Hydrogeophysics of coastal aquifers - geophysical applications to the assessment of groundwater properties in coastal gravel and karst aquifers
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Airborne, terrestrial and marine geophysics have been employed to examine coastal zone hydrogeology in two very different aquifer types in Ireland. Modelling of regional airborne electromagnetic data informed by ground-based ERT allowed the determination of the aquifer electrical resistivity/conductivity distribution within a locally important coastal sand and gravel aquifer on the east coast. The effective electrical conductivity as a function of porosity for the groundwater body was estimated with salinity and clay mass fraction constraints from supplementary drilling. The hydraulic conductivity depth function was estimated after calibration with a hydraulic conductivity measurement in the field allowing a determination of lateral variations in groundwater hydraulic conductivity across the sand and gravel aquifer, showing potential for upscaling to catchment scale water resource management. On the west coast of Ireland, groundwater movement in two catchments of a regionally important coastal karst aquifer was examined with terrestrial and marine geophysics. This hydrogeophysical examination confirmed the extension of faulting offshore and groundwater egress/saltwater ingress along fault. The examination of subterranean conduit and epikarstic flow paths and intertidal and submarine groundwater discharge provided new evidence for previously predicted terrestrial and submarine pathways confirming the existence of active SGD. Discrete conduit network modelling, informed by the terrestrial geophysics coupled with ancillary hydrogeological observations characterised the hydrogeology of one of the catchments by determining flow pathways and their likely hydraulic mechanisms indicating a complex conduit network of constrictions and bypass channels with multiple inlets and outlets. This work augments our understanding of groundwater movement in the coastal zone for the management of coastal aquifer systems and provides transferrable practices to assist in catchment-scale assessments of coastal aquifers.