Conference proceeding
Applications of electrical resistivity imaging for characterizing groundwater-surface water interactions from local to regional scales
American Geophysical Union Fall Meeting, Vol.2012
American Geophysical Union 2012 fall meeting (San Francisco, 01/12/2012 - 17/12/2012)
12/2012
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Abstract
Surface water (SW) and groundwater (GW) interact across multiple spatial and temporal scales and their interaction is important for ecological and biogeochemical functions. The mixing of GW and SW has been challenging to simultaneously map with sufficient detail and coverage. Fortunately, ambient differences in salinity of waters occupying geologic formations and sediment are an ideal target for electrical resistivity imaging (ERI). We present examples of the application of ERI for mapping GW discharge and for understanding GW-SW interactions at: (1) a large regulated river, (2) neighboring lakes with differing salinity, (3) fringing coral reefs and lagoons, (4) beaches, and (5) estuaries. In all these cases, the ER tomograms were critical for improving conceptual understanding of GW-SW interactions. At the Lower Colorado River in Austin, Texas (USA), time-lapse ERI was conducted across a 12-hour dam-release cycle when the river stage varied by 0.7 m. Using temporal variability in electrical resistivity (ER) signatures, we identified a shallow well-flushed hyporheic zone, a transition zone where SW and GW mix, and a stable deep zone hosting only GW. In alkaline lakes in the Nebraska Sand Hills (Nebraska, USA), ER surveys using boat-towed cables allowed for mapping the 3D electrical structure underneath the lake. The tomograms were used to distinguish flow-through lakes, which have decreasing subsurface ER from GW inflow to outflow area, from pure GW discharge lakes, which have uniformly stratified increasing-with-depth ER profiles. Moreover, GW plumes in both discharge and recharge zones were clearly outlined underneath the lake. More than 30 km of ER profiles collected via boat-towed surveys over a fringing coral reef in the Philippines identified areas of high ER within the reef that coincide with resistive zones in the seawater. Analysis of (super 222) Rn of bottom waters and vertical conductivity-temperature-depth measurements show the persistence of fresh GW input into the ocean where low salinity and high (super 222) Rn areas coincided with high ER areas. In Muri Lagoon in Rarotonga Island of the Cook Islands, boat-towed ER surveys similarly showed areas underneath the lagoon that have groundwater that is fresher than seawater. Likewise, there was (super 222) Rn high concentrations throughout the lagoon. Closer to shore, ER surveys using fixed electrodes showed complex 3D mixing processes between seawater and terrestrial-sourced fresh groundwater in beach sediment. Lastly, both boat-towed and fixed surveys across the salt wedge of Werribee Estuary west of Melbourne, Australia, outlined the estuarine salt wedge and its relationship with and effect on fresh and nutrient-laden groundwater discharging to the estuary. The examples discussed illustrate that ERI is a powerful and convenient tool for mapping GW discharge and GW-SW interactions across different scales and diverse environments.
Details
- Title
- Applications of electrical resistivity imaging for characterizing groundwater-surface water interactions from local to regional scales
- Creators
- M. B Cardenas - University of Texas, Austin, Geological Sciences Austin, TX USA United StatesK. M BefusP. B ZamoraJ OngV. A ZlotnikP. L CookD. R TaitD ErlerI. R SantosF. P SiringanAnonymous
- Publication Details
- American Geophysical Union Fall Meeting, Vol.2012
- Conference
- American Geophysical Union 2012 fall meeting (San Francisco, 01/12/2012 - 17/12/2012)
- Publisher
- American Geophysical Union
- Identifiers
- 991012979165002368
- Academic Unit
- Centre for Coastal Biogeochemistry; Faculty of Science and Engineering; Science
- Language
- English
- Resource Type
- Conference proceeding