Karst Vulnerability Mapping: Examples of Application of RISKE 2 Method

The RISKE 2 method consists in a first assessment of the intrinsic vulnerability of a karst groundwater resource based on the mapping of five criteria: Rock type, Infiltration, Soil, Karstification and Epikarst. The definitions of the criteria as well as their practical implementation through the test on several field sites in France and Europe have been recently improved.

The definitions of the criteria may be summarized as:

- R for Rock type: lithology (proportion of clay minerals, thickness of the bedding) and degree of fracturing of the aquifer rocks outcropping are the main parameters of this criterion;

- I for Infiltration: mainly defined by morphological and speleological parameters in order to distinguish between concentrated and diffuse infiltration.

- P for Protection: the presence of soil (S) or the existence of an epikarst (E) has the same effect of temporary storage of water close to the surface, and the same function of protection of the underlying aquifer towards infiltration. The stack of S and E maps allows the definition of P criterion, keeping the more protective of the two indexes for P.

- K for Karstification: characterised by the degree of development of the karstic drainage at the system scale.

We applied this new methodology to several karstic catchment areas geologically and structurally different (karstified limestones in south-western France, karstified chalk in northern France, fractured-porous limestones in Malta) in order to improve the method (, and define guidelines to be used to define namely protection zones for water supply capture works. We also compared the RISKE 2 final vulnerability map to the map obtained with other European methods for the same field sites (COP, PI, EPIK). We will present the results of these new applications.