ANIMATING SEASONAL CHANGES IN GROUNDWATER LEVELS OF THE MAHOMET AQUIFER

Dedicated monitoring networks provide critical information regarding the behavior of an aquifer and how it responds to stresses over different time intervals. For example, the Mahomet Aquifer in central Illinois has a number of dedicated monitoring wells to assess the impacts of various stresses, including seasonally variable irrigation demands. These monitoring wells are often equipped with pressure transducers to allow for analysis of data over both short- and long-term time intervals. While a hydrograph developed for a single well is useful for local analysis, the impacts of multiple stresses over different time intervals on a regional scale are more complicated to visualize.

To overcome this visualization problem, we developed a number of potentiometric surfaces through time for the Mahomet Aquifer. A MATLAB script was developed to select monitoring data over the appropriate time interval, calculate means, and interpolate values for missing data points. The water levels were contoured using the finite-difference code MODFLOW. Constant head cells were assigned for 1) measured water levels and 2) streams that are hydraulically connected to the aquifer. No recharge or other flux boundary conditions were used. An appropriate transmissivity was assigned based on previous studies in the Mahomet Aquifer region, although the potentiometric contours were insensitive to transmissivity. Finally, the potentiometric surfaces were arranged in sequential order to produce an animation of water level change through time. Consequently, the influence of different stresses on a regional scale could more readily be identified. Furthermore, changes in groundwater flow rates calculated by MODFLOW were also animated using this approach.