  Bedload transport occurs when a bed composed of sedimentary grains becomes
mobile in response to the shearing by a flow of liquid. It shapes the
landscapes of Earth and other planetary bodies by promoting the formation and
growth of various multiscale geological features. Estimating the rate at which
such processes take place requires accurate bedload flux predictions. However,
even for highly idealized conditions in the laboratory, study-to-study
variability of reported bedload flux measurements borders an order of
magnitude. This uncertainty stems from physically poorly supported, typically
empirical methods of determining the transport-driving bed shear stress,
especially for very narrow or shallow channel flows, and from study-to-study
grain shape variations. Here, we derive a non-empirical method of bed shear
stress determination and apply it to a number of independent
grain-shape-controlled data sets, based on well-controlled experiments and
CFD-DEM simulations, for a very diverse range of transport conditions. An
existing physical bedload model, here generalized to account for grain shape
variability, predicts almost all these data within a factor of 1.3, whereas a
prominent alternative model (Deal et al., Nature 613, 298-302, 2023) seems
falsified.
