The slope gradient is one of the most important factors affecting soil erosion by the surface runoff. Under the same rainfall condition, the surface runoff velocity could be drastically different on different slopes, and thus the amount of eroded soil could also be very different. The slope in the basin varies between 0 and 33 degrees.
The longitudinal bed profiles of main rivers are shown in the adjacent figure. The graph shows elevation (metres above sea level, masl) of river bed as a function of distance from a selected common downstream point, in this case, the High Aswan Dam. Most rivers in the Eastern Nile exhibit much steeper slope in their upper reaches compared to the rivers that originate in the Equatorial Lakes region. The rivers in their steep slope reaches have high energy gradients and are capable of transporting high sediment loads, as observed in the rivers originating in the Ethiopian highlands. In contrast, the rivers originating from the Equatorial Lakes region (Victoria Nile, Albert Nile and Bahr El-Jebel) show breaks in the slopes of the river bed, which are points where the river passes through lakes and swamp areas.
