Preprints
https://doi.org/10.5194/egusphere-2023-2694
https://doi.org/10.5194/egusphere-2023-2694
10 Apr 2024
 | 10 Apr 2024
Status: this preprint is open for discussion.

Post-fire Variability in Sediment Transport by Ravel in the Diablo Range

Hayden L. Jacobson, Danica L. Roth, Gabriel Walton, Margaret Zimmer, and Kerri Johnson

Abstract. Post-fire changes to the transport regime of dry ravel, which describes the transport of individual particles downslope, are poorly constrained on a regional level but critical to understand as ravel may contribute to elevated sediment fluxes and associated debris-flow activity observed post-fire in the western United States. In this study, we evaluated post-fire variability in dry ravel travel distance exceedance probabilities and disentrainment rates through a series of field experiments simulating ravel with particles collected in situ. We conducted experiments between March 2021 and March 2022 on soil-mantled hillslopes in the Diablo Range of central coastal California following the Santa Clara Unit Lightning Complex fire of August 2020 with the goal of identifying a regime of “bounded” (light-tailed) or “runaway” (heavy-tailed or nonlocal) motion for different particle sizes between 3 and 35 mm. We conducted this study on both grassy south-facing slopes and oak woodland north-facing slopes. We tracked the post-fire evolution of particle transport regimes by fitting a probabilistic Lomax distribution model to the empirical travel distance exceedance probabilities of different particle sizes on a range of experimental slopes. Our experimental results indicated that a general transition from more runaway to more bounded transport occurred for our largest experimental particles (median intermediate axis of 28 mm) on south-facing slopes as vegetation recovered within the first year post-fire, while small and medium particles (median intermediate axes of 6 and 13 mm respectively) on south- or north-facing slopes and large particles on north-facing slopes did not experience notable changes in transport behavior. After the first year, seasonal variation in vegetation characteristics, such as grass density, appeared to control particle motion.

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Hayden L. Jacobson, Danica L. Roth, Gabriel Walton, Margaret Zimmer, and Kerri Johnson

Status: open (until 04 Jun 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2694', Emmanuel Gabet, 09 May 2024 reply
Hayden L. Jacobson, Danica L. Roth, Gabriel Walton, Margaret Zimmer, and Kerri Johnson

Data sets

Lomax2 Hayden L. Jacobson https://doi.org/10.5281/zenodo.10048974

Model code and software

Lomax2 Hayden L. Jacobson https://doi.org/10.5281/zenodo.10048974

Hayden L. Jacobson, Danica L. Roth, Gabriel Walton, Margaret Zimmer, and Kerri Johnson

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Short summary
Loose grains travel farther after a fire because no vegetation is left to stop them. This matters since loose grains at the base of a slope can turn into a debris flow if it rains. To find if grass growing back after a fire had different impacts on grains of different sizes on slopes of different steepness, we dropped thousands of natural grains and measured how far they went. Large grains went farther 7 months after the fire than 11 months after, and small grain movement didn’t change much.