LANDSLIDES, LAND MANAGEMENT, AND PUBLIC SAFETY: A RECONNAISSANCE LEVEL REVIEW OF LANDSLIDES TRIGGERED BY THE JANUARY 2009 STORM, WHATCOM COUNTY, WASHINGTON

The early January 2009 rain-on-snow storm that affected northwest Washington generated numerous landslides, some of which initiated on land managed by the Washington State Department of Natural Resources in Whatcom County. Some of these landslides impacted, to varying degrees, about four dozen adjacent privately or publicly owned properties. During the past seven months we have been conducting reconnaissance level reviews of these slides. Part of our work was to determine if these slides initiated on actively managed lands or not and, if so, to provide a preliminary opinion as to the influence that timber harvest and associated forest road construction might have had on landslide development. The scope of our analysis is qualitative, with our opinions based on field observations of site conditions and our experience in the forest evaluating past and future slope stability.

Approximately 50 percent of the landslides we traversed initiated in areas that either had never been logged or where it had been decades since the last timber harvest. Another 30 percent of the landslides initiated in buffers associated with more recent timber sales. The buffers excluded timber harvest activities in an effort to avoid timber harvest on potentially unstable slopes. Approximately 20 percent initiated in areas where management occurred prior to the current Washington State Forest Practices Rules (FPR) and would now be classified as potentially unstable landforms. It appears that the January 2009 storm was an unusually stressing event and that it was the trigger for the overwhelming majority of the landslides evaluated. There were only a few instances where it appeared that land management was a contributing factor to landslide initiation. This suggests that the current FPR effectively identify high hazard landforms that are prone to slope instability. Such landforms require geologic review when timber harvest or forest road building activities are proposed in those areas.

This storm event and associated landslides also highlight the importance of educating the public about landslide potential when homes are located at the base of steep slopes and that landslides pose a public safety hazard regardless of upslope land management activities. One avenue for this education process is through county critical areas ordinances.