State and local public works crews are assessing the damage left from last week's flooding.
In Columbia County, a section of Highway 47 near Mist was washed away by the surging flood waters. Work to repair that section of the highway is underway this week.
"We have hired a contractor to make repairs on OR 47 in Mist and work started yesterday," Oregon Department of Transportation (ODOT) spokesman Don Hamilton said. "There is no estimate on completion as we need to have the pipe manufactured. We may have a better timeline by the end of the week."
The significant rainstorms have eased but the heightened travel danger across the region remains, according Hamilton.
“If you are traveling, you need to be very careful,” Hamilton said following the Highway 47 washout Friday, Jan. 7. “We have had a lot of water in Northwest Oregon and there is lots of danger. You need to watch for high water, landslides and falling trees and tree limbs.”
A Portland man died after his vehicle was struck by a falling boulder on the Washington side of the Columbia River Gorge, according to Washington State Police.
Damage assessments and clean up are also being conducted following landslides that occurred in the Columbia River Gorge.
Landslides are caused by a combination of factors, including the type of geology, the slope, and usually water, according to the Oregon Department of Geology and Mineral Industries (DOGAMI) Geologist Robert A. Houston
“With repeating storms, the soils do not have enough time to drain and so the water builds up in the soil and leads to failure or a landslide,” Houston told the Chronicle in a published interview in February 2020.
According to a DOGAMI executive summary report about the landslide hazards in Columbia County, landslides and debris flows are common in the Oregon Coast Range due to the combination of high precipitation, steep slopes, and landslide-prone geologic units. Cutting through the northern Coast Range, the U.S. Highway 30 (Oregon State Highway 92) corridor is prone to slope instability.
The study indicates that the Highway 30 corridor in Columbia and Clatsop Counties is at significant risk from landslide hazards. Landslides cover 25% of the study area, and 33% of the City of Clatskanie is covered by large, deep landslides. The large number of people and structures residing on these deposits highlights the potential danger present and shows the need for public awareness on landslide hazards.
“The areas that have had landslides before (historic and prehistoric or ancient) are the areas of first concern,” Houston said. “This is because landslides tend to happen in the same places repeatedly through reactivation or the combination of factors talked about in the above question.”
People, structures and roads located below steep slopes in canyons and near the mouths of canyons may be at serious risk. Dangerous places can include:
- Canyon bottoms, stream channels and areas of rock and soil accumulation at the outlets of canyons.
- Bases of steep hillsides.
- Road cuts or other areas where slopes of hills have been excavated or over-steepened.
- Places where slides or debris flows have occurred in the past.
According to DOGAMI’s A Homeowners Guide to Landslides, a landslide is the downward slope movement of rock, soil or debris. Debris flow, earth flow, rock fall, mudflow, mudslide, and slump are also terms for landslide.
Landslides can take human life. However, even a few inches of slope movement can disrupt septic, sewer and water lines and crack foundations severely damaging or destroying your home, according to the guide.
If you live on or near a steep slope, the guide encourages you to look for warning signs of landslides by evaluating your property for signs of landslide movement. Many, but not all, signs of landslide activity are listed below. A high score may indicate the presence of a landslide.
Inside Your Home:
- Cracks in walls
- Nails popping out of walls
- Bulging walls
- Separation of chimney from walls
- Creaking/popping noises
- Light switches coming out of walls
- Doors/windows hard to shut
- Twisted beams
- Cracks in floors
- Water seeping into basement
Outside Your Home:
- Changes in surface drainage
- Bulges in retaining walls or tilting of walls
- Cracks developing in the soil
- Pistol-butted or bent trees
- Broken water, utility, or sewer lines
- Cracks in sidewalks or foundation
- Stretched or leaning utility lines
The guide also recommends actions property owners can take to reduce the chances of landslides, which include:
- Draining water from surface runoff, downspouts, and driveways well away from slopes.
- Planting native ground cover on slopes.
- Consulting with a professional before significantly altering existing slopes uphill or downslope of your home.
The Oregon Department of Transportation (ODOT) is also keeping a close watch on the landslide potential in Columbia County following significant rainstorms.
ODOT officials said there are a number of areas on all of the Oregon coast range highways that are being monitored daily for slides by ODOT crews, including on Highway 30 at milepost 33 and milepost 39 between Columbia City and Rainier.
ODOT conducted a $1.3 million rockfall repair in 2018 to scale back a rocky cliff to solve a landslide threat at milepost 63 near Clatskanie.
During periods of heavy rainfall, travelers should recognize that there is a higher likelihood that slides can happen, according to ODOT officials, who said said drives need to slow down, drive carefully, pay attention to their driving, avoid distractions, and watch for hazards.
According to DOGMI, average annual repair costs for landslides in Oregon exceed $10 million, and severe winter storm losses can exceed $100 million. As population growth continues and development into landslide susceptible terrain occurs, damage and loss from this natural hazard will continue to grow.
For more information:
- View the DOGAMI web map to see landslide areas https://gis.dogami.oregon.gov/maps/slido/
- View the homeowner’s guide to landslides at https://www.oregongeology.org/Landslide/ger_homeowners_guide_landslides.pdf