Comparing turbulent flow and bank erosion with controlled experiments in a field-scale meandering channel

Bank erosion commonly occurs in alluvial rivers, shaping landscapes and riparian habitats and impacting water quality and infrastructure. Several models have been proposed that link shear stresses to bank erosion. However, data to test these hypotheses for characteristic geometries of meandering channels are sparse and technically challenging to acquire. Here we present results from a controlled experiment in a naturalistic channel to isolate the relationships between turbulent flow and nascent bank erosion. We ran the experiments at the Outdoor StreamLab (St Anthony Falls Laboratory, University of Minnesota) and gathered high-precision, contemporaneous measurements of the turbulent flow field and topography near a standardized, erodible bank at five locations along a single meander. The measurements show that the rate of bank erosion varied both along the channel and vertically and, local bank erosion was not correlated with any single hydrodynamic parameter. Upstream of the meander apex, erosion correlated with the near-bank time-averaged streamwise velocity magnitude while downstream of the apex, bank erosion correlated more strongly with near-bank turbulence parameters and depth. These results support field measurements that suggest that fluid shear contributions to outer bank erosion reflect multiple components of turbulent flow structure in river meanders.