PHYSICAL MODELING OF THE WAKULLA-SPRING CREEK KARST CONDUIT SYSTEM

The Wakulla-Spring Creek conduit system, located within the Woodville Karst Plain, is a unique laboratory for evaluating a karst system in a coastal environment. The karst plain extends from the vicinity of Tallahassee, Florida to the Gulf of Mexico. An extensive underwater conduit system extends for the northern boundary of the karst plain to the Gulf of Mexico. The conduit system is the most extensively explored set of underwater passageways in the United States. Over 55 km of conduits have been mapped by cave divers. Dye tracing has extended mapping the connectivity of conduits at locations that are currently inaccessible to divers. Sinuosity of the conduit systems is approximately 1.5. Two first-magnitude springs (Wakulla and Spring Creek Springs) discharge within the karst plain and account for approximately 30-40 percent of the water budget within the region. Both Wakulla Springs (located 13 km inland from the Gulf) and Spring Creeks Springs (located on the Gulf) exhibit flow variations associated with tidal cycles. Flow in the conduit system can also bifurcate depending input from surface flow. During low flow conditions water backs up at Spring Creek Springs and flow is rerouted to Wakulla Springs. Conduit diameter ranges from 5-30 meters with an average diameter of 10 meters. The geometry of the conduits has been mapped using sonar transducer arrays and videography. Several modeling studies have been applied to this system, but the conduit component of these models generally assumed a simple linear system with arbitrary surface roughness. The calculated flow in the conduit component of the models is normally calculated to be significantly higher than the 0.8-2.4 km/day flow measured by dye tracing.

To provide a more realistic means of evaluating the effect of conduit geometry on flow, a bench top model has been constructed to evaluate hydrodynamic parameters including: sinuosity, bifurcation of conduit channels, variation in conduit diameter and the variation of conduit shape and roughness. The discharge terminus of the model system is designed to include the ability to produced variation in head pressure to reproduce fluctuation of tidal level (and water density) at spring discharge points in the Gulf of Mexico. Scaling of the model in terms of conduit diameter is approximately 1:1500.