Seminário: The impacts of Tertiary dolerite dyke intrusions on the groundwater flow regime and saline intrusion into the Triassic Sherwood Sandstone, Northern Ireland
O seminário do Departamento de Geofísica será apresentado pelo Dr. Ulrich S. Ofterdinger (Queen's University Belfast - School of Natural and Built Environment).
The impacts of Tertiary dolerite dyke intrusions on the groundwater flow regime and saline intrusion into the Triassic Sherwood Sandstone, Northern Ireland
The presence of subsurface discontinuities such as low-permeability dyke swarms pose significant challenges for managing water resources in such heterogeneous aquifer systems. The presented study investigated the Triassic Sherwood Sandstone formation in Northern Ireland, a key aquifer unit in Northern Ireland, to evaluate the impact of sub-vertical Tertiary dolerite dyke systems on the regional groundwater flow regime as well as specifically on the pattern of saline intrusion into the aquifer. The interpretation of ground and aerial magnetic surveys produced a deterministic solution to dyke locations. By measuring relative permeabilities of both the dykes and the sedimentary host rock, equivalent directional permeabilities, that determine anisotropy calculated as a function of dyke density, were obtained. This provides parameters for larger scale equivalent blocks, which can be directly imported to numerical groundwater flow models. In an extension of the regional modelling study, multiple-point statistics (MPS) techniques were tested to determine the ability to delineate heterogeneity from aerial magnetics data in the regional sandstone aquifer intruded by low permeability volcanic dykes. An integrated multi-physics approach was applied to quantify the effect of the dolerite dykes on flow and saltwater intrusion in the coastal sandstone aquifer. The presence of the dykes results in alterations of groundwater flow and patterns of saltwater intrusion and the numerical simulations confirm their role as relative barriers. Preferential flowpaths occur parallel to observed dyke orientations. Freshwater inflows from upland recharge areas concentrate on the land-facing side of the dykes and saltwater penetration is higher on their sea-facing side. This has major implications for managing groundwater resources in highly heterogeneous dyke-intruded aquifer systems.