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Date of Award

Spring 2025

Document Type

Masters Thesis

Department or Program Affiliation

Geology

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Pfeiffer, Allison

Second Advisor

Mitchell, Robert J. (Geologist)

Third Advisor

Czuba, Jonathan A.

Abstract

Large sediment pulses deposited in river channels can alter channel morphology and amplify downstream flood hazards. In the Suiattle River of Washington State, abrasion controls the downstream impact of sediment supply from Glacier Peak, a stratovolcano that regularly supplies the channel with large sediment pulses. This phenomenon is evident by the persistence of strong volcanic grains on the streambed and the rapid downstream loss of weak volcanic grains to fine sediment. Although cobbles and boulders dominate pulses in the channel, the Suiattle has an unusually high supply of fine sediment and contributes to fine sediment impacts downstream. Despite the evidence that the abrasion of coarse sediment during downstream transport drastically impacts the balance of fine and coarse sediment in the channel, little to no work – in the Suiattle or other real landscapes – has been done to determine the importance of abrasion on the dynamics of sediment pulse evolution in a highly abrasion-prone setting. In this study, I use the Suiattle River’s geometry and sediment characteristics as a real-world framework to explore how sediment pulses evolve under different modeled scenarios of abrasion. I apply the Network Sediment Transporter (NST), a 1D morphodynamic and Lagrangian sediment transport model within Landlab, to simulate channel response to a large sediment pulse. I evaluate three scenarios: (1) no abrasion, (2) abrasion rates based on Schmidt Hammer Rock Strength (SHRS) measurements as a proxy for lab-derived tumbler abrasion rates, and (3) doubled SHRS values to account for known underprediction. Each scenario is driven by a ~2% exceedance flow derived from a distributed hydrology model, with intermittent high flows (~0.1% exceedance) to enable the transport of large particles. The model results show that increased abrasion enhances the mobility of bed material and substantially increases the production and transport of fine sediment. In contrast, changes in bed elevation are relatively insensitive to abrasion alone.

Instead, channel geometry (channel width) emerges as a key control on sediment deposition and export. These findings emphasize the utility of abrasion-inclusive sediment transport modeling and highlight how topographic and geomorphic factors shape sediment pulse evolution. Future work should continue to develop the numerical modeling tools associated with the NST, which will help facilitate a more detailed exploration of the effects of abrasion and heterogeneous sediment characteristics in the rivers of the western Cascade Mountains.

Type

Text

Keywords

Abrasion, volcanic sediment pulses, 1-D model, Suiattle River, Lagrangian, Network Sediment Transporter

Publisher

Western Washington University

OCLC Number

1524911186

Subject – LCSH

Fluvial geomorphology--Washington (State)--Suiattle River; Sediment transport--Washington (State)--Suiattle River--Mathematical models; Sedimentation and deposition--Washington (State)--Suiattle River; River sediments--Sampling--Washington (State)--Suiattle River

Geographic Coverage

Suiattle River (Wash.)

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

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