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Vigiak, Olga; Malago, Anna; Bouraoui, Faycal; Vanmaercke, Matthias; Obreja, Florin; Poesen, Jean; Habersack, Helmut; Feher, Janos; Grogelj, Samo (2017): Modelling sediment fluxes in the Danube River Basin with SWAT. In: Science of the Total Environment, Vol. 599: pp. 992-1012
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Abstract

Sediment management is of prior concern in the Danube Basin for provision of economic and environmental services. This study aimed at assessing current (1995-2009) sediment fluxes of the Danube Basin with SWAT model and identifying sediment budget knowledge gaps. After hydrologic calibration, hillslope gross erosion and sediment yields were broadly calibrated using ancillary data (measurements in plots and small catchments, and national and European erosion maps). Mean annual sediment concentrations (SSC) from 269 gauging stations (2968 station-year entries;median 19 mg/L, interquartile range IQR 10-36 mg/L) were used for calibrating in stream sediments. SSC residuals (simulations-observations) median was 2 mg/L (IQR 14;+22 mg/L). In the validation dataset (172 gauging stations;1457 data-entries, median 17 mg/L, IQR 10-28), median residual was 9 mg/L (IQR 9;+39 mg/L). Percent bias in an independent dataset of annual sediment yields (SSY;689 data-entries in 95 stations;median 52 t/km(2)/y, IQR 20-151 t/km(2)/y) was 21.5%. Overall, basin-wide model performance was considered satisfactory. Sediment fluxes appeared overestimated in some regions (Sava and Velika Morava), and underestimated in others (Siret-Prut and Romanian Danube), but unbiased elsewhere. According to the model, most sediments were generated by hillslope erosion. Streambank degradation contributed about 5% of sediments, and appeared important in high stream power Alpine reaches. Sediment trapping in reservoirs and floodplain deposition was probably underestimated and counterbalanced by high stream deposition. Factor analysis showed that model underestimations were correlated to Alpine and karst areas, whereas underestimations occurred in high seismicity areas of the Lower Danube. Contemporary sediment fluxes were about one third of values reported for the 1980s for several tributaries of the Middle and Lower Danube. Knowledge gaps affecting the sediment budget were identified in the contributions of some erosion processes (glacier erosion, gully erosion and mass movements), and in-stream sediment dynamics. (C) 2017 The Authors. Published by Elsevier B.V.