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Cave stream Missouri Department of Conservation photo

My primary research interest is understanding the linkages between hydrology and biology of karst systems. Hydrogeologic topics include

• determining spatial and temporal changes in the rates and mechanisms of recharge to karst basins;
• predicting the response of the basins to recharge events.

Interests with a biological slant are

• understanding disturbances to the habitat of the Southern and Ozark cavefishes and
• understanding disturbances to the habitat of the stream gravels along cave streams.

Current Projects

Sediment transport through karstic basins

Scour disturbances can cause death of animals that live within the sediment of streambeds. Scout disturbances are driven by storm events that mobilize streambed sediment. The Karst Research group is investigating the relation between rainfall intensity, duration, and magnitude and the frequency, duration, and magnitude of scour events in Springfield Plateau basins.

Disturbance events also occur in the large phreatic karstic basins, typical of the Salem Plateau of Missouri and the Floridan aquifer. In these cases, disturbances are thermal and geochemical perturbations and rarely involve movement of the large (centimeter scale) cobbles described above. However, these thermal and geochemical perturbations stress the aquatic organisms, such cavefish and cave crayfish.

Response of basins to recharge events

Predicting the response of karstic basins to recharge events involves two components: understanding and predicting the spatially and temporally variable recharge to the basins and understanding and predicting how water and solutes are transported through the basins.

Recharge to karstic basins occurs through seepage through the unsaturated zone (a distributed source), through seepage through the bottoms of losing streams (a line source), and through swallets where stream flow directly into cave systems. The rates at which recharge occurs thought these mechanisms is poorly known. Temporally, these rates likely vary with soil moisture and soil properties, vegetation status, rainfall intensity, and slope. Spatially, each karstic basin will have different recharge mechanisms occurring at different times and in different locations. For instance, in many karstic basins in Missouri, there are few swallet holes and many streams that lose water via seepage. In Kentucky, there are many swallet holes. Thus recharge is temporally and spatially non-uniform. However understanding recharge to karstic basins is an important step in being able to predict groundwater flow through these basins. The Karst Research Group has instrumented a losing stream reach with temperature dataloggers and using the technique of Constantz and others, we are determining rates of water infiltration out of the bottom of the streambed. In the instrumented basin, there are no swallet holes proper, only losing reaches and seepage through the unsaturated zone. Using detailed soil maps and soil properties, we are calculating rates of infiltration from the unsaturated zone. We are comparing the combined rates of recharge (infiltration) to the measured discharge from the basin, thus, we are trying to balance the water budget for the basin.

Once water has recharged the basin, flow of water occurs through intergranular pores (primary or matrix porpsity), fractures, and conduits. In the instrumented basin, primary porosity is very low, however the basin is fractured and riddled with conduits. Several approaches are being used by the Karst research group to model flow of water through such systems. We use a pipe-flow model that does not accurately account for the small fractures but very accurately accounts for the conduits. We use lumped system models that derive characteristic response functions, however that derivation is dependent on understanding the temporal and spatial distribution of recharge (see above). The new field of wavelets holds promise for deriving characteristic functions of the basins and we are also pursuing that field. Overall, the goal is to predict flow and transport and the Karst Research Group will use which tool which works best for a given basin.

I have served on NSF panels and been an Associate Editor for the Journals Water Resources Research and Ground Water.

Department of Geological Sciences
College of Arts and Science
University of Missouri-Columbia