Year of Award

2025

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Geosciences

Department or School/College

Geosciences

Committee Chair

Dr. Andrew Wilcox

Commitee Members

Dr. Payton Gardner, Dr. Bob Hall

Keywords

Resilience, geomorphology, large floods, mountain rivers

Subject Categories

Geomorphology

Abstract

As hydroclimatic extremes intensify, large floods increasingly reshape river systems and threaten infrastructure. Fluvial geomorphic resilience, defined as a river’s resistance to, and recovery from, flood disturbance, offers a useful framework for understanding river response and guiding management. We assessed resilience at two scales: (1) a detailed geomorphic and hydraulic analysis of the June 2022 flood on East Rosebud Creek, Montana, which was part of broader flooding in the Greater Yellowstone Ecosystem, and (2) a broad-scale comparison of 12 flood-impacted alluvial mountain rivers across North America and Europe. We quantified resistance using active channel width ratios (WR) and recovery using post-flood channel evolution (Wrec) and recovery rate (Rt). East Rosebud Creek showed strong spatial variability in disturbance among two defined segments, with Segment 1 experiencing nearly 20 times more disturbance than pre-flood conditions at its peak. HEC-RAS modeling at East Rosebud Creek revealed up to 3.7 m of vertical incision based on discrepancies between surveyed and simulated maximum water surface elevations, while also providing insight into the channel’s resistance post-flood. At the segment-scale, multilevel regression showed a positive log-transformed relationship between normalized flood peak exceedance above the Q1.5 (Qp*) and mean WR, and a negative linear relationship between mean slope and mean Rt. East Rosebud Creek results suggest that slope, confinement, and grain size influence resistance, and vertical disturbance is important even when not reflected in width-based metrics. We anticipate that flood effects will result in increased average resistance and decreased average recovery in Segment 1. Broad-scale results suggest that slope-driven limits on vegetation growth shape recovery. Understanding patterns of resilience can improve flood adaptation strategies and inform targeted management in vulnerable rivers like East Rosebud Creek.

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