HYDRA model: Simulation of salt intrusion in coastal aquifers using Visual Basic and GIS

A GIS-linked tool, which simulates salt intrusion in coastal aquifers, is presented. The tool was created by means of Microsoft Visual Basic ver. 6 programming language, and was linked to the GIS program MapInfo ver. 7. The Visual Basic code applies the Galerkin finite element method using triangular elements. The code is divided into two distinct parts: one for the simulation of the phenomenon in steady-state and one in transient state. For steady-state simulation the system of non-linear equations is solved using a GausseSeidel iterative solver. When simulating a transient phenomenon, a modified NewtoneRaphson iterative solver is used. All spatial data, such as aquifer and boundary geometry or well location, are introduced and managed in the GIS environment. Temporal data, such as pumping or recharge time series, are introduced in a relational database or spreadsheet, such as Microsoft Access or Microsoft Excel. The result is a user-friendly computer tool, which incorporates the advantages provided by GIS and relational databases in the simulation of such complex physical systems.