ESTABLISHING THE EXCHANGE OF WATER BETWEEN CONDUITS AND MATRIX IN THE SANTA FE RIVER SINK/RISE SYSTEM USING WATER-LEVEL DATA

The exchange of water between conduits and matrix is an important aspect of karst development as well as the maintenance of groundwater quality in karst aquifers. The Santa Fe River Sink/Rise system provides a relatively controlled study area, where the inputs and outputs of the conduit system can be readily determined. The Santa Fe River originates in North Central Florida and flows south for approximately 40 km until it reaches the Cody Scarp. At the edge of the escarpment, the river sinks and flows underground for approximately 5 km through conduits before re-emerging at a first magnitude spring called the River Rise. Water levels, temperature, and specific conductivity have been collected from twelve karst windows between the River Sink and Rise for the past two years. These data have been used to estimate the water velocity through the subsurface conduits between the Sink and the Rise and the net volume of water lost or gained from the conduits during high and low flow events. Six monitoring wells were recently installed into matrix rocks at various distances from mapped conduits. Combined data from the wells and the conduits allow an analysis of the gradient between the conduit and matrix. The direction of gradients between conduit/matrix corresponds to net gains/losses from the conduit system. Analyses indicate that the gradient between conduit and matrix varies proportionally with the net change in discharge between the Sink and Rise when the conduit system is gaining water, but is more complex when the conduit system is losing water.