This morning there were only a few reported landslides, one that occurred near Port Angeles that unfortunately resulted in the death of Neal Richards of WSDOT, who was struck by a branch while working on clearing the landslide. The only other reported landslides so far was by Jefferson County, who said they have received reports of mudslides. As the morning goes on, we should be able to gather more information on these landslides.

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A landslide has come down across Highway 20 at about 4pm, July 29 (2009). The landslide follows days of high heat and thunderstorms. Here is the rain total for the last few days.

July precipitation totals with landslide location

July precipitation totals with landslide location

I am switching the format around a bit to include Google Maps into the posts for a more interactive view.

According to the WSDOT website: “They have about 300 yards of mud and debris in a 10-foot-deep swath across the highway to remove, and need to ensure the slope is stable before they will reopen the road.” That is a good sized debris flow.

The debris flow appears to have come down somewhere near (or maybe in?) Swamp Creek, a tributary to Granite Creek.

Update

Here is some more information from the fine folks at WSDOT. The amount of material removed for the landslide was approximately 650 (or more) cubic yards of material. A dump truck carries, on average, 10 cubic yards, so we are looking at 65 dump truck loads of dirt. The work was completed by WSDOT road crews (sometimes this get contracted out for landslides) and the cost was probably a bit more than $3,000. That is dependent on a few factors, wages and equipment, but also dirt transportation and deposit (which becomes more costly the further out you have to go).

Here are some images from the WSDOT Flickr Site

SR 20 Debris Flow, looking up slope, of July 29, 2009 (WSDOT Photo)

SR 20 Debris Flow, looking up slope, of July 29, 2009 (WSDOT Photo)

SR20 Debris Flow over roadway, of July 29, 2009 (photo from WSDOT)

SR20 Debris Flow over roadway, of July 29, 2009 (photo from WSDOT)

Each week we will feature a new landslide in Washington State. Washington State is covered with dynamic and sometimes quirky landslides.

Pe Ell Landslide, Pe Ell, Lewis County

The Pe Ell Landslide failed during the December 3rd Storm of 2007, closing State Route 6 just west of Pe Ell.

Pe Ell Landslide - Photo by WSDOT

Pe Ell Landslide - Photo by WSDOT

The debris avalanche/slide flowed across the highway and pushed a truck into the living room of the house across the way. Remarkably, most of this was caught on tape by the residences of the house.

Pe Ell landslide impact of house - WSDOT Photo

Pe Ell landslide impact of house - WSDOT Photo

On December 11, Kelsay and I arrived at the landslide. The drive through the Chehalis valley was spooky to me, a lingering stench filled the air and misery could be seen all around. Home after home, farm after farm all showed damage from the floods. By time we arrived, WSDOT had already arranged for an emergency contract with Scarsella (on December 9th) to begin work on clearing State Route 6. Unfortunately, with all of the heavy equipment working on the site, we decided to stay on the periphery of the landslide and investigate the damage to the structures.

The damage was localized to the western lobe of the landslide. It impacted the houses at a low speed, warping and pushing them.

Pe Ell landslide impact to a house - DNR/DGER Photo

Pe Ell landslide impact to a house - DNR/DGER Photo

Pe Ell Landslide impact to second house - DNR/DGER Photo

Pe Ell Landslide impact to second house - DNR/DGER Photo

Meanwhile, WSDOT was working hard on figuring out the landslide. The WSDOT Geotechnical Division has access to many really neat tools to help with their investigations. Here is a 3-D representation of the landslide mass created by their division:

Pe Ell Landslide 3D Model - WSDOT Geotechnical Division

Pe Ell Landslide 3D Model - WSDOT Geotechnical Division

They also compiled a small scale geologic map of the landslide mass (with an amazing aerial photo of the landslide):

Pe Ell Landslide Geologic Map - WSDOT Geotechnical Division

Pe Ell Landslide Geologic Map - WSDOT Geotechnical Division

In the end, WSDOT removed over 47,000 cubic yards of material to stabilize the landslide mass at a cost of around $4 million dollars. The project was completed on March 13th, 2008, over three months after the storm.

The landslide prompted a debate on logging, landslides, and highway safety. The landslide itself was logged weeks before the storm. The interesting part, this landslide wasn’t caused by root strength loss, it was probably too deep anyway to have much impact. The lack of canopy, however, might have played a roll in the landslide initiation. Canopy plays a role in reducing the rate rainfall from reaching the ground (to a certain point) or slow melting of snow on the ground by reducing rain rates and buffering changing temperature. It is difficult to say in an intense storm how much it might have slowed the rainfall, or reduced snow melt (by reducing the warm rain and temperature from reaching the snow), but the lack of trees, even with this intense rainfall, probably did increase the likelihood for its initiation.

Cause aside, the cost of repairing these landslides is expensive. This is just one of probably hundreds of landslides to fall on our highway systems each year. Figuring out why these landslides fail and if we can either mitigate or possibly find better management practices to help reduce landslides would help save millions of dollars and reduce injury and death.

Interstate 90 through the Snoqualmie Pass/Hyak area is a very unstable area and has resulted in numerous rockfalls each year. WSDOT has conducted a Report to the Governor on Snoqualmie Pass (and other highways) and can be accessed here. According to the report, at least 5 fatalities have been caused by rockfalls on Interstate 90:

7/25/1970: 1
2/5/1998: 1
9/11/2005: 3
Source: WSDOT, Transportation Data Office, Collision Data and Analysis Branch

So, there shouldn’t have been much of a surprise when Interstate 90 was closed due to a rockfall. Here is an excerpt from WSDOT:

“Falling boulder closes eastbound I-90 at North Bend for five hours

Date: Tuesday, May 12, 2009

HYAK – Eastbound Interstate 90 closed to all traffic at North Bend earlier today. The road is now open. WSDOT crews closed the road at 2 a.m. after a large boulder fell off the hillside, bounced over the concrete jersey barrier and came to rest in the eastbound lanes. The boulder did not hit any vehicles, but a commercial truck struck the boulder.

WSDOT’s geotechnical experts climbed to the top of the hill to assess the situation and determined the road was safe to reopen at 7:15 a.m., Tuesday, May 12.

“We only opened the road when our experts told us it was safe for drivers,” said Paula Hammond, Washington State Secretary of Transportation. “Safety is our number one concern.”

An initial review of the site shows it is not on WSDOT’s list of unstable slopes. A more likely cause is the freeze thaw cycle in the area. …

“This can happen,” said Don Whitehouse, WSDOT Regional Administrator. “When you build a road through a mountain pass, rocks will fall. Our job is to make the area as safe as possible for drivers.”

Between 6 a.m. and 7 a.m. geotechnical experts hiked up the rocky slope, found two loose boulders, and pushed those onto the roadway below. Crews cleared the debris and reopened the road to all traffic.”

The boulder involved in the rockfall is quite small:

WSDOT Rockfall Highway 90

WSDOT Rockfall Highway 90

WSDOT Scarp of Rockfall Area

WSDOT Scarp of Rockfall Area

WSDOT Damage from Boulder

WSDOT Damage from Boulder

Luckily, no one was killed in this event, unlike the rockfall in 2005.