Year of Award

2017

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Forestry

Other Degree Name/Area of Focus

Forest Management

Department or School/College

W.A. Franke College of Forestry and Conservation

Committee Chair

Dr. Kelsey Kencso

Committee Co-chair

Dr. W. Payton Gardner

Commitee Members

Dr. Lisa Eby, Dr. H. Maurice Valett

Keywords

Restoration, alluvial aquifer recharge, natural storage, hydraulic exchange, baseflow

Publisher

University of Montana

Subject Categories

Water Resource Management

Abstract

Stream restoration is increasingly being considered as a climate change mitigation tool, altering the storage and exchange capacities of streams and their adjacent alluvial aquifers. While previous research has shown that added geomorphic complexity and increased width-to-depth ratios can enhance hydraulic exchange and alluvial aquifer storage, few studies have used field data to link these changes in form to baseflow generation. In this paper, we quantify the effect of stream restoration on nested scales of hydraulic exchange and temporal patterns of alluvial aquifer recharge and discharge. Our work compares a restored and degraded reach on Ninemile Creek, Montana following extensive placer mining in the late 1800’s. Using a combination of topographic and morphologic surveys, well transects, piezometers and tracers, we monitored hydraulic exchange processes across multiple spatial scales and six flow stages. We then used 222Radon and synoptic discharge measurements to evaluate reach-scale alluvial aquifer recharge and discharge over the 2016 hydrograph recession. We found that changes in channel form increased transient storage and induced feature-scale vertical exchange not observed in the degraded reach. However, vertical exchange flux and depth in the restored reach were limited by reduced subsurface hydraulic conductivity. Lateral gradients showed increased alluvial aquifer recharge and underflow in the restored reach, in contrast to persistent alluvial aquifer drainage seen in the degraded reach. The cumulative impact of restoration resulted in a longer period of alluvial aquifer recharge early in the season, and higher volumetric discharge at baseflow. Our results support the theory that restoration can increase storage and baseflow discharge, while emphasizing that site-specific influences can outweigh the intended effects of restoration. This work is a critical step towards understanding the efficacy of restoration in improving late season flows in the context of a changing climate and increased demand for water resources.

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© Copyright 2017 Christine M. Brissette