Preliminary water flow monitoring of a vertical fractures system in a sandstone rock mass

Manuela Deiana (a), Francesco Bonacini (a), Federica Cilona (a), Matteo Formicola (a), Mircea Margarit Nistor (a), Alessandro Corsini (a) & Francesco Ronchetti (a)
(a) Department of Chemical and Geological Sciences, University of Modena and Reggio E. Largo S. Eufemia, 19, 4121, Modena, Italy. E-mail: francesco.ronchetti@unimore.it

Fractured sandstone by tectonic and gravity actions could be classified as aquitard or aquifer according to the number and aperture of the fractures inside the rock mass. This kind of rock mass outcrops not frequently and sparsely in the Apennine and Alps chains. In the Emilian Apennines, which is mainly composed by sedimentary rocks (rich in clay), this type of rock is part of the Epiligurian Succession that outcrops for a 20% of the chain. The aim of the paper is to highlight the first results of the semi-continuous water flow monitoring (discharge, electrical conductivity and temperature) of the spring that represents the drainage point of a vertical fractures system. This network joint characterizes the vertical scarp of a sandstone slab with thickness of 100 meters. The results shows that the spring flow rate, the water electrical conductivity and temperature are influenced by the rainfall distribution pattern. Consequently every rainfall event the spring discharge and water electrical conductivity increase, while the water temperature decreases. The new infiltrate water reacts the spring with a delay of 10-60 hours. The discharge variability index is around 270%. The fractured system is characterized by replacement effect of the preexistent groundwater. During the infiltration event, dissolution phenomena are observed along the wall of the fractures. A preliminary groundwater budget calculation highlights that only a potential infiltration coefficient higher that 75% is admitted to justify the total annual volume discharge from the fractures.

water-flow monitoring, northern Apennine, sandstone, fracture.