Land subsidence induced by groundwater extraction: the case of Bologna

A comprehensive investigation of the subsidence induced in the area of Bologna (Italy) by groundwater extraction is presented. Initially, the geological pattern of the region is reviewed in order to identify the large scale subsoil features governing the water flow regime and the ground displacements. Several types of data, covering the different aspects of the problem are then combined into a Geographical Information System and interpolated data by means of geostatistical analyses. A detailed reconstruction of subsidence over the considered area is accomplished by processing available topographical measurements. The subsoil stratigraphy, the physical, hydraulic and the mechanical characteristics of the different geotechnical units are estimated by integrating the results of available geotechnical site and laboratory investigations. The groundwater regime is investigated by correlating the water head measures recorded on several pumping wells distributed over the area of Bologna. A groundwater flow simulation model has been finally formulated in order to derive the undisturbed pre-existing water level, to identify the effects of the actual groundwater withdrawal and to predict the modifications induced by possible future exploitations.