Characterization of groundwater and surface water mixing in a semiconfined karst aquifer using time-lapse electrical resistivity tomography

Steven B. Meyerhoff, Reed M. Maxwell, André Revil, Jonathan B. Martin, Marios Karaoulis, Wendy D. Graham

Research output: Contribution to journalArticlepeer-review

26 Scopus citations

Abstract

Groundwater flow in karst includes exchange of water between large fractures, conduits, and the surrounding porous matrix, which impacts both water quality and quantity. Electrical resistivity tomography combined with end-member mixing analysis (EMMA) and numerical flow and transport modeling was used to study mixing of karst conduit and matrix waters to understand spatial and temporal patterns of mixing during high flow and base flow conditions. To our knowledge, this is the first time EMMA and synthetic geophysical simulations have been combined. Here we interpret an 8 week time-lapse electrical resistivity data set to assess groundwater-surface mixing. We simulate flow between the karst conduits and the porous matrix to determine fractions of water recharged to conduits that has mixed with groundwater stored in the pore space of the matrix using a flow and transport model in a synthetic time-lapse resistivity inversion. Comparing the field and synthetic inversions, our results enable us to estimate exchange dynamics, spatial mixing, and flow conditions. Results showed that mixing occurred at a volumetric flux of 56 m3/d with a dispersivity around 1.69 m during the geophysical experiment. For these conditions, it was determined that conduit water composition ranged from 75% groundwater during base flow conditions to less than 50% groundwater in high flow conditions. Though subject to some uncertainties, the time-lapse inversion process provides a means to predict changing hydrologic conditions, leading to mixing of surface water and ground water and thus changes to water quantity and quality, as well as potential for water-rock reactions, in a semiconfined, sink-rise system.

Original languageEnglish (US)
Pages (from-to)2566-2585
Number of pages20
JournalWater Resources Research
Volume50
Issue number3
DOIs
StatePublished - Mar 2014
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Water Science and Technology

Keywords

  • electrical resistivity tomography
  • geophysics
  • groundwater and surface water interactions
  • synthetic modeling

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