Work planned for Yellowknife airport to deal with thawing permafrost

The Yellowknife airport is planning for some work in the coming years on its runways, to deal with thawing permafrost.

Yellowknife Regional Airport manager Randy Straker says geotechnical engineers were contracted last year to look at ground settling found on the runways.

"They basically said climate change resulting in permafrost loss was the contributor to the settling that we're seeing at the airport. Settling is never a good thing when you're talking runways," said Straker.

Permafrost is present in ground that has been at 0 C or lower for at least two years in row. When permafrost thaws, it can cause ground movement including settling or subsidences and those can be more severe in areas where there was more ice in the permafrost.

After the N.W.T. government sought proposals from contractors in February 2023 to complete the geotechnical study at the airport, Tetra Tech was contracted for $232,066. Engineers took observations and drilled for core samples in areas where the ground was settling.

Straker says Tetra Tech presented its findings in March of this year after studying ice and moisture content as well as surveying areas for permafrost or bedrock. He says they found that the permafrost beneath the airport had changed significantly over the last decades.

"In 2005, all bore-holes that they drilled at the time encountered permafrost except for two. During the study done last year, only five of 14 bore-holes encountered permafrost," he said.

Straker said in locations where there was still permafrost, it had "degraded significantly."

Yellowknife Regional Airport manager Randy Straker says Tetra Tech presented its findings in March of this year after studying ice and moisture content as well as surveying areas for permafrost or bedrock. (Liny Lamberink/CBC)

He says currently there are no immediate threats to the runway but getting the scientific data helps determine the sort of work that may be needed in the next five to ten years.

Infrastructure a crucial factor to thawing

Permafrost thaw across the North has put some infrastructure at risk, including buildings and homes, as well as roads.

Steve Kokelji, a senior permafrost scientist at the Northwest Territories Geological Survey, says climate change is one factor causing ground settling but disturbing the natural state on the ground is an important part to consider as well.

He noted how vegetation, soil and snow on the ground can affect how energy is exchanged from the atmosphere to the ground. That changes when areas are developed and built on.

"Regardless of whether the climate is stable or the climate is cooling, or you're in the high Arctic where it's cold or in the subarctic where it's warmer — when you actually take those natural conditions away and replace them with infrastructure, that changes," said Kokelji.

On places like a runway or a road, Kokelji said clearing snow can help cool the ground beneath because snow acts an insulator. But when snow is removed and collects on the edges, it can accelerate the warming of the soil beneath there, he said.

Kokelji said there are measures that infrastructure managers can take to cool permafrost and slow thawing, but those tend to be expensive.

Straker said there are currently 13 projects the airport is looking to include in its initial capital improvement plan. He said the hope is to have the plan completed by the end of this year.

He said repair work to the runways could include removing some asphalt and a bit of the underlying groundwork and then levelling it. Another option is a much deeper dig under the runway to fix what's below by replacing sediment with a different type of base and putting asphalt again on top.

Straker said repairs to keep runways safe and operational are especially important in northern communities, given that medical travel and transporting food or cargo are just a few key services that people rely on.

"Yellowknife airport, it's not a city airport. We are a regional airport and very critical for remote communities and sovereignty," he said.