Reconstructing Sediment Transport by Migrating Bedforms in the Physical and Spectral Domains

Characteristics of migrating bedforms are often used to indirectly quantify the volumetric sediment flux in fluvial environments. Yet, the range of bedform scales that actually contribute to the sediment transport remains elusive. We performed a series of experiments under four different transport stages in a large-scale sediment recirculating flume. Three independent variables were simultaneously measured: 2D spatio-temporal bathymetry z(x, y, t), high frequency temporal bed elevations at fixed locations z(t), and temporal change of the sediment weight carried by migrating bedforms near the channel outlet q_m(t). Both the measured spatio-temporal bed evolution and the sediment discharge were analyzed using bedform tracking and Fourier decomposition. We found that small, rapidly migrating secondary bedforms emerge as a main contributor to the sediment transport and to the propagation of larger primary bedforms that slowly migrate underneath. This critical information allows us to define the range of transport-contributing scales that must be accounted for in a scale-dependent sediment mass flux model to enable the estimation of the total bedform transport from bed elevation time series.