Author(s): A. F. Ahmed; M. R. Abdelbary
Linked Author(s): Usama Ijaz Farhat Ajaz Ahmed
Keywords: Sediment transport; Reservoir sedimentation; Channel adjustment; Large dams side effects; Meandering; River bed degradation
Abstract: Aswan High Dam was completed in 1970 on the Nile, 7 km south of Aswan city, mainly for long term storage and flood protection. The peak discharges have reduced from more than 1 billion m 3 ·day -1 during flood to 250 million m 3 ·day -1 after the construction of the dam. Suspended sediment concentration has reduced from more than 4,000 ppm during flood to less than 200 ppm downstream the dam nowadays. The river has to adjust to these changes. To cope with the decreased discharges and sediment load, the river is adjusting its slope to reduce its energy. This is done in two ways, first: River bed degradation by erosion of upper reaches and deposition in the lower reaches. Second: The river is trying to follow a longer path to the sea by meandering through its course. This is accomplished by eroding one of the banks and deposition on the opposite bank. As a result, low level channel has become narrower and more sinuous. Another reason for decreased capacity of the river is the encroaching the flood plains by the people living on the river banks. Decreased discharges and low water levels after the construction of Aswan High Dam made the people feel secure and encourage them to encroach the river banks by constructing houses and other permanent structures. In this paper, river morphological and hydrological data are presented to illustrate the Nile behavior as far as the capacity to covey discharges is concerned.
Year: 2004