Sunday, November 16, 2014

BNSF Railroad and Unstable Bluffs near Bellingham

In late 2012 and early 2013 there were close to 100 shallow landslides that closed the rail line between Seattle and Everett, Washington due to wet weather and slopes above the railroad tracks becoming repeatedly saturated (railroad-landslide-closures). There was even a landslide that hit a moving train during that period.

The rail line just northwest of Bellingham has not been closed by landslides, but faces a significant risk of landslides in the future as the railroad track runs along the top of a steep eroding shoreline bluff.  

Its worth enlarging this picture to see the failure scarps at several places on the slope as well as a drain pipe installed to reduce water on the slope. 

Railroad without much space 

I routinely assess steep shoreline bluff slopes and recommend setbacks for homes from the top edge of steep shoreline bluffs - this section of railroad would not conform with recommended setbacks. But like homes close to the edge of a potentially unstable slope, the view is great. And I have enjoyed the view from the train while heading up to Vancouver, BC.
 The beach is very narrow at least along parts of the bluff and high water routinely reaches the toe of the slope causing erosion.
Shallow surface failure on bluff

The bluff is underlain by unconsolidated late ice age deposits of silt and clay and sand and gravel. The small slide shown above is the result of the toe of the slope being eroded by waves and then the slide area slowly working its way up the slope.

This reach of shore is exposed to south and west winds and has a large enough fetch and orientation such that large waves can be generated and combined with large storm surges.

A future challenge for the railroad.  

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