Developing Potentiometric Surfaces and Flow Fields with a Head-Specified MODFLOW Model.

Investigating changes in an aquifer system often involves comparison of observed heads from different synoptic measurements, generally with potentiometric surfaces developed by hand or a statistical approach. Alternatively, head-specified MODFLOW models, in which constant head cells simulate observed heads, generate gridded potentiometric surfaces that explicitly account for Darcy's Law and mass balance. We developed a transient head-specified MODFLOW model for the stratified Cambrian-Ordovician sandstone aquifer system of northeastern Illinois to analyze flow within its 275 m deep cone of depression.