Can Snohomish County plan for landslides?

Should the Oso landslide disaster change land use and permitting in Snohomish County?

Although the area was known to be prone to landslides, the tragedy that occurred on March 22 was far beyond what anyone had imagined possible. In recent decades, we know that studies were performed, reports were issued, and even meetings held at the Oso Fire Station. The focus of those investigations was largely on the impacts of the previous slides along the Stillaguamish River to flood risks and salmon populations.

We also know that the slide area had been studied previously for potential buyouts due to frequent flooding as were other similarly prone places around the county. Ultimately, decisions were made in 2004 to not proceed with buyouts for the Steelhead Haven area, and instead to focus efforts on other even more flood-prone areas. Again, the focus was on flooding, not the potential landslide hazards.

Technology is available to help us to better identify and understand landslide hazard zones. In the days following the slide, LIDAR images (Light Detecting and Ranging) taken of the area revealed that the river valley to the east and to the west had previously experienced many, some even larger, landslides. These probably occurred over the past 10,000 years. While this type of information is sometimes used for natural resources management such as logging, it has largely not yet made its way into land use and permitting by local governments.

Snohomish County’s existing regulations are based on the best available science at the time they were adopted. Generally, although there are some exceptions, construction in landslide hazard areas require setbacks of a minimum of 50 feet or half the height of the slope, whichever is greater. The March 22 slide dwarfed both distances.

Questions about what we should do bring up further questions. What is the role of county government? Is it to protect people from 100 percent of all natural hazards? Is it to protect them to some reasonable level? What is a reasonable level? Is the role of government to inform people of known hazards and let them make their own decisions? Or should there be no role whatsoever and people should be able to build and live wherever they want, regardless of known hazards?

One month after the slide, I proposed a temporary moratorium on building near identified landslide hazard areas in the county. This moratorium would have applied to properties be within one-half mile of a mapped hazard area — a distance that would have covered the Highway 530 disaster. The resulting map, a surprise to us all, showed that there are almost no areas in the county that would be outside the moratorium zone. Additional maps showing the areas within one-quarter and one-eighth miles revealed the same challenge.

LIDAR imagery gaps currently exist within Snohomish County and across the state. Many areas have never been mapped. The estimated cost to fill those gaps is approximately $4 million for Western Washington. The landslide hazard maps project initiated many years ago by the Washington State Department of Natural Resources was later stopped prior to completion by the Legislature in order to cut costs.

Make no mistake, LIDAR technology is no panacea. By itself, LIDAR can’t tell us that this slide or that slide occurred at a date certain, nor can it tell us when the next slide will take place. But it is an important and valuable tool because it helps to recognize patterns based on historical activity.

We know that we cannot protect everyone from every known natural hazard. If we developed rules to protect everyone everywhere from such things as landslides, floods, wildfires, tsunamis, volcanic lahars and earthquakes, there would not be a square inch in Snohomish County available for people to live or work. The reality is that we live in an area that is very geologically active. The privilege to revel in its beauty does not come without risks.

So where do we go from here?

I propose that we:

Invest in updating our information systems with reasonably available technology;

Provide a special notice with all building permits located within one-half mile of a landslide hazard zone regardless of whether or not a permit is already vested to existing regulations;

Require geotechnical assessments be performed and liability waivers be signed for new construction located within these hazard areas. If someone chooses to build there then they must also accept the inherent risks. No public liability or bailout using taxpayer dollars;

Develop a smart landslide hazard rating system that accounts for site specific characteristics such as slope, geology, hydrology and other risk factors;

While we are building this smarter system, let’s increase the required setbacks near slide prone areas to three times the height of the slope and ensure people receive notification when they are building or buying in higher risk areas;

Partner with the federal, state and other local governments to develop a standard hazard warning system that can be easily understood by all;

Work with the federal, state and local governments to enhance information sharing within departments and agencies at all levels;

Direct the County Executive’s Office to initiate a comprehensive review and recommend potential amendments to existing county codes related to hazard areas.

The Snohomish County Council will hold a public hearing to discuss these issues at 10:30 a.m. Wednesday. If you are unable to attend but would like to share your thoughts you can also email them to

The magnitude of the mudslide was a terrible, unforeseeable tragedy. It would be another tragedy if we did not advance our understanding of these types of events, provide our citizens with the best information we can, and seek to improve our rules and regulations based on what we have learned.

Dave Somers is chairman of the Snohomish County Council.

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