AN EVALUATION OF MODFLOW_USG (Master Final Thesis)

Abstract:

The majority of software for groundwater modeling is based on finite difference and

finite element methods. In 2013, the United States Geological Survey ( USGS)

released a new version of MODFLOW, called MODFLOW-USG, in order to support

UnStructured Grids. Soon enough, graphical user interface (GUI ) provided the

new version of Groundwater Vistas (ver. 6) in order to support MODFLOW-USG

software packages.

In the first part of this thesis, a study area, previously modeled using a structured

version of MODFLOW (i.e. MODFLOW2000), is developed in MODFLOW-USG in

order to evaluate its new features and capabilities in comparison with the older

version.

In the second part of the study, MODFLOW-USG is applied to another study area,

previously modeled with MODFLOW-2005, in order to simulate the transport of

heat through a borehole heat exchanger using the new transport package provided

by MODFLOW-USG and make a comparison with the results obtained through

MODFLOW-2005. Different approaches for the grid design and the u-pipe

representation are applied for finding the best possible solution.

The results of the comparisons between structured and unstructured versions of

MODFLOW show that for simple problems (as the one of the first part of this study),

MODFLOW-USG could provide flexibility in grid design resulting in fewer grid cells

and consequent faster running process. However, the second part of this study,

where a very refined grid is required, due to the complexity of the problem,

MODFLOW-USG turns out not to be able to provide the correct results with an

unstructured grid, while the grid generation is still better with MODFLOW-USG.

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