Thursday, December 13, 2018

Sauk River Dynamic Channel Migration

The Sauk River is a tributary River to the Skagit. It is in part fed by waters from Glacier Peak and in late summer is cloudy from glacial sediment. After a dry stretch of winter weather, the rive was clear when I recently visited the Sauk a bit up stream from its confluence with the Skagit. 

The Sauk is a dynamic river that moves about on its valley floor. I have made a few geology assessments considering channel migration and subsequent erosion hazards on the Sauk. Others have as well (http://skagitcoop.org/programs/restoration/sauk-river-migration-analysis/). My recent trip up the Sauk allowed me to take a look at a river reach I had evaluated 15 years ago.

Well casing has survived the erosion so far

Concrete and piping at former home site

Foundation and septic tank lid

Ongoing bank erosion

For modest homes along the river, stopping channel migration on the Sauk is prohibitively expensive. Besides the permitting issues, the Sauk is a big river with very high flood flows, and thus bank protection would require large scale engineered structural solutions beyond the reach of small rural home owners. Channel movement on some reaches of the Sauk has been as much or more than quarter mile. The lower end right before the confluence is especially dynamic and can readily be seen along the Concrete-Sauk Road.

Lower end of Sauk with broad areas stripped of trees by recent channel movement

That movement has found its way to the valley edge and took a bite out of the Concrete-Sauk Road.


Overflow channel aimed at the Concrete-Sauk Road

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