had predicted.
No doubt tensions will rise over the coming months, but it’s worth remembering that the (valid) concerns about the GERD are all long-term — nobody’s dying of thirst in the next 12 months because Ethiopia is stealing their water. The more immediate risk to human life stems from political leaders inciting violence in the name of water security.