A comprehensive hydro-geomorphic study of cliff-top storm deposits on Banneg Island during winter 2013–2014
|Author(s)||Autret Ronan1, Dodet Guillaume1, Fichaut Bernard1, Suanez Serge1, David Laurence1, Leckler Fabien2, Ardhuin Fabrice3, Ammann Jerome4, Grandjean Philippe5, 6, Allemand Pascal5, 6, Filipot Jean-Francois7|
|Affiliation(s)||1 : Univ Bretagne Occidentale, IUEM, LETG Brest Geomer, UMR CNRS 6554, F-29280 Plouzane, France.
2 : Serv Hydrog & Oceanog Marine, F-29200 Brest, France.
3 : UBO, IRD, IFREMER, CNRS,Lab Oceanog Phys & Spatiale,UMR 6523, F-29200 Brest, France.
4 : Univ Bretagne Occidentale, IUEM, Lab Domaines Ocean, UMR CNRS 6538, F-29280 Plouzane, France.
5 : Univ Lyon 1, F-69662 Villeurbanne, France.
6 : ENS Lyon, CNRS UMR5570, F-69662 Villeurbanne, France.
7 : France Energies Marines, 15 Rue Johannes Kepler,Site Vernis, F-29200 Brest, France.
|Source||Marine Geology (0025-3227) (Elsevier Science Bv), 2016-12 , Vol. 382 , P. 37-55|
|WOS© Times Cited||25|
|Keyword(s)||Cliff-top storm deposit, Block transport, Extra-tropical cyclone, Run-up, Coastal erosion, Brittany|
|Abstract||Large clastic cliff-top storm deposits (called CTSDs) are one of the most remarkable signatures that characterizes extreme storm wave events on coastal cliffs. Hence, the study of CTSDs is of key importance for understanding and predicting the impacts of extreme storm wave events on rocky coasts or establishing proxies for storm intensity. The present study uses new data including hydrodynamic measurements in both deep and intertidal waters, and records of CTSDs displacement and deposition across Banneg Island during the stormy winter 2013–2014. Two drone-based surveys were carried out in January 2013 (pre-storms) and in April 2014 (post-storms). In addition, complementary field observations were carried out during the winter, providing a comprehensive and detailed dataset. Concerning the hydrodynamic measurements, nine pressure sensors deployed along four cross-shore profiles on the western coast of the island, recorded wave and water level conditions between December 2013 and April 2014. Aerial orthorectified photographs and digital elevation model of differences provide a detailed spatial description of cliff erosion and the reworking of cliff-top storm deposits. After the storms, 172 fresh scars corresponding to quarrying in the bed rock were localized above high spring tide water level, 507 blocks were transported up to 40 m inland, at altitudes of 8 to 14 m above mean sea level, and the tracks of 170 of them were identified. The water levels and wave parameters estimated from the pressure sensor measurements provided accurate information on the maximum water elevation reached during the largest storms at the sensor locations and were extrapolated to provide run-up elevation along the four survey profiles for the whole winter 2013–2014. The results demonstrate that a large number of overwash episodes occurred, at times of high tides and energetic waves. These episodes generally correspond to morphological changes. This study confirms the major role played by extreme storm wave events on CTSDs quarrying, transport, and deposition on Banneg Island, and clearly identify the events of major evolutions.|