Assembly opens Beach Road neighborhood

 

April 15, 2021

Courtesy of Haines Borough.

The map, included in the "Winter Reconnaissance - Preliminary Findings Report'' produced by Landslide Technology earlier this month, is based on state LiDAR data collected in May 2014. It shows significant features and slope elevation in the Beach Road area prior to the Dec. 2 landslide.

The Beach Road neighborhood will open to the public for the first time since Dec. 2 after the Haines Borough Assembly voted Tuesday to rescind a resolution limiting access. At the same meeting, assembly members formed a Beach Road task force to consider short-term and long-term access issues.

On Dec. 2, a landslide on Mount Riley killed two residents, destroyed several houses and left most homes on Beach Road Extension separated from town. The Haines Borough limited neighborhood access while awaiting the results of a geotechnical study.

The findings report from the study was published in Tuesday's assembly packet. It attempts to answer questions including why the Dec. 2 landslide occurred where it did, the likelihood and risk level associated with various geologic hazards threatening the neighborhood, how to mitigate risk when accessing the neighborhood, and next steps for the borough.


"Going into when they first revealed (the report) to us, I was extremely nervous that we wouldn't get much to move forward on, but after the first presentation, (interim manager) Alekka (Fullerton) and I came out of the office and said, 'Did we just hear all the good news we thought we heard?'" Mayor Douglas Olerud said.

In each section of the report, engineers from Landslide Technology were careful to emphasize the preliminary nature of the findings.

"The preliminary findings provided herein are based on desktop studies of available information and observations gathered during a snow-hindered winter reconnaissance. Until completion of a more detailed/unhampered (above-ground) reconnaissance and subsurface investigation, these findings should be considered preliminary and incomplete," reads the second paragraph of the executive summary.


Despite the findings' preliminary nature, Beach Road property owners and borough officials said it gave them hope.

"I felt really encouraged by it. They outlined what they thought were the main causes of the slide. One was the weather, which was the trigger. But for some reason the slide occurred there and not elsewhere," said local geologist Cindy Buxton, who owns property in the "red zone" on Beach Road.


The report describes a "lobe of material" near the top of the slide path that was observed in pre-slide LiDAR imaging of the zone and is "interpreted to be a significant source of area for the Beach Road landslide." High groundwater pressure, caused by heavy rains, likely triggered movement at the toe of the lobe.

The report hypothesizes that the area where the slide occurred had thicker deposits of "colluvium" (loose, unconsolidated sediment that tends to collect at the base of steep slopes) than the surrounding area because of a fault line running up the hillside on the town side of the slide path.

"The fault would have broken up the bedrock which would have been otherwise solid, allowing water to infiltrate and weather the rock, making it more susceptible to sliding. The other thing noted by (state geologists) was that at the top of the slide, a stream was pouring right into it. You have water, broken rock, a steep slope, and it led to a slide," Buxton said. "I find that encouraging because that means it's localized. It gives you some confidence that the same conditions aren't everywhere else in the neighborhood."


The report lists eight potential geologic hazards that could still pose a threat to the neighborhood, rating each in terms of risk and likelihood of occurrence. Landslide Technology senior associate engineer George Machan, primary author of the report, said he thinks the list encompasses most potential threats.

Scenarios include catastrophic failure of landslide debris, localized failure of debris, loose boulders rolling downhill, crumbling of slopes near the top of the slide path, slumping of the tension crack observed in ground adjacent to the slide, failure of bedrock slopes on either side of the slide, failure of colluvial slopes on either side of the slide, and erosion of the bedrock newly exposed by the slide.


Most scenarios were given low to moderate risk and likelihood of occurrence ratings with the exception of the catastrophic failure of the existing slide debris, failure of adjacent colluvial slopes and erosion of the newly exposed bedrock. The catastrophic failure of slide debris is classified as "a high-risk event with low likelihood of occurrence." The colluvial slope failure is considered moderate to high risk with low to moderate likelihood of occurrence. Bedrock erosion is considered low to moderate risk with a high likelihood of occurrence.


The crack observed in the ground adjacent to the Dec. 2 landslide is classified as a "low-to moderate-risk event with moderate likelihood of occurrence" in the report. Prior to the report, state geologists had flagged the crack as a potentially serious threat to the neighborhood, although they said they lacked the data to accurately assess the risk level and likelihood of occurrence.

Machan said the crack was likely created when the adjacent slope failed on Dec. 2.

"As debris moved downslope, it dragged on the ground to the side, and that dragging effect could cause some of the slope to displace," he said in an interview Tuesday. "We're suspecting it's not very deep and could have a limited amount of material. It's more likely a daily, slow-moving process, not a catastrophic one."


According to the report, if the crack were to give way, it would likely fall into the same slide path as before.

Machan said the hazard assessments, like the rest of the report, are preliminary at this point. "Based on what we know, that's how we'd categorize them right now," he said.

The report recommends conducting spring reconnaissance to verify the preliminary findings. The state is in the process of negotiating this contract. It will likely cost somewhere close to $345,527, the price of the winter reconnaissance, according to state geotechnical engineer Travis Eckhoff, who oversaw the winter project.

Although the assembly unanimously supported opening the temporary access road, which until then had been limited to Beach Road residents on ATVs or on foot, they acknowledged the need for ongoing monitoring, particularly as temperatures warm.

"I would expect as things thaw, that that kind of a road will deteriorate," Machan said, addressing assembly members at Tuesday's meeting.

Assembly member Paul Rogers listed a series of safety measures he would like to see put in place.

"We need a sign there that says, 'Travel past this point is at your own risk.' We need to try to make the road stable enough so that if we need an ambulance out there, we can get an ambulance out there... I also think we need, in addition to that, some weekly observations of the road for the foreseeable future," Rogers said.


Todd Winkel, a Beach Road resident who spoke during public testimony, expressed appreciation for the assembly decision. For the past several months, Winkel and other neighborhood residents have been urging the assembly to restore access and power.

"This has been my favorite assembly meeting of the year," Winkel said, adding that he thinks the borough needs to improve communication with residents moving forward.

The newly formed Beach Road task force will include two neighborhood residents and will take up safety considerations for road reopening at its first meeting on Friday.

Courtesy of Haines Borough.

The map, included in the "Winter Reconnaissance - Preliminary Findings Report'' produced by Landslide Technology earlier this month, is based on state LiDAR data collected in December. It shows significant features and slope elevation in the Beach Road area after the Dec. 2 landslide.

In addition to the two Beach Road members who, as of Tuesday evening, had yet to be named, the task force includes construction experts Don Turner Jr. and Matt Boron, public facilities director Ed Coffland, interim manager Alekka Fullerton, assembly members Jerry Lapp and Cheryl Stickler, and safety experts and Beach Road property owners Julie and Noble Anderson.

 
 

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