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Hydrological and hydrogeological specificities of Mediterranean catchments - examples of karstic systems


Dörfliger Nathalie

Within the HyMex workshop, the major characteristics of the hydrological Mediterranean basin will be briefly reviewed, considering the link between geological history and hydrological and hydrogeological processes and also the figure of anthropogenic pressures. As a consequence of a similar geological history at the scale of the whole Mediterranean region, the watersheds exhibit similar hydrogeological patterns and physiographic features (huge pilling-up of limestone rocks, widespread and more or less karstified; deep sedimentary basins from Plio-Quaternary periods, constituting presently heavily exploited coastal aquifers).
The whole hydrological cycle's characteristics derive from the transfer functions fixed by these properties of the watersheds compartments (surface states, soils, vadose zone, ...), their initial state, and the evolution of the boundary conditions. Hydrological modelling at catchment scale is carried out under two approaches, (i) a global approach with transfer functions identification (i.e. GR4, Gardenia, Tempo, ...) and (ii) a distributed approach considering flow equations in the unsaturated and saturated zone (i.e. POWER, ...). This will be discussed in details in the presentation of I. Braud (Cemagref, Grenoble).
The global approach is generally used for the karst systems modelling; the signal treatment and inverse modelling (Pinault et al., 2001; Pinault et al., 2004) carried out on karstic systems (unary and binary with endo or exo water input) allows determining various transfer functions that could be associated to runoff, infiltration, temporary storage, fast and slow flow within the aquifer and predictive scenarios. Signal treatments allow also identifying at the scale of large watersheds, the karst relative contribution during either the low or the high water stage. Karst aquifers functioning may influence flooding process, as the Nîmes case study illustrates this process with some flash floods (Maréchal et al., 2006). Examples on numerous transfer functions of various Mediterranean karstic systems will be discussed.
Perspectives in terms of needs will be presented such as genetic karst models in order to develop and improve multi objectives water management of karstic systems, and to take into consideration anthropogenic and climatic driving forces.