From Oregon Dept. of Geology
THE NATIONAL WEATHER SERVICE HAS ISSUED A FLOOD WATCH IN EFFECT THROUGH FRIDAY MORNING FOR RIVERS AND CREEKS IN NORTHWEST OREGON AND SOUTHWEST WASHINGTON. HEAVY RAIN AND SNOWMELT IS CAUSING RIVERS AND CREEKS TO RISE SHARPLY. MINOR FLOODING IS POSSIBLE ON SEVERAL RIVERS, ESPECIALLY THOSE DRAINING THE NORTH AND CENTRAL OREGON COAST RANGE. NOTE THAT FLOOD WARNINGS ARE ALREADY IN EFFECT FOR THE MARYS AND LUCKIAMUTE RIVERS IN THE WILLAMETTE VALLEY.
A FLOOD WATCH MEANS THERE IS A POTENTIAL FOR FLOODING BASED ON CURRENT FORECASTS. LANDSLIDES AND DEBRIS FLOWS ARE POSSIBLE DURING THIS FLOOD EVENT. DEBRIS FLOWS ARE DANGEROUS, RAPIDLY MOVING LANDSLIDES. STEEP SLOPES, CANYONS, GORGES AND THE MOUTHS OF MOUNTAIN STREAMS ARE THE LOCATIONS AT GREATEST RISK. PERSONS THAT LIVE OR MAY TRAVEL THROUGH THESE LOCATIONS SHOULD BE ALERT TO THE POSSIBILITY OF DEBRIS FLOWS DURING OR SHORTLY AFTER PERIODS OF INTENSE RAINFALL. NEVER DRIVE THROUGH FLOODED AREAS. THE WATER MAY BE TOO DEEP TO ALLOW FOR SAFE PASSAGE OR THERE MAY BE UNSEEN DAMAGE TO THE ROADWAY.
Care should be taken when traveling over the mountains during this time. The most dangerous places 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.
Debris flows are rapidly moving landslides that can destroy everything in their paths. They can easily travel a mile or more, depending on the terrain. They will contain boulders and logs and transport those in a fast-moving soil and water slurry.
Some areas are more hazardous than others when the danger of landslides is high. If there is a flood warning, stay away from the river. Stay away from steep slopes during intense rainstorms. Knowing ahead of time where the danger areas around your home for potential landslides might be is the first step in being prepared.
Follow these steps:
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 is wet outside, be careful when cleaning up the mess. A small mudslide can actually be part of a larger landslide. Cleanup should not be done until after the storm.