For those wondering like me where the water is supposed to come from:
Authorities have said that water for the artificial river will come from recycled agricultural drainage and groundwater.
This doesn't really strike me as a long term solution though, unless Egypt has vast reserves of groundwater.
The article gives another reason:
In addition, in recent years there have been droughts in East Africa as well, which can't have been good for the amount of water the Nile carries, and the dam you mention just adds to the whole thing.