How research contributes to the adaptive management of the Rhone delta?
In the Rhone delta, water exchange and the different uses of water are conditioned by the climate, agricultural hydraulic management, and the geographical limitations imposed by the river and marine environment. In this complex system, policy makers and managers lack a tool for helping them make decisions and forecasts. This newsletter reports on the latest studies in which the Tour du Valat is involved.
A delta takes form through a natural process in which it expands and shrinks, under the combined influence of a river and the sea. For more than one and a half centuries, human intervention, intended to enhance its economic value and ensure people’s safety, has negatively affected this process in the Camargue. The system of dykes has made these wetland ecosystems highly dependant on a supply of water from the Rhone, which is mainly used for agricultural purposes.
The Ile de Camargue’s increasing vulnerability
Today, the delta is facing several risks:
- The risk of flooding: extreme local precipitation, overflowing rivers, and/or tidal surges can saturate the soil and/or damage protective dykes, which increase the risk of submersion. The overflowing of the Rhone since 1993 has shown that a risk linked to the failure of these structures does exist. Likewise, the coast line protection has been an important issue in the management of this coastal area for decades. In addition, flooding risks have been increasing due to the effects of climate change, with more frequent and stronger extreme climate events and the rising sea level.
- The risk of water shortages: due to a significant water deficit (average annual evaporation is more than twice the amount of precipitation), agricultural activity in the delta relies on irrigation. Meanwhile, on these salty lands, the extremely low level of the river (period of the year in which the flow of this water course is at its minimum) facilitates the rise of the wedge (interface between fresh water and sea water) in the two branches, which can make the water pumped unfit for crop irrigation.
- The risk of pollution: the water pumped contains pollutants, such as heavy metals, pesticides, and other organic pollutants, produced by the activities carried out in the Rhone basin. The intensive farming in the Camargue also generates flows of pesticides and fertilisers, and part of their residues ends up downstream in the Camargue National Reserve.
Modelling the hydro systems is required to develop decision-making help tools
Faced with these risks and the future effects of climate change, site managers and policy makers need models enabling them to simulate how the hydrological systems in the delta function to guide them in making decisions concerning future development, and also for the purposes of crisis management (floods). That is why Tour du Valat hydrologists are developing tools for the hydrological modelling of the Ile de Camargue. A significant part of this job consists in imagining hydro-climatic scenarios and proposing management rules that can evolve in function of global change.
Several research projects initiated and funded by the French Ministry of Ecology and Sustainable Development (MEEDDM) have been carried out in the Camargue. Results have been obtained and recommendations formulated, and now the chief objective is to transfer the tools and knowledge acquired to the site managers.
Examples of projects in which the Tour du Valat is involved:
- Within the framework of the LITEAU 1 programme, hydrologists have worked on the consequences of the hydro-saline variability of a Mediterranean lagoon complex (the Vaccarès system) on fish stocks (2000-2003);
- Within the framework of the IMPLIT project – the GICC2 programme(Management and Impact of Climate Change), the analysis of the limiting conditions on the hydraulic management of the Ile de Camargue in an extreme hydro-climatic context has enabled us to propose new approaches and possible development plans in response to the foreseeable effects of climate change (2005-2007).
- The GIZCAM project (Constraints, limits and perspectives for Integrated Coastal Zone Management in the Rhone river delta), which is part of the LITEAU 2 programme, was finished in 2009. The Tour du Valat, which coordinates the project, developed a model for simulating how the Ile de Camargue’s hydrology functions, on the basis of a more modular approach, makes it possible to integrate new options for hydraulic management. Sedimentary and saline flows were also measured in relation to this hydraulic management.
The Camargue is not going to disappear tomorrow; however, it is experiencing new developments, due to the effects of global change.
It is up to policy makers and site managers, on the basis of the tools developed and the knowledge acquired, to formulate and implement strategies to adapt to these changes and enable us to anticipate and evolve with them in a way that will make human activities less vulnerable.
Finally, it is up to all of us to create an ongoing dialogue between scientists, site managers, and policy makers, and to keep local citizens informed.