Accurate conceptual models of groundwater systems are essential for correct interpretation of monitoring data in catchment studies. In surface-water dominated hard rock regions, modern ground and surface water monitoring programmes often have very high resolution chemical, meteorological and hydrological observations but lack an equivalent emphasis on the subsurface environment, the properties of which exert a strong control on flow pathways and interactions with surface waters. The reasons for this disparity are the complexity of the system and the difficulty in accurately characterising the subsurface, except locally at outcrops or in boreholes. This is particularly the case in maritime north-western Europe, where a legacy of glacial activity, combined with large areas underlain by heterogeneous igneous and metamorphic bedrock, make the structure and weathering of bedrock difficult to map or model. Traditional approaches which seek to extrapolate information from borehole to field-scale are of limited application in these environments due to the high degree of spatial heterogeneity. Here we apply an integrative and multi-scale approach, optimising and combining standard geophysical techniques to generate a three-dimensional geological conceptual model of the subsurface in a catchment in NE Ireland. Available airborne LiDAR, electromagnetic and magnetic data sets were analysed for the region. At field-scale surface geophysical methods, including electrical resistivity tomography, seismic refraction, ground penetrating radar and magnetic surveys, were used and combined with field mapping of outcrops and borehole testing. The study demonstrates how combined interpretation of multiple methods at a range of scales produces robust three-dimensional conceptual models and a stronger basis for interpreting groundwater and surface water monitoring data.
Airborne conductivity and magnetic data are provided under licence from the TELLUS Project, which was funded by DETI and by the Building Sustainable Prosperity scheme of the Rural Development Programme (Department of Agriculture and Rural Development of Northern Ireland). The Digital Elevation Model was grant funded by NERC ARSF GB12/07. We thank Carsten Rücker and Thomas Günther for permission and assistance in the use of their BERT code and Vaughan Purnell for assistance in optimising BERT for the QUB HPC facility. The contributions of MSc students in Environmental Engineering at QUB to data collection in the catchment are acknowledged. The GPR was borrowed from the Geological Survey of Ireland equipment pool. We also acknowledge the GNSI/NIEA and Mountstewart Estate for access to the estate and borehole infrastructure. This work is based on research grant-aided by the Irish Department of Communications, Energy and Natural Resources under the National Geoscience Programme 2007–2013. We acknowledge the contribution of two anonymous reviewers and Robert Wyns in improving the final manuscript.
- catchment hydrology
- aquifer characterisation
- hard rock
- multi-scale geophysical characterisation
- conceptual models