Stochastic Investigation of the GERD-AHD Interaction Through First Impoundment and Beyond

The Grand Ethiopian Renaissance Dam (GERD) is currently being constructed on the Blue Nile. In the short term, water inflow to the Aswan High Dam (AHD) reservoir will be reduced as water is abstracted during GERD’s first impoundment. In the long-term, the inflow to AHD will be affected due to flow regulation and additional evaporation losses from GERD. This chapter presents a stochastic analysis of the impacts of GERD on AHD. Synthetic Nile flow series that preserve the Hurst exponent of the flow are generated using a Fractional Gaussian Noise (FGN) model. Results from the simulation of 1,000 equally probable Nile flow series using a simplified GERD-AHD system model are analyzed. The results indicate a very high downstream risk when GERD is operated as an annual storage reservoir, which questions the economic attractiveness of GERD in a regional context when operated solely for hydropower energy maximization. Operating GERD as a long-term storage reservoir results in reduced, yet still considerable impacts. Optimal GERD filling and operation policies aimed at minimizing downstream risks through a comprehensive regional economic, environmental, and social analysis are urgently needed.