Groundwater flow systems in turbidites of Northern Apennines (Italy): natural discharge and high speed railway tunnels drainage

A conceptual model of groundwater flow systems in turbiditic fractured aquifers is proposed, taking into account natural discharge pattern of the hydrogeologic system and the system perturbation induced by tunnel drainage. Silico-clastic and marly calcareous turbidites outcrop extensively in Northern Apeninnes (Italy) and paper deals with the assessment of the aquifer-like behaviour of these units, up to now considered as aquitards, as reflected by the huge amounts of groundwater locally drained by tunnels for the high speed railway (HSR) connection between Bologna and Florence. The study is based on the analysis of a huge amount of hydrological data (springs, streams and tunnels discharge) collected by a monitoring activity performed for a 10 years time-span, integrated by hydrochemical and isotopic analysis on surface and tunnel waters and a stream-tunnel tracer test. In a turbiditic aquifer recession analysis permits to discriminate groundwater flow systems, to calculate recharge relative to the up-stream reach portion and to locate springs more vulnerable to tunnel drainage impacts. Natural discharge is stream-focused and, as the tunnel drainage is for 85% formed by active recharge groundwater, the impact on the stream base-flow is severe with abatement of natural discharge budget component up to 2/3 of natural value.