A method for developing a large-scale sediment yield index for European river basins
Résumé
Background, aim, and scope Sediment fluxes within continental areas play a major role in biogeochemical cycles and are often the cause of soil surface degradation as well as water and ecosystem pollution. In a situation where a high proportion of the land surface is experiencing significant global land use and climate changes, it appears important to establish sediment budgets considering the major processes forcing sediment redistribution within drainage areas. In this context, the aim of this study is to test a methodology to estimate a sediment yield index at a large spatial resolution for European river basins. Data and methods Four indicators representing processes respectively considered as sources (mass movement and hillslope erosion), sinks (deposits), and transfers of sediments (drainage density) are defined using distributed data. Using these indicators we propose a basic conceptual approach to test the possibility of explaining sediment yield observed at the outlet of 29 selected European river basins. We propose an index which adds the two sources and transfers, and subsequently subtracts the sink term. This index is then compared to observed sediment yield data. Results With this approach, variability between river basins is observed and the evolution of each indicator analyzed. A linear regression shows a correlation coefficient of 0.83 linking observed specific sediment yield (SSY) with the SSY index. Discussion To improve this approach at this large river basin scale, basin classification is further refined using the relation between the observed SSY and the index obtained from the four indicators. It allows a refinement of the results. Conclusions This study presents a conceptual approach offering the advantages of using spatially distributed data combined with major sediment redistribution processes to estimate the sediment yield observed at the outlet of river basins. Recommendations and perspectives Inclusion of better information on spatial variability should refine the approach. In this respect, basin classification and partition can be useful when applying the model to homogeneous areas. Moreover, to assess the relative effect of each sediment redistribution process, indicators could be weighted for each basin typology.