| Solutions to fundamental groundwater flow and transport equations are incorporated into a geographic information system (GIS) as map algebra functions which operate on spatially distributed hydrogeologic data. These functions include a discrete form of Darcy's law to generate flow field maps and to assure conservation of mass, two particle tracking procedures to calculate advection along streamlines, and two gaussian dispersion functions to determine the distribution of a solute in the porous medium from both instantaneous and continuous sources. The modular design of the functions allows for calculation of advection and dispersion of any source which can be modeled as a collection of one or more point sources. The functions are applied in the two-dimensional block-centered finite difference raster GIS environment, using maps of aquifer saturated thickness, porosity, isotropic transmissivity, and head elevation. Additional values are supplied for location and strength of the sources, first-order decay coefficient of the solute, longitudinal and transverse dispersivities, retardation in the porous medium, and time horizon. From these data are calculated a flow field, advection path, and map of concentration of the dispersed constituent. Complex simulations involving transient head fields and multiple transient sources are performed by superimposing results of single-source solutions. All of these calculations take place within the native GIS environment. |
