Clackamas Countys greater susceptibility to landslides is back in the spotlight with storms hitting the region over the weekend.
Oregon City officials shut down the popular Waterboard Park last week after a boulder toppled off a hillside and stopped just shy of two homes. Meanwhile, the massive mudslide March 22, in Oso, Wash., Saturday, caused more deaths than any Pacific Northwest landslide in the past 100 years.
According to geological experts, those deaths may have been preventable if Snohomish County had invested in more maps that assess landslide risk using Lidar technology. Portlands West Hills and the area surrounding Oregon City are particular hotbeds, according to official warnings.
As particularly hazardous, recently Lidar again targeted Oregon Citys Newell Creek Canyon, where the Forest Edge development was built for hundreds of residents in 1994 amid expert testimony about the apartment complexs effect on the movement of an ancient landslide.
Landslides in late 2010 again alarmed Forest Edge residents after the area moved substantially in 2006 following heavy rains, forcing the evacuation and subsequent demolition of two buildings. The property owner had to pay to relocate a sewer-pump station and stormwater piping systems, and made surface repairs while regrading driveways and landscaping.
Maps from the Oregon Department of Geology and Mineral Industries (DOGAMI) show landslide risks in the northwestern part of Oregon, but Snohomish emerged a symbol of disparities among counties after government cutbacks prevented updating maps in the area where search teams are still looking for survivors. Due to the many local landslides, Clackamas County was in 2009 declared a national disaster area, which opened up funding from FEMA used to create a new set of maps to show where landslides have occurred in the past, and where they might occur in the future.
Most counties dont look as extensively at natural hazards, but the Salem and Portland areas have up-to-date maps documenting past landslides as well as thousands of potential risk areas, said Bill Burns, a DOGAMI engineering geologist. He and other DOGAMI experts are saying that the saturated soil conditions caused by spring storms could lead to additional landslides, especially in the Northern Oregon Cascades, Coast Range and Columbia River Gorge.
The Troutdale formation on top of the Columbia River basalt is especially susceptible to the slow-moving larger landslides such as is occurring at Forest Edge, Burns said. But flood deposits from the historic Missoula flood tend to blanket slopes with silt and sand that creates shallower and potentially more dangerous soil under homes.
These are relatively younger, looser materials than the Columbia River basalt, Burns said. It covers most of Northwest Clackamas County, and the type of material that it is makes it much more susceptible to landslides. Were concerned about those yellow areas as well, because we dont want people to think, Oh, these are safe areas.
According to DOGAMI, the most dangerous places throughout the rainy season are below steep slopes and near the mouths of canyons. You can learn more about landslides and debris flows and how to prepare for them at oregongeology.org.
OC homeowners caught unaware
Average annual repair costs for landslides in Oregon run more than $10 million, so potential homeowners should look at these maps to decide whether or not to apply for landslide insurance (which is difficult to obtain) or whether to live in the area at all.
Oregon City police said the boulder dislodged around 6 a.m. and toppled down a bluff at Waterboard Park just off Promontory Avenue and stopped just before hitting two homes with families sleeping inside. Steve Shirley lives near Waterboard Park and shuddered at the thought of what could have happened after the boulder came tumbling down the hill with a trail thats popular with runners.
If this hillside comes down, it could be bad. Im hearing about the stuff in Washington right now with all the rain weve had, and theres some people running up the trail up there, and you can see where its already washed off, Shirley said.
Police put up signs, blocking off all entrances to Waterboard Park, which used to serve as a thoroughfare for traffic before mudslides and geological activity shut it down.
Neighbors and park goers told KOIN 6 News that they are hoping for a solution, but with some $1.2 million in unfunded projects, fixing the historic park could prove challenging, according to Oregon Citys Public Works Director John Lewis, who is bringing in experts to assess the danger.
Its too early to tell, I dont know what the plan is there. Obviously, the city has funding for basic repairs. This could have much bigger implications to it, Lewis said.
Unincorporated Oregon City resident Christine Kosinski has frequently testified to what she fears would occur after the city approved concept plans for South End, Park Place and Beavercreek Road, where she said landslides and hazardous geological issues would pose serious threats to life and property. In the absence of regulation, she hopes new homebuyers ask the right questions and become aware of environmental issues surrounding the purchase of certain properties.
Taxpayers will want to ask themselves if certain developments may pose increased risk which may equate to the taxpayers picking up the tab for such disasters, Kosinski said. Once landslides occur, the property owner is caught unaware and left with sometimes huge debt to either rebuild or repair damages to their homes or property.
If you are in one of these areas that have higher risks for landslides, there are many things you can do. Risk-reduction activities include controlling the stormwater or hiring a geological engineer to give you recommendations, which range from a simple retaining wall to a more complicated drilling rig to examine what type of materials lie underneath a site.
Most of the communities down there are still absorbing this material and deciding what to do about it, Burns said. Our part of this process is to get the science out there, and the next part is taken on by other folks like consultants to make a recommendation to a developer.