Before rainy season really kicks in, the city has advice for people on “landslide-prone” property – steps you can take immediately, as well as a free landslide-awareness workshop here in West Seattle in a few weeks (in addition to one in North Seattle). Read on for the city’s full announcement:

The start of the wet season has begun in Seattle, and heavy rain can increase the chance of landslides due to soil saturation, which reduces slope stability. November is Seattle’s wettest month (8.96 inches of rainfall in November 2009). Since Nov. 1, 2.51 inches of rain has fallen at Sea-Tac Airport-exceeding the seasonal average by 1.2 inches, and pushing the area over the landslide threshold.

Property owners of landslide-prone sites are advised to clear drains and take other simple measures, such as: checking downspouts, to make sure they are functioning and routed to a safe location; and inspecting sloping areas of their property for indications of slope movement (such as cracks in the ground, and newly tilting trees) and erosion.

To help residents understand how they can better manage their landslide-prone property, the City of Seattle has set up two free public landslide awareness meetings. The meeting presentation will include a discussion of the causes of landslides, proper drainage for sloping sites, and vegetation maintenance on slopes. This will be followed by a question and answer session and time for one-on-one discussions with professionals in the field, including the City of Seattle, The American Society for Civil Engineers, The Association of Engineering Geologists, The International Society of Arboriculture, and Associated Building Contractors.

Landslide Awareness Meeting Details

Nov. 20 – 10:00 a.m. to Noon
Northgate Community Center Multipurpose Room
10510 5th Ave. NE (across from Northgate Mall)

Dec. 4 – 10:00 a.m. to Noon
South Seattle Community College
Judge Warren & Nobie Chan Education Center
6000 16th Ave. SW (across from the north parking lot)

Seattle Landslides

The landslide record that was documented in the Seattle Landslide Study indicates that 86 percent of landslides that have occurred in the city have some human influence such as excavating and filling on steep slopes, broken pipes and uncontrolled storm water.

Since the devastating landslide season of 1996/1997, which involved over 300 reported landslides, the city has taken steps to prepare to respond to slides and construct mitigation projects to reduce the potential for slides to occur. It has also been presenting these public landslide awareness meetings for owners of landslide prone property.

If a landslide damages your property and you have an immediate concern for your safety, leave the premises and call 9-1-1. Seattle property owners with structures that may be affected by or endangered by a landslide should contact a Geotechnical professional for structural evaluation.

To view the current conditions of the USGS rainfall threshold for landslides, please visit: http://landslides.usgs.gov/monitoring/seattle/rtd/plot.php.

For more information about Seattle landslides or the City of Seattle free landslide
awareness meetings, please visit:
www.seattle.gov/dpd/emergency/landslides