Analysis and Discussion of Karst Conduit Waves

Coastal karstic aquifers are affected by the tides, primarily due to pressure variations moving inland via tunnels or conduits. This behavior is clearly demonstrated by recent measurements made in the Woodville Karst Plain near Wakulla Springs. The decay rate, λ, and phase speed, V, of these waves are determined by statistical analysis of observations of water levels (made every 5 minutes) over a period of 144 days at two locations 16.6 km apart: one at the coast close to Spring Creek Springs and one at a borehole that connects to a karst tunnel close to Wakulla Spring. The calculated values are λ = 7.87 x 10^–5 m^–1 and V = 2.0 m s^–1 for diurnal tidal modes and λ = 9.25 x 10^–5 m^–1 and V = 4.4 m s^–1 for semi-diurnal tidal modes. These decay rates are equivalent to e-folding scales of 12.7 and 10.8 km, respectively. The decay rate is smaller and the phase speed is larger than predicted for a Darcian aquifer by factors of roughly 100, illustrating the profound influence that a conduit can have on aquifer dynamics.