Date of Award:

12-2024

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Committee Chair(s)

Belize A. Lane

Committee

Belize A. Lane

Committee

Colin B. Phillips

Committee

Brendan P. Murphy

Abstract

Wildfires significantly increase sediment input to rivers through various pathways, including post-fire debris flows. Understanding how mountain rivers respond to these sediment inputs is crucial for predicting and managing downstream impacts on infrastructure, water security, and aquatic habitats. While the causes and characteristics of post-fire debris flows have been extensively studied, the morphological changes in downstream fluvial channels remain poorly understood. This study uses scripted spatial analysis toolsets, high-resolution pre- and post-fire DEMs, repeat cross-sectional surveys, time-lapse footage, and pebble counts to document channel responses to sediment supply in a burned steep mountain stream in the upper Colorado River Basin, USA. We observed the re-working of post-fire debris-flow deposits in the channel and identified the primary drivers on sediment mobilization, namely spring snowmelt and summer monsoons. By correlating initial types of channel changes with valley-scale attributes, we identified potential predictors of these responses in other fire-prone watersheds. Following initial debris flow events, new debris flows occurred three years post-fire, introducing another sediment pulse from both new and repeat hillslope catchments. Channel surveys indicated a rapid re-adjustment towards pre-fire geometry before the second major sediment input, but continued monitoring revealed a prolonged vulnerability and extended recovery timeline. These findings underscore the importance of long-term field and remote sensing-based channel analysis to enhance our understanding of mountain channel responses to post-fire debris flows.

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