Year of Award

2015

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Forestry

Other Degree Name/Area of Focus

Hydrology and Watershed Management

Department or School/College

College of Forestry and Conservation

Committee Chair

Kelsey Jencso

Commitee Members

Jim Riddering, Marco Maneta

Keywords

hydrology, hillslope, watershed, groundwater, hydraulic conductivity, hydrologic connectivity

Subject Categories

Hydrology | Other Earth Sciences | Other Physical Sciences and Mathematics

Abstract

Much research in forested headwater catchments has focused on the role of topography for organizing subsurface flow and the hydrologic connectivity of upland flow paths to stream networks. However, little work has been conducted to evaluate how localized and hillslope scale patterns of hydraulic conductivity and soil depth contribute to spatial patterns of water table duration, magnitude, and connectivity. I monitored shallow groundwater dynamics in wells distributed across a 1st order hillslope in the Lubrecht Experimental Forest, Montana. Additionally, I collected in-situ measurements of soil saturated hydraulic conductivity and soil depth at 10m intervals across the study hillslope and compared these values to the well hydrologic response. Similar to previous studies, my results indicated that upslope accumulated area was a first-order control on the duration of soil saturation. However, I found that local soil hydraulic properties modulate hillslope scale controls on the duration, magnitude, and extent of groundwater development. Generally, local contributing areas with higher saturated hydraulic conductivity values exhibited lower magnitudes of water table depth and variability in water table depths, lower median water table height, and less cumulative duration of hydrologic connectivity with upslope landscape positions. Additionally, areas with more variable bedrock topography required higher antecedent wetness conditions for the development of transient water tables. These results demonstrate not only the importance of hillslope scale topography for controlling hillslope water table dynamics, but the need to also consider local patterns of soils characteristics and bedrock topography. This study advances the science of hydrology by addressing previously unresolved questions regarding the relative roles of spatial patterns in topography, hydraulic conductivity and soil depth on local and hillslope scale shallow water table dynamics. A better understanding of these local and nonlocal processes may contribute to improved conceptualizations of factors affecting runoff generation and the degree of watershed scale hydrologic connectivity that influences discharge dynamics in forested mountain watersheds.

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© Copyright 2015 Casey E. Ryan