HESS Hydrology and Earth System Sciences HESS Hydrol. Earth Syst. Sci. 1607-7938 Copernicus Publications Göttingen, Germany 10.5194/hess-17-1067-2013 Suspended sediment concentration–discharge relationships in the (sub-) humid Ethiopian highlands Guzman C. D. 1 Tilahun S. A. 2 Zegeye A. D. 1 3 Steenhuis T. S. https://orcid.org/0000-0003-0508-9350 1 2 Department of Biological and Environmental Engineering, Cornell University, Ithaca, NY, USA School of Civil and Water Resources Engineering, Bahir Dar University, Bahir Dar, Ethiopia Amhara Regional Agricultural Research Institute (ARARI), Bahir Dar, Ethiopia 11 03 2013 17 3 1067 1077 Copyright: © 2013 C. D. Guzman et al. 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://hess.copernicus.org/articles/17/1067/2013/hess-17-1067-2013.html The full text article is available as a PDF file from https://hess.copernicus.org/articles/17/1067/2013/hess-17-1067-2013.pdf

Loss of top soil and subsequent filling up of reservoirs in much of the lands with variable relief in developing countries degrades environmental resources necessary for subsistence. In the Ethiopia highlands, sediment mobilization from rain-fed agricultural fields is one of the leading factors causing land degradation. Sediment rating curves, produced from long-term sediment concentration and discharge data, attempt to predict suspended sediment concentration variations, which exhibit a distinct shift with the progression of the rainy season. In this paper, we calculate sediment rating curves and examine this shift in concentration for three watersheds in which rain-fed agriculture is practiced to differing extents. High sediment concentrations with low flows are found at the beginning of the rainy season of the semi-monsoonal climate, while high flows and low sediment concentrations occur at the end of the rainy season. Results show that a reasonably unique set of rating curves were obtained by separating biweekly data into early, mid, and late rainfall periods and by making adjustments for the ratio of plowed cropland. The shift from high to low concentrations suggests that diminishing sediment supply and dilution from greater base flow during the end of the rainfall period play important roles in characterizing changing sediment concentrations during the rainy season.

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