January 25, 2006

On January 25, 2006 the Steelhead Haven landslide began what would become the largest since 1967. Residents reported seeing some large sediment slumps early in the week, but it wasn't until Wednesday that the entire slope gave way and pushed thousands of cubic yards of earth across the river over 200 feet, covering the sand bar in the aerial photo below. One fisherman wasn't aware of the slide until the water began rising around his waders.

By Saturday January 28th, the river recut through an abandonned channel on the adjacent floodplain. Residents and agency staff reported the eerie sound of trees constantly snapping as the river pushed them over. In an unprecedented move, Snohomish County worked with the Army Corps of Engineers to help remove trees and excavate this channel to prevent flooding the many homes built on the Channel Migration Zone. By Monday the river had risen from 2000 cfs (cubic feet per second) to 15,000 cfs. The Corps and the County placed rock and wood to protect homes from the rising water.

As of Feb. 13, the new channel and the slide appear stable for the time being. However, the community is still at risk from erosion and continued headcutting and widening of the new channel. A public meeting will be held later in February. Meanwhile the County and the Corp will continue to monitor the slide for further changes and fulfill permitting obligations for the emergency measures that were taken.

The top photos is courtesy of Snohomish County, as is the following link to a full length presentation (8MB file): Geology is now.