WHAT CAUSES PARADOXICAL BEHAVIOR IN GROUNDWATER LEVELS IN RESPONSE TO PRECIPITATION EVENTS?

The purpose of this research is to explain the paradoxical behavior of groundwater levels with fluctuations in precipitation. Decreases in precipitation from one month to the next are sometimes followed by increases in the water table or potentiometric surface and, conversely, monthly increases in precipitation are sometimes followed by decreases in groundwater levels. Together these are referred to here as paradoxical responses. Our hypothesis is that paradoxical responses can be explained in many cases through considering mass balance. For example, groundwater levels may increase even in a month in which precipitation has decreased if the recharge (inflow) exceeds the outflow of the aquifer. To test this hypothesis, a linear reservoir model is being created to represent the mass balance of an aquifer system. Field data from a local aquifer system, including 30 years of record from 21 wells, provide a historical record of paradoxical events to model. The study is examining the extent to which the mass balance model can explain the paradoxical behavior.