Catchment-scale heterogeneity of flow and storage properties in a weathered/fractured hard rock aquifer from resistivity and magnetic resonance surveys: implications for groundwater flow paths and the distribution of residence times

J.-C. Comte, U. Ofterdinger, A. Legchenko, J. Caulfield, R. Cassidy, J. A. Mezquita Gonzalez

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Abstract

Groundwater pathways and residence times are controlled by aquifer flow and storage properties, which, in weathered/fractured hard rock aquifers, are characterized by high spatial heterogeneity. Building on earlier work in a metamorphic aquifer in NW Ireland, new clay mineralogy and analyses of geophysical data provided high spatial resolution constraints on the variations in aquifer properties. Groundwater storage values derived from magnetic resonance sounding and electrical resistivity tomography were found to largely vary laterally and with depth, by orders of magnitude. The subsequent implementation of hillslope, two-dimensional numerical groundwater models showed that incorporating heterogeneity from geophysical data in model parametrization led to the best fit to observations compared with a reference model based on borehole data alone. Model simulations further revealed that (1) strong spatial heterogeneity produces deeper, longer groundwater flow paths and higher age mixing, in agreement with the mixed sub-modern/modern ages (mostly <50 years) provided by independent tritium data, and (2) areas with extensive weathering/fracturing are correlated with seepage zones of older groundwater resulting from changes in the flow directions and are likely to act as drainage structures for younger groundwater on a catchment or regional scale. Implications for groundwater resilience to climate extremes and surface pollution are discussed together with recommendations for further research.
Original languageEnglish
Pages (from-to)35-58
Number of pages24
JournalGeological Society Special Publications
Volume479
DOIs
Publication statusPublished - 10 May 2018

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Groundwater flow
hard rock
Magnetic resonance
Aquifers
Catchments
groundwater flow
Groundwater
electrical resistivity
residence time
Rocks
aquifer
catchment
groundwater
Mineralogy
tritium
Seepage
Tritium
Weathering
Boreholes
hillslope

Cite this

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title = "Catchment-scale heterogeneity of flow and storage properties in a weathered/fractured hard rock aquifer from resistivity and magnetic resonance surveys: implications for groundwater flow paths and the distribution of residence times",
abstract = "Groundwater pathways and residence times are controlled by aquifer flow and storage properties, which, in weathered/fractured hard rock aquifers, are characterized by high spatial heterogeneity. Building on earlier work in a metamorphic aquifer in NW Ireland, new clay mineralogy and analyses of geophysical data provided high spatial resolution constraints on the variations in aquifer properties. Groundwater storage values derived from magnetic resonance sounding and electrical resistivity tomography were found to largely vary laterally and with depth, by orders of magnitude. The subsequent implementation of hillslope, two-dimensional numerical groundwater models showed that incorporating heterogeneity from geophysical data in model parametrization led to the best fit to observations compared with a reference model based on borehole data alone. Model simulations further revealed that (1) strong spatial heterogeneity produces deeper, longer groundwater flow paths and higher age mixing, in agreement with the mixed sub-modern/modern ages (mostly <50 years) provided by independent tritium data, and (2) areas with extensive weathering/fracturing are correlated with seepage zones of older groundwater resulting from changes in the flow directions and are likely to act as drainage structures for younger groundwater on a catchment or regional scale. Implications for groundwater resilience to climate extremes and surface pollution are discussed together with recommendations for further research.",
author = "J.-C. Comte and U. Ofterdinger and A. Legchenko and J. Caulfield and R. Cassidy and {Mezquita Gonzalez}, {J. A.}",
note = "Special Publication: Fractured Bedrock Environments: Managing Catchment and Subsurface Resources Funding Geological Survey of Ireland Jean-Christophe Comte Department of Communications, Energy and Natural Resources Ulrich Ofterdinger Agence Nationale de la Recherche Anatoly Legchenko",
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T2 - implications for groundwater flow paths and the distribution of residence times

AU - Comte, J.-C.

AU - Ofterdinger, U.

AU - Legchenko, A.

AU - Caulfield, J.

AU - Cassidy, R.

AU - Mezquita Gonzalez, J. A.

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N2 - Groundwater pathways and residence times are controlled by aquifer flow and storage properties, which, in weathered/fractured hard rock aquifers, are characterized by high spatial heterogeneity. Building on earlier work in a metamorphic aquifer in NW Ireland, new clay mineralogy and analyses of geophysical data provided high spatial resolution constraints on the variations in aquifer properties. Groundwater storage values derived from magnetic resonance sounding and electrical resistivity tomography were found to largely vary laterally and with depth, by orders of magnitude. The subsequent implementation of hillslope, two-dimensional numerical groundwater models showed that incorporating heterogeneity from geophysical data in model parametrization led to the best fit to observations compared with a reference model based on borehole data alone. Model simulations further revealed that (1) strong spatial heterogeneity produces deeper, longer groundwater flow paths and higher age mixing, in agreement with the mixed sub-modern/modern ages (mostly <50 years) provided by independent tritium data, and (2) areas with extensive weathering/fracturing are correlated with seepage zones of older groundwater resulting from changes in the flow directions and are likely to act as drainage structures for younger groundwater on a catchment or regional scale. Implications for groundwater resilience to climate extremes and surface pollution are discussed together with recommendations for further research.

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