River sediment discharge to the oceans: present-day controls and global budgets

Empirical relationships between river sediment yields and a large number of hydroclimatic, biological, and geomorphological parameters are investigated at the global scale. For a set of 60 major world river basins, the environmental characteristics were extracted from various global computer data sets, and natural river sediment fluxes were taken from the literature. It is found that sediment yields can be best correlated by forming the products of hydroclimatic and geomorphological factors, that is, runoff intensity, basin slope, an index characterizing rock hardness, and an index characterizing rainfall variability over the year. The best parameter combination varies to some extent when the rivers are grouped according to their average climatic situation, but it is always a combination of the above mentioned parameters that yields the most significant models. In arid climates, however, regression coefficients are greater than in humid climates, indicating that erodibility is much greater than in arid climates. When extrapolated to the total continental area on the basis of the corresponding data sets, the empirical models result in a total sediment flux of about 16 Gigatons discharged to the oceans every year, which is in good agreement with previous estimates derived from compilations of world-wide river data. Consequently, two global maps are proposed showing the spatial distributions of river sediment yields on the continents as well as the inputs of these sediments to the oceans in a grid point scale. By far most of the sediments originate from the young orogenic belts of the continents, mainly due to a combination of steep morphologies and high runoff intensities