Washover fan deposits resulting from perigean spring tides: An example from Cape Cod, Massachusetts, USA

Abstract

In early 2021, the dune at Duck Harbor Beach (Wellfleet, MA, USA) was overtopped by high water levels, forming a washover fan that continues to grow through persistent overwash events. Overwash events occur near-monthly on most spring tides, regardless of weather, and have occurred for nearly four years. This is unique because the vast majority of washover fans occur because of storms and generally build in elevation requiring increasing water levels for overwash to occur. The overwash has salt-killed ~48.5 ha of trees and shrubs, and the system has begun to transition from freshwater to saltwater. We document the development of this tidal washover fan, including a detailed examination of changes in elevation and grain size during the early January 2022 events. Understanding how this system has developed will inform our understanding of the fate of other low-lying coastal areas, which are growing increasingly vulnerable to the effects of sea-level rise and ecosystem change.