HOW MUCH DATA DO WE NEED TO CHARACTERIZE EXCHANGE BETWEEN GROUNDWATER AND SURFACE WATER?

Efficient use of resources dictates we collect enough data to address a particular scientific question and no more. The amount of data needed to appropriately quantify exchange between groundwater and surface water depends not just on the question but also on the spatial and temporal heterogeneity of the exchange. Data collected with seepage meters installed in a wide range of settings indicate a broad range of data requirements. At a lake in northern Minnesota that was flooding homes, one measurement would have been sufficient to indicate groundwater was substantially ameliorating high lake stage. In other settings where exchange between groundwater and surface water was small and typically inconsequential, episodic events occurred that substantially altered the exchange. In those situations, seepage response to episodic events would have gone undetected without frequent measurements made on a continual basis. The small value added by each measurement made during stable conditions was countered by the exceptional value of data collected during extreme hydrologic events. Continual measurements of seepage are labor intensive, logistically challenging, and impractical for many studies. Relating direct seepage measurements to other methods more conducive to unattended monitoring provides a cost-effective way to detect the timing, magnitude, and duration of exceptional exchanges between groundwater and surface water that occur in response to episodic hydrologic events.