Multifractal analysis on modelling karst spring discharge

Karstic watersheds are highly complex hydrogeological systems that are characterized by a multiscale behaviour corresponding to the different pathways of water in these systems. The main issue of karstic spring discharge fluctuations consists in the presence and the identification of characteristic time scales in the discharge time series. The aim of this talk is to present the use of multifractal analyses to identify the structure of karst variability according to the time scale and complexity. To do this, we use karst spring discharge modelling by KARSTMOD and synthetic models with different complexity degrees. The KARSTMOD conceptual model was used to model precipitation/discharge at a small karst spring in Normandy (Norville, France). The optimal model configuration is structured in four different reservoirs E, L, M and C (interpreted respectively as epikarst, high-inertia/highly capacitive matrix, fissure network and conduits). KARSTMOD internal flow are well correlated to natural tracers of the system (conductivity and turbidity). KARSTMOD internal flow components were analyzed based on multifractal analysis in order to highltght the scale properties of the rainfall-runoff relations in Norville karst aquifer. The perspective of this study is to identifiy for natural karst springs a fractal signature of water variability according to the time scale and structure.