The partner interview

Why did you decide to call on the services of BRGM? 

Stéphane Roumeau –  The Thau Basin is a seawater lagoon in the south of France, located near the town of Sète (Hérault). It is the largest body of water in the Occitanie region. The Thau Basin Water Authority is a Public Regional Basin Authority (EPTB [Établissement Public Territorial de Bassin]), whose role is to manage water resources for a particular catchment basin or aquifer. Here, we cover 25 municipalities and, in addition to simply managing the water resources, we are also responsible for regional spatial planning and the regional coherence plan (SCOT). We are the only water authority in France with that remit. Obviously, one of the issues we have to deal with is water salinity. We have problems with water shortages, linked to the state of our aquifer. Another key aspect that we pay particular attention to is water quality, since the lagoon alone accounts for 10% of France's shellfish production. These are just some of the reasons why we call on the services of BRGM. Today, our management approach also needs to take climate-change mitigation strategies into consideration.

Could you briefly describe the projects conducted?

S.R. – We already had a long-standing partnership with BRGM concerning the management of the coastline, which notably involved the development of support programmes for spatial planning, which helped to stabilise the coastline in the 2000s. So, when we launched the DEM'Eaux Thau project, which lasted for five years, we commissioned BRGM to manage the project. The project involved studying the local water resources, in order to have a better understanding of the structure and operation of the complex karst hydrosystem in the basin area. In particular, the project studied the system of La Vise and its underwater spring, which is affected by a reverse-flow (inversac) phenomenon, resulting in temporary intrusions of brackish water into the aquifer. BRGM set up a web platform to observe the aquifer and the spring, along with a 3D hydrogeological model and an aquifer management tool.

How would you assess this partnership?

S.R. – Today, one of the main reasons that the local council is better informed and more aware about the issue of water-resource management is really thanks to BRGM's detailed, in-depth expertise and input. I was particularly struck by how interested the local councillors were in the scientific results. Incidentally, this partnership enabled us to discover the underwater source of the thermal-water deposit of Balaruc-les-Bains, France's leading spa. This added an extra bit of 'magic' to the work. I should point out that when the project ended, BRGM did not simply leave us on our own with our data and results; they provided further support, notably concerning the inversac phenomenon, for which they put in place an experimental programme on regulating the underwater spring in question.