Rock avalanche deposits enhancing surface water/groundwater interaction at the boundaries of a fractured carbonate aquifer (maiella mountain, central italy).

This study describes the preliminary results obtained in two areas of Maiella ridge carbonate aquifer (Abruzzi, central Italy), where the surface runoff drainage of Aventino and Vella Rivers is influenced by deposits of limestone Rock Avalanches of Lettopalena and Campo di Giove located respectively on the Eastern and Western side. Discharge measurements and chemical – isotopic analyses are the tools used to evaluate the flow through the deposits of Rock Avalanches and to verify conceptual models of the groundwater flow. Physical and mechanical characterization of rock avalanche deposits obtained by laboratory tests (particle size analysis of soil, specific gravity determination, Proctor compaction and permeability tests) have allowed us to confirm the role played by these bodies respect with the groundwater flow of the carbonatic hydrostructure of Maiella. In fact, the sandy/silty gravel component of the landslide body of Lettopalena encourages total seepage to groundwater of surface water of the river Aventino. The groundwater drained from the rock avalanche deposits feeds the river downstream, in correspondence with San Giustino spring group, after having mixed and diluted with groundwater coming from the basal aquifer of Maiella, whose average elevation of recharge area by isotope data is about 2000 meters a.s.l. On the western side, the sand and silty-gravelly deposits of Campo di Giove Rock Avalanche justify the bypass role played by the landslide body respect with the groundwater flow coming from the Maiella hydrostructure, acting as a local shallow aquifer. In fact, the hypothesis of interaction of groundwater flow coming from detritic aquifer and from adjacent carbonatic aquifer is supported by hydrogeological and chemical analysis. The flow rate erogated by the Campo di Giove Rock Avalanche into the Vella River in dry seasons was estimated to be over 50 L/s. Furthermore, the enrichment in Sodium, Potassium and Chloride of some springs located at lower altitudes highlights the interaction of groundwater fed by the carbonatic aquifer of Maiella hydrostructure with the debris deposits of Rock Avalanche.