FRESHWATER-SALTWATER FLOW DYNAMICS IN COASTAL MULTIPLE-AQUIFER SYSTEMS (GROUNDWATER)

Saltwater intrusion in multi-aquifer systems is a classical result of excessive groundwater development. Efficient planning and proper management of coastal aquifers requires a quantitative understanding of the pattern of movement, mixing between freshwater and saltwater, and the elements that influence these processes. The major problem is to predict the motion of the saltwater body in the aquifer in response to variations in the components of the freshwater mass balance. Building a management tool that is accurate and efficient demands a thorough understanding of the dynamics of the coupled freshwater flow and saltwater flow. The case of multiple-aquifer system is further complicated when a leaky aquitard is present.; In regional scale management problems the vertical flow and the dispersion in the mixing zone between the freshwater and saltwater are negligible. The interest is in reproducing the general shape and position of the interface due to stresses imposed on the system.; A quasi three-dimensional, finite element model (GW-Sharp) that is capable of simulating the coupled freshwater and saltwater flow separated by a sharp accounts for the physical complexity of field problems such as homogeneous or heterogenous, isotropic or anisotropic aquifer properties, leaky or impermeable confining layers, steady state conditions or transient conditions, toe or lens shape of interface, and confined or unconfined aquifers.; GW-Sharp was tested against the well known analytical saltwater intrusion solutions for a coastal confined aquifer, a coastal unconfined aquifer, and a coastal two-aquifer system. The results of the numerical model matched perfectly the analytical solutions for all three cases. The Model produced reliable and efficient results when used to simulate the advancement of the interface due to reduction in the seaward flow, and advancement of the interface due to coastal pumping well.; GW-Sharp was utilized to simulated a number of multiple-aquifer systems. These simulations demonstrated the capability of this model to represent the freshwater-saltwater dynamics in multiple-aquifer systems and produce the effect on the interface position due to modifications in the flow regime of the system.