Three-Dimensional Hydraulic Characterization in a Karst Aquifer Using Cross-Correlation Analysis of Water Level Data

The Santa Fe River Sink-Rise system in north-central Florida is an eogenetic karst flow system that has developed in the Upper Floridan aquifer. Over the span of three years, we collected water level, electrical conductivity, and temperature data at eighteen monitoring locations along the system with an output interval ranging from two to five minutes. The data collection sites included River Sink (where the Santa Fe River sinks underground upon encountering a sinkhole to flow through conduits), five intermediate karst windows, the spring River Rise, seven deep wells (screened from 22-31 m below the land surface), and four shallow wells (screened from 2-10 m). We conducted a cross-correlation analysis on the water level data to determine the speed of pressure propagation throughout the system to facilitate 3D hydraulic characterization. Well and karst window observations allow us to track the propagation of hydraulic head and groundwater flow back and forth between the regional aquifer's rock matrix and the conduit. During steady flow conditions throughout the year, flow is from the regional aquifer into the conduit. During high flow events, flow recharges the regional aquifer from the conduit. In addition, the four shallow wells are adjacent to four deeper wells, allowing us to assess vertical pressure propagation. We compare our hydraulic characterization to existing conduit maps and ongoing analyses of seismic and tilt data collected concurrently to identify unknown, but highly transmissive areas in the aquifer. The cross-correlation analysis of water level data helps us develop a more comprehensive understanding of the system's hydraulic architecture.