Comparison of management scenarii in a regional groundwater system

Abstract

The groundwater system in the Milan area represents the main water supply for civil and industrial uses. Since the 1950s its natural equilibrium has been conditioned by notable water table fluctuations; in particular during the last decade a remarkable rise in the groundwater level has led to a real state of emergency. Many buildings and subsurface structures were constructed in the 1970s, and they were not designed to coexist with groundwater: at present the foundation and the underground structures of many important constructions (hospitals, parking, subways) are under the water table affecting their durability and security. A complete understanding of the dynamics of the aquifer system is the first step to manage the emergency and to plan opportune interventions. To achieve this purpose, a 3D finite element model is developed for an area bounded by the rivers Po, Ticino, Adda and the pre‐Alps. A reliable model of this groundwater system requires current and historical data on a number of key parameters: geology (deep and surface), topography, surface water rivers and channels and their hydraulic characteristics, groundwater levels, recharge from rainfall, pumping from aquifer for civil and industrial uses. The numerical scheme is applied in both the saturated and in the unsaturated zone. The numerical model is calibrated in both steady and unsteady state flow. Different scenarios are performed to simulate the response of groundwater system to various stresses: an increasing of water pumping in the city of Milan, a particularly rainy season, the reopening or the obstruction of spring lines located in South Milan. The results of the model can be a useful tool to optimize intervention, thereby reducing costs of management.