Modeling the Influence of Upper and Lower Shoreface Dynamics on Barrier Island Evolution

Abstract Barrier island resilience to climate impacts depends on sediment redistribution between the subaqueous shoreface and subaerial barrier during sea‐level rise and storms. However, autogenic interactions between the upper and lower shoreface and their influence on the subaerial barrier are poorly characterized. Here, we explore the influences of various shoreface components on barrier morphology using a model of barrier and shoreface evolution under sea‐level rise, the Articulated Barrier Shoreface (ABSF) Model. This reduced‐complexity model divides the shoreface into upper and lower shoreface panels that respond independently to sea‐level rise and deviations from the equilibrium slope. We couple the ABSF with the Lorenzo‐Trueba & Ashton, 2014, https://doi.org/10.1002/2013jf002941 model (LTA), a barrier island evolution model driven by overwash and sea‐level rise. Through this coupled framework, we examine the influences of upper and lower shoreface slopes, their respective depths, and sensitivity to wave climate on long‐term barrier evolution. Results show that the relative depths of the upper and lower shoreface toes influence barrier response to rising seas, alongside overwash flux and closure depth. Notably, the lower shoreface response to sea‐level change lags that of the upper shoreface over decades, diminishing the resilience of the barrier over centennial timescales by slowing the overall barrier response. In fact, the ABSF model predicts barriers will drown faster and more than predicted with a linear shoreface. Results highlight the shoreface as an important sediment reservoir for barrier islands and that differences in upper and lower shoreface responses can reduce barrier resilience to sea‐level rise due to limited lower shoreface sediment accessibility.