The following is a statement by County Executive Pat McCarthy regarding landslide risks in Pierce County:
In the wake of the Oso slide, I convened a meeting of county experts in such areas as land-use planning, emergency management, roads, rivers and information technology to discuss Pierce County's level of risk for a catastrophic landslide.
Existing records in Pierce County don’t reveal landslides that come anywhere close to the magnitude of the Oso slide, which comprised an estimated 6 to 7 million cubic yards of earth. We regularly handle small slides - 10 to 100 cubic yards - that involve material slipping off of wet slopes, but not wholesale collapses of hillsides, especially in populated areas. This year alone, our public works crews have responded to 42 small slides that affected county roadways. The largest slide in our road division's records was a 1998 event in which 10,000 cubic yards of earth wiped out a portion of Cromwell Drive near Gig Harbor.
The county has gone above and beyond what some of our peers do with LIDAR technology. We have been working for months on an updated landslide risk map based on slopes, and that new data will be added to our permitting system in the next week. Property owners in unincorporated Pierce County can look up their parcels in the “About My Property” section of our website and see any known hazards, such as landslides, flooding and erosion. Our system flags such properties when building permit applications are filed, and the property owners are required to submit geotechnical analyses in many cases.
We have been focused in recent years on mitigating and planning for catastrophic events involving flooding and volcanic lahars. There's plenty of geological evidence to show those are the biggest risks, and our practice shows that if we know about it, we’ll do something about it. The scope of the Oso slide has certainly been eye-opening, and we will be consulting with the USGS and other partners, as well as further analyzing our own data to see if this should be added to our ongoing risk analysis and mitigation.
Our role as a local government is to balance the need to protect the public from harm and to protect private property rights. We have done a lot of work regarding lahars and floods. Right now, we don’t have any data that says catastrophic landslides are a bigger risk than is currently known.