A NEW DEBRIS FLOW MAPPING PROTOCOL USING ARCGIS COLLECTOR MOBILE PLATFORM, EXAMPLES FROM OREGON’S 2020 BURN AREAS

Post-fire debris flow hazards west of the Cascade Range in the Pacific Northwest are poorly understood, in part because most work has focused in arid southern California and the intermountain Western U.S. The regional precipitation style, geomorphology, and ecosystems differ from the more fire-prone arid landscapes of the Western U.S. In 2020, western Oregon experienced several concurrent, very large wildfires, which caused fatalities, mass evacuations, and costly destruction of property. Wildfire can increase the potential for floods, landslides, and debris flows, and several debris flows occurred within burn areas in the rainy season of 2020-2021. Tragically, one fatality was caused by a landslide-triggered debris flow originating within the 2017 Eagle Creek burn area. Data from the field is therefore critical to improve the overall understanding of wildfire impact on floods, landslides, and debris-flow hazards in this region. In particular, these data are needed to determine the rainfall threshold to separate a flood from a landslide or debris flow response. Despite the need for empirical data, there have not been standardized protocols for field mapping of floods, landslides, or debris flows. In order to establish a consistent protocol, we are developing a mapping schema using ArcGIS Collector, a mobile-mapping platform. This will be used to collect flood data, and debris flow data at different points along a debris flow path (initiation, transport, and deposition). These data include metrics such as incision depth, deposition depth, and sediment sorting descriptions. The mapping approach is being tested, and refined by field experience, through a collaboration between the USGS and the Oregon Department of Geology and Mineral Industries (DOGAMI) in five recent burn areas in western Oregon. The final product will be a mobile-mapping tool that can be rapidly deployed with a variety of partners to obtain standardized spatial data of floods, landslides, and debris flows with a special focus on burn areas. This presentation will focus on initial field data collection from several debris flow events in burn areas during the winter of 2020-2021 and early versions of the mobile-mapping platform. We hope to improve the platform based on external feedback.