Potential Danger of Debris Flows Issued for Large Portions of Western Oregon

The experts say drivers should not assume highways are safe.

Photo of Lake Oswego slide courtesy: Gert Zoutendijk/City of Lake Oswego

(PORTLAND, Ore.) - The National Weather Service in Portland says residents need to be prepared for the potential of debris flows and landslides as part of a Flood Watch issued for large portions of Oregon.

Affected areas include the Cascade Foothills in Lane County, Cascades in Lane County, the Central Coast Range of western Oregon, the central coast, Willamette Valley, the Coast Range of the northwest Oregon, the Greater Portland Metro area, Lower Columbia, Northern Cascades, Upper Hood River Valley and the western Columbia Gorge.

Flood related problems are also expected in southwest Washington. Areas of concern include the greater Vancouver area, I-5 Corridor in Cowlitz County, the south Washington Cascade Foothills, south Washington Cascades, south Washington coast, Western Columbia River Gorge and Willapa.

James Roddey, Earth Sciences Information Officer with the Oregon Department of Geology, says debris flows rapidly moving landslides. Steep slopes, canyons, gorges and the mouths of mountain streams are the locations of greatest risk.

"People who live in or near these locations should be alert to the possibility of debris flows during or shortly after periods of intense rainfall."

Roddey says residents should stay alert.

"Listen to the radio, TV, or a weather radio for flood watches, which include the potential for debris flows. If told to evacuate, do so immediately."

He also says it is important to listen for unusual sounds that might indicate moving debris, such as trees cracking or boulders knocking together. A trickle of falling mud or debris may precede larger landslides.

Roddey's advice for people in affected areas is to leave immediately if you think there is danger of a landslide.

"If water in a river or stream 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," Roddey said.

The experts say drivers should not assume highways are safe. Be alert when driving, especially at night. Don't overdrive your headlights. It is important to remember that embankments along roadsides may fail, sending rock and debris onto the road.

Landowners and road managers should check road drainage systems and conduct needed maintenance in case the predicted heavy precipitation does occur.

The official statement from the National Weather Service can be found at: weather.gov/alerts/or.html