Date of Award:

12-2021

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Committee Chair(s)

Patrick Belmont (Committee Chair), Brendan Murphy (Committee Co-Chair)

Committee

Patrick Belmont

Committee

Brendan Murphy

Committee

Larissa Yocom

Abstract

Post-fire debris flows represent the most erosive and potentially hazardous consequence associated with increasing wildfire severity. While an abundance of research has explored where they are likely to occur and their potential magnitude, investigations into understanding how they impact downstream resources are limited. Recent advancements are seeking to link predictive models together to be able to predict how erosion after wildfire may impact reservoirs and aquatic habitat downstream. However, there are two key missing pieces into our ability to examine watershed-scale impacts of post-fire erosion. These include having accurate predictions of how much sediment is likely to be deposited by post-fire debris flows and our ability to predict the sizes of sediment deposited by post-fire debris flows. Based on previous research and new fieldwork, we compiled a novel data set of depositional volumes and GSDs for 60 post-fire debris flows across the Intermountain West. This represents the largest data set of post-fire debris flow volumes outside of Southern California, and the largest aggregate data set of post-fire debris flow GSDs of which we are aware. With this data, we first evaluated existing models for post-fire debris flow volume prediction, which were largely developed using data from Southern California. Because these existing debris flow models don’t accurately predict volumes in our data set, we constructed a new post-fire debris flow volume prediction model for the Intermountain West using a combination of Random Forest modeling and regression analysis. Additionally, we constructed four post-fire debris flow sediment size predictive. These predictive models offer a first in-depth investigation into the upstream, landscape controls on the sediment sizes of post-fire debris flows. This study aims to improve post-fire debris flow characterization and better inform predictions of how post-fire sediment is transported downstream. This information will allow for improved assessments of post-fire threats to reservoir storage capacity, as well as aquatic habitat, in a diverse range of watersheds across the Intermountain West.

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