TWO-DIMENSIONAL FLOW AND TRANSPORT SIMULATION OF THE NILE ESTUARY INVESTIGATING IMPACTS OF SEA LEVEL RISE Mohamed Mahgoub, Ayman Jourieh, Reinhard Hinkelmann Chair of Water Resources Management and Modeling of Hydrosystems, TU Berlin, Gustav-Meyer-Allee 25, C. TIB1-B14, 13355, Berlin. PH: +493031472313, FAX: +493031472430 E-Mail: mohamed.mahgoub@wahyd.tu-berlin.de Abstract The possible changes in the flow and salinity balance in the Nile estuary due to the anticipated sea level rise were investigated in this research. For this purpose mathematical modeling was used to simulate two-dimensional flow and salinity transport processes. The computational domain comprises the last reach of the Rosetta branch of the Nile River between the last barrage and the Mediterranean Sea. The TELEMAC2D modeling system which solves the two-dimensional (velocity- averaged) Saint-Venant equations has been chosen for the numerical simulation of the reach under study. The results revealed that for average conditions the water level variations are very small and the flow velocities are very small, too, with a maximum of about 8cm/s. The sensitivity of the model to the turbulence viscosity and friction coefficient is very small. The intrusion of the salt water will increase from 4.8 km for an idealized storm under average conditions to be about 7.1km, 9.6km and 12.7km when the sea level increases by 0.25m, 0.5m and 1m respectively. To maintain the current balance an extra water flow has to be discharged from the last barrage. Introduction In the last few decades several observations and natural phenomena proved that the global climate changed in terms of temperature and rainfall, this change could have negative direct and indirect consequences on all the earth (IPCC, 2007; UNFCCC, 2007). One of the consequences that has taken great interest is the sea level rise which may affect the low lying areas close to the shores (Agrawala et. al., 2004; Ludwig & Vellinga, 2008; El Raey, 2010) and the fresh water at the mouths of the rivers, as the case of the Nile River. The Nile River bifurcates at El-Qanater city (about 20 km north to Cairo) into two branches which are Rosetta branch (the western) and Damietta branch (the eastern), the two branches enclosing the Nile Delta and forming the Nile estuary. The two branches discharge the Nile water into the Mediterranean Sea. The discharge of the two branches is controlled through several water structures. The flow that is discharged into the sea (considered as waste from the water budget of the country) is the minimum flow that supports the navigational purposes, the natural processes in the river and to make balance with the sea water. Any changes in the sea level or in the Nile flow due to climate change could change the balance that currently exists between the fresh water and the saline water and hence it will affect the water management of the Nile estuary. Mathematical modeling has emerged as a powerful tool in water resources management; it allows simulation of environmental water and prediction of the possible impacts due to the anticipated changes. Few works have been found where mathematical models for Nile River Estuary have been carried out using different modeling systems and tools; the focus of these trials was sedimentation processes. Mahmoud et. al. (2006) used SOBEK modeling system to make a one dimensional (1-D) model of Rosetta promontory to identify its actual capacity to pass the emergency and flood flows and the capacity in case of dredging. The research constructed a model to the last 30 km of Rosetta branch investigating the hydrodynamic behavior in different flow conditions. Moussa & Aziz (2007) used GSTARS 2.0 Model (developed by the U.S. Bureau of Reclamation) to calculate the amount of sediment discharge of Damietta branch of the Nile River and comparing several formulas used in this context. Hence, mathematical modeling was used in this research to model the River Nile estuary to investigate the extension of saline water intrusion into the Nile River and its impact on the water management in Egypt regarding the sea level rise. Therefore following objectives were investigated: a. Simulating the two-dimensional flow and salinity transport processes in the Nile estuary, that is considered as the baseline scenario b. Comparing the baseline scenario to different scenarios of sea level rise c. Pointing out the remarkable changes in the hydrodynamics and salinity transport d. Examining the possible water management options for the different sea level rise scenarios and investigating the impact on the total water budget for the country 1