Firm holds second town hall about landslide findings
April 7, 2022
Further monitoring is needed to predict when future slides are most likely to occur in the December 2020 Beach Road landslide, representatives of geotechnical firm Landslide Technology told community members at a town hall on Tuesday.
George Machan, senior engineer at the firm, gave an abridged presentation similar to the one he gave at a town hall two weeks ago about the firm’s updated findings report, which was based on several months of data collection and analysis from the 2020 landslide area.
Machan highlighted, as the report concluded, that the 2020 landslide path is “marginally stable” and still at risk of future slides and that continued monitoring and data collection would help determine specifics about potential slide activity.
The hillside immediately adjacent to the path, on either side, appears more stable than the debris-covered slope but still at risk, the updated findings report said. Machan advised at the first town hall not to build homes directly in the 2020 landslide path.
Several questions from community members on Tuesday revolved around the firm’s understanding of the dynamics among rainfall, groundwater pressure and slope stability and to what extent certain metrics like rainfall could be used to predict slides or as a guide for safety.
Landslide Technology senior geologist Charlie Hammond said the firm has limited data, given that it’s only been monitoring for a matter of months, and he would be cautious about using the firm’s analysis to-date to make projections.
“It’s too small of a database to use,” Hammond said. “This dataset could only improve with more monitoring.” He added that two full seasons of monitoring likely would be needed to make projections. Since there hasn’t been a major storm since Landslide Technology began monitoring the hillside, it’s hard to know exactly how much rain is too much, the consultants said.
Beach Road property owner Cindy Buxton asked if the borough could use groundwater data, if not rainfall levels, to devise safety protocols.
“I still think there are things that we need to learn from (the piezometers). It’s hard to set a threshold based on what we know so far,” Machan said. “When you do experience a five-inch or a seven-inch rainstorm, or some other big ones, those data points will matter and will allow setting thresholds. Right now I don’t know what that is. We’re not able to put a number on it at this point.”
Landslide Technology’s contract with the Alaska Department of Transportation to continue monitoring expires in September.
Haines Borough Mayor Douglas Olerud said at some point this spring geologists from Landslide Technology and R&M will walk Beach Road with neighborhood residents to point out areas that could be issues or positive features and also to provide borough staff and officials with feedback for mitigation planning. Olerud said the borough would be in touch with landowners when it has more information about the schedule.