Document Type

Thesis

Date of Degree Completion

Fall 2023

Degree Name

Master of Science (MS)

Department

Geological Sciences

Committee Chair

Lisa Ely

Second Committee Member

Carey Gazis

Third Committee Member

Hannah Shamloo

Fourth Committee Member

Paul James

Abstract

The importance of stream restoration in providing a healthy ecosystem is widely recognized. The Washington State Department of Transportation (WSDOT) has implemented environmental changes to facilitate habitat restoration and wildlife passage along the Interstate 90 Highway (I-90) corridor where it passes over the Cascade Mountains. Prior to the I-90 corridor expansion, Price and Noble Creeks passed under the highway though culverts, limiting passage of aquatic species or wildlife below the highway. In 2019 the stream channel crossings were expanded, and the size/shape of these creeks were engineered to mirror what would be seen in a natural environment. Since construction, erosion has resulted in some channel reaches experiencing a range of geomorphic changes, while other channel reaches have aggraded or remained stable. This research revolves around three objectives: Predicting the future evolution of the channel geomorphology, identifying the possible factors responsible for the differential erosion and deposition in the two channels, and assessing the efficacy of the I-90 stream crossings in supporting habitat connectivity for aquatic species. Hydrographs of both creeks were based on camera footage of measurements from February 2022 through July 2023. HEC-RAS hydraulic modeling from surveyed channel cross-sections was used to calculate flow velocity and discharge, which ranged from 1.01 m3/s during peak seasonal flow to 8.99 m3/s for simulated bankfull overflow. Areas of channel stability vs. erosion were determined by measurements of sediment deposition and bank erosion. The Price Creek channel is steeper and narrower than Noble Creek and exhibits more areas of bank erosion. Large wood was associated with some, but not all, areas of erosion or deposition. These data provide information about the possible causes of the channel changes and the utility of the engineered channels to provide effective habitat and passage for aquatic species. Data collected above and below the engineered portions of the creeks illustrate greater variation in stream channel bedforms than in the channels directly under the highway. While the constructed segments of Price and Noble Creeks do not perfectly mimic their natural counterparts, the observed evolution of the channel geometry indicates an increase in channel complexity that is likely to continue in the future. These changes are, overall, advantageous to enhancing habitat connectivity.

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