Quantifying Bank Erosion and Floodplain Storage in Mid-Atlantic River Corridors: Accuracy, Timescales, and Applications to Watershed Management

The contemporary balance between bank erosion and floodplain storage has important implications for sediment budgets and watershed management of particulates transported by rivers, but quantifying these processes is challenging and the results are rarely considered in watershed models and management plans. Here we obtain localized estimates of decadal average bank erosion rates from aerial imagery and dendrochronology. To extrapolate these results throughout our study watershed, empirical correlations are used in a GIS framework that relates observed erosion rates to local channel curvature, tree canopy density, and inferred locations of exposed bedrock. Floodplain deposition rates are obtained from radionuclide analyses and extrapolated to unmeasured areas based on analyses of topography and frequency of floodplain inundation. Error analyses indicate, however, that the resulting watershed scale estimates are of such low precision that they may not be useful for guiding management decisions. Furthermore, these estimates are only useful for current conditions. Implementing watershed best management practices will induce changes in rates of erosion and deposition, and these changes will cascade downstream over timescales that are controlled by floodplain residence times, which in the mid-Atlantic region span decades to millennia. Useful management predictions will necessarily not only include assessment of current conditions, but must also incorporate methods for predicting the location and timing of benefits imposed by watershed restoration as they slowly progress downstream towards a watersheds outlet.