Implementation of groundwater numerical models in geological contexts of urban areas

Abstract

The work presented in this thesis is a combined process of conceptual and numerical modeling of Rome’s aquifer system; it is carried out by a phase of data collecting and archiving ,and a phase of study in depth of the conceptual geological setting (both phases realized in collaboration with Igag-CNR); then, the geological setting has been translated into a hydrogeological framework, starting from hydrologic and hydrogeologic data and previous regional studies; this phase included extraction of information from the database and the data elaboration into cross sections and modeled surfaces. Finally, the conceptual hydrogeological model has been used to build a numerical model by using the finite-difference code MODFLOW2000® and the graphical interface GroundwaterVistas® 5.41(ESI). Modeled area extends on a basin-scale in an area of 237402 m2 including high urbanization zones, as the hystorical center of the City; the complexity of the geological setting of the roman sector, the complications in groundwater and surface water flux due to the modification of the natural hydrologic setting and the lack of valid series of head data, river flux and k measurements, strongly increase the uncertainty on model results.The work has been developed by those steps - Creation of database capable to collect hydrogeological data as: well logs, head measurements, spring discharge, pumping tests;

- Collecting 2950 well data ; 326 have been used to construct cross sections and top surfaces;

- building top surfaces of: Plio-pleistocene complexes (including Monte Vaticano and Monte Mario Formation), Ponte Galeria Formation, alluvial basal gravel; moreover, the maximum erosional surface of Tiber alluvial valley has been built

- implementation of a quasi-3D steady state numerical model set up with 8 layers, a horizontal cell discretization of 50 x 50 meters, for a total area of 237402 m2

- model calibration, carried out on following parameters: recharge in urban and non urban areas, complexes hydraulic conductivities, General Head boundaries hydraulic conductivity, drain and river bed hydraulic conductivity; calibration was performed by a trial-and-error method based on head target residuals statistics and by 5 autosensitivity analysis;

- Computation of inflows and outflows both for the whole model and for each hydrostratigraphic unit.

- Comparison between the 10-years averaged aquifer system’s water balance (Capelli et alii, 2005) and the model’s water budget.