19 Dec 2022
19 Dec 2022
Status: this preprint is open for discussion.

The Influence of Large Woody Debris on Post-Wildfire Debris Flow Sediment Storage

Francis K. Rengers1, Luke A. McGuire2, Katherine R. Barnhart1, Ann M. Youberg3, Daniel Cadol4, Alexander N. Gorr2, Olivia Hoch2, Rebecca Beers3, and Jason W. Kean1 Francis K. Rengers et al.
  • 1U.S. Geological Survey, Geologic Hazards Science Center, Golden, CO
  • 2University of Arizona, Tucson, AZ
  • 3Arizona Geological Survey, Tucson, AZ
  • 4New Mexico Tech, Soccoro, NM

Abstract. Debris flows transport large quantities of water and granular material, such as sediment and wood, and this mixture can have devastating effects on life and infrastructure. The proportion of large woody debris (LWD) incorporated into debris flows can be enhanced in forested areas recently burned by wildfire because wood recruitment into channels accelerates in burned forests. In this study, using four small watersheds in the Gila National Forest, New Mexico, that burned in the 2020 Tadpole Fire, we explored new approaches to estimate debris flow velocity based on LWD characteristics and the role of LWD on debris flow volume retention. To understand debris flow volume model predictions, we examined two models for debris flow volume estimation: (1) the current volume prediction model used in U.S. Geological Survey debris flow hazard assessments, and (2) a regional model developed to predict the sediment yield associated with debris-laden flows. We found that the regional model better matched the magnitude of the observed sediment at the terminal fan, indicating the utility of regionally calibrated parameters for debris flow volume prediction. However, large wood created sediment storage upstream from the terminal fan, and this volume was of the same magnitude as the total volume at the terminal fans. Using field and lidar data we found that sediment retention by LWD is largely controlled by channel reach slope and a ratio of LWD length to channel width between 0.25 and 1. Finally, we demonstrated a method for estimating debris flow velocity based on estimates of the critical velocity required to break wood, which can be used in future field studies to estimate minimum debris flow velocity values.

Francis K. Rengers et al.

Status: open (until 15 Feb 2023)

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Francis K. Rengers et al.

Francis K. Rengers et al.


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Short summary
Debris flows often occur after wildfires. These debris flows move water, sediment, and wood. The wood can get stuck in channels and create piles of sediment within channels. We investigated how the channel and wood size/shape influence how much sediment is stored. We also used a series of equations to estimate how the wood size/shape would reflect the velocity needed to break the wood. These data will help improve models and insight from future field investigations.