HOW MUCH HETEROGENEITY NEEDS TO BE CONSIDERED IN THE GROUNDWATER-SURFACE WATER INTERFACE

Groundwater-surface water interactions are commonly discussed in the context of gaining or losing streams and baseflow or runoff. Examples used to explain these interactions usually consist of diagrammatic cross sections or hydrographs and discussions often occur on basin scales using average annual fluxes. Assumptions of homogeneity underly most of these conceptual ideas and are generally considered acceptable, even though it is well-known that the systems are heterogeneous. Increasing demand for limited water supplies coupled with land-use changes that affect recharge and runoff, climate change, and anthropogenic controls on flows have increased the frequency of litigation and encouraged consideration of more heterogeneity. Therefore, how much heterogeneity should be considered? Recent studies in the northern segment of the Brazos River Alluvium aquifer provide insight, and possibly, direction to this question. Although groundwater and surface water are generally connected, connections are often not consistent through space or time. Where they are connected, effectiveness of connectivity may vary. Differences in stream channel lithologies, geologic and hydrologic compartmentalization of the alluvial aquifer, and temporal fluxes in water levels influenced by weather and reservoir management demonstrate important influences on heterogeneity. Consideration of such system characteristics may be necessary to answer complex management and legal questions more effectively.