Abstract
Abstract. Sustainable management of the coastal resources requires a better understanding of the processes that drive coastline change. The coastline is a highly dynamic sea-terrestrial interface. It is affected by forcing factors such as water levels, waves, winds, and the highest and most severe changes occur during storm surges. Extreme storms are drivers responsible for rapid and sometimes dramatic changes of the coastline. The consequences of the impacts from these events entail a broad range of social, economic and natural resource considerations from threats to humans, infrastructure and habitats. This study investigates the impact of a severe storm on coastline response on a sandy multi-barred beach at the Belgian coast. Airborne LiDAR surveys acquired pre- and post-storm covering an area larger than 1 km2 were analyzed and reproducible monitoring solutions adapted to assess beach morphological changes were applied. Results indicated that the coast retreated by a maximum of 14.7 m where the embryo dunes in front of the fixed dunes were vanished and the foredune undercut. Storm surge and wave attacks were probably the most energetic there. However, the response of the coastline proxies associated with the mean high water line (MHW) and dunetoe (DuneT) was spatially variable. Based on the extracted beach features, good correlations (r>0.73) were found between coastline, berm and inner intertidal bar morphology, while it was weak with the most seaward bars covered in the surveys. This highlights the role of the upper features on the beach to protect the coastline from storm erosion by reducing wave energy. The findings are of critical importance in improving our knowledge and forecasting of coastline response to storms, and also in its translation into management practices.
Highlights
The coastline is a highly dynamic sea-terrestrial interface
The mean high water line (MHW) isocontour was extracted from the digital elevation model (DEM) corresponding to the elevation of 4.39 m TAW, a value used since several decades as a proxy, while the DuneT was detected as a sudden increase of roughness across the beach
Results indicated that the coast retreated up to 14.7 m where the embryo dunes in front of the fixed dunes were vanished and the foredune undercut
Summary
The coastline is a highly dynamic sea-terrestrial interface. Approximately 31% of the world’s coastline is sandy of which 24% is subject to erosion (Luijendijk et al, 2018). Sandy beaches are important for the economic and recreational activity as well as for coastal protection because they form a natural buffer against erosion and flooding for lowlands. In the context of climate change, the elevation of water levels combined with changing of wave conditions through sea-level rise and storminess, dramatically menace sandy coasts and inland infrastructure (Feagin et al, 2005). Beach response to storms is highly variable due to the nature of the storm forcing factors (water levels, waves, winds), the characteristics of the coast such as the presence of morphological features (e.g. berm, bar bedforms) and geologic setting (Cooper et al, 2004). Understanding coastline impact requires collecting datasets for monitoring its natural change in suitable temporal and spatial resolution which is challenging, especially in relation to a storm occurrence. The acquisition of consecutive LiDAR surveys allows to monitor successfully the changes of the coastline as well as the 3D morphological variation of the beach system (Saye et al, 2005, Pye and Blott, 2016)
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