A GIS APPROACH TO INTEGRATION OF HYDROGEOLOGIC-FRAMEWORK COMPONENTS OF THE MESILLA BASIN AQUIFER SYSTEM, SOUTHWESTERN NEW MEXICO BORDER REGION
GIS coverages were created using ESRI ArcInfo® and ERDAS Imagine® software. Surface geology maps for the region where digitized using ArcInfo 8.0 on a UNIX platform and cartographically and spatially corrected using satellite and aerial imagery on a Dell® Workstation running Windows 2000 Professional and ArcGIS 8. Basemap data was acquired in digital form from the USGS. Selected borehole geophysical logs, with known geographic coordinates, where scanned into digital form using Adobe PhotoShop 6® and digitized using Adobe Illustrator 9®. The digitized logs were used to create geologic cross-sections for the basin.
The classification of mapping units for the surface and sub-surface geology was modified within the GIS to create a hydrogeologic framework model for the basin. The basin-fill hydrogeologic framework is defined on the basis of (1) composition of lithofacies assemblages (LFAs), which are organized into hydrostratigraphic units (HSUs), and (2) the nature of basin-boundary and intra-basin structural controls. Major aquifers are formed by coarser-grained LFAs associated with the ancestral Rio Grande fluvial systems. These poorly consolidated units are informal subdivisions of the Plio-Pleistocene upper Santa Fe Group and overlying valley- and basin fill. The HSUs are assigned a numerical value and this information is added to the GIS. The HSUs are matched with geologic mapping units, with some units being merged based on the HSU value, to create surface and sub-subsurface hydrogeologic maps.