Multiscale investigation of dynamic stage-driven groundwater/river water interaction using surface-based and underwater 4D Electrical Resistivity Tomography
Abstract
The interaction between groundwater and surface water (GW-SW) plays a governing role on the physical, chemical, and biological function of many natural hydrologic systems. Because understanding of the interplay between hydrological dynamics and biogeochemical processes within the GW-SW interaction zone is incomplete, significant effort has been devoted to developing new methods of assessing GW-SW.
In this work we present a multiscale study of GW-SW interaction along a dynamic, dam-regulated high-order river corridor (the Columbia River in southern WA, USA) using surface-based and under water time-lapse 3D Electrical Resistivity Difference Imaging. As stage driven pressure gradients drive river water into and out of the adjacent aquifer GW-SW interaction zone, corresponding changes in bulk conductivity are imaged to reveal dominant flow paths and active zones of GW-SW interaction. We begin with a 400 m by 400 m surface array, which confirms and refines the locations of dominant river water intrusion flow-paths through high permeability paleochannels extending up to 300 m into the river-adjacent aquifer during three months of monitoring. Those results prompted a secondary array covering approximately 40 m by 10 m along the river bed, to traverse the paleochannel boundary at its contact with the contemporary river channel. Higher resolution static images provided at this scale reveal the 3D structure of the paleochannel, and, combined with known pore fluid conductivity values, enable inferences about the compositions sedimentary units resolved within the imaging zone. Time lapse imaging using the same array during stage variations delineate active zones of GW-SW interaction within the channel with a resolution of 1-2 meters. Overall, the multiscale imaging effort identified and enabled research to focus on a critical zone of GW-SW interaction, namely the contact of a high permeability paleochannel with the contemporary river channel. It also provided enhanced understanding of GW-SW interaction and the detailed hydrogeologic structure by which it is governed. We advocate for increased use of these tools facilitated through the Worldwide Hydrobiogeochemistry Observation Network for Dynamic River Systems (WHONDRS) at https://whondrs.pnnl.gov/ .- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.H11H1566J
- Keywords:
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- 0496 Water quality;
- BIOGEOSCIENCESDE: 1805 Computational hydrology;
- HYDROLOGYDE: 1895 Instruments and techniques: monitoring;
- HYDROLOGYDE: 1916 Data and information discovery;
- INFORMATICS