Date of Graduation
5-2026
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Geosciences (PhD)
Degree Level
Graduate
Department
Geosciences
Advisor/Mentor
Befus, Kevin
Committee Member
Shaw, John
Second Committee Member
Ruhl-Whittle, Laura
Third Committee Member
Duncan, Leslie
Fourth Committee Member
Covington, Matthew
Keywords
Coastal; Groundwater; Hydrogeology; Modeling; MODFLOW
Abstract
In this dissertation, I examined groundwater–surface water interactions under changing environmental conditions and assessed the role of geophysical data in improving groundwater model forecast variance. Three separate studies form this dissertation. Two examined the impact of environmental changes on coastal groundwater. The other examined the relationship between groundwater model forecast variance reduction and the use of geophysical data to increase model hydrogeologic refinement—increasing the resolution of the representation of hydrogeologic structure—through discretization and parameterization. The first study focused on the Herring River watershed in Massachusetts, where tidal restoration—restoring tidal conditions to a hydrologic system where engineered controls currently reduce tidal propagation upstream—and sea-level rise are changing the hydrologic dynamics by increasing surface water levels in and around the watershed. This research examined how increases in surface water due to tidal restoration and sea level rise will influence groundwater discharge patterns and water table depth using steady-state groundwater flow models. The model results revealed that sea-level rise decreases overall groundwater discharge due to reduced recharge areas but increases discharge to interior waterways through a seaward shift in the groundwater divide. Tidal restoration, conversely, reduces discharge to interior waterways when compared to tidally controlled conditions. Both sea-level rise and tidal restoration expanded the area with emergent groundwater—where the water table is above or at the land surface—while reducing the amount of area with groundwater just below the land surface, shallow groundwater, which has implications for vegetation shifts and microbial respiration. The second study investigated seasonal variability in groundwater discharge and its sensitivity to recharge, pumping, and sea-level fluctuations for the Mobile Bay region of Alabama using a transient groundwater flow model. Findings indicated that groundwater discharge to Mobile Bay averages 2.5 percent of surface-water inflow to the bay and varies seasonally, with higher discharge during winter and spring when recharge is greater, and pumping is lower. Additionally, I found that the amount of emergent groundwater was strongly correlated with sea-level changes, while the depth of non-emergent groundwater responds more to recharge and pumping trends. The third study moved beyond coastal systems to evaluate how incorporating geophysical data into model hydrogeology reduced forecast variance. Through the comparison of the results of uncertainty analysis of two groundwater models, one of which used geophysical data to highly parameterize and discretize the model and another that used the data to a lesser degree, the research demonstrated that model parameters informed by geophysical data reduced forecast uncertainty for groundwater head and flow paths. This finding demonstrated the value of integrating geophysical data to improve forecast variance in a groundwater flow model for Shellmound, Mississippi. Collectively, these studies provide insights into how groundwater systems respond to climatic and anthropogenic changes and establish a framework for leveraging geophysical data to reduce model forecast variability. The findings of the coastal groundwater projects have broad implications that will help with planning for sea level rise for future coastal management projects. Additionally, the increased understanding that using geophysical data for refining model hydrogeology can reduce forecast uncertainty will assist in the planning of future groundwater modeling projects by helping guide the prioritization of data to collect.
Citation
Richins, J. G. (2026). Increased Knowledge of Groundwater Flow Quantities and Trajectories with Sea Level Changes and Through Hydrogeologic Refinement. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/6148
