Skye Bensel Thesis Proposal

Title: Examining Seasonal Variations of Subsurface Water Storage in the Critical Zone with Geophysical Imaging

Abstract: Weathering in the Critical Zone (CZ) not only transforms bedrock into regolith but also increases the moisture storage potential of the subsurface by producing porosity. In the subsurface, water may be stored in the soil/regolith layer (i.e., soil moisture) or in the matrix and fractures of weathered bedrock (i.e., rock moisture). Examining the seasonal variation of subsurface water storage develops a better understanding of water partitioning in the CZ, specifically under a warming climate with extreme weathers. In this study we focus on monitoring subsurface water storage dynamics with time lapse Electrical Resistivity Tomography (ERT) at two sites in semi-arid Idaho Batholith. While one monitoring site (~72 m) is in the rain-to-snow transition zone, the other site (~144 m) is at the snow-dominated elevation. The subsurface CZ structure of the two sites are determined using seismic refraction imaging. Daily to biweekly ERT data are collected from the early summer through early winter. The ERT data are inverted to reconstruct the subsurface resistivity distribution, which are used to estimate the subsurface water storage. Combining geophysical methods with hydrometeorological data, we examine how the subsurface moisture responds to the 2023 extreme snowfall in Idaho. The data collected from this study will help us better understand and predict how mountainous hydrologic system responds to extreme weathers, which are key for stakeholders to make more informed decisions on water resources management.

Advisor: Qifei Niu

Committee Members: Anna Bergstrom, Lejo Flores, Jim McNamara

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