Development of Neutrally Buoyant Sensors for Tracing Conduits in Karst Aquifers, 20-R9707

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Principal Investigators
Ronald T. Green
Ben A. Abbott
Joshua D. Kenney
Ronald N. McGinnis
Gregory C. Willden

Inclusive Dates:  04/02/07 – 10/01/09

Background - Effective management of groundwater resources relies heavily on realistic and accurate groundwater flow models. SwRI recently developed MODFLOW-DCM, a groundwater flow model with the ability to simulate both conduit flow and matrix flow in a karst aquifer. Applications of MODFLOW-DCM have highlighted the critical need to better locate and characterize karst conduits. Conventional methods currently used to characterize karst conduits include tracer tests and mapping by cave divers. Currently, there is no other technology that can provide this type of detailed information. A great need exists, therefore, to develop new tools to characterize conduits to support karst aquifer flow modeling tools.

Approach - The approach of this project is to develop and demonstrate an inexpensive, neutrally buoyant, sensor node technology for measuring velocity, pathway traveled, and conduit size based on sensors that flow with water conveyed via karst conduits. The sensors would be emplaced in conduits up-gradient from spring orifices. Access to the conduits can be gained either at sinkholes that connect to conduits or wells that intersect conduits.

Accomplishments - Prototype field sensors were developed and field tested in karst conduits (i.e., wet caves). The prototype sensors contained six pairs of ultra-sound sensors for mapping conduit morphology and velocity of groundwater flow and a magnetometer for providing absolute direction. Algorithms were developed to resolve collected data into conduit paths and geometries and velocity of flow. The prototype sensor successfully mapped a segment of Honey Creek Cave near San Antonio, Texas.

Rendering of the cave passage using sonar and magnetometer data collected during the Honey Creek Cave prototype sensor deployment

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