Preprints
https://doi.org/10.5194/essd-2023-459
https://doi.org/10.5194/essd-2023-459
11 Jan 2024
 | 11 Jan 2024
Status: this preprint is currently under review for the journal ESSD.

Insights from topo-bathymetric and oceanographic dataset for coastal flooding studies: The French Flooding Prevention Action Program of Saint-Malo

Léo Seyfried, Laurie Biscara, Héloïse Michaud, Fabien Leckler, Audrey Pasquet, and Marc Pezerat

Abstract. The Action Program for Flood Prevention of Saint-Malo, France, requires the assessment of coastal flooding risks and the development of a local flooding warning system. The first prerequisite is a knowledge of the topography and bathymetry of the bay of Saint-Malo; the acquisition of new multibeam bathymetric data was performed in 2018 and 2019 to densify existing topo-bathymetric datasets and produce two high resolution (20 m and 5 m) topo-bathymetric digital terrain models. Second, the hydrodynamics associated with coastal flooding were investigated through a dense and extensive oceanographic field experiment conducted during winter 2018–2019, using a network of 22 moorings with 37 sensors : the network included 2 directional buoys, 2 pressure tide gauges, 18 wave pressure gauges, 4 single-point current meters, 7 current profilers and 4 acoustic wave-current profilers from mid-depth (25 m) up to the upper beach and the dike system. The oceanographic dataset thus provides an extended overview of hydrodynamics and wave processes in Saint-Malo bay, from coastal up to over-flooding and over-topping areas. It helps to identify the physical drivers of the coastal flooding, and provides a quantification of their respective contributions. In particular, the wave processes at the foot of the protection structures can be observed: in this macrotidal environment, during high spring tides, short and infragravity waves propagate up to the protection structures, while the wave set-up remains negligible, and overtopping by sea packs can occur. The combination of high-resolution topo-bathymetric and oceanographic datasets allows the construction, calibration and validation of a wave and hydrodynamic coupled model that is used to investigate more deeply flooding processes, and might be integrated in a future local warning system by Saint-Malo intercommunality.

The topo-bathymetric and oceanographic datasets are available freely at doi: https://doi.org/10.17183/MNT_COTIER_GNB_PAPI_SM_20m_WGS84, https://doi.org/10.17183/MNT_COTIER_PORT_SM_PAPI_SM_5m_WGS84 and https://doi.org/10.17183/CAMPAGNE_OCEANO_STMALO (SHOM, 2020a, b, 2021).

Léo Seyfried, Laurie Biscara, Héloïse Michaud, Fabien Leckler, Audrey Pasquet, and Marc Pezerat

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on essd-2023-459', Anonymous Referee #1, 31 Jan 2024
    • AC1: 'Reply on RC1', heloise michaud, 14 Feb 2024
    • AC2: 'Reply on RC1', heloise michaud, 28 Feb 2024
  • RC2: 'Comment on essd-2023-459', Anonymous Referee #2, 31 Jan 2024
    • AC3: 'Reply on RC2', heloise michaud, 28 Feb 2024
Léo Seyfried, Laurie Biscara, Héloïse Michaud, Fabien Leckler, Audrey Pasquet, and Marc Pezerat

Data sets

Coastal topo-bathymetric DEM of a part of the Norman-Breton gulf Shom https://doi.org/10.17183/MNT_COTIER_GNB_PAPI_SM_20m_WGS84

Coastal topo-bathymetric DEM of the harbor of Saint-Malo and its surroundings Shom https://doi.org/10.17183/MNT_COTIER_PORT_SM_PAPI_SM_5m_WGS84

Sea Campaign for the French Flooding Prevention Action Program of Saint-Malo Shom https://doi.org/10.17183/CAMPAGNE_OCEANO_STMALO

Léo Seyfried, Laurie Biscara, Héloïse Michaud, Fabien Leckler, Audrey Pasquet, and Marc Pezerat

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Short summary
In Saint-Malo, France, an initiative to enhance marine submersion prevention began in 2018. Shom conducted an extensive sea campaign, mapping the bay's topography and exploring coastal processes. High-resolution data improve knowledge of the interactions between waves, tide and surge, and determine processes responsible for submersion. Beyond science, these findings contribute crucially to a local warning system, providing a tangible solution to protect the community from coastal threats.
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