INFERRING HYDROLOGIC ARCHITECTURE FROM THE PROPAGATION OF WATER LEVEL SIGNALS AT A KARST SINK-RISE FLOW SYSTEM

The Santa Fe River in north-central Florida sinks underground at River Sink in O’Leno State Park, flows through a complex conduit system while periodically reemerging at several intermediate karst windows, and finally reemerges at River Rise in River Rise Preserve State Park. Large conduits have been mapped by cave divers that are up to ~20 m in diameter at depths of ~30 m below the surface. There are additional conduits that have not been mapped and other likely unknown conduits. Our objective was to analyze how water level signals propagate to infer the hydrologic architecture throughout the karst system. Water level data were collected every 2–4 minutes from May 2018 to May 2021 at seven karst windows and 11 wells that are screened to depths from 2.4–9.8 m and 22.3–30.5 m below the land surface for the shallow and deep wells, respectively. We identified 104 distinctive water level features (peaks and troughs), each of which occurred at most or all karst windows and wells. We also identified the times it takes the features to propagate between different monitoring locations: propagation times from River Sink to River Rise (just under a straight-line distance of 5 km) average ~3 hours, from River Sink to intermediate karst windows are even shorter, and from River Sink to the wells with distances of ~0.05–1 km from the known conduits range from an average of ~6–~29 hours. The rapid propagation times between River Sink and River Rise suggest that unmapped portions likely largely consist of water-filled conduits where pressure signals propagate up to ~1500 m/s, especially with travel times of electrical conductivity and temperature signals that may take several days to traverse the flow system. Hawg Sink seems to be less connected to the other surface water monitoring locations and more impacted by additional flow paths, based on unique attributes of the electrical conductivity and temperature records. We plot propagation times to the wells as a function of distance between the wells and the conduits to identify relatively low and high permeability portions of the aquifer, where the relatively high permeability portions may indicate the existence of unknown conduits. Our results suggest that the analysis of water level signal propagation has potential to predict key features of the hydrologic architecture of karst aquifers.