The Role of Storm-Driven Seaward Sediment Flux in Coastal Barrier Dynamics Is an Enduring Puzzle

Coastal barrier systems are low-lying environments that bear the brunt of storm impacts, with cumulative and complex consequences for barrier evolution. Most studies of barrier responses to storms examine what happens when water and sediment get driven landward across a barrier from its ocean side. Sherwood et al. (2023, ) investigate the effects of overland flow and sediment transport forced across a barrier in the opposite direction-from its sheltered side, seaward. Using high-resolution imagery of a barrier island observed before and after a hurricane, Sherwood et al. (2023, ) show that outwash flow across the barrier shifted several times more sediment by volume than is typically reported for beach and dune erosion from onshore forcing. Their findings are remarkable because they are not exceptional: a related survey of barriers along the Atlantic and Gulf Coasts of the USA observed patterns of outwash morphology essentially everywhere. Insights into outwash morphology open exciting questions regarding the overlooked role of storm-driven seaward sediment transport in barrier dynamics, with important implications for post-storm barrier recovery and barrier evolution over decades to centuries. Plain Language Summary Coastal barrier systems-beaches backed by dunes, marshes, and often a lagoon or sound-offer natural protection to coastal floodplains by absorbing some of the physical impacts of storms, including hurricanes. Most studies of storm impacts on coastal barriers investigate changes that occur when a storm drives water and sediment landward, over a barrier from its ocean-facing side. But storms also drive sediment-laden flows in the opposite direction: over the back of a barrier from its more sheltered side, toward the ocean. Here, I highlight work by Sherwood et al. (2023, https://doi.org/10.1029/2022jf006934) that details extensive patterns of erosion and accretion from outwash flow seaward over a barrier during a hurricane. Added up over time, sediment shifting landward and seaward across a barrier shapes the barrier landscape and affects how the barrier may respond to future storm impacts. Sherwood et al. (2023, https://doi. org/10.1029/2022jf006934) offer findings with important implications for understanding how coastal barriers evolve in space and time, and address a question that is fundamental to many geomorphic systems: when a large volume of sediment moves during an extreme weather event, where does it all go?

Automated summary

This study investigates the effects of overland flow and sediment transport forced across a barrier in the opposite direction during hurricanes. The findings show that sediment shifting seaward across the barrier is significant and has important implications for post-storm barrier recovery and evolution.