Soil erosion and discharge in the Blue Nile Basin: Trends and challenges

Abstract

Future river discharge predictions seldom take into account the degrading landscape. The objective of this study was to investigate the relationship of river discharge and sediment concentrations, and the effect of changing landscape and climate on discharge and sediment transport in the Ethiopian Blue Nile basin. This study used past precipitation records and the Parameter Efficient Distributed (PED) model to examine how the relationship between precipitation, discharge, and sediment concentration changed with time. All input data to the PED model were kept constant except for a conversion of permeable hillside to degraded soil in time. The results of this study show that with a gradual increase of the degraded areas from 10∈% in the 1960s to 22∈% in 2000s, the observed discharge pattern and sediment concentration can be simulated well. Simulated annual runoff increased by 10∈% over the 40-year periods as a result of the increase in degraded soils. Sediment loads appeared to have increased many times more, but this needs to be further validated as data availability is limited. In general, the results indicate that rehabilitating the degraded and bare areas by planting permanent vegetation can be effective in decreasing the sediment concentration in the rivers. Research should be undertaken to evaluate the effectiveness of vegetation planting.