Présentations Colloques

Oral Presentation
Session 8.05: Karst aquifers
Sinreich Michael
Quantifying the natural protection of karst aquifers
Tracing experiments are recognized as an essential tool for validating vulnerability mapping in karst terrains. The proposed approach first includes the development of a standardized artificial recharge scenario for conducting and comparing tracer test in karst environments. Based on accurate discharge and tracer concentration monitoring at the karst system discharge area, non-reactive tracer attenuation, mass recovery and mean transit time over the duration of the main breakthrough curve is used for the quantitative assessment and validation of spatial groundwater vulnerability.**Comparative tracer tests performed at several Swiss karst systems typically illustrate that recovery rates differ significantly for injections within the same catchment even in case of limited contrast of a single vulnerability mapping criteria (e.g. a few decimeters of soil thickness). Multi-tracer tests focused successively on each sub-system controlling the water and contaminant flow in karst settings allowing a better quantification of conservative solute concentration attenuation from the soil surface to the discharge area. Storage in the soil and subsoil thereby showed to play the most important role in relation to intrinsic vulnerability in many karst systems. **A protection unit was defined based on the quantitative interpretation of numerous tracer experiments and classes of vulnerability criteria were assigned accordingly. This protection unit corresponds to the smallest protection effect or vulnerability class, respectively, that can be determined for a mapping criterion, and which generate a quantifiable influence on the tracer breakthrough curve (maximum concentration, mass recovery, transit time).**