WASHINGTON'S STATEWIDE LANDSLIDE INVENTORY: FIRST PUBLIC DRAFT

The production of the public draft of a statewide GIS-based landslide inventory is the first major step in Washington State’s development of a Landslide Hazard Zonation database. This new, publicly available dataset provides land managers and researchers with a powerful piece of information in a format that is both queryable and updateable. It has been created to form the basic information for a consistent landslide-based hazard assessment. The goal of the Landslide Hazard Zonation (LHZ) project is to create a vastly improved slope stability screening and management tool by better describing and mapping all potentially unstable slopes where forest practices might occur. In addition to identifying landforms with landslide hazard, landforms are linked (via the landslide inventory) to a level of hazard and sensitivity to land management. The LHZ objectives are to create an integrated screening tool that: 1. Exists within and is used from GIS; 2. Uses existing data effectively; 3. Has a consistent method of hazard assessment of potentially unstable landforms by following a designated mapping methodology; and 4. Is useful to and accessible by all stakeholder groups. The first public draft of the landslide inventory is a compilation of the individual efforts of 128 watershed-based assessments by timber, tribal, state, and federal interests. The compilation also includes many non-watershed based studies by state, federal, and academic institutions. When the landslide inventories and mass wasting map units were collected, it was apparent that few authors used the watershed analysis standardized format for data collection. A data architecture was developed so that these inventories could be compiled into a standardized format. The individual studies were normalized to the data architecture by creating a set of decision tables for every item in the original data to the values in the compiled data. Where the original data was incomplete, the missing data values were calculated from existing data layers using GIS’ overlay abilities. The inventory contains detailed information on both deep seated and shallow landslides, including data source, certainty of identification, field verification, and triggering mechanisms. It also has built in ability to link the compiled data back to the original dataset.