Prediction of the flooding of a mining reservoir in NW Spain

•Flooded mines constitute underground water reservoirs which should be managed.•Candín-Fondón mining reservoir (NW Spain) has an estimated capacity of 8 million m3.•The flood, modelled using FEFLOW and GRAM, would take 4 years after stopping pumping.•Porosity, permeability, storage coefficient and recharge are critical parameters.•Mining reservoirs should be characterized to avoid undesirable flooding discharges.

Abandoned and flooded mines constitute underground reservoirs which must be managed. When pumping is stopped in a closed mine, the process of flooding should be anticipated in order to avoid environmentally undesirable or unexpected mine water discharges at the surface, particularly in populated areas. The Candín-Fondón mining reservoir in Asturias (NW Spain) has an estimated void volume of 8 million m3 and some urban areas are susceptible to be flooded if the water is freely released from the lowest mine adit/pithead. A conceptual model of this reservoir was undertaken and the flooding process was numerically modelled in order to estimate the time that the flooding would take. Additionally, the maximum safe height for the filling of the reservoir is discussed.