Yeah, I can sort of see both sides of it. My understanding is that Egypt has adapted to and rather depends on the flooding: A nice evened out flow does not work well for them. The Aswan Dam itself has been a big problem in this regard. Lack of flooding and silt delivery to the floodplains has resulted in decreasing soil fertility and increased soil salinity.
Further, Ethiopia will almost certainly come to be dependent on using and selling as much electricity as possible whilst having a consistent supply during the dry season(s?) or droughts. Given the immense storage capacity, there’s no sense in letting energy in the form of stored water go to waste during the wet season, and there’s no sense in running it all through the generators then, as other hydro plants are at maximum capability then, too. Whose interests will come first, in Ethiopia?
Just the mere concept of another country having such potential control over one’s own country’s existential need (water) has to scare the heck out of the Egyptians. They know how unstable the region is. What if bad actors take power in Ethiopia?
There will even be significant evaporative losses of water stored in the new lake. More water could conceivably come from the White Nile River, as most of it’s volume disappears in vast swamplands in South Sudan. (Transpiration and evaporation.) A great canal was begun to bypass the swamps, but political upheaval in South Sudan has killed that project.
On their side, the Ethiopians surely look dimly on the idea of Egypt having near 100% say in how Ethiopia manages it’s dam.
I kept thinking that the excess wet season power capacity could somehow be used to pump surplus wet season water into elevated reservoirs in Egypt. But where in Egypt to do this, and without (again) large evaporative losses — well, I just don’t know...
Of note is that while the Nile is long, total water flow is dwarfed by, say, even our own Ohio River (almost 3x larger flow @ discharge.)
Links:
https://www.history.com/this-day-in-history/aswan-high-dam-completed
https://forces.si.edu/soils/02_08_03.html
The psychological well-being of Egypt is inextricably tied with the waters of the Nile, and to a lesser extent, the ancient monuments which are found in plenty. This has been the case for at thousands of years. I think the Egyptian opposition to the dam has a lot to do with that, rather than any rational considerations.
The Aswan High Dam’s Lake Nasser suffers from that same evaporation problem, and between destruction of the shrimp fishing industry in the Delta, and the fouling of groundwater and aquifers, *and* the resulting crumbling of monuments, the High Dam has been a disaster.
Because the waters just set there evaporating, the lake levels have always been hard to maintain. From a physical standpoint, the longer the fall, the more electricity can be generated from the same cubic meter of water, so keeping the lake level at or near max should be a priority. The higher the lake level, the less water needed to generate the same amount of electricity, in turn the level is simpler to maintain.
In short, the dam also hasn’t delivered its supposed benefits, other than flood control. But the flooding was also the reason for the agricultural season, again, going back thousands of years. As Herodotus wrote, “Egypt is the gift of the Nile”.