Identifying subsurface features in the lagan and enler valleys in Northern Ireland using airborne tellus geophysics data

The City of Belfast in the North of Ireland is underlain by the Triassic Sherwood sandstone aquifer. Increasing abstractions from the aquifer over recent years mean that quantitative assessment of the resource is becoming increasingly important. In addition to this physical pressure, the qualitative status of the groundwater body may be affected by landfilling activity in the urban fringe area surrounding Belfast City. New datasets from the Tellus survey give enough information to allow the identification of subsurface features such as individual dykes, dyke swarms, sills, or combinations of such which may be a factor influencing groundwater flow regimes. A GIS of the compiled data was developed, and using total magnetic intensity mapping and variations on this, it was possible to identify and delineate subsurface anomalies. The igneous intrusions in the study area trend almost perpendicularly to the Lagan Valley and the flow of the River Lagan, and preliminary interpretations have determined that they are subvertical. Previous investigations have shown that flow in this region is mainly from the sides of the Valley towards the course of the River Lagan. To this end, topography driven groundwater flow may be enhanced by preferential dyke-parallel flow.