A Numerical Investigation of Sediment Dynamics over the Cape Fear River basin during Hurricane Florence

In 2018, Hurricane Florence swamped the Cape Fear River basin as the ninth-most-destructive hurricane ever hit the United States. While Florence has attracted lots of attention as an optimal case to study extreme floods, its influence on local sediment dynamics has not been investigated yet. In this study, we adapted a physics based, fully distributed soil erosion and sediment transport model, WRF-Hydro-Sed, to investigate the source, conveyance, and fate of sediments over the Cape Fear River basin during Hurricane Florence. To assure its robustness, the model was calibrated and evaluated against streamflow and suspended sediment observations at selected USGS gages. Our results suggest that the spatial-temporal distribution of soil erosion was largely controlled by the rainband structure evolution, slow movement, and L-shaped track of the storm. The first pulse of sediment during the hurricane was sourced from the coastal area, which contributes most to the total sediment delivered to the Cape Fear River Estuary. The headwater area of the river basin served as the second most important source of the sediment due to its steep topography. Our study is important as one of very few studies trying to examine the important but long-neglected role of catastrophic hurricanes in moving and delivering sediments from land to the ocean along the US east coast.