Maria Giovanna Tanda

Contaminant release history identification in 2-D heterogeneous aquifers through a minimum relative entropy approach

The minimum relative entropy (MRE) method has been applied in a wide variety of fields since it was first introduced. Woodbury and Ulrych (Water Resour Res 29(8): 2847–2860, 1993, Water Resour Res 32(9): 2671–2681, 1996) adopted and improved this method to solve linear inverse problems in aquifers. In this work, the MRE method was improved to detect the source release history in 2-D aquifer characterized by a non-uniform flow-field. The approach was tested on two cases: a 2-D homogeneous conductivity field and a heterogeneous one (the hydraulic conductivity presents three orders of magnitude in terms of variability). In the latter case the transfer function cannot be described with an analytical formulation, thus, the transfer functions were estimated by means of a numerical procedure. In order to analyze the method performance in different conditions, two datasets have been used: observations collected at the same time at 20 different monitoring points, and observations collected at 2 monitoring points at several times. The observed data have been processed with and without a random error and the Boxcar and Gaussian probability distribution functions were considered as a priori information. The agreement between the true and the estimated data has been evaluated through the calculation of the normalized Root Mean Square error. The approach was able to recover the release history even in the most difficult case.

Collection and Analysis of the Reactivation Data of the Historical Sand Boils in the Po River Levees

A recent study (Aielli et al. 2017) about sand boil reactivations in the major Po river banks (Italy) has demonstrated how a structured database of historic information can significantly contribute to better understanding of seepage phenomena and provide a practical tool for safe management of hydraulic works. The primary aim of the present work is to enhance the information collected in the database (DB), which cover the whole course the Po river, to the beginning of the delta. In particular, an improved estimation of the critical height (i.e. height of the water level in the river which causes a sand boil reactivation) for sand boil phenomena is discussed herein. The maximum height without reactivation and the minimum height with reactivation have been evaluated for each recorded sand boil. The DB information and processing of the available data allow defining how the values of the critical heights are distributed along the course of the river. The DB information, connected to the alert thresholds and to the early warning system, can provide an indication of the possible reactivations of the piping phenomena in advance, enabling efficient coordination of the emergency actions against backward erosion piping progression.

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.

Influence of a highway embankment on a flood event

Abstract A mathematical model (ROUTWEIR type) is applied to the evaluation of the influence of a highway embankment during a flood occurred in 1977 in Northern Italy. The whole area involved in the inundation (almost 40 sq.km) is represented by a network of 1786 triangular cells with 964 vertices. Inflow hydrographs of the three rivers crossing the area are evaluated by means of a rainfall-runoff model together with hydrographic data collected during the flood. Several runs were carried out to calibrate model parameters on the basis of the observed water levels in some locations. After calibration, simulation of the same flood is performed with the network modified to represent conditions prior to the highway construction. Comparing the results with and without the highway in place, the hydraulic impact of the structure is determined.