Reference, completed project

Corsica: cause of flooding in the port of Bonifacio in 2021 and 2022

In the spring of 2021 and the summer of 2022, in calm weather, the port of Bonifacio was flooded, causing significant material damage. In response, the DDT2A and BRGM initiated a study to gain a clear understanding of these events, explain their causes and, in particular, establish whether they were caused by a seiche wave.

26 November 2024

Installation and calibration of a pressure sensor (Bonifacio, 2023).

The need

To better manage and prevent these episodes of local coastal flooding, BRGM set up a hydrodynamic data acquisition system to characterise water levels in the Bonifacio gully.

The results

In the summer of 2023, BRGM began recording measurements of waves and water levels (using underwater pressure sensors), as well as atmospheric pressure and wind speed and direction in the Bonifacio gully. These measurements were scheduled to continue until autumn 2024.

An analysis of the initial results shows that flooding may occur in the port when several conditions coexist:

sufficient tide-related variations in water level,
the specific topography of the quays in the port of Bonifacio (low points),
the morphology of the gully, causing the generation and propagation of a seiche wave (stationary oscillations in a closed or semi-closed basin) in the port,
episodes of low atmospheric pressure.

The next phase of the study will look at the influence of the wind in pushing the water from one side of the gully to the other, and of seasonal and interannual variations of the mean sea level. The gradients in water level variation generated by the various processes and their possible concomitance will be analysed using a longer data series.

Through our agreement with BRGM, we are already familiar with their expertise and support capacity, and we have established a relationship of trust that is essential to our work. The results of the study will enable us to plan ahead and adapt our future projects to take account of this flooding. We have also updated our back-up plan. We are focusing on providing support for retailers by identifying the equipment and resources they need to prevent flooding. We will be applying to the "Barnier fund" with this objective in mind.

Chrystelle Longuet-Milleliri, Assistant Services Manager, Municipality of Bonifacio

Calibration of a pressure sensor to measure waves and water levels (Bonifacio, 2023)

Using the results

The results of the study should make it possible to understand the influence of each parameter on variations in the water level. On a larger scale, we will need to establish the link with offshore waves and the values of meteorological parameters in order to start shaping a solution to forecast future flooding.