THE FORMATION OF THE EGYPTIAN NILE FLOODPLAINS AND THE DILEMMA OF THE NILE SYSTEM SEDIMENTS BUDGET

We have used remote sensing and geophysical data to estimate the amount of sediments deposited along the floodplains of the Egyptian Nile since it was connected to the rest of Sub-Sahara Africa Nile ~800,000 years ago. Our analysis suggests that ~4,000 km³ of fertile soil - removed from the Ethiopian Plateau and Lake Plateau Region - was deposited within the Egyptian Nile which is controlled by the ~6 Ma old Eonile canyon. This indicates deposition rate of ~ 125 m³/km²/year, which is 10 times greater than the rate of erosion within the Ethiopian Plateau; estimated to be 12.5 m³/km²/year since the incision of the Blue Nile on the plateau ~30 Ma ago. However, our estimated deposition rate along the Egyptian Nile floodplains is within the range of present day erosion rate of the Blue Nile catchments' area estimated from river sediments load to be between ~125 and 490 m³/km²/year. The vast discrepancy between the depositional rate along the Egyptian Nile floodplains and the erosion rate of the Ethiopian Plateau by the Blue Nile as estimated from the geological record can be explained by one or more of the following reasons: (1) Dramatic acceleration of incision of the Blue Nile in the Ethiopian Plateau since ~1 Ma resulting in an increased rate of erosion; hence increased amount of sediment flux received in Egypt. This is supported by recent studies which indicate that the incision rate of the Blue Nile on the Ethiopian Plateau has increased significantly in the past ~6 Ma. (2) The White Nile might have equally been a major supplier of sediments eroded from the Lake Plateau Region and deposited along the Egyptian Nile floodplains; (3) The time when the Egyptian Nile was connected to the Sub-Sahara Africa Nile is more older than the suggested ~800,000 years. This work represents a first-hand calculation of the Nile System sediments budget through time and would further benefit from: (1) Better understanding of the geometry of the Eonile canyon to constraint the thickness of the fertile soil layer; (2) Geochronological studies to better constrain when the fertile soil first appeared in Egypt; (2) Geochemical studies to constrain contributions of sediments carried by the Blue and White Niles to the building of the floodplains of the Egyptian Nile; (3) Better constrains on the ancient and present rates of erosion and deposition within the Nile Basin.