ON THE DEVELOPMENT OF A STATEWIDE LANDSLIDE INVENTORY

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 can be queried and updated. Having this data as a GIS-based product allows queries to be mapped, adding the spatial component to queries aiding in land management decisions and forest regulation. The first public draft of the landslide inventory is a compilation of the individual efforts of many timber, tribal, state, and federal agents. When the landslide inventories were collected, few authors used a standard format for data collection. Variances in naming conventions, data collection protocols, quantity and quality of data were identified. To compile these data, a common data architecture was developed. The individual inventories were normalized to the data architecture by creating a decision table for every item in the original data to the values in the compiled data. Each decision table was reviewed for consistency. In some instances, the original author collected very little information related to each landslide. Where the original data was incomplete, the missing data values were calculated from existing data layers using GIS’ overlay abilities. The database itself is composed of two spatial attributes (polygon and arc), and two tabular attributes (unique number and type of feature). The unique number is related to a database of information about each landslide, such as data source, landslide process, landform, delivery, land use, size, and original number (to allow a user to link the data back to the original dataset). The inventory contains detailed information on both deep seated and shallow landslides. Deep-seated landslides have a separate related table (via the unique number) that contains information specific to that type of landslide (e.g. level of activity). The data is publicly available on request to the WA-DNR Forest Practices Division, via compact disc. In the near future, this data will be available via web download and web-based mapping on the WA-DNR FPARS website. Further updates to this data are ongoing through the Landslide Hazard Zonation Project and by submission of data (electronic or paper) to the LHZ Project Leader.