LINEAR SYSTEMS MODEL OF THE OZARK AQUIFER

In the Ozark region of Missouri, USA, the karstic Ozark Plateau aquifer is an important source of fresh water. Our ability to predict the response of large karstic basins to contaminant pulses and recharge events is limited due to an inability to model flow through these highly hetereogeneous and anisotropic basins. The linear systems approach holds potential for use as a predictive model because detailed knowledge about the internal structure of the basin is not required. Perceived drawbacks to this approach are the lack of an easy-to-use method to derive a characteristic function; lack of understanding of how variable the characteristic function is; and lack of studies in which comparisons between predictions and observations are made.

The characteristic functions of Big, Greer, Alley, Bennett, and Maramec spring basins were calculated using the unit-hydrograph technique. The unit-hydrograph method is simple to use and the results from the unit hydrograph technique correspond to the results obtained using the more complicated deconvolution technique. By deriving multiple characteristic functions for five basins for six recharge events, an analysis of variance shows that the primary control on changes in the shape of the characteristic functions of a basin is due to storm events (short-duration locally intense storms as opposed to long-duration gentle rainfalls).

Using the derived characteristic functions, the discharge from Maramec spring basins due to large isolated storms, multiple-day events, and a year-long precipitation record were calculated. For the hydrologically closed Maramec Spring basin, the correlation between predicted and observed discharges was 0.94. With regard to water quality, a point and a non-point source characteristic response functions were used to predict the change in the specific conductance of the spring water. For the non-point source, a correlation of 0.97 was obtained between observations and predictions. For the point-source, the correlation was low (0.11), although the prediction matched the first and last appearances of the contaminant very well. Given the findings of this research, the linear systems approach is a useful predictive tool that would enable better management of ground water resources in karstic basins.