Saltwater In Coastal Aquifers Research Articles

Response Analysis of Multi-Layered Volcanic Aquifers in Jeju Island to the 2011 M9.0 Tohoku-Oki Earthquake

Seismic waves caused by earthquakes can lead to the movement of fresh groundwater and saltwater in coastal aquifers. The groundwater level, temperature, and electrical conductivity in coastal monitoring wells on the volcanic island of Jeju all responded to the 2011 M 9.0 Tohoku-Oki earthquake. As a result of the earthquake, groundwater temperature and electrical conductivity patterns demonstrated freshwater outflow and saltwater inflow through the monitoring wells in multi-layered coastal aquifers. The seismicity also affected the behavior of ocean tides occurring at depth along the multi-layered coastal aquifers. These observations prove that the use of multi-depth systems for monitoring groundwater level, temperature, and electrical conductivity are more effective than single monitoring systems for understanding the exact behavior of multi-layered aquifers as well as efficiently detecting earthquake-induced or anthropogenic impacts on aquifers in coastal, karstic, or volcanic areas.

Numerical modelling and hydrochemical characterisation of a fresh-water lens in the Belgian coastal plain

The distribution of fresh and salt water in coastal aquifers is influenced by many processes. The influence of aquifer heterogeneity and human interference such as land reclamation is illustrated in the Belgian coastal plain where, around A.D. 1200, the reclamation of a tidally influenced environment was completed. The aquifer, which was filled with salt water, was thereafter freshened. The areal distribution of peat, clay, silt and sand influences the general flow and distribution of fresh and salt water along with the drainage pattern and results in the development of fresh-water lenses. The water quality in and around the fresh-water lenses below an inverted tidal channel ridge is surveyed. The hydrochemical evolution of the fresh water lens is reconstructed, pointing to cation exchange, solution of calcite and the oxidation of organic material as the major chemical reactions. The formation and evolution of the fresh water lens is modelled using a two-dimensional density-dependent solute transport model and the sensitivity of drainage and conductivities are studied. Drainage level mainly influences the depth of the fresh-water lens, whereas the time of formation is mainly influenced by conductivity.

An analytic element model for transient axi-symmetric interface flow

The problem of axi-symmetric flow of two immiscible fluids is solved by use of the analytic element method. A sharp interface divides the flow into two domains with different but homogeneous fluids. The sharp interface is realistic for truly immiscible fluids, and is an approximation for miscible fluids such as fresh and salt water in coastal aquifers. A specific discharge potential is introduced which is discontinuous across the interface. The jump in the specific discharge potential depends both on the difference in fluid viscosity and fluid density. The discontinuous specific discharge potential is realized by use of a singularity distribution along the interface. For the case of axi-symmetric flow, the singularity distribution may be approximated by a set of either sink rings or vortex rings. The approach is implemented in a computer program, which is validated by simulating the movement of a spherical inclusion of one fluid in an infinite domain of another fluid, and comparing the results with an exact solution. Finally, the practical use of the program is demonstrated by simulating a saltwater upconing problem underneath a partially penetrating well. The critical pumping rate for which the interface remains stable is determined and compared with both a laboratory experiment and numerical calculations reported in the literature.

GEOCHEMICAL INTERPRETATIONS OF GROUNDWATER FLOW SYSTEMS1

ABSTRACT. Interest in the geochemistry of groundwater is increasing owing to the great number of current projects involving underground liquid waste storage, artificial recharge of potable water, accidental contamination of groundwater bodies, sanitary landfills, and pollution monitoring. Geochemical techniques used to facilitate the understanding of a groundwater system range from extremely simple to those requiring sophisticated theories, equipment, and procedures. An interpretation of the simple trilinear diagram for samples collected from the Yucatan Peninsula of Mexico provided evidence that the fresh‐water body was only a few tens of meters thick and was underlain everywhere by an extensive body of salt water. A geochemical technique that has been used effectively to identify the source of salt water in coastal aquifers is measurement of the carbon‐14 concentrations. Carbon‐14 has been used in a regional carbonate aquifer to determine the velocity of groundwater movement, rates of chemical reactions, and distribution of hydraulic conductivity. The application of principles of irreversible thermodynamics to groundwater systems provides a basis for constructing models which permit prediction, over both time and space, of changes in head distribution and chemical character of the water resulting from imposed stresses on the system. In essence, proper application of irreversible thermodynamics combines the potential theory of Hubbert with principles of reversible chemical thermodynamics, such as solution of carbonate minerals, to describe and explain controlling chemical reactions and processes of groundwater systems.