Year of Award

2026

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Geosciences

Other Degree Name/Area of Focus

Geosciences, Geophysics, Hydrogeology

Department or School/College

Department of Geosciences

Committee Chair

W. Payton Gardner

Commitee Members

Hilary R. Martens, Zachary H. Hoylman, Donald F. Argus, Adrian A. Borsa

Keywords

Geodesy, Groundwater, Hydrology, Surface Loading, Water Resources, Western US

Abstract

Redistribution of freshwater near the Earth’s surface produces elastic deformation that can be measured using geodetic technologies such as the Global Navigation Satellite System (GNSS). Observations of load-induced deformation enable continuous estimates of terrestrial water storage (TWS) with relatively high resolution, offering new insights on terrestrial hydrology at scales unattainable using other methods. This dissertation investigates the use of GNSS displacement timeseries for the study of freshwater resources and their applications in improving our understanding of mountain groundwater systems, understudied sources of water storage and release within mountainous regions.

Estimating changes in TWS from GNSS displacement time series requires assumptions to be made about the Earth’s interior properties. Through a series of case studies, we explore the impact of 1D and 3D Earth structure on estimates of TWS made across various spatial and temporal scales appropriate for local, regional, and global studies of freshwater. We demonstrate that TWS estimates made at short spatial scales (< 10 km) are highly sensitive to Earth structure, where incorrect assumptions can yield errors up to 75%. We then present the first GNSS-inferred estimates of TWS while considering the impact of 3D Earth structure, quantifying error in water storage estimates within major mountain ranges of the western United States, such as the Sierra Nevada. Errors associated with 3D Earth structure at these regional scales (>10km) are small relative to the current uncertainties in GNSS-inferred estimates of water.

We then use two decades of GNSS displacement time series to constrain changes in groundwater storage within the Sierra Nevada and Cascades, finding mountain groundwater systems to be highly dynamic and significant sources of water storage within mountainous regions, demonstrating that significant periods of precipitation can drive groundwater storage from historical lows to above normal conditions in periods of six months or less. Then using the annual drainage of groundwater storage from these regions, we estimate the hydraulic properties of these major mountain groundwater systems, finding the hydraulic conductivity of both regions to be nearly an order of magnitude greater than previous estimates, indicating fracture networks and weathered bedrock are more pervasive at regional scales than previously thought.

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© Copyright 2026 Matthew J. Swarr