Ozark Plateau Aquifer: Response to Recharge Events

The Ozark Plateau Aquifer is the source of water for many municipalities and is home for a variety of subterranean animals. Thus the quality and quantity of that water is important for health of humans and for health of subterranean ecosystems. However, predicting the movement of groundwater and contaminants through this aquifer is difficult due to the karstic nature of aquifer. Previously, linear, stationary filters were used to predict the response of the aquifer to isolated recharge events and to a year-long series of recharge events. Whereas the predictions matched the timing and magnitude of peak discharge, the predictions consistently failed to predict the prolonged tail observed on the recessional limb of hydrographs. Research efforts currently focus on the characterization of nonlinear filters, such as gamma functions, that can be used to model the response of the aquifer to recharge events and contaminant pulses. Gamma functions are useful as these functions include two parameters that allow better resolution of the tailing behavior and of the timing and magnitude of the peak discharge. Discharge data from several first-order springs that drain the Ozark Plateau Aquifer are analyzed to determine the values of the parameters of the gamma function. The gamma functions were used to model the discharge behavior of the springs when subjected to rainfall events. Comparisons between observed and modeled discharge records are made for isolated recharge events and for year-long records.