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	By linking the SwRI DCM module to the industry-standard MODFLOW model, SwRI scientists are able to simulate the rapid recharge of runoff into karst aquifers through sinkholes and caves such as Cripple Crawfish Cave on Onion Creek near Buda, Texas. (Photograph reprinted courtesy of David A. Johns, City of Austin)

Karst aquifers, which exhibit fast groundwater flow through dissolution conduits and pathways, account for 25% of the groundwater resources of the world and the U.S. Because the hydrogeologic characteristics of karst aquifers differ significantly from porous media aquifers, they require specialized characterization and management techniques.

Southwest Research Institute (SwRI) established a karst hydrology program to address the environmental and water resources management challenges associated with karst aquifers. To support the karst hydrology program, SwRI has developed:

• Sophisticated parameter estimation methods for karst media

• Surface-based geophysics and geologic structure models

• Specialized water resource management techniques

	SwRI scientists developed specialized DCM software to improve groundwater management models for karst aquifers. This calculated hydraulic head contour map is in a karst zone in the Barton Springs segment of the Edwards Aquifer in south-central Texas.

MODFLOW-DCM Groundwater Flow Model

SwRI created a new software tool, MODFLOW-DCM, that works with the industry standard groundwater flow model, MODFLOW, to simulate turbulent conduit and diffuse matrix flows in karst aquifers. Using a client's existing MODFLOW management model, the SwRI software tool captures:

• Confined conduit or open channel flow in karst solution features

• Matrix-conduit hydraulic interactions

• Either sparse discrete conduit networks or a pervasive conduit continuum

The SwRI karst program is supported by:

• Electrical, electromagnetic, and magnetic geophysical survey methods

• Geological structural controls on groundwater flow investigations

• Parameter estimation and geostatistical data analysis

• Bayesian Inversion optimization techniques

• Dual- and multi-continuum transport modeling

Using innovative nonlinear geostatistical methods, SwRI scientists reinterpreted aquifer test results and hydraulic head data to estimate the spatial distribution of hydraulic conductivity for the Edwards Aquifer in south-central Texas. The five major springs (illustrated in the map) are generally located near zones of high hydraulic conductivity.

For more information about the karst hydrology program at SwRI or solutions for environmental and water resources management challenges or how you can contract with SwRI, please contact Ronald T. Green, Ph.D., at rgreen@swri.org or (210) 522-5305, or Scott Painter, Ph.D., at spainter@swri.org or (210) 522-3348.
 

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Southwest Research Institute^® (SwRI^®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 12 technical divisions.

September 16, 2009