A GIS-BASED METHODOLOGY FOR CHARACTERIZING KARST HYDROLOGIC SYSTEMS

Hydrologic processes in karst systems are difficult to evaluate using simple analytical models because porous media flow, fracture flow, conduit flow, and open channel flow may occur simultaneously. Flux between surface-water and ground-water systems may also vary as a river reach crosses units with differing lithologic characteristics, and springs often form where the contact between high and low permeability units outcrop at the surface. Because of these complexities it has been common practice to integrate the principles of surface-water hydrology and ground-water hydrology into studies of karst hydrology.

When evaluating complex earth systems it is often necessary to define control volumes and apply analytical models to understand the processes occurring within the volumes. For example, most hydrologic studies begin with the definition of a study area for which a water budget can be computed. This seemingly simple step might be more difficult in a karst system because of interactions between sub-components of the hydrologic system. Defining the basic watershed or drainage basin is a typical starting point for surface-water studies. Similarly, no-flow boundaries based on geologic constraints or ground-water divides formed from equipotential maps are a typical starting point for ground-water studies. These two boundaries may not coincide in karst sytems, but can be delineated very easily using a Geographic Information System (GIS), raster data representing the topography, and hydrogeologic data. This may be the first step in karst system analysis followed by analysis of the spatial relationships between these boundaries and related topographic, geologic, and hydrologic features. The purpose of this study is to develop a logical sequence of steps for karst system analysis and implement these steps in a GIS. GIS-based analytical models can be implemented as part of this sequence to improve understanding of the karst system. This GIS implementation should increase the efficiency of hydrologic evaluations and improve understanding of interactions in karst systems.