Friday, June 14, 2024

Study Ranks Chelan County 7th in U.S. for Landslide Vulnerability

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CHELAN COUNTY – Landslide season just began, and Chelan County is ranked seventh in the nation for landslide vulnerability, according to a recent study.

Gutter Gnome compared 743 counties with moderate to very high landslide risk according to FEMA, and ranked them based on three factors: landslide risk, landslide triggers, and financial risk. 

Of the highest ranked counties, most were located in Oregon, California, and Washington. Chelan County ranked eighth in both landslide risk and financial risk categories, and 91st in landslide triggers. Snohomish County was right behind Chelan, landing in the top ten for the landslide trigger category. 

While Chelan County ranked high in landslide risk, actual landslide occurrence is fairly infrequent, according to Chelan County’s 2020 Multi-Jurisdiction Natural Hazard Mitigation Plan. The plan credits the reason being that much of the land in the county is on bedrock, which is not susceptible to landslides. However, the plan reads, “because of the steep topography and narrow valleys of Chelan County, the potential for slides is high all year round,” which may contribute to a higher risk ranking.

The 2018 Washington State Enhanced Hazard Mitigation Plan reported 23 significant landslide events in Chelan County since 1960, tied with Skagit County. According to Chelan County’s plan, “This would equate to an annual probability of 39.7% or a recurrence interval of 2.52 years for that period.”

Among the landslide triggers listed in Gutter Gnome’s study were earthquakes, droughts, wildfires, and historical average yearly precipitation, which typically cause larger, or deep seated, landslides. Chelan County’s plan also accounts for human factors such as construction, drainage or groundwater alterations, and changes in vegetation as potential causes for smaller, or shallow seated, landslides.

Landslides can pose risks to both property and people. According to Chelan County’s plan, the replacement value of property at high risk of deep seated landslides totals more than $172 million. For property at moderate risk for shallow seated landslides, the replacement value totals more than $1.8 billion.

The plan also states that almost 12 percent of the total planning area population lives in an area that is at moderate to high risk of deep seated landslides, and 18 percent are in areas at risk of shallow seated landslides.

Gutter Gnome suggests people can limit their property’s exposure by avoiding building on steep slopes, regrading their properties, planting trees that help with erosion control, and improving rainwater dispersal methods. Researching where landslides occur in the area, signing up for emergency alerts, and having an evacuation plan are also recommended.

Taylor Caldwell: 509-433-7276 or taylor@ward.media

 

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