AN INTER-WATERSHED COMPARISON STUDY OF BEDROCK CONTROLS ON SHALLOW SUBSURFACE FLOW AND STREAMFLOW RESPONSE

Author

Robert LivesayFollow

Year of Award

2018

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Forestry

Department or School/College

W.A. Franke College of Forestry and Conservation

Committee Chair

Dr. Kelsey Jencso

Committee Co-chair

Dr. W. Payton Gardner

Commitee Members

Dr. Benjamin Colman

Keywords

Hydrology, streamflow, geology, groundwater, forestry

Subject Categories

Water Resource Management

Abstract

Bedrock controls on watershed response have been actively studied in recent years, however, most conclusions are based on surface water analysis leaving unresolved questions about the nature of bedrock flow paths and ultimately their control on watershed response. In this study, we investigated bedrock controls on watershed response by simultaneously monitoring the hydrology of two adjacent watersheds underlain by dissimilar geologic formations (monzonite vs. meta-sandstone) and by characterizing subsurface conditions through bedrock drilling and fracture mapping. We hypothesized, when soils saturate, the underlying bedrock geology may influence the partitioning of shallow subsurface flow (SSF) between soil and bedrock flow paths, resulting in a divergence in hillslope runoff response between each watershed. We found SSF occurred for longer periods and at greater magnitudes in the monzonite watershed relative to the meta-sandstone watershed. Furthermore, hillslopes underlain by monzonite bedrock drained more rapidly compared to the hillslopes underlain by meta-sandstone bedrock. Paired hydrometric observations of soil and bedrock flow systems linked hillslope discharge to bedrock exfiltration at the slope base. The bedrock driven control on hillslope discharge promoted a stark divergence in the streamflow response between each watershed. These findings provide strong evidence supporting a bottom up view of watershed function, where bedrock flows systems are a fundamental control on the hydrologic response of hillslopes and stream networks. Conclusions from this study bolster the need to further investigate how differences in bedrock properties across mountainous watersheds will influence the resilience of headwater basins in the face of climate change.

Recommended Citation

Livesay, Robert, "AN INTER-WATERSHED COMPARISON STUDY OF BEDROCK CONTROLS ON SHALLOW SUBSURFACE FLOW AND STREAMFLOW RESPONSE" (2018). Graduate Student Theses, Dissertations, & Professional Papers. 11223.
https://scholarworks.umt.edu/etd/11223