Hydrogeological conceptual model of the upper Chienti River Basin aquifers (Umbria-Marche Apennines)

Abstract

An updated conceptual model of groundwater flow of carbonatefractured aquifers of Apennine basin of the Chienti River (MarcheRegion) has been developed. This model derives from the applicationof classical hydrogeological approach, which is based on adetailed field survey, by upscaling methodology, aimed to localizethe main spring locations (15 springs) and to evaluate their meandischarge (total discharge of about 3280 L/s). Acquired data havebeen combined with the hydrogeological evaluation of the geologicalstructuralsetting, for defining the hydrogeological role of the lithologicalcomplexes and of the structural setting (faults and thrusts),conditioning groundwater flow direction and amount. The geologicalstructuralsetting is typical of Central Apennine in the Umbria-Marchean succession. The bottom carbonate unit corresponds to thecarbonate platform, overlapped by calcareous complexes havingmarly beds and marly-clayed complexes of pelagic facies, by a totalthickness of about 2500-3000 m. Compressive tectonic processes, ina E-verging thrust-and-fold belt, combined with intense translationalmovements gave rise to significant overthrusts at regional scale. Thecores of anticlines host large basal aquifers, hydraulically separatedby low-permeability boundary due to marly and clay complexes,respect with the surrounding Scaglia aquifers. Groundwater flowmoves mainly along N-S direction, parallel to the main thrusts,which act as no-flow limit. The proposed hydrogeological modelincludes seven local aquifers. There are two independent basalaquifers, feeding a deep groundwater flow in the basal carbonatecomplexes, including areas out of the hydrographic basin of ChientiRiver. Spring fed by these basal aquifers have a mean discharge of1460 L/s. Additional five aquifers characterized by less deep andmore local groundwater flow correspond to the Scaglia complexes,with a mean discharge of about 1820 L/s. The extension and the limitsof all these aquifers have been verified by the evaluation of effectiveinfiltration values, to define the recharge area of each spring group.The resulting conceptual model has been independently validated bychemical and isotopic analyses of groundwater, which confirmed orrequire modification of the preliminary model obtained by thehydrostructural approach.