Big dams have tended to be a disaster for the indigenous people and the ecosystem.  Even if you don't care about that, you would face decades of desparate opposition.  Africa is not China, nor is it Northern Quebec.

Just the carbon release from the flooded rainforest alone would probably offset much of the benefit in the short term.

Better to build a series of smaller dams-- which is what the British proposed for Aswan, but Nasser wanted a great big dam and all of the attendant prestige.  So we got 'Lake Nasser' and some of the world's most precious archaeological sites were flooded, forever.  And there is massive evaporation, salt destruction of the temples at Luxor, etc.

A stereotype of "big dams" without looking at specifics.

Grand Inga could produce the equilavent of 40 or so nuclear plants.  Provide a stable power supply without greenhouse emmissions.  Equal to roughly the entire world's installed windpower ! Get an entire continent on renewables !!

Inga I & II and been in operation for decades.  Marginal additional rainforest covered with Grand Inga.

The smaller dams have been built, Inga I & II (II is being expanded, new turbines added).

Grand Inga could supply power when droughts reduce supply in smaller river systems.  Total rainfall will not decline with global warming, but increase.  And an Africa wide grid (Africa is second largest continent) of local hydro and Grand Inga should be quite stable with global warming.

About 120 years of hydrology data.  Rainfall from two seperate systems that are mirror images of each other make a best case for Grand Inga.

I reject your criticism.  Perfect appears to be the only acceptable solution for you.  

Grand Inga seems as close to perfect as any unrealized real world solution that I have seen.  (Niagara Falls hydro, 4 GW, is best energy source in the world IMO).  Massive positive gains with minimal downside.  A good % of world's nitrogen fertilizer as a side benefit (think reduced NG use and less global warming).

It would be good to read something on it.  I know nothing about the specific project.

I am just a sceptic of that kind of megaproject. The outcomes tend to fall short of the promises.  Usually there was a less grand, less risky strategy that could have been applied as I cited re the Nile.

The drought problem remains. Maybe the world's rainfall goes up, maybe Africa's rainfall is stable/ goes up.  Maybe.

I am prejudiced on Niagara (or rather St. Lawrence Power which was kind of a grandson).  My father built a part of it ;-), and my parents met there ;-).  

Probably Churchill Falls was an even bigger success, but marred by the fact that Newfoundland signed an agreement with Quebec that had no CPI price escalator.  Quebec Hydro has been banking billions on that deal ever since.

Well the problem with this are too numerous to list, but the largest and  severest one is this is the thinking that has put us where we are -- we're going to remake the earth -- and it's certainly not going to get us out.
I actually tend to disagree with this.  The problem we have is due to our unintentional impact on the Earth.  We have operated in a damaging fashion because we haven't looked at the large scale impacts of our actions.  If we accepted our ability to effect the environment that would be a step in the right direction.  No matter what we're going to impact the Earth, if we try to do so with an eye on the big picture, and how we can change things for the better, we stand to do much better than we currently are doing.  
Aswan was before my time, but my understanding is that the key to building a high dam was not prestige but irrigation.  

Lake Nasser significantly increased arable acreage in Eygpt (vague memories of 1/3 & 40%) and removing the annual flooding allowed double cropping on existing farmland.  Farmland, not prestige or electrical power, was, AFAIK, the motivation for the Aswan High Dam and all of the negative effects.

You missed one of, if not the most important negative.  The Nile delta fisheries were destroyed.

If Egypt thought that the negatives exceeded the positives, they could raise & lower Lake Nasser with the annual flood or just destroy the dam.

Again, vague memories of facts.