Data-Driven Modeling of a Karst Aquifer System

Karst aquifers are dynamic systems in which the dissolution of soluble rock creates primary flow paths, including fractures and conduits, that serve as enhanced recharge points, secondary porosity, and discharge outlets. Consequently, the hydrological behavior of these systems becomes highly localized and challenging to describe, given that the locations, geometry, and distribution of fractures and conduits are typically poorly constrained. However, geophysics, including geodetic and seismological techniques, offers a unique opportunity to acquire a more comprehensive understanding of the complexities inherent in these systems, given that recharge-discharge processes likely induce measurable ground deformation. Therefore, our motivation led us to deploy a network of co-located tiltmeters, seismometers, and hydrological sensors near a well-constrained karst conduit network within the Santa Fe River Sink-Rise system (Sink-Rise system) in northern Florida, US.

This dissertation explores the dynamics of fluid exchange between karst conduits and the porous rock matrix, including the hydrologically induced deformational response. This investigation employs a fully coupled poroelastic finite element modeling approach, utilizing constraints from hydrological and geophysical observations acquired at the Sink-Rise system. Chapter 1 uses synthetic data to investigate endmember behavior between Paleozoic and Cenozoic aged aquifers, including confined and unconfined scenarios. Additionally, Chapter 1 addresses the impact of conduit size and depth. Furthermore, Chapter 1 integrates Sink-Rise system data into the model input, and the model parameters are manually adjusted so the solution aligns with the water level and tilt observations. Chapter 2 conducts a signal characterization study to identify seismic noise sources and utilizes a pseudo-3D ambient seismic noise tomography approach to visualize and identify the hydrogeological units encompassing the Sink-Rise system. Finally, Chapter 3 extends the poroelastic model by incorporating a layered model geometry, which is interpreted and parameterized based on seismic tomography findings. Additionally, Chapter 3 optimizes the hydrological parameters of the layered geometry, considers karstic lake loading and poroelastic exchange, and a 3D conduit geometry derived from the Sink-Rise system.

--------------------------------------------------------------------The findings suggest that the Sink-Rise system exhibits characteristics of a partially confined aquifer, and the poroelastic response is contingent upon the interconnection between the model's geometry and parameterization. Also, this study illustrates the capability of geodetic techniques to detect, locate, and describe the geometry of pressurized karst voids. Furthermore, this study demonstrates the broader applicability of geophysics in addressing hydrogeological considerations.