Increasing Frequency of Coastal Erosion Indicated by a Hindcast Model of Storm‐Driven Forcing Calibrated With Beach Stratigraphy

Abstract

Beach stratigraphy at North Beach, Sandy Hook, New Jersey is used to calibrate a model of coastal erosion, establish a model‐based erosion threshold, and evaluate how often threshold conditions have been exceeded since 1979 through hindcast analysis. Ground penetrating radar (GPR) was used to identify 20 stratigraphic surfaces generated in response to storm‐driven erosion, and centimeter‐accurate GNSS data were used to constrain their formation between 2009 and 2019 CE. To quantify the forcing conditions generating the preserved erosion surfaces, we ran more than 1000 48‐hr XBeach simulations using tide‐gauge and offshore wave buoy data. We then statistically emulated the XBeach output and calibrated it with observed beach‐profile change using a semi‐empirical model that we used to identify the storms most likely to have produced the preserved erosion surfaces. The modeling results suggest storms exceeding a water‐level threshold of 1.3 m above MSL and significant wave heights of 3.8 m resulted in significant coastal erosion. Analysis of hindcast wave conditions and water‐level data suggests an approximately two‐fold increase in the exceedance frequency of this storm threshold between 1979 and 2023 CE. The inferred erosion threshold is tested using pre‐, during‐, and post‐event observations from a recent 10 January 2024 storm that exceeded threshold conditions. We assess that beach stratigraphy is underutilized for the study of impacts and frequency of coastal storms that cause significant erosion, and our results demonstrate how model‐data integration can be used to broaden inferences made from stratigraphic data.