Spatial Trends and Drivers of Bedload and Suspended Sediment Fluxes in
Global Rivers
Abstract
Bedload flux is notoriously challenging to measure and model. The
dynamics of bedload therefore remains largely unknown in most fluvial
systems worldwide. We present a global scale bedload flux model as part
of the WBMsed modeling framework. Our results show that the model can
very well predict the distribution of water discharge and suspended
sediment and well predict bedload. We analyze the model’s bedload
predictions sensitivity to river slope, particle size, discharge, river
width and suspended sediment. We found that the model is most responsive
to spatial dynamics in river discharge and slope. We analyze the
relationship between bedload and total sediment flux globally and in
representative longitudinal river profiles (Amazon, Mississippi, and
Lena Rivers). We show that while, as expected, the proportion of bedload
is decreasing from headwater to the coasts, there is considerable
variability between basins and along river corridors. The latter is
largely responsive to changes in suspended sediment and river slope due
to dams and reservoirs. We provide a new estimate of water and sediment
fluxes to global oceans from 2,067 largest river outlets (draining 67%
of the global continental mass). Estimated water discharge (30,579
km3/y) corresponds well to past estimates however sediment flux is
considerably higher. Of the total 22 Gt/y estimated average sediment
flux to global oceans, 19 Gt/y is transported as washload, 1 Gt/y as
bedload, and 2 Gt/y as suspended bed material. The largest 25 rivers are
predicted to transport over 55% of total sediment flux to global
oceans.