Erosive and accretive response of a natural beach to storm events

Abstract

Coastal zones are low-lying areas that support highly dynamic and productive ecosystems of great ecological and economic value. Anthropic and natural processes coexist and interact between them mediated by environmental fluctuations. The nature of coastal areas makes them susceptible to climate change effects. For instance, sea level rise and the increased frequency and intensity of storms and surges have a great impact on the morphodynamics of sandy beaches. Understanding how these environments behave under today's changing conditions is key to proposing efficient adaptation measures and management strategies.  However, the wide range of modulators involved in beach morphodynamics, and their high dynamism, make the integrated monitoring of these areas costly (time, human, and  economic resources) and challenging. Despite technological improvements and the increased availability of low-cost instrumentation and data (video monitoring systems, satellites’ observations, near-real-time oceanographic instruments/data), long-term and high-frequency data-sets, including morphological and wave data, remain scarce. Since 2011, the ICTS SOCIB (Balearic Islands Coastal Observing and forecasting System) has been monitoring three beaches of the Balearic Islands through the deployment of Modular Beach Integral Monitoring Systems (MOBIMS). MOBIMS aims to fill the gap of high-resolution and continuous beach monitoring by combining data from hybrid field surveys-remote sensing systems. MOBIMS is composed of low-cost open-source video monitoring imagery (SIRENA), Acoustic Wave and Current Profilers (AWAC), meteorological stations, and bi-annual high-resolution bathymetries and topographic surveys, as well as sediment granulometry. In this study, we present the analysis of the Son Bou Beach (Menorca, Spain) MOBIMS dataset generated over the last 12 years (2011-2022). The analysis focuses on characterizing the response of Son Bou beach to extreme events (i.e., storms), by means of shoreline position-change detection. Over 170 shorelines were derived from the SIRENA video-monitoring system, and meteorological and oceanographic data corresponding to 150 coastal storms were collected. The most energetic events eroded the beach, moving the shoreline landward significantly; but, accretive storms were also found, increasing the width of the beach. The presence of a coastal lagoon and the well-preserved dunes was crucial to understanding the beach response and its behaviour under different wave conditions.