Un suivi morphosédimentaire a été réalisé sur deux sites finistériens afin d'évaluer la fonctionn... more Un suivi morphosédimentaire a été réalisé sur deux sites finistériens afin d'évaluer la fonctionnalité du procédé STABIPLAGE ® : la plage des Sables Blancs sur laquelle 5 structures en épi ont été mises en place afin de bloquer une partie du transit longitudinal ; la plage de Boutrouilles équipée d'une structure longitudinale en pied de dune afin de fixer le trait de côte. Dans les deux cas, les STABIPLAGE ® remplissent leur rôle de défense côtière tant que les conditions hydrodynamiques sont peu énergétiques. En période de fortes tempêtes, l'action des courants de retour et/ou de la submersion marine exacerbée, induit des phénomènes d'érosion que les STABIPLAGE ® ne peuvent enrayer.
Page 1. Dynamique morphosédimentaire des cordons dunaires de Tréduder et de Saint-Michel-en-Grève... more Page 1. Dynamique morphosédimentaire des cordons dunaires de Tréduder et de Saint-Michel-en-Grève (baie de Saint-Michel-en-Grève - Côtes d>Armor) entre 1990 et 2003 (MORPHOSEDIMENTARY DYNAMICS OF TREDUDER ...
La connaissance du littoral, sa protection, son aménagement nécessitent un suivi des changements ... more La connaissance du littoral, sa protection, son aménagement nécessitent un suivi des changements qui s'y produisent. Toutefois, en France, devant l'étendue des façades maritimes à couvrir, les techniques de mesures in situ ne peuvent être appliquées de façon systématique. Dans ce cas, les techniques de télédétection spatiale ou aérienne sont des approches complémentaires. A partir de ces plates-formes, des images stéréoscopiques multi-temporelles sont, après une série de traitements photogrammétriques appropriés, directement exploitables sous formes d'orthophotographies et de Modèles Numériques de Terrain (MNT). Ce type de produits permet notamment la quantification des changements morphosédimentaires à l'interface Terre-Mer (transport transversal et longitudinal de sédiments, érosion,...). Actuellement, la résolution spatiale des MNT générés à partir d'images aériennes ou satellitaires (<50 cm) est insuffisante pour la plupart des applications sur la frange littorale. En outre, dans le cas d'interventions consécutives à un événement extrême (tempête, raz de marée, pollution…), ces systèmes manquent de souplesse (trajectoires prédéfinies, contraintes d'altitude, de vitesse, coût de mise en oeuvre...) L'utilisation de drones constitue donc une alternative intéressante pour des suivis de précision ou des interventions rapides.
This study analyses long-term (1841-1872-1895-1974) changes in the Grand Rhône prodeltaic lobe to... more This study analyses long-term (1841-1872-1895-1974) changes in the Grand Rhône prodeltaic lobe to (1) quantify the accumulation, (2) determine the evolution of relict prodeltaic lobes and (3) establish long-term relationships between river sediment discharge, the shoreface and the continental shelf. Our results show a reduction of the sedimentation of the prodeltaic lobe at the main river mouth, since 150 yr by a factor of 3.7 (12.63 to 3.41 × 10 6 m 3 yr − 1 ). At the minor mouth of the river, erosion dominates and speeds up during the same period (−0.53 to −1.34 × 10 6 m 3 yr − 1 ). These changes are found to directly result from the river sediment input decrease related to the natural decreasing of the frequency of major floods (end of the Little Ice Age), the reforestation in the catchment area, the dam construction and the dredging activities (since the 1950s). Our results indicate that while there is large sediment accumulation in the area around a growing prodeltaic lobe, there is also a reduced contribution of the river sediments to the non-adjacent beaches of the mouth. Following a shift in the river channel and mouth, the relict prodeltaic lobes (Petit Rhône-St Férreol, Bras de Fer and Pégoulier) are reworked by waves and their sediments contribute partially to the growth of the spits (Espiguette, Beauduc and Gracieuse). This suggests that there is a "time-shift" between the input of river sediment to the sea and the build up of a beach. The chronic erosion of the coastline is likely to continue in the future since (1) a river shift is not possible, because the river channels are controlled by dykes and human intervention, (2) the decrease of river sediment input and (3) the relict prodeltaic lobes constitute sedimentary reservoirs that are gradually being used up.
... The only wave measurements available for Brittany coasts for this storm event are those that ... more ... The only wave measurements available for Brittany coasts for this storm event are those that were recorded by the directional waverider located near Les Pierres ... is used in case of irregular waves (wave steepness, Ho/Lo of 0.007 Ho/Lo 0.07) breaking on slopes of 0.03 tan 0.2. ...
On 10th March 2008, the high energy storm Johanna hit the French Atlantic coast, generating sever... more On 10th March 2008, the high energy storm Johanna hit the French Atlantic coast, generating severe dune erosion on Vougot Beach (Brittany, France). In this paper, the recovery of the dune of Vougot Beach is analysed through a survey of morphological changes and hydrodynamic conditions. Data collection focused on the period immediately following storm Johanna until July 2010, i.e. over two and a half years. Results showed that the dune retreated by a maximum of almost 6 m where storm surge and wave attack were the most energetic. Dune retreat led to the creation of accommodation space for the storage of sediment by widening and elevating space between the pre-and post-storm dune toe, and reducing impacts of the storm surge. Dune recovery started in the month following the storm event and is still ongoing. It is characterised by the construction of "secondary" embryo dunes, which recovered at an average rate of 4-4.5 cm per month, although average monthly volume changes varied from − 1 to 2 m 3 .m − 1 . These embryo dunes accreted due to a large aeolian sand supply from the upper tidal beach to the existing foredune. These dune-construction processes were facilitated by growth of vegetation on low-profile embryo dunes promoting backshore accretion. After more than two years of survey, the sediment budget of the beach/dune system showed that more than 10,000 m 3 has been lost by the upper tidal beach. We suggest that seaward return currents generated during the storm of 10th March 2008 are responsible for offshore sediment transport. Reconstitution of the equilibrium beach profile following the storm event may therefore have generated cross-shore sediment redistribution inducing net erosion in the tidal zone.
Gravel spits of Brittany have experimented a long morphosedimentary evolution over the last mille... more Gravel spits of Brittany have experimented a long morphosedimentary evolution over the last millenia. Based on analysis of several back-barrier holocene sediment stratigraphies, distinct phases of construction and barrier breakdown were recognized, indicating the role played by storminess and sediment supply during the late-holocene period. Over the last centuries and decades, a deficit of sediment bubget affecting several gravel spits is highlighted. Therefore, actual coastal evolution of most of them is mainly dominated by cannibalization, landward retreat by rollover and complete destruction of the spits in some places. This coastal erosion is related to the lack of significant offshore sediment input or from the erosion of unconsolided cliffs. Locally, anthropogenic forcing have axacerbated the erosion processes by sediment minings and/or the construction of hard defense structures. For the swash-aligned gravel spits, frequency and magnitude of overwash processes is controlling the rate of landward retreat by rollover. This morphodynamic behaviour is illustrated by topo-morphological surveys realised between 2002 and 2012 on Sillon de Talbert spit which has experienced a complete crestal removal during the 10 March 2008 Johanna storm. Although this event have a 50-100yrs occurence, the barrier has exhibited a rapid crestal rebuilding by overtopping processes, illustrating the great resilience of the spit. Thus, coastal erosion management strategies mainly based on hard defense structures are gradually abandoned for new management policies based on soft operations. Nowadays, gravel spits of Brittany are also considered as a geological heritage and management plans are establishing by local authorities.
Un suivi morphosédimentaire a été réalisé sur deux sites finistériens afin d'évaluer la fonctionn... more Un suivi morphosédimentaire a été réalisé sur deux sites finistériens afin d'évaluer la fonctionnalité du procédé STABIPLAGE ® : la plage des Sables Blancs sur laquelle 5 structures en épi ont été mises en place afin de bloquer une partie du transit longitudinal ; la plage de Boutrouilles équipée d'une structure longitudinale en pied de dune afin de fixer le trait de côte. Dans les deux cas, les STABIPLAGE ® remplissent leur rôle de défense côtière tant que les conditions hydrodynamiques sont peu énergétiques. En période de fortes tempêtes, l'action des courants de retour et/ou de la submersion marine exacerbée, induit des phénomènes d'érosion que les STABIPLAGE ® ne peuvent enrayer.
Page 1. Dynamique morphosédimentaire des cordons dunaires de Tréduder et de Saint-Michel-en-Grève... more Page 1. Dynamique morphosédimentaire des cordons dunaires de Tréduder et de Saint-Michel-en-Grève (baie de Saint-Michel-en-Grève - Côtes d&gt;Armor) entre 1990 et 2003 (MORPHOSEDIMENTARY DYNAMICS OF TREDUDER ...
La connaissance du littoral, sa protection, son aménagement nécessitent un suivi des changements ... more La connaissance du littoral, sa protection, son aménagement nécessitent un suivi des changements qui s'y produisent. Toutefois, en France, devant l'étendue des façades maritimes à couvrir, les techniques de mesures in situ ne peuvent être appliquées de façon systématique. Dans ce cas, les techniques de télédétection spatiale ou aérienne sont des approches complémentaires. A partir de ces plates-formes, des images stéréoscopiques multi-temporelles sont, après une série de traitements photogrammétriques appropriés, directement exploitables sous formes d'orthophotographies et de Modèles Numériques de Terrain (MNT). Ce type de produits permet notamment la quantification des changements morphosédimentaires à l'interface Terre-Mer (transport transversal et longitudinal de sédiments, érosion,...). Actuellement, la résolution spatiale des MNT générés à partir d'images aériennes ou satellitaires (<50 cm) est insuffisante pour la plupart des applications sur la frange littorale. En outre, dans le cas d'interventions consécutives à un événement extrême (tempête, raz de marée, pollution…), ces systèmes manquent de souplesse (trajectoires prédéfinies, contraintes d'altitude, de vitesse, coût de mise en oeuvre...) L'utilisation de drones constitue donc une alternative intéressante pour des suivis de précision ou des interventions rapides.
This study analyses long-term (1841-1872-1895-1974) changes in the Grand Rhône prodeltaic lobe to... more This study analyses long-term (1841-1872-1895-1974) changes in the Grand Rhône prodeltaic lobe to (1) quantify the accumulation, (2) determine the evolution of relict prodeltaic lobes and (3) establish long-term relationships between river sediment discharge, the shoreface and the continental shelf. Our results show a reduction of the sedimentation of the prodeltaic lobe at the main river mouth, since 150 yr by a factor of 3.7 (12.63 to 3.41 × 10 6 m 3 yr − 1 ). At the minor mouth of the river, erosion dominates and speeds up during the same period (−0.53 to −1.34 × 10 6 m 3 yr − 1 ). These changes are found to directly result from the river sediment input decrease related to the natural decreasing of the frequency of major floods (end of the Little Ice Age), the reforestation in the catchment area, the dam construction and the dredging activities (since the 1950s). Our results indicate that while there is large sediment accumulation in the area around a growing prodeltaic lobe, there is also a reduced contribution of the river sediments to the non-adjacent beaches of the mouth. Following a shift in the river channel and mouth, the relict prodeltaic lobes (Petit Rhône-St Férreol, Bras de Fer and Pégoulier) are reworked by waves and their sediments contribute partially to the growth of the spits (Espiguette, Beauduc and Gracieuse). This suggests that there is a "time-shift" between the input of river sediment to the sea and the build up of a beach. The chronic erosion of the coastline is likely to continue in the future since (1) a river shift is not possible, because the river channels are controlled by dykes and human intervention, (2) the decrease of river sediment input and (3) the relict prodeltaic lobes constitute sedimentary reservoirs that are gradually being used up.
... The only wave measurements available for Brittany coasts for this storm event are those that ... more ... The only wave measurements available for Brittany coasts for this storm event are those that were recorded by the directional waverider located near Les Pierres ... is used in case of irregular waves (wave steepness, Ho/Lo of 0.007 Ho/Lo 0.07) breaking on slopes of 0.03 tan 0.2. ...
On 10th March 2008, the high energy storm Johanna hit the French Atlantic coast, generating sever... more On 10th March 2008, the high energy storm Johanna hit the French Atlantic coast, generating severe dune erosion on Vougot Beach (Brittany, France). In this paper, the recovery of the dune of Vougot Beach is analysed through a survey of morphological changes and hydrodynamic conditions. Data collection focused on the period immediately following storm Johanna until July 2010, i.e. over two and a half years. Results showed that the dune retreated by a maximum of almost 6 m where storm surge and wave attack were the most energetic. Dune retreat led to the creation of accommodation space for the storage of sediment by widening and elevating space between the pre-and post-storm dune toe, and reducing impacts of the storm surge. Dune recovery started in the month following the storm event and is still ongoing. It is characterised by the construction of "secondary" embryo dunes, which recovered at an average rate of 4-4.5 cm per month, although average monthly volume changes varied from − 1 to 2 m 3 .m − 1 . These embryo dunes accreted due to a large aeolian sand supply from the upper tidal beach to the existing foredune. These dune-construction processes were facilitated by growth of vegetation on low-profile embryo dunes promoting backshore accretion. After more than two years of survey, the sediment budget of the beach/dune system showed that more than 10,000 m 3 has been lost by the upper tidal beach. We suggest that seaward return currents generated during the storm of 10th March 2008 are responsible for offshore sediment transport. Reconstitution of the equilibrium beach profile following the storm event may therefore have generated cross-shore sediment redistribution inducing net erosion in the tidal zone.
Gravel spits of Brittany have experimented a long morphosedimentary evolution over the last mille... more Gravel spits of Brittany have experimented a long morphosedimentary evolution over the last millenia. Based on analysis of several back-barrier holocene sediment stratigraphies, distinct phases of construction and barrier breakdown were recognized, indicating the role played by storminess and sediment supply during the late-holocene period. Over the last centuries and decades, a deficit of sediment bubget affecting several gravel spits is highlighted. Therefore, actual coastal evolution of most of them is mainly dominated by cannibalization, landward retreat by rollover and complete destruction of the spits in some places. This coastal erosion is related to the lack of significant offshore sediment input or from the erosion of unconsolided cliffs. Locally, anthropogenic forcing have axacerbated the erosion processes by sediment minings and/or the construction of hard defense structures. For the swash-aligned gravel spits, frequency and magnitude of overwash processes is controlling the rate of landward retreat by rollover. This morphodynamic behaviour is illustrated by topo-morphological surveys realised between 2002 and 2012 on Sillon de Talbert spit which has experienced a complete crestal removal during the 10 March 2008 Johanna storm. Although this event have a 50-100yrs occurence, the barrier has exhibited a rapid crestal rebuilding by overtopping processes, illustrating the great resilience of the spit. Thus, coastal erosion management strategies mainly based on hard defense structures are gradually abandoned for new management policies based on soft operations. Nowadays, gravel spits of Brittany are also considered as a geological heritage and management plans are establishing by local authorities.
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Papers by Serge Suanez