Ethiopian Rivers

Abstract

The scientific literature about the geomorphology and hydrology of Ethiopian rivers is very poor, though large and socially important rivers have their source in this country. The largest rivers deliver their waters into the Mediterranean Sea or the Indian Ocean, whereas the most of the smaller ones have an endorheic drainage. Flow data were collected from different sources, and the longest as possible time series were considered. A new index, the runoff concentration index is used by analogy with the precipitation concentration index to analyze the monthly variation of runoff. Characteristic discharges such as bankfull discharge or longer return time discharges are calculated as well. Due to the remarkable variety of physiography of Ethiopia landscapes and recent tectonics, rivers show different drainage network and channel morphology. Their main features are described, and recent geomorphological changes are analyzed. Flow data are investigated and a number of correlations with catchment parameters, capable also to predict discharge in ungauged rivers, are reported. Runoff changes through time do not show any significant trend, whereas the sediment yield of Ethiopian river is of the same order of magnitude of much larger African rivers indicating a high soil erosion rate of Ethiopian highlands.