The National Weather Service has issued a flood watch for portions of Northwest Oregon and Southwest Washington from Monday to Wednesday, and the potential for heavy rainfall in coming days has staff at the Linn County Road Department concerned about landslides, especially in the north canyon area.
County Engineer Chuck Knoll said staff members are especially concerned in the Mill City and Gates areas, which were heavily damaged by wildfires in September.
“There are some places where there are steep slopes along the road corridors and there could be landslides,” Knoll said. “The tops of some of the trees are green, but the bottoms of the trees are burned. There also were many trees in which the roots burned. If you remove the root structure, that may affect the stability of road shoulders in steep areas.”
Knoll said the Road Department has been monitoring some of the steep areas to determine if emergency work or more long-term repairs are needed.
“Yes, we are concerned,” he said. “We had some issues a couple weeks ago, and this current storm may bring up to eight inches of rain. It’s concerning.”
A list of roads closed due to flooding will be posted on the Linn County Road Department website at http://www.co.linn.or.us/Roads/roads.asp.
Salina Hart, chief of reservoir management and water quality for the Army Corps of Engineers, said mid-valley dams are not in the refilling stage and have reservoir capacity to retain some of the anticipated rainfall and then release it in a managed way to decrease flooding potential downstream.
“We usually rely on rainfall for refilling starting Feb. 1,” Hart said. “The current rainfall doesn’t really contribute to our refill, but we will regulate our water release in both the North and South Santiam Rivers as needed.”
Hart said the effect of the massive wildfires in the north canyon in September can already be seen in how rapidly water flows in the North Santiam River, and water release from Detroit Reservoir will be adjusted accordingly.
Grass and trees that would normally slow water runoff are damaged or completely gone, allowing water to run off more rapidly than normal.
Sand bags will be available at the Scio Public works and City Hall; Sweet Home City Hall and Public Library; Albany Public Works; Brownsville Recreation Center; Knife River at 28690 Highway 34, for Albany and Corvallis and 41816 Stayton Scio Road SE, Stayton.
The National Weather Service warning includes the Cascades and Cascades Foothills, Coast Range and Willapa Hills, Columbia River Gorge, Willamette Valley and Greater Portland metro area, Lower Columbia and I-5 corridor in Cowlitz County, Northwest Oregon and Southwest Washington coast, as well as a portion of southwest Oregon, including the Curry County coast and south-central Oregon coast.
National Weather Service staff say heavy rain can trigger landslides, rockfall and debris flows in steep terrain, and the risk is higher in burn areas.
Find the latest information at https://alerts.weather.gov/cap/or.php?x=1.
Debris flows are rapidly moving, extremely destructive landslides. They can contain boulders and logs transported in a fast-moving soil and water slurry down steep hillsides and through narrow canyons. They can easily travel a mile or more.
If your home, work or driving route is in a watch area:
• Stay alert. Track the flood watch by radio, TV, weather radio or online. If told to evacuate, do so immediately.
• Listen. Unusual sounds might indicate moving debris, such as trees cracking or boulders knocking together. A trickle of falling mud or debris may precede larger landslides. If you think there is danger of a landslide, leave immediately.
• Watch the water. If water in a stream or creek suddenly turns muddy or the amount of water flowing suddenly decreases or increases, this is a warning that the flow has been affected upstream. You should immediately leave the area because a debris flow may soon be coming downstream.
• Travel with extreme caution. Assume roads are not safe. Be alert when driving, especially at night. Embankments along roadsides may fail, sending rock and debris onto the road.
For more landslide and debris flow information, go to https://www.oregongeology.org/Landslide/debrisflow.htm.
Contact Linn County reporter Alex Paul at 541-812-6114.