LANDSLIDE HAZARD ZONATION, WASHINGTON: RESULTS FROM 1ST YEAR OF DATA COLLECTION

The goal of this project is to eliminate the error of omission during the forest practices permitting process by identifying, describing, and mapping unstable landforms. The mapping is done by applying a consistent assessment methodology to priority forested watersheds in the state. As a precursor to this project, all available digital landslide inventories and mass wasting map units were collected and compiled into two GIS databases. These compiled datasets are available for free download at dnr.wa.gov/forestpractices/data , under the tabs marked “Landslides” and “Landslide Hazard Zones”. These hazard zones include information from watershed analysis, from this project, and other hazard zones. These datasets are updated on the website quarterly. The extant data collection facilitated in the identification of unmapped or partially mapped watersheds that need to be mapped in this project. Forty-four watersheds were identified as being partially mapped and thus were mapped this year. A prioritization of the remaining mapping work for the next 3 years was based on two criteria: the amount of land modeled as high hazard (based on previous slope modeling work) and the amount of land that was available for harvest (recent LandSat image minus harvest applications). Two other websites were created to facilitate public involvement and access to the products as they are being created (dnr.wa.gov/forestpractices/lhzproject). One page is for public comment on draft assessment products. Another is for public access to the final products. Products from this project include two maps (at 1:24:000 or better): landslides and hazard zones; and a document that describes the units and triggering mechanisms. Included on the final products page are implementation guidelines and the mapping protocol. Posting the implementation guidelines provides a clear, consistent intent of the purpose and the use of these products. Posting the protocol provides a transparent mechanism for the public to understand how the products were created. During this first year, a technical advisory group (UPSAG) that is a subset of the Cooperative Monitoring, Evaluation and Research (CMER) committee convened to revise the mass wasting module of watershed analysis to improve inter-operator consistency and to meet the specific needs of the project.