KArst system Self-organization for water resource Protection and vulnERability – KASPER

Sustainable exploitation of karst systems requires to understand how these complex structures are formed with important impact on their hydrodynamic, vulnerability to contaminant, and storage capacity. The traditional paradigm of karst formation assumes that both dissolution and erosion occur at the same time, leading to the formation of conduits under the action of acidic water. However, some field observations tend to show that the chemical and mechanical processes are decoupled during the formation of karsts, explaining the presence of ghost-rock (or altered-rock) that are formed before the breakthrough of the system. In order to improve our understanding of karst formation, we propose a multi-disciplinary multi-scale approach relying on the following steps. (i) Two kinds of numerical models will be developed based on assumptions related to either the traditional view of karst formation or the ghost-rock theory. Existing software will be coupled to simulate flow, reactive transport processes, geochemical reactions and speciation, and linked to laboratory experiments. (ii) Laboratory experiments of carbonate sample dissolution will be conducted with various initial heterogeneities in the samples and several monitoring tools used all along the experiments (X-ray tomography images, tracers, geophysical measurements…). (iii) Field measurements and multi-scale comparison in link with the conclusions provided by the numerical models and laboratory experiments will be performed. This step will be done on the Durzon site in Larzac with the Karst3D database. This will lead to improve our understanding of how and where conduits and cavities form in karst systems, but also of the properties of the surrounding matrix rock and its storage capacity. These are key information for a sustainable exploitation of these systems, in particular in the context of climate change that might impact the potential for karstification of these natural environments.