Groundwater flow modelling of a tunnel-drained fractured aquifer: validation through creek base-flow continuous monitoring

This paper concern the implementation and validation of a numerical flow model based on the data collected and related to the bored section of a base tunnel through the Appenninic chain (Veccione watershed, Upper Reno basin, Tuscany, Northern Italy). The hydrologic input data employed in the simulation are the results of an hydrogeological program based on a discontinuous monitoring of springs, creeks discharges and tunnel’s drainage rate from 1995 to 2001. Moreover a detailed geological survey of the area was developed to identify the main tectonic patterns. Three different numerical models were set up, all based on the numerical code Modflow: the first one is a steady-state model calibrated on piezometric levels, springs and creeks discharge in undisturbed conditions; the second one is a transient model relative to the time span between 1999 and 2004 calibrated with the tunnel drainage to nowdays; the third is a transient model to verify the long term effects (till 2015). To improve the validation of the second transient model, were compared data coming from continuous stream stage monitoring systems with model outputs . The study focus on tunnel’s interference with groundwater flow system and the possibility to employ a finite differences code as a predictive tool in fractured aquifers