To assess whether the hydrometric level of an artificial lake in a quarry near Milan (Italy) could be assigned as a Dirichlet boundary condition for the phreatic aquifer in a fine scale groundwater flow model, hydrological measurements of piezometric head and rainfall rate time series have been analysed by spectral and statistical methods. The piezometric head close to the quarry lake proved to be well correlated with seasonal variations in the rainfall. Furthermore, geoelectrical tomography detected no semi-permeable layer between the phreatic aquifer and the lake, so the contact between surface and ground water is good. Finally, a time-varying prescribed head condition can be applied for ground water flow modelling.

Keywords: ground water flow, boundary conditions, surface and ground water interactions, geoelectrical tomography, statistical analysis.