T92 Applications of Landslide Inventories: Creating Hazard Maps and Guiding Policy

Monday, 19 October 2009
8:00 AM - 12:00 PM
E147/148

A HISTORY AND EVALUATION OF WASHINGTON STATE'S FOREST PRACTICES RULES FOR UNSTABLE SLOPES

Paper number: T92-14
Program: Technical Sessions
Time: 11:30 AM – 11:45 AM

Authors

Abstract

In 1992, Washington State began using a watershed analysis process that included an assessment of mass wasting to identify unstable slopes requiring protection; these efforts were conducted as part of State Forest Practices Rules. Through the 1990’s, qualified experts certified by Washington State Department of Natural Resources completed scientific assessments of approximately 70 watersheds. The experts produced landslide inventories from aerial photography and supplemental field work and created hazard maps of potentially unstable landforms; collectively, these products cover approximately 2,785,000 acres of Washington State.

Washington State Forest Practices Rules were extensively revised in 1999 through the Forests & Fish Agreement. During the Forests & Fish Negotiations, a stakeholder team of unstable slopes experts and policy personnel distilled the results of the watershed analyses and proposed rules that identify and protect landform-based unstable slopes. The landform-based unstable slopes rules have been implemented on private and state timberlands since March, 2000. By 2002, a scientific advisory group working within the Adaptive Management Program had written a protocol called Landslide Hazard Zonation (LHZ) which more rigorously outlined data collection for the landslide inventory and detailed a process for delineating potentially unstable slopes and assigning a hazard rating. Landslide inventories and unstable slopes mapping for an additional 30 watersheds and 6 other blocks totaling 1,115,000 acres have been accomplished under the LHZ Protocol. The LHZ protocol provides a standardized and systematic database to help evaluate the validity of the rule-identified landforms. Other research to test the effectiveness of Washington State Forest Practices Rules is ongoing and includes a field-based inventory of landslides that evaluates different harvest and road treatments following the December 2-3, 2007, storm in southwest Washington.