A series of landslides hit Sitka more than eight years ago during heavy rain, with the largest striking a new subdivision and killing three workers. It prompted the community, led by the Sitka Sound Science Center, to set up a landslide warning system.
The system includes rain gauges and soil-moisture sensors spread around town, with a website that advises people of the risk level of a landslide.
It took about four years to develop the system — and a lot of federal grant money.
“We started when we had our landslide. We started calling scientists and asking: ‘What do we need to know about landslides,’” Lisa Busch, executive director at the science center, said Friday, Nov. 23.
The system includes 10 rain gauges spread out north and south of downtown, and soil-moisture sensors, she said.
It does not include motion sensors, which are not very useful for the fast-moving, watery debris flows that roar down a hillside, she explained.
The rain gauges and moisture sensors transit real-time data, which is collected and analyzed by a geoscientist for the low-, medium- or high-risk warnings posted to the website at sitkalandslide.org.
The high-risk warning includes the message: “Multiple landslides are very likely to occur in the Sitka area. There have been three storms in the last 20 years with similarly intense rainfall, and all three of them initiated multiple landslides.”
Sitka has gone to a medium-risk warning twice in the past year, Busch said.
The website also provides a terrain map, showing areas of low to high susceptibility of landslides.
“Rain intensity is definitely a factor” in slides, she said. “The climate scientists say we’re going to have more events. … People are realizing this is what it means to respond to climate change.”
Besides learning more about heavy rains and the potential for landslides, each community should decide what level of risk people are comfortable with, and if they want to designate safe places for residents to gather during high-risk periods, Busch said.
One thing the Sitka team has learned from its gauges is that rainfall can vary widely across the same community. “They’ll be as different as four inches,” she said of the reading from gauges around town.
The National Science Foundation awarded a $5 million, five-year grant in February 2022 to the Sitka Sound Science Center to start work on a network that someday could reach across Southeast.
The money is not enough to set up a system for every community, nor will it cover ongoing operational expenses of a full network.
The project was designed to develop monitoring and warning systems in collaboration with tribal entities in six communities: Yakutat, Skagway, Hoonah, Klukwan, Kasaan and Craig.
The money will also go toward the Kutí Project, which will use data from sensors and historical records to develop “predictive models of the impacts of extreme weather events in Southeast Alaska,” according to the science center’s grant announcement. “It will study the impacts of atmospheric rivers on this region’s coastlines.”
Kutí is the Lingít word for “weather.”
The Central Council of the Tlingit and Haida Indian Tribes of Alaska also is on the Kutí team, along with several state and federal agencies and two universities in Oregon.
Alaska’s senior U.S. senator, Lisa Murkowski, succeeded in getting a $500,000 federal grant this year through the U.S. Geological Survey to help train people in the measuring equipment. The Sitka Sound Science Center and Tlingit and Haida will share in the grant, Busch said.
Managing and analyzing the data from the gauges and sensors is a big part of the job, she said. It could cost a million dollars a years to operate a warning system across Southeast Alaska, from Metlakatla to Lynn Canal.
The biggest of the slides that hit Sitka on Aug. 18, 2015, killed Elmer Diaz, 26, his brother Ulises Diaz, 25, and William Storz, 62, who were working at a new subdivision under construction. It came after 2.6 inches of rain fell in a 10-hour period, including 1.5 inches in a three-hour stretch that morning.
There were at least six landslides in various parts of town that day.
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