On warming North Slope, one flood response last year cost pipeline operator $10 million

This photo shows damage along the trans-Alaska pipeline corridor during a spring 2019 flood of the Sagavanirktok River on the North Slope. (Photo courtesy Alyeska Pipeline Service Co.)

As winter turned toward spring last year, a potential problem popped up about 25 miles into the trans-Alaska pipeline’s 800-mile route, where it sits alongside the Sagavanirktok River on the North Slope.

The company that runs the pipeline, Alyeska Pipeline Service Co., notified the Alaska Department of Natural Resources.

“They saw the ice was building up, and it looked like it was going to go over the top of their flood control structures,” said Tony Strupulis, DNR’s state pipeline coordinator.

The ensuing flood cost more than $10 million to fix; the damage is still being repaired. And as the North Slope has become wetter and warmer, its rivers have been running at record high levels.

Scientists say they expect those types of trends to continue as Alaska’s climate changes. But they also say there’s still some uncertainty around some of the data on snow and rainfall, and they add that the degree to which climate change will affect the pipeline is still not clear.

“I don’t know the near-term future or long-term future. But the effort to maintain the pipeline will have to improve — they’ll have to spend money to protect it,” said Horacio Toniolo, a civil engineering professor at University of Alaska Fairbanks who’s studied the Sagavanirktok River.

The pipeline system is a robust piece of infrastructure. Adjusting for inflation, it cost $35 billion to build, and the damaged stretch was mostly buried underground. But there’s an unavoidable threat that runs alongside it on the broad, flat area of the North Slope south of Prudhoe Bay: the Sagavanirktok, or Sag River.

Last spring, the river’s normal channel filled up with something called aufeis — basically sheets of layered ice that divert its normal flow. The aufeis, plus an unusually warm spring and quick melt, sent the Sag River toward the pipeline, eroding away Alyeska’s protective barriers.

“It was a pretty broad swath, a new channel that came in and actually scoured away enough material so that there was a section of pipe that was uncovered,” Betsy Haines, Alyeska’s senior vice president for operations and maintenance, said in a phone interview.

The erosion exposed about 90 feet of pipe to the river’s flow — a serious problem that increases the risk of a puncture or spill, though that didn’t happen in this case. Repairing the damage and building taller barriers will cost Alyeska between $10 million and $15 million, Haines said.

The event comes as the North Slope is undergoing some major changes connected to global warming. The region has seen a temperature increase in the past half-century of more than 6 F — by far the largest of anywhere in Alaska.

Precipitation rose by 10 percent over the same period, and scientists expect those trends to continue. But Haines said Alyeska hasn’t observed effects on the pipeline that will force big-picture changes in the way the company handles the risk posed by the Sag River. And she added that the pipeline’s design for resisting floods was solid.

“Might we change it in the future? (We) might,” she said. “But it would go back to collecting the data, working it across the different industries and educational institutions, and really trying to draw through that analysis things that can be a little bit more substantiated or predictable.”

She added: “We don’t call it climate change or global warming. What we’re dealing with are hard facts, and from an engineering perspective, trying to understand those.”

Alyeska doesn’t deny that climate change is happening, and Haines said the company — owned by BP, ExxonMobil, ConocoPhillips and UnoCal — has, over the past few years, put more effort into understanding what’s happening with the permafrost under areas of the pipeline. But she said it’s still too early to draw any conclusions.

The average flow in the Sag River, meanwhile, has been increasing. And the past two years were its highest on record.

But because there have long been large year-to-year swings in rain and snow on the North Slope, scientists say the recent increases aren’t enough to establish a “statistically significant” trend. The change could still be just random variation, said Rick Thoman, a climatologist at the Alaska Center for Climate Assessment and Policy.

“For temperatures, by any measure, those have increased beyond all doubt,” Thoman said. For precipitation, he added, “the noise, if you will, is large — much larger than with temperature. So, it takes a much stronger trend or over a much longer period of time.”

Flooding from the Sag River has caused damage in other spots along the pipeline corridor in recent years — most notably in 2015, when it forced the closure of the Dalton Highway used to haul supplies to the North Slope’s oil fields. The damage, according to reports at the time, stemmed from heavy rains the previous summer, a deep winter freeze and rapid spring thaw with record temperatures.

Research led by a scientist at the American Association for the Advancement of Science predicts climate change could cause more than $5 billion in damage to Alaska infrastructure.

Alyeska, which ships the fossil fuels that scientists say are the main driver of global warming, does not have a position on policy measures that could reduce carbon emissions, like the Paris climate agreement, Haines said.

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