The construction of the Grand Ethiopian Renaissance Dam (GERD) on the Nile River has triggered much debate between Ethiopia, Sudan, and Egypt on the dam's effects. Once completed, the GERD will be Africa's largest hydropower plant. This study analyzes the implications of cooperative long-term operation of the GERD for Nile riverine flooding downstream of the dam. A daily river system model of the Eastern Nile is developed using RiverWare to examine how cooperative long-term operation of the GERD would affect the occurrence of three flood alarm levels (alert, critical, and flooding) in Sudan downstream of the dam. A reconnaissance-level flood inundation model is developed for the Nile within Khartoum State (Sudan's capital) using the GIS Flood Tool of USGS to assess the GERD's impacts on the flood extent in the state based on simulated flows from the river system model. Assuming the GERD is operated to achieve a 90% power reliability and active upstream-downstream data sharing between Ethiopia and Sudan on the dam's daily outflows, results show that the GERD would reduce the occurrence of the three alarm levels. Based on 34 simulated river flow sequences, the proportion of years with at least one flooding alarm day at Khartoum Gage declined from 37% without the GERD to 11% with the GERD. Seasonal coordination and planning between Ethiopia and Sudan are necessary to mitigate the remaining riverine flood hazard. Although cooperative long-term operation of the GERD could play a positive role in reducing the riverine flood hazard in Sudan, the associated river flow alterations would adversely impact recession agriculture and the environment.