Date of Award

Spring 2020

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geosciences

Committee Chair

Glenn Shaw

First Advisor

Andrew Bobst

Second Advisor

Marvin Speece

Third Advisor

Beverly Hartline

Abstract

In the semiarid and arid western United States, it is important to understand the potential effects of stream restoration on surface-water and groundwater. In this study, we evaluate the seasonal and annual hydrologic impacts of beaver-dam analogue (BDA) restoration in the Blacktail Creek (BTC) Watershed south of Butte, Montana. We monitored surface water flow, groundwater levels, temperature, and specific conductance primarily using a control-treatment study design. In treated reaches, groundwater levels were closer to the ground surface and showed less seasonal fluctuation. Changes in overall streamflow in the control reaches had stream losses and gains varying from -21.0 to 19.9 % while treatment reaches had stream gains of 12.5 to 17.6 % of water returning to the stream through groundwater discharge. Using specific conductance values and streamflow, the total dissolved load was greater in the treatment reaches compared to the control reach. Two-components mixing model showed that treatment reaches had a greater overall groundwater contribution to the stream during high-flow periods compared to control reaches. Control and treatment late-season vertical hyporheic exchange flows had similar vertical exchange flows but there were greater overall horizontal flows in the treatment reach. BDA implementation creates small off-channel ponds; provides increased groundwater gradients away from the stream during late-season periods, and gradients to the stream during drier years. BDAs increase ecosystem resilience while storing water during reduced snowpack years. Groundwater discharge to streams in treatment reach and groundwater recharge in control reach is evident during high-runoff periods. BDAs can be an effective management tool when applied to the proper setting with a well-defined restoration goal.

Comments

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Degree in Geoscience: Hydrogeology Option

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