TY - JOUR
T1 - Impact of temporal beach grain size variability on aeolian sediment transport and topographic evolution in a microtidal environment
AU - Lamy, Antoine
AU - Robin, Nicholas
AU - Smyth, Thomas
AU - Hesp, Patrick
AU - Rene, Camille
AU - Feyssat, Pierre
AU - Raynal, Olivier
AU - Hebert, Bertil
N1 - Funding Information:
The authors thank Obscat and the Parc Naturel Marin du Golfe du Lion for their financial support. The corresponding author is funded through a ministerial PhD grant from the French government . The authors thank Météo-France for supplying meteorological data, CANDHIS/CEREMA for wave data and all the contributors to the fieldwork. The authors would like to thank the editor-in-chief, C. Van Ijzendoorn and anonymous reviewers who helped to improve this article.
Publisher Copyright:
© 2024 The Authors
PY - 2024/5/15
Y1 - 2024/5/15
N2 - While the impact of the spatio/temporal variability of grain size on morphological beach state is reasonably well understood, relatively little is known on its impact at a scale of days/months on aeolian sediment transport. This study focuses on five short intensive wind events during which aeolian sediment transport measurements, beach surface sampling and elevation change surveys were carried out for 1 to 3 days, over a 16-month period on a microtidal beach dominated by offshore winds. Monthly observations show a high temporal variability in beach grain size in relation to the decoupling between hydrodynamic and aeolian processes, from medium sand after a marine storm and inundation of the beach, to very coarse sand after several weeks of storm-force winds. During each wind event, topographic change on the beach ranged from zero, to 0.55 m. The time scale of coarsening depended on the initial beach grain size and could be very fast when the beach was composed of medium sand (e.g. 388 μm sand changed to coarse sand of 547 μm in 40 h). In contrast, it took one month to transition from a coarse median beach grain size of 883 μm to a very coarse one of 1323 μm. This variability in grain size results in dramatically different rates of sediment flux. For example, during average wind speeds of 10 to 14 m/s the sediment flux when the beach was composed of medium sized sand ranged between 21 and 154 kg/m/h compared to 0.4 to 50 kg/m/h when the beach was composed of coarse and very coarse sized grains. Overall, this study highlights the importance of beach grain size variability on aeolian sediment transport and shows that for similar incident wind and climatic conditions aeolian sediment transport rates vary dramatically. The study demonstrates the importance of taking care when using a constant median grain size in the calculation of long-term aeolian sand transport on beaches with heterogeneous spatial and temporal beach grain size variability.
AB - While the impact of the spatio/temporal variability of grain size on morphological beach state is reasonably well understood, relatively little is known on its impact at a scale of days/months on aeolian sediment transport. This study focuses on five short intensive wind events during which aeolian sediment transport measurements, beach surface sampling and elevation change surveys were carried out for 1 to 3 days, over a 16-month period on a microtidal beach dominated by offshore winds. Monthly observations show a high temporal variability in beach grain size in relation to the decoupling between hydrodynamic and aeolian processes, from medium sand after a marine storm and inundation of the beach, to very coarse sand after several weeks of storm-force winds. During each wind event, topographic change on the beach ranged from zero, to 0.55 m. The time scale of coarsening depended on the initial beach grain size and could be very fast when the beach was composed of medium sand (e.g. 388 μm sand changed to coarse sand of 547 μm in 40 h). In contrast, it took one month to transition from a coarse median beach grain size of 883 μm to a very coarse one of 1323 μm. This variability in grain size results in dramatically different rates of sediment flux. For example, during average wind speeds of 10 to 14 m/s the sediment flux when the beach was composed of medium sized sand ranged between 21 and 154 kg/m/h compared to 0.4 to 50 kg/m/h when the beach was composed of coarse and very coarse sized grains. Overall, this study highlights the importance of beach grain size variability on aeolian sediment transport and shows that for similar incident wind and climatic conditions aeolian sediment transport rates vary dramatically. The study demonstrates the importance of taking care when using a constant median grain size in the calculation of long-term aeolian sand transport on beaches with heterogeneous spatial and temporal beach grain size variability.
KW - Aeolian sand transport
KW - Offshore wind
KW - Beach grain size
KW - Gulf of Lions
UR - http://www.scopus.com/inward/record.url?scp=85187001079&partnerID=8YFLogxK
U2 - 10.1016/j.geomorph.2024.109126
DO - 10.1016/j.geomorph.2024.109126
M3 - Article
VL - 453
JO - Geomorphology
JF - Geomorphology
SN - 0169-555X
M1 - 109126
ER -