Water Resources of the United States

PROJECT ALERT NOTICE (WA) Oso landslide, update

Date: Sun, 30 Mar 2014 01:51:25 EDT

Summary: There have been no significant changes since yesterday: the North Fork Stillaguamish River continues to flow across the debris dam that formed due to a large landslide and the water continues to gradually erode a larger channel.

There have been no significant changes since yesterday: the North Fork Stillaguamish River continues to flow across the debris dam that formed due to a large landslide and the water continues to gradually erode a larger channel.

Lake levels measured by one of two buoys that were deployed yesterday can now be viewed at http://wa.water.usgs.gov/data/oso.html (station 12166200).

Heavy rains have started and the National Weather Service has forecast a peak of 7,200 cubic feet per second at the North Fork Stillaguamish River at Arlington (4,200 cubic feet per second at Oso) for early Sunday morning. Higher flows in combination with a rising lake level (0.9 feet over the last 24 hours) may allow for floating debris in the lake behind the landslide to move downstream. The National Weather Service has issued a flood advisory.

Increased flows will accelerate erosion of the debris dam. Catastrophic failure of the debris dam is considered unlikely but conditions will be monitored closely.

Two USGS scientists were on site today to monitor the landslide with local and state agencies and develop an automated landslide monitoring system, and two USGS scientists measured streamflow discharge and turbidity at the newly installed gage about two miles downstream from the landslide (station 12166300). Starting today, a USGS scientist has been stationed at FEMA's coordination center in Bothell, WA, to provide assistance and coordinate with other federal agencies.

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