James Boswell
Analysis of a two-dimensional finite difference groundwater model and its applications to Bass Lake Indiana BSES Senior Research Project 2002

Abstract
Bass Lake has shown significant water level drops of up to three feet during the years of 1999 and 2000.  Similar, but more extreme lake level drops occurred between 1963 and 1965.  The hydrology of Bass Lake and the surrounding area was simulated using a two-dimensional finite-difference groundwater model, in an attempt to identify the causes of these drops.  The results of the model show that the flow in the area surrounding Bass Lake is predominantly from the southeast to the northwest. Therefore, the dunes to the southeast could be considered a main recharge zone for this aquifer system.  The model also accurately depicts times of drought and associated decreasing lake levels.  The model simulated the drop between 1964 and 1966 as well as the recent lowering in 1999 and 2000.  However, the model over-estimates the drops in the water table.  Although this model did not show a high degree of accuracy when comparing the actual lake level elevations to the modeled lake-level elevations, it did show the correct regional groundwater flow pattern as well as the increasing/decreasing trends in lake level.  The trends in the modeled values were similar to the trends in the actual values, showing that drought or dry years can lead to large drops in lake level and thus lake area.  The fact that the model overestimated these drops based only on precipitation and evaporation data suggests that this system is sensitive to these hydrologic fluxes.  Therefore, withdrawals of water from increased pumping would cause additional lake-level decreases.  The surrounding wells generally protrude into the deeper aquifers.  However, the deeper aquifer material is connected to the shallow aquifer material.  Therefore, as this area becomes more populated, increased pumping of these deeper aquifers could lead to even higher drops in lake level.