County tracking slow slide near Index

Over the past 12 months, the hillside south of Sunset Falls near Index has continued its slow-moving downward journey, gobbling up Mt. Index River Road and making its way to the Skykomish River.

As the landslide continues to grow, so does the momentum behind the Snohomish County Public Utility District's proposal for a new hydroelectric facility at the base of Sunset Falls. The Sunset Fish Passage and Energy Project would reroute water from the south fork of the Skykomish River, taking advantage of the river's unique Z-shape. The diverted water would travel through roughly 2,200 feet of subterranean tunnels to a semi-underground powerhouse at the base of Sunset Falls.-á

The tunnels about 83 feet underneath the river would be blasted out of bedrock using controlled dynamite charges. Project opponents fear that blasting in such close proximity to an active landslide could be dangerous to nearby residents.

The project's proposed intake site is situated east of the landslide; the powerhouse to the north.

In January, PUD filed its Draft License Application (DLA) with the Federal Energy Regulatory Commission (FERC), the agency tasked with licensing hydroelectric projects. The submission triggered a 90-day comment period, which concluded on April 27.

The PUD has its Final Licensing Application (FLA) slated for submission later this year. -á -á

The project has faced widespread opposition from property owners, conservation groups, tribal agencies and other stakeholders. Opponents have asserted that because of the landslide, Sunset Falls no longer meets PUD's own criteria for locating new hydroelectric projects. A total of seven criteria were outlined in PUD's 2013 Pre-Application Document, one of which stipulates that areas of consideration should have "no known geological hazards or unstable areas that would preclude construction.GÇ¥

On April 27, FERC received a 27-page letter of opposition co-authored by 11 conservation agencies, including American Whitewater, the Sierra Club and the Mountaineers. On Page 22 it states, "A major landslide immediately adjacent to the project began in December 2013 and continues to grow. This geologic issue is well known and has been widely reported in the local media as a "massive landslide.' GÇ¥

The landslide first became active in mid-December 2013, partially blocking Mt. Index River Road. The roadway was a crucial thoroughfare at the time, because it was the only access to U.S. 2. In order to evaluate the slide, PUD deployed a field engineer from GeoEngineers on Dec. 20, 2013, who concluded that "additional major movements are not likely.GÇ¥

But less than a month later, the hillside shifted again, knocking out power and stranding numerous residents. The Snohomish County Department of Emergency Management (DEM) sought an emergency proclamation for the Index slide on March 16, 2014. Six days later, the Oso slide took place, drawing county resources to help in recovery efforts.

Mt. Index Riversites residents were hit hard, left without access to U.S. 2 for several months. Those lucky enough to have gotten a vehicle out prior to the road becoming completely impassable would leave their cars parked at the base of the falls and hike back to their homes.

Eventually, PUD came in and helped the community fund an access bridge, which crosses over Canyon Falls and connects near the area known as "GGÇ¥ section. -á -á

The hillside in Index never stopped moving. One of the challenges Snohomish County faced in its response to the Index slide was private land ownership. The area surrounding Sunset Falls, including Mt. Index River Road, is all private property, which stymied opportunities for governmental assistance.

County Planning & Development Services (PDS) staffers Randy Sleight, chief engineering officer, and senior site inspector Mike Braaten, have been closely monitoring the slide since it started. Initially, the role of PDS was to ensure public safety by tagging at-risk residences to prohibit occupancy.-á

Sleight and Braaten have watched the slide move and shift over time, closely documenting its evolution with photos and video.

The Index landslide is considered to be a slow moving, deep-seated rotational landslide. This is evidenced by trees and household structures that appear to be knocked backward toward the upper part of the slope, rather than thrust forward down the face of the slide. Mt. Index River Road no longer exists. In its place is a slow-moving sea of grey mud, which is now feeding directly into the river.

The jagged head scarp at the top of the slope has eaten further and further into the hillside, and numerous secondary scarps have formed underneath, forming a stair-step effect. The flat area at the top of the slope, once home to numerous trees, has vastly diminished over time. Initially, Sleight and Braaten estimated it was roughly 50 to 80 feet wide. Now it's less than 10.

"It's maybe five feet and you're starting to go down the other side now,GÇ¥ Braaten said.

The appearance of the slide is striking, and the integrity of the ground through its central region is completely unpredictable. Areas in the clay that give an impression of firmness are apt to give way almost immediately with the pressure of a footstep, causing rapid, instantaneous sinking in the muck.

Sleight said he took one wrong step and sunk up to his knees.

"It looks like a moonscape now,GÇ¥ Sleight said.

During a recent site visit, Braaten reviewed video captured by nearby property owner Lora Cox and her partner, Dr. Pete Rainey. She and Rainey were out hiking near the falls in February, when they heard a loud crackling sound. Cox captured video footage of significant movement occurring in the middle of the slide, including falling trees and a massive gush of what appears to be water pouring down the face of the hillside.

Braaten showed the video to Sleight, and the two conducted additional reconnaissance at the site.

As they surveyed the area, Braaten and Sleight realized that the elevation of the gushing water was roughly the same as the river, less than 700 feet away and directly behind the slide near the intake site. This led them to consider the possibility that the river may be in the process of rerouting itself, essentially creating a shortcut to Sunset Falls by forcing its way through the hillside.

It's not uncommon for rivers with major bends to try to straighten themselves out, Sleight said.-á

But deeper analysis of the surrounding topography and its geologic composition caused them to retract that hypothesis. Geotechnical reports reflect that the area was formerly a valley between two bedrock formations that became filled with transitional beds of glacial sediment. Holes permeating the beds act as a conduit for groundwater, a condition referred to as "piping.GÇ¥

By climbing up the face of the landslide, it is possible to discern the holes in its different levels.

"If the river was trying to sneak through there and do a short cut, it would be coming constantly out those lower holes, but that's not the case right now. The lower holes are dryer and we're seeing water coming down from the smaller, upper holes,GÇ¥ Sleight said. "It leads me more to think that this is what we would refer to as transitional beds with small pockets of piping.GÇ¥

Recent clearcutting to the east may have contributed to the hill's instability, Braaten and Sleight said.

Braaten estimates the slide has nearly quadrupled in size since December 2013, and noted it has been joined by another, separate landslide to the west.

As far as risks associated with the PUD's proposed tunnel, Sleight said he was not concerned about the tunnel construction triggering more slides. The larger concern, he said, would be if the river actually was rerouting itself, which would render the project moot.

They plan to closely monitor the slide's future progress.

In the DLA, the PUD has outlined a number of blasting recommendations for mitigating negative impacts. During tunnel construction, one or two blasts would occur daily, using the minimum amount of explosives necessary to cause the bedrock to fracture. They would implement micro-second delays that would "limit the magnitude of the ground vibrations and spread the accelerations over a longer period of time.GÇ¥-á

Meters would be used during construction to monitor slope movements.

"With these measures in place, Project construction is not expected to cause any conditions that would precipitate landslides. These measures would also minimize noise, vibration and fugitive dust,GÇ¥ states the DLA.

Rainey owns a home less than a half-mile downstream from the landslide. He has referred to the slide as a "loaded gun pointed at my house,GÇ¥ and does not feel that PUD has adequately studied its implications. He estimates its current size to be roughly 900 feet wide, 700 feet deep and 250 feet high from the base of Sunset Falls to the top of the ridge, which he says is much larger than what is depicted on maps and photographs included with the DLA.

He is not dismissing the theory that the river could be working to reclaim an old course. In his April B25 comment to FERC, Rainey pointed out that if the groundwater was being supplemented by water coming from the river, it would explain why the slide is so active in its middle region. Based on his frequent visual surveys of the area, Rainey told FERC there is continuous water flow in certain parts of the slide, which he has observed "long after weeping from other surfaces has stopped.GÇ¥-á

Rainey alleges the PUD's study of the ongoing landslide has been insufficient, calling study conducted via phone consultation with state geologists "hearsayGÇ¥ that would be "inadmissible in a court and has no business being in a license application.GÇ¥-á

"The landslide presents considerable safety risks for residents immediately downstream from the Project site, as well as for anyone engaged in construction of the Project,GÇ¥ wrote Rainey. "SnoPUD has not conducted any meaningful investigation of the landslide proper since January 2014, when the slide was still a baby. It has subsequently relied on speculations from geologists who have never visited the landslide.GÇ¥

For more information on the Sunset Fish Passage and Energy Project, visit www.snopud.com/PowerSupply/hydro/sfpep.ashx?p=1956.