Identification of fast preferential flow distribution in a complex snow-governed karst system based on an inference of secondary faults, doline distribution, and tracer tests experiments: An application to Mount Lebanon

Six tracer experiments were undertaken under different flow periods to delineate the catchment area and identify transport parameters in two snow-governed springs Laban and Assal in Mount Lebanon used for water supply. The two springs yield different responses to snow melt, ambient temperature in high flow and in recession despite their common origin from the same Albian-Cenomanian rock sequence. These discrepencies were attributed partly to different facies within the aquifer (limestone and dolostones). Yet faults and secondary fractures also play an important role in defining preferential flows in such a complex system. Secondary faults and fractures are difficult to depict in the field and were assessed via fracture analysis. In this work, primary faults with their characteristics (displacement and trends) are input in a Havana software (developed by Norsk Regnesentral; SAND 2021) based on field data used to simulate new faults. The model generates a secondary set of faults from a truncated fractal distribution, yielding thus different realizations of the set of secondary faults depending on the parametrization of the fractal model. The realizations will be validated with field data, doline distribution, and fracture analysis as well as tracer experiments results. This work allows to combine physical data with geostatistical techniques to optimize the delineation of the catchment and preferential flow in complex vulnerable karst systems.