RAPID LANDSLIDE INVENTORIES FROM LIDAR: SIMPLIFYING THE INVENTORY PROCESS TO SHARE LANDSLIDE DATA QUICKLY

The process of creating a detailed landside inventory with spatial and tabular data can be time-consuming and labor-intensive, especially for large project areas. The Washington Geological Survey’s Landslide Hazards Program (LHP) developed a streamlined landslide mapping protocol (SLIP) to allow geologists to rapidly map landslide landforms from lidar. The SLIP approach allows geologists to quickly share a landslide inventory with outside user groups (counties, cities, state agencies, etc.) and create a tool to assist decision-makers in the prioritization of areas for future detailed landslide mapping.

The SLIP process differs from typical landslide mapping protocols by omitting attribute data typically associated with most landslide inventories, such as landslide type, associated geology, date of movement, etc. and only categorizes the geologist’s confidence of the landslide’s presence. High confidence landslides are digitized as a polygon and lower certainty landslides are marked with a point. When digitizing these areas, the protocol does not separate specific landslide landforms such as the main scarp, flanks, internal scarps, and instead includes all of these features into one polygon.

In March 2016, the LHP began a pilot project that involved landslide inventory, susceptibility, and vulnerability mapping in Pierce County, the second most populous county in the state. We began with a SLIP map of the county, excluding Mount Rainier National Park, and identified 235 high confidence landslide polygons and 1,176 lower certainty landslide points. We then reviewed the SLIP data with county personnel including planners, GIS specialists, emergency managers, and engineers to identify areas to be mapped and attributed in detail following Oregon’s Department of Geology and Mineral Industries’ protocol. The stakeholders chose to focus detailed mapping in population centers, along major highway corridors, and water bodies, excluding many of the timber managed areas. In the timber managed areas, the SLIP data points were converted to polygons and attributed with mapper confidence, providing a basic county-wide landslide inventory. By implementing the SLIP method, the LHP and Pierce County were able to focus on critical areas for detailed mapping and utilize their time more effectively.