USE OF REMOTE OBSERVATIONS, MODELING, AND POLYCYCLIC AROMATIC HYDROCARBONS (PAHS) TO IMPROVE UNDERSTANDING OF THE ONSET OF POST-FIRE DEBRIS FLOWS

Wildfires alters the surficial processes that can contribute to increased surface runoff and mobilization of sediments exacerbated during rain events. Similarly, wildfires also release and mobilizes harmful chemicals such as polyaromatic hydrocarbons (PAH). In this research, we aim to study the effects of geomorphic changes in debris flow initiation for subsequent years.

We perform geomorphic and soil analysis of closely related basins within the 2020 Lake Fire in Southern California to identify the differences between a basin with and without debris flow. More specifically, we collected field samples and measurements prior to the first wet season for our debris flow prediction model input and used high resolution satellite imagery to determine debris flow initiation following the survey. Our model corroborates our satellite observations suggesting there were no significant rainfall events in the first year to trigger debris flows despite varying grain sizes across basins. PAH signatures are consistent with pyrogenic sources in samples collected in basins while the signatures of samples on ridges show the potential for some petrogenic input. Moreover, we suspect PAH content in soil is controlled by several different factors rather than grain sizes alone.

We intend to collect repeat DEM in the subsequent years to identify source of initiation and understand how debris flow initiation changes over time. We also seek to understand how terrain and seasonality relate to PAH concentrations and source signatures. This study allows us to provide us insight to the physical and chemical impacts of postfire debris flow to communities in Southern California.