February 17, 2014
You may recall the July 23, 2013 PUD commission meeting where citizen concerns about liquefaction on the right bank of the proposed Sunset Falls diversion were discussed. In the meeting PUD staff characterized the underlying silt and clay as being “consolidated” and “formed under immense pressure”, however unlike most of Snohomish County, these soils were not associated with ice contact. The sediments that comprise the right bank are water bearing and are susceptible to liquefaction according to the “liquefaction susceptibility map of Snohomish County, Washington” – available online.
During the Pleistocene (Vashon Stage), the Puget Lobe of the cordilleran ice sheet made its last major advance. During this advance most of the major rivers flowing westward out of the North Cascades were dammed by glacial ice and morainal debris. Also during this time, the continental ice sheet and the alpine glaciers existing in the North Cascades never coalesced, leaving much of the westward flowing valleys ice-free. With the mouths of these valleys dammed, glacial lakes were created within these major river drainages (Tabor et al,1993).
The glacial dam (embankment) for the Skykomish River was located approximately one mile west of Index, which is west of Sunset Falls. This embankment exceeded 1000 feet in height and reached a maximum elevation of approximately 1600 feet. With the embankment in place, glacial Lake Skykomish was created backing water up the Skykomish River Valley for many miles. During the period in which the Skykomish River was dammed, a thick sequence of rhythmically bedded glacial lacustrine sediments (silt and clay) was deposited. In the vicinity of Index, these glaciolacustrine deposits are relatively thick and reached an elevation of approximately 800 feet. (If built, the Sunset Falls diversion would be at elevation 650 feet). As the Puget Lobe began to thin as a result of glacial retreat, the spillway of glacial Lake Skykomish began to erode down through the embankment resulting in a continual lowering of the base level of the lake. As the base level of the lake lowered, the glaciolacustrine sediments were incised by the Skykomish River – ultimately to the level in which the river flows today (Badger, 1990).
The ongoing slow landslide at Sunset Falls is also associated with these sediments that were deposited on the steep slopes adjacent to the river. The road owners have exhausted their financial resources and have further exacerbated the problem by incrementally removing the toe of the slide, leading to further instability. Repairs will cost hundreds of thousands of dollars and most likely take years to complete.
It is very troubling that false assurances have been provided regarding the geologic hazards at Sunset Falls, however there is still time for the commission to require an updated assessment before committing additional resources to the proposed project.
Thanks for listening,
February 3, 2014
Do you recall the “low impact criteria checklist” prepared by Snohomish PUD for the Sunset Falls Hydro Project? (Slide 6 of the Sunset Falls “Project Update Jan 2013”).
One of the items on the checklist that I would like to bring to your attention is the item titled “No known geological hazards or unstable areas”.
This checklist was used in the Sunset Falls presentation to the PUD commissioners on Jan 8th, 2013. It was also used in testimony before the State Congressional Energy, Environment and Telecommunications Committee on January 24, 2013, regarding Sunset Falls Hydro. It is published on the SnoPUD website and is included in the materials that SnoPUD directs reporters and the general public about the Sunset Falls Hydro Project. This checklist PowerPoint slide was also enlarged and displayed at both SnoPUD Public Open Houses, Feb 27th and 28th 2013 on the Sunset Falls Hydro Project.
Unfortunately it is well known that the Sunset Falls site is subject to frequent and severe landslides, although you will not find this information prominently discussed in the pre-application document for the proposed Sunset Falls hydro project. For example BNSF railroad relocated its line at Sunset Falls in the 1960’s due to landslide risk.
Snohomish PUD is poised to invest millions of dollars studying the proposed project, which is fine, except for the fact that a massive landslide has blocked access to the proposed study site. According to the Washington State Department of Emergency Management, this slide event is in its beginning stage and its ultimate impacts have not been fully determined. What is known is that the only roadway adjacent to Sunset Falls is essentially impassible and initial estimates for repair of the current slide are on the order of several hundreds of thousands of dollars at a minimum. The local residents who are the owners of the road do not have the resources to make the repairs. The area of current concern is a small section within a much larger zone of frequent landslides that is located directly above the proposed power tunnel.
This problem is about to be dumped in your lap on the eave of your investment of millions of dollars in the approved project study plans.
How is this possible considering the fact that you have been repeatedly assured that “No known geological hazards or unstable areas” exist?
Thanks for listening,