Abstract
The Nile River is the source of more than 97% of Egypts freshwater. Building the Grand Ethiopian Renaissance Dam on the Blue Nile may be lessen the Egyptian water share during the damfilling period. It may also increase the chances of flooding in case of the dams collapse. The potential effect of that dam on the stability and efficiency of the Rosetta promontory, the terminal of the Nile River with the Mediterranean Sea, is investigated by using the Coastal Modeling System software. Field data of wave, wind, tide, sediment characteristics and bed morphology are used to construct and calibrate the model. The developed model scenarios contain the reduction in the water discharge to the sea in increments of 25% from 25% to 100% which corresponds to the dam-filling period from 6 to 2 years. The other scenarios allow the maximum discharge through the Nile branch continuously for two months to represent the case of the dams destruction. These scenarios are based on the assumption that the dam will be used only for hydropower generation. The first four scenarios show a limited effect on the promontorys stability and efficiency compared to the recent condition. That is due to the recent limited water discharge through the promontory due to the water scarcity in Egypt and the multi-usage strategy of the water resource applied by the Egyptian government. On the other hand, the flooding scenarios showed an increase in the inlets cross section leading to a relatively large local scour especially in front of the western bank protection work which threats the structures stability. Moreover, the sedimentation spit inside the inlet will be relocated in front of the exit which affects the efficiency of the navigation channel. In addition, it was found that the wave run up and overtopping increase the risk of flood in the cultivated low lands around the promontory specially behind the western side. The wave height and energy inside the inlet dramatically increased after the flooding particularly at the western side bank which will affect the stability of the bank protection work. These side effects can be eliminated by reinforcing the side bank protection work in a limited zone and save the minimum promontory cross section from a flood of 1450 m(2).