H21J-01:
A field comparison of techniques to quantify surface water – groundwater interactions
Tuesday, 16 December 2014: 8:00 AM
Ricardo Gonzalez-Pinzon1, Adam S Ward2, Christine E. Hatch3, Adam N Wlostowski4, Kamini Singha5, Michael N Gooseff4, Roy Haggerty6, Jud W Harvey7, Olaf A Cirpka8 and James T. Brock9, (1)University of New Mexico Main Campus, Albuquerque, NM, United States, (2)University of Iowa, Iowa City, IA, United States, (3)University of Massachusetts Amherst, Department of Geosciences, Amherst, MA, United States, (4)Colorado State University, Fort Collins, CO, United States, (5)Colorado School of Mines, Golden, CO, United States, (6)Oregon State University, College of Earth, Ocean and Atmospheric Sciences, Corvallis, OR, United States, (7)USGS, Reston, VA, United States, (8)University of Tübingen, Tübingen, Germany, (9)Desert Research Institute, Reno, NV, United States
Abstract:
The challenge of quantifying surface water-groundwater interactions has led to the development of several techniques, from centimeter-scale probes to whole-system tracers, including chemical, thermal, and electrical methods. We co-applied several of these techniques within a single experimental reach in a third-order stream. The techniques that we used include: conservative and “smart” reactive solute tracer tests, measurement of hydraulic heads, distributed temperature sensing, vertical profiles of solute tracer and temperature in the streambed, and electrical resistivity imaging. Results from the field experiment consistently indicated that surface water-groundwater interactions were not spatially expansive, but were high in flux through a shallow hyporheic zone surrounding the 450-m study reach. The NaCl and resazurin tracers suggested different surface-subsurface exchange patterns between the upper two thirds and lower third of the reach. Subsurface sampling of tracers and vertical thermal profiles quantified relatively high fluxes through a 10–20 cm deep hyporheic zone with chemical reactivity of resazurin indicated at 3, 6 and 9 cm sampling depths. Monitoring of hydraulic gradients along transects starting ~ 40 m away from the stream indicated that groundwater flow prevented the development of a larger hyporheic zone, which was shown (from MINIPOINT samples) to progressively vanish from the stream thalweg with depth in the streambed and distance toward the banks. Finally, FO-DTS did not detect extensive inflow of groundwater into the stream and electrical resistivity imaging showed limited large-scale hyporheic exchange. From the experience gained in our experiment, we recommend the following reasoning to decide which technique(s) should be implemented in a particular study: 1) clearly define the nature of the questions to be addressed, i.e., physical, biological or chemical processes, 2) identify the spatial and temporal scales that want to be covered explicitly and those required to provide an appropriate context for interpretation, and 3) engage in collaborative research efforts that maximize the generation of mechanistic understanding and reduce the costs of implementing multiple techniques.
