Hydrogeology of the middle valley of the Velino River and of the S. Vittorino Plain (Rieti, central Italy)

Abstract

This paper deals with findings from hydrogeological investigations, which were conducted in the middle valley of the Velino River and in the S. Vittorino Plain from 1986 to 2008. These areas hold linear and localised springs with a total average discharge of over 26 m3/s. Measurements of stream and spring discharge, physico-chemical characterisation of waters, hydrochemical analysis of major ions, piezometric and monitoring surveys permitted to update the understanding of the various groups of springs and assess their normal base-flow and their absolute base-flow discharge in particularly dry periods (1990 and 2008). The multi-year variability of discharge from the individual groups of springs proved to be correlated with spring elevation. The paper also proposes a conceptual model of groundwater flow, updated and fine-tuned with respect to previous models. Under the model, the key factors controlling the points of discharge of groundwater are: i) the fractured carbonate aquifers supplying the regional groundwater of the Giano-Nuria-Velino Mts. hydrogeological system; ii) the Mt. Paterno-Canetra hydrogeological unit, through which a substantial portion of groundwater flows and, above all, iii) the multi-layered aquifer of the Quaternary intramontane plain of S. Vittorino, where carbonate groundwater mixes with dominantly gaseous deep fluids rising from the main discontinuities.