Abstract. Channel processes under high magnitude flow events are of central interest to river science and management as they may produce large volumes of sediment transport and geomorphic work. However, bedload transport processes under these conditions remain poorly understood due to data collection limitations and the prevalence of physical models that restrict feedbacks surrounding morphologic adjustment. The extension of mechanistic bedload transport equations to gravel-bed rivers has emphasised the importance of variance in both entraining (shear stress) and resisting (grain size) forces, especially at low excess shear stresses. Using a fixed-bank laboratory model, we tested the hypothesis that bedload transport in gravel-bed rivers collapses to a more simple 1D function (i.e., with mean shear stress and median grain size) under high excess shear stress conditions. Bedload transport was well predicted by the 1D equation based on the depth-slope product, whereas a 2D equation accounting for the variance in shear stresses did not substantially improve the correlation. Back-calculated critical dimensionless shear stress values were higher for the 2D approach, suggesting that it accounts for the relatively greater influence of high shear stresses, whereas the 1D approach assumes that the mean shear stress is sufficient to mobilise the median grain size. While the 2D approach may have a stronger conceptual basis, the 1D depth-slope product approach performs unreasonably well under high excess shear stress conditions. Further work is required to substantiate these findings in laterally adjustable channels.