|Rendition of Grand Ethiopian Renaissance Dam/Wikipedia|
Once the reservoir is filled, the Blue Nile flows as before with only an adjustment for evaporation from the reservoir. But this could be an advantage because the rate of evaporation will be lower than if the water is stored in the much hotter area behind the Aswan High Dam.
For those of you interested in the technical aspects of this hugely important issue, I recommend a 2008 study titled "Sediment in the Nile River System" by Abdalla Abdelsalam Ahmed and Usama Hamid A.E. Ismail and a 2010 article in the Nile Basin Water Science and Engineering Journal titled "Investigation of Step Trends of the Nile River Flow Time Series" by Ageel I. Bushara and Tagreed Abdelrahim. All of these authors are Sudanese. They explain the importance of the variable flow of all Nile tributaries from one year to another and the timing of the high and low flows of the rivers.