LANDSLIDE EMERGENCY RESPONSE – FINDINGS AND LESSONS LEARNED BY THE WASHINGTON GEOLOGICAL SURVEY'S RESPONSE TO THE DECEMBER 3, 2007 AND JANUARY 7-9, 2009 STORMS

In two years, two destructive storms have bombarded Washington State, spawning thousands of landslides. In each of these storms, the DNR Washington Geological Survey participated in state and local level emergency response by inventorying landslides and related damage and providing local jurisdictions with geologic expertise. GIS, GPS, and social networking platforms proved valuable for collecting and quickly disseminating large data volumes for emergency response.

Average pre-storm landslide density in watersheds across western Washington was 0.121 landslides per square mile per year, with a range of 0.002 to 0.842. These numbers were derived from aerial photo and ground surveys of 74 watershed administrative units (WAU), with photos ranging from 1939 to 2006. The December 2007 storm triggered movement of almost 2,000 landslides, an average landslide rate of 1.88 landslides per square mile per year in 14 WAU, with a range of 0.135 to 7.911 (highest in the Chehalis Headwaters WAU). The January 2009 storm kicked off an estimated 1,500 landslides, an average landslide rate of 0.969 landslides per square mile per year in 20 WAU, with a range of 0.109 to 5.923 (highest in the Kosmos WAU).

The Washington Geological Survey has progressively developed state of the art, low cost methods for rapid documentation of widespread landslides. GIS was used for landslide cataloging and social media to quickly relay information to government agencies, private industries, and the public. Aerial reconnaissance from fixed wing planes employed GPS devices to track flight paths and geo-reference photos of landslides. These geo-referenced photos were used to heads-up digitize landslides into GIS. Attributes such as landslide process, land use, delivery, and damage were assessed from aerial photos while other attributes, such as slope gradient and aspect, were determined from GIS applications. Initially, landslides were reported as a point shapefile and on a statewide map, also listing areas of road impacts and damage to structures. A more real-time approach has been adopted to utilize programs such as a modified Google “My Maps” to relay information to the public instantly. Photos with descriptions are now uploaded onto flicker and media such as blogs and twitter are used to inform the public of ongoing activities and threats.