Effect of volcanic dykes on coastal groundwater flow and saltwater intrusion: A field‐scale multiphysics approach and parameter evaluation

Abstract

Volcanic dykes are common discrete heterogeneities in aquifers; however, there is a lack of field examples of, and methodologies for, comprehensive in situ characterization of their properties with respect to groundwater flow and solute transport. We have applied an integrated multiphysics approach to quantify the effect of dolerite dykes on saltwater intrusion in a coastal sandstone aquifer. The approach involved ground geophysical imaging (passive magnetics and electrical resistivity tomography), well hydraulic testing, and tidal propagation analysis, which provided constraints on the geometry of the dyke network, the subsurface saltwater distribution, and the sandstone hydrodynamic properties and connectivity. A three‐dimensional variable‐density groundwater model coupled with a resistivity model was further calibrated using groundwater and geophysical observations. A good agreement of model simulations with tide‐induced head fluctuations, geophysically derived pore water salinities, and measured apparent resistivities was obtained when dykes' hydraulic conductivity, storativity, and effective porosity are respectively about 3, 1, and 1 orders of magnitude lower than the host aquifer. The presence of the dykes results in barrier‐like alterations of groundwater flow and saltwater intrusion. Preferential flow paths 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 dyke‐intruded aquifers, including in coastal and island regions and provides wider insights on preferential pathways of groundwater flow and transport in highly heterogeneous aquifer systems.

Groundwater in catchments headed by temperate glaciers: A review

“…Specific geological features can (relatively) protect an aquifer from seawater intrusion, e.g. volcanic dykes (Comte et al, 2017), or thick clay layers , or both (Vittecoq et al, 2015).…”

Well productivity in the Ponta Grossa dike Swarm, Brazil: An integrated study with magnetic data inversion and clustering analysis of model solutions

“…In permeable sedimentary rocks, a group of dikes tends to compartmentalize the flow in the 2 granular aquifer (da Rosa Filho et al, 2003), often providing preferential flow paths parallel to the dikes (Babiker and Gudmundsson, 2004). A set of dikes may obstruct the regional groundwater flow (Comte et al, 2017) or provide zones of enhanced permeability with preferential groundwater flow along their strike (Senger et al, 2015). For example, Dickson et al (2014) developed a groundwater flow model for a granular (Triassic sandstone) aquifer to explore the impact of intrusive dike swarms in the aquifer dynamics by combining field measurements of host rock and dike properties with airborne and ground magnetic data.…”

Experimental and Numerical Analysis on Hydraulic Characteristics of Coastal Aquifers with Seawall

“…where p has influence on the neighbouring cell (meaning that repeated calculations are required), and the superscript m represents the number of iterations at each time step. The calculation is repeated until the designated convergence condition is satisfied, and the updated pressure and flow velocity at each cell based on the repetitions are then expressed as the following Equations (17) and (18), respectively.…”