Contribution of geophysical methods at catchment-scale to validate and refine hydrogeological conceptual models of Irish complex hard rock aquifers
Abstract
Approximately 60% of the island of Ireland is underlain by complex aquifers, comprising highly heterogeneous hard rock overlain by discontinuous unconsolidated sediments of glacial or alluvial origin. Such aquifers are rarely adequate for public or industrial exploitation but remain of importance for both local water supply and contribution to surface waters. Their heterogeneous and discontinuous nature makes study through traditional hydrogeological methods (i.e. borehole and surface water monitoring) particularly arduous because of the difficulty of extrapolating local data to the aquifer or catchment scale. Generic conceptual models of such systems have been developed for many decades in varied geological and hydrological hard rock environments globally. Such models, however, need to be adapted and refined for each case study. Because of the multiple-scales at which geophysical methods can be applied, their application is particularly relevant to fill the gap between the local hydrogeological data and the aquifer complexity at the catchment-scale. In an Irish aquifer composed of weathered/fractured micaschists, high-resolution resistivity tomography, magnetic resonance sounding and electromagnetic mapping have been applied to characterize structural heterogeneity as well as to validate and refine the original generic conceptual model. In particular, these investigations confirm the layering of the aquifer due to weathering and erosion processes previously suggested by multiple-depth pump tests and water table monitoring as well as borehole geophysics and hydrochemical sampling. Resistivity and electromagnetic results reveal the importance of lateral variations in the weathering profile (bed thicknesses/ bevels) and the existence of both deep fractured bands, following the regional geological trend, and discontinuous thick glacial fill. Furthermore, magnetic resonance soundings attest the relative high permeability and porosity of these fractured zones, which is also confirmed by the re-interpretation of hydrochemical data. This refined view of the groundwater conceptual model of the catchment provides a consistent three-dimensional basis for the numerical modeling of the aquifer system.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.H13D0987C
- Keywords:
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- 0925 EXPLORATION GEOPHYSICS / Magnetic and electrical methods;
- 1804 HYDROLOGY / Catchment;
- 1835 HYDROLOGY / Hydrogeophysics;
- 1847 HYDROLOGY / Modeling