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From the Oregon Department of Geology and Mineral Industries
The National Weather Service has issued a flood watch that includes a special weather statement advising residents and travelers in western Oregon, north of Florence and Cottage Grove, and SW Washington, of the increased potential for debris flows as a result of large amounts of rain.
This is especially true in the Coast Range and the Cascade Mountains as heavy rain is expected through Monday.
Debris flows are dangerous, rapidly moving landslides. Steep slopes, canyons, gorges and the mouths of mountain streams are the locations of greatest risk. People that live in, or may travel through, these locations should be alert to the possibility of debris flows during or shortly after periods of intense rainfall.
- 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.
"Debris flows are rapidly moving landslides that can destroy everything in their paths," said James Roddey, Earth Sciences Information Officer for the Oregon Department of Geology and Mineral Industries (DOGAMI). "Dangerous debris flows can easily travel a mile or more, depending on the terrain. They'll contain boulders and logs and transport those in a fast-moving soil and water slurry."
"People want to know what they should do when they hear about the potential for debris flows and landslides," said Roddey.
"Some areas are more hazardous than others when the danger of landslides is high. People know that if there's a flood warning, they should stay away from the river. We also want them to start thinking about staying away from steep slopes during intense rainstorms. Knowing ahead of time where potential landslides areas are around your home is the first step in being prepared," explains Roddey.
- Stay alert. Listen to the radio, TV, or a weather radio for flood watches, which include the potential for debris flows and if told to evacuate, do so immediately;
- 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;
- If you think there is danger of a landslide, leave immediately;
- 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;
- Assume highways are not safe. Be alert when driving, especially at night. Don't overdrive your headlights. 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.
Cleaning up after landslides can also be hazardous. "When it's this wet outside, people need to be careful when they're cleaning up the mess. A small mudslide can actually be part of a larger landslide," explains Roddey. "Cleanup should not be done until after the storm."