Storm Wind Flow and Sediment Dynamics on Adjacent Coastal Dunes With Contrasting Morphologies During One Storm Event

Abstract

This study presents the first high-resolution spatial and temporal analysis of wind flow, sediment transport and topographic evolution under simultaneous storm conditions across two morphologically contrasting beach-dune systems, characterized by a gently sloping dune face (11°) and a steep, scarped dune face (36°). Results demonstrate that the dune slope strongly controls near-surface wind acceleration, the development of secondary airflow structures (amplitude, spatial positions), and the continuity of sediment transport pathways. Over the gentle slope, airflow accelerates progressively up the stoss face, promoting sustained, landward-directed sediment fluxes across the entire beach–dune system and enabling efficient sediment recycling. In this configuration, beach-derived contributions account for only 12%–15% of the total sediment flux. In contrast, the steep scarp induces flow deceleration and separation at the dune toe, limiting sediment transfer from the beach and favoring seaward-directed transport associated with secondary vortices at the crest. These contrasting airflow organizations result in fundamentally different storm responses. The gently sloping dune undergoes landward translation with minimal net volume change, whereas the scarped dune experiences dominant marine erosion, leading to a 4 m retreat of the dune front and a sediment loss of ∼30 m3 m−1. A new conceptual model of storm-driven airflow over contrasting dune morphologies is proposed, illustrating how inherited dune slope governs airflow structure and circulation patterns. Overall, these results identify inherited dune morphology as a primary control on airflow organization, sediment pathways, and dune resilience during extreme events.