2024 CSDMS meeting-057


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How does abrasion impact the fluvial morphodynamics of a volcanic sediment pulse, Suiattle River, WA?

Ashanie Long-Reid, (She/her),Western Washington University Bellingham Washington, United States. ashanie.reid@yahoo.com
Allison M. Pfeiffer, Western Washington University Bellingham Washington, United States. pfeiffa@wwu.edu
Jonathan A. Czuba, Virginia Tech Blacksburg Virginia, United States. jczuba@vt.edu
Eric W.H. Hutton, University of Colorado at Boulder, Community Surface Dynamics Modeling System Integration Facility Boulder Colorado, United States. eric.hutton@colorado.edu
Robert J. Mitchell, Western Washington University Bellingham Washington, United States. rjmitch@wwu.edu

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 and new studies on the variability of abrasion, no work – in the Suiattle or elsewhere – has been done to determine the importance of abrasion on sediment pulse evolution in a highly abrasion-prone setting. Here, we test the extent to which abrasion acts as a control on sediment pulse transport from large mass wasting deposits of heterogeneous sediment characteristics. We employ the use of the Network Sediment Transporter, a 1-D river morphodynamics and Lagrangian modeling component in Landlab, to explore channel response to a large sediment pulse in the Suiattle River basin, tracking bed elevation and grain size changes and compare model results of variable sediment abrasion scenarios. We simulate abrasion as the mass of the grain loss per distance traveled and the scenarios include: no abrasion, a distribution of Schmidt Hammer Rock Strength (SHRS) measurements (a proxy for tumbler-derived abrasion rate), and a doubling of the SHRS proxy to account for the underprediction of the tumbler and a lack of in-place abrasion. We drive the model with a 2-year exceedance flow from discharge data from a distributed hydrology model to account for the complicated rain/snow hydrology of this mountainous region. Our initial results indicate negligible variances in bed elevation solely attributable to abrasion. Instead, our primary findings highlight the importance of the canyon reaches in modulating the coherence of the pulse as it transports downstream. Before the canyon reaches, a coherent wave of bed elevation change is apparent in all model runs, with modest differences between abrasion scenarios. Downstream of this canyon reach, this coherence dissipates.