Effects of natural and human forcing on mesoscale shoreline dynamics of Saint-Michel-en-Grève bay (Brittany, France)

• Main Authors: Suanez, Serge, S., Stéphan, Pierre
• Other Authors: Littoral, Environnement, Télédétection, Géomatique (LETG - Brest), Littoral, Environnement, Télédétection, Géomatique UMR 6554 (LETG), Université de Caen Normandie (UNICAEN), Normandie Université (NU)-Normandie Université (NU)-Université d'Angers (UA)-École Pratique des Hautes Études (EPHE), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université de Brest (UBO)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut de Géographie et d'Aménagement Régional de l'Université de Nantes (IGARUN), Université de Nantes (UN)-Université de Nantes (UN)-Université de Caen Normandie (UNICAEN), Université de Nantes (UN)-Université de Nantes (UN), Programme PROLITTORAL (2002-2006) correspondant à une action concertée entre la Région Bretagne, les 4 départements bretons (22, 29, 56 et 35) et l'Agence de l'Eau, soutenue par des fonds européens (FEDER)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2011
• Subjects: Sediment budget; monitoring; shoreline changes; dune erosion; storm; human forcing; [SDU.STU.GM]Sciences of the Universe [physics]/Earth Sciences/Geomorphology; [SDE.ES]Environmental Sciences/Environment and Society; North Atlantic; North Atlantic oscillation
• Online Access: https://hal.science/hal-00556014; https://hal.science/hal-00556014/document; https://hal.science/hal-00556014/file/Suanez_Stephan_2011.pdf

International audience By monitoring shoreline changes and subaerial beach volume in Saint-Michel-en-Grève bay in northern Brittany over the past 20 years, the mesoscale sediment budget was assessed. Previous work has shown that both natural and human forcing have played an important role in the long-term changes of the bay, but the respective causes of each type of forcing have not previously been studied in detail. This study shows that between 1990 and 2009, a large volume of sediment input resulted in rapid accretion of dunes in the bay head. Sedimentation rates reached an average of 0.1m3/m2/yr over the whole study period. This positive sediment budget confirms the trend of sediment accumulation noted since the end of the 19th century. Nevertheless, temporal variation in the sediment budget can be related to changes in the frequency and magnitude of storms surges and resulting high tides. Shoreline erosion/accretion records dating from 1990 were compared with extreme water levels. Relatively high shoreline retreat rates during periods of 1999-2002 and 2006-2008 were associated with a relatively large number of storm surges. Slower erosion and relatively rapid accretion occurred between 1990 and 1999 and during a more recent period, when there have been relatively few major storm surges. Erosion phases were related to the occurrence of extreme spring high tides and wave action associated with storms. Storms and surges in the northern Brittany Channel are associated with Atlantic depressions whose direction and rate of movement have a strong influence on wind speeds, wave energy and the height of tides. However, sediment budget of Saint-Michel-en-Grève bay head beach, in terms of shoreline erosion/accretion changes, is not directly related to the North Atlantic Oscillation index. Tide condition leading to high or low water level plays a major role by controlling erosion or accretion processes. Human forcing was identified as feedback processes due to the modification of morphological and hydrodynamic ...