A KARST HYDROLOGIC OBSERVATORY IN THE WOODVILLE KARST PLAIN OF NORTH FLORIDA

The Woodville Karst Plain (WKP) has recently become one of the best documented and instrumented karst basins in the world. More than 40 km of underwater conduits that converge on two first-magnitude (average discharges exceeding 15 m3/s) springs (Wakulla and Spring Creek) have been surveyed and mapped, with cave-radio/GPS by underwater explorers in the Woodville Karst Plain Project (WKPP). Building on these assets, a collaborative research effort between the Florida Geological Survey, Florida State University, the Hydrogeology Consortium, Hazlett-Kincaid, Inc., Cambrian Groundwater, and the WKPP was begun in 2001 to characterize flow patterns in the WKP, and support basin-scale hydrologic modeling and future scientific studies of karst in Florida.

Six oceanographic meters have been installed at key conduit junctions as far as 1,500m upstream of Wakulla Spring and at depths of approximately 80m, plus a seventh in the main vent. The meters record velocity, temperature, and conductivity at 15 minute intervals and transmit the data to the surface via cables deployed down a set of three wells drilled into the cave system. Sampling tubes have been installed at each of the meters, which are now regularly sampled by the Northwest Florida Water Management District. In addition, numerous conduit junctions in Leon Sinks cave system have been instrumented with sampling tubes that lead to the land surface via sinkholes. The tubes provide year-round real-time access to the conduit flow system. Funding is being sought for additional meters to complement those already installed.

Numerous quantitative tracing experiments have been conducted in the basin using the tubes to access the flow paths. Tracer breakthrough curves have established minimum velocities of between 800 and 6000 m/day over pathways up to 16km long, which equate to travel-times (ages) of about 10 days, refuting earlier age estimates based purely on samples collected from springs and sinkholes. See www.hazlett-kincaid.com/FGS for further details. The water samples indicate three sources of the water discharging at Wakulla spring, one or more disappearing streams, and two separate sources of groundwater that differ significantly in depth. Further, the nitrates that are polluting Wakulla Spring originate in only two of the six sampled conduits.