WASHINGTON STATE’S NEW LANDSLIDE INVENTORY MAPPING PROTOCOL

With the formation of the new Landslide Hazards Program at the Washington Geological Survey (WGS), landslide mapping efforts in Washington State have shifted from inventories in managed forest lands to areas where people live, work, and recreate. Due to this change of scope and the recent collection of high-resolution lidar, the WGS published in April 2017 the “Protocol for Landslide Inventory Mapping from Lidar Data in Washington State.” The objective of the WGS protocol is to establish standardized methods for the creation of a GIS-based landslide inventory to ensure all data is inventoried in a consistent manner. The protocol includes techniques describing how to create lidar derivatives to assist in the interpretation of landslides and contains an ESRI file geodatabase template with pull-down menus (domains) for ease and consistent data entry. The mapping procedures are similar to the landslide inventory protocol developed by the Oregon Department of Geology and Mineral Industries in 2009 and vary only slightly due to programmatic needs and regional differences.

The WGS tested the new protocol in several areas in Washington State. The first county-wide landslide inventory in Washington was completed in July 2017 for Pierce County, the second most populous county in the state. WGS mapped 1,800 mi² and 1,276 landslides within the county. The WGS next focused on a 900 mi² project area in the Columbia River Gorge. Over 2,100 landslides have been mapped in this project which is scheduled to be published by the end of 2017. Currently, the WGS is mapping in a 1,300 mi² area in King County, focusing on the most populous areas with high-quality lidar. These landslide inventory databases are intended to provide users (planners, emergency managers, general public, geologists, public works, etc.) with basic information regarding landslides in order to reduce the impacts of landslides on property, infrastructure, and human life.