Monitoring saline intrusion and dynamic management of withdrawals in Nice

Eau d’Azur owns around twenty boreholes located in the alluvial groundwater of the Var, which supply part of the metropolitan area. This represents around 400,000 inhabitants in winter and 600,000 in summer.

There are water catchments all along the Var, some of them very close to the sea. This proximity to the coast encourages salt water intrusion during pumping, threatening to render some boreholes unusable.

We have therefore been commissioned by the Nice water authority in 2021 to set up enhanced saltwater monitoring to help them manage their catchments.

Eau d’Azur called on our hydrogeological consultancy to carry out a preventive study, before the water catchments were irreparably affected by the salt water wedge. The difficulty with brackish water lies in the fact that once it has entered the water table, it is impossible to push it back out because it is denser than fresh water.

We therefore carried out extensive data collection to study and understand the behaviour of the aquifer in order to adapt to it:

• Measurement of water salinity at different times of the year and under different weather conditions (drought, high water, etc.)
• Geophysical surveys to pinpoint the exact position of the saltwater wedge.
• Installation of our patented SMD probes (2 probes installed) to enable us to monitor the salinity of the water table at different depths.

The SMD probes are linked to our EMI application, which enables Eau d’Azur to monitor the situation of the salt water table in real time.

This live display of data encourages dynamic management of the catchments. In this way, abstractions are distributed to areas where salt water is not present, taking into account the conditions of the water table and the seasons.

In this way, they ensure that saline intrusions are kept under control to ensure the long-term survival of their catchments.