Combining Conventional Data Collection Techniques to Identify Surface-subsurface Exchange Components

Developing an appropriate data collection scheme to measure and infer surface-subsurface interactions is not always straightforward due to complex spatial and temporal variability in exchange flow paths and hydrologic connectivity. In the context of a case study, we used a variety of conventional data collection techniques ranging from point to reach spatial scales in combination to better understand the complete picture of surface-subsurface interactions. Additionally, we used these techniques to sort out contributions of individual hyporheic and groundwater exchange components, establish how different data sets can be complementary, and determine where gaps in information arise. Techniques included net changes in stream discharge over two consecutive reaches using both rating curves and dilution gaging, longitudinal channel water balances at a sub-reach scale, groundwater table and stream water surface elevations, shallow vertical head gradients, streambed and aquifer hydraulic conductivities, and water chemistry. Despite each individual data type or method providing valuable information regarding subsurface exchanges, only at some locations were the dominant exchange components identifiable. At most locations, however, subsurface exchange was clearly a combination of hyporheic and groundwater exchanges that could not be separated out even when combining information provided by various techniques. As a result, this study emphasizes that individual data types describing surface water-groundwater exchanges are often not adequate to provide conclusive information. While many data types used in combination will result in a better understanding of the complexity of these interactions, there is still an obvious need for more advanced methods to identify and quantify subsurface exchanges