Karst Hydrology Initiative

Karst is a complex geological environment where surface water and ground water are highly interconnected and distinctive physiographic and hydrologic features develop as a result of dissolution of soluble bedrock such as limestone. Karst topography occurs over nearly 15 percent—or about 1.2 million km²—of the continental United States, and in about 40 percent of the land area located east of the Mississippi River. Typical karst physiographic features include sinkholes, sinking or losing streams, caves, underground streams, and springs. Related karst hydrologic features include (1) disrupted surface drainage patterns or the absence of surface streams, (2) internal drainage of storm-water runoff by sinkholes and sinking, (3) aquifers characterized by rapid and turbulent subsurface flow through pipe-like or channel-like solutional openings called conduits, and (4) resurgence of subsurface waters at large karst springs.

Because of the presence of conduits, karst aquifers possess a number of unique and problematic hydrogeologic properties compared to typical granular and fractured-rock aquifers. For example, the flow of water through conduits is rapid, turbulent, and highly anisotropic. Flow velocities in well-developed and well-integrated conduits ranging on the order of 100s-1000s of feet per day are not uncommon. Under these conditions, Darcy’s Law, the fundamental equation used to characterize ground-water flow in most aquifers, does not apply. As a consequence, conventional methods of hydrogeologic characterization based on the application of Darcy’s Law—such as hydraulic tests of wells, water-table or potentiometric-surface mapping, and numerical ground-water modeling—often provide erroneous information about karst aquifers.

Better methods of regional characterization of complex karst aquifers and improved karst analytical and data-management tools are among the goals of the Ground-Water Resources Program (GWRP) of the U.S. Geological Survey (USGS). The GWRP encompasses regional studies of ground-water systems, multidisciplinary studies of critical ground-water issues, improved access to ground-water data, and hydrogeologic research and methods development. The program provides unbiased scientific information and many of the analytical and data-management tools that are used by Federal, State, and local management and regulatory agencies to make important decisions about the Nation's ground-water resources.

The Karst Hydrology Initiative (KHI) project is a study effort being conducted by the GWRP to develop improved methods of using Geographic Information System (GIS) technology to collect and synthesize regional karst hydrogeologic data and improve quantitative analysis of shallow conduit-dominated karst aquifers, especially with regard to karst water budgets and hydrologic responses. Work being done as part of the KHI project is also providing information to address three research areas of high priority to the GWRP including: (1) effective characterization of ground-water flow in shallow aquifer systems; (2) better understanding of ground water and surface water interaction; and (3)improved regional hydrogeologic frameworks.

All research and study activities conducted as part of the KHI project are directed by the Kentucky Water Science Center (KWSC) and are focused on the major karst aquifers within the Interior Low Plateaus region of the central United States (fig. 1). The regional study area includes large parts of Kentucky, Alabama, Indiana, and Tennessee underlain by karstic Mississippian, and to a lesser extent, Ordovician limestone rocks. Major environmental or water-resource management issues in the regional study area include: 1) characterization of the availability and quality of ground water; (2) delineation of spring recharge areas or source-water protection areas; (3) determination of water budgets for spring basins and karstic watersheds; (4) availability of hydrologic and water quality data needed to support surface and ground-water regulatory programs and stream-use designations; (5) reduction or elimination of non-point source pollutants in runoff drained by sinkholes or sinking streams; and (6) protection of cave habitats and threatened or endangered cave species, and (7) identification and mitigation of karst geohazards, such as flooding and the formation of cover-collapse sinkholes. The ability to evaluate and manage these resource and geohazards issues is dependent on the availability of suitable karst hydrogeologic data, on the interpretation of these data, and the effectiveness of analytical, resource-management, or decision-support tools that utilize these data.

Additional information about karst hydrogeology, karst in Kentucky, and about the KHI project, can be obtained by contacting Chuck Taylor, KWSC, (phone) 502-493-1931, (email) cjtaylor@usgs.gov.

Slide 1: Aerial photo of collapsed section of roadway near Bowling Green, KY

Figure 1. Major karst areas in the Interior Low Plateaus study region. Karst areas underlain by Mississippian limestones are shaded green, and by Ordovician limestones are shaded tan. Grey shading indicates areas with no karst or only minor karst.