At its peak, the ice storm of Jan. 19 knocked out the juice for 270,000 Puget Sound Energy customers. Some waited a week for the lights to come back on.
Trees did most of the damage. Ice-coated limbs and branches sagged and fell into electrical wires.
In the dark, it was easy to blame the utility for not trimming enough trees beforehand – but Siegfried Guggenmoos says the bigger culprit stares out of a mirror. In other words, it’s us, more specifically, our stuff: the trees in our yards, along our fences, on private land.
Guggenmoos is a special kind of specialist – an expert in vegetation management in the context of electric power transmission. He tracks patterns in what he calls “the utility forest.”
Now 62, he likes to say he got a degree in horticulture and became a mercenary.
Academic research led him to the study of brush control and herbicides under power transmission lines, and that led to a job as a system forester in Alberta, Canada, where Guggenmoos is based.
He’s written studies for utilities in two countries, including PSE in 2009. The gist of his findings: most of the trees that damage power lines grow on private property.
BETTER RELIABILITY
Cutting them down could improve power reliability by as much as 40 percent. The trouble is, people like their trees.
“There’s a choice between the level of reliability you have and the trees,” Guggenmoos said. “It really comes down to that. We can improve the reliability, but it means cutting down the trees.”
His 2009 study for PSE was commissioned after windstorms in 2006 cut power across the region, raising questions about the utility’s emergency response methods.
Guggenmoos found that the utility’s tree-trimming program was “well executed” and effective within public rights-of-way, but that much of the damage from falling trees occurs outside that boundary.
“What I found was that tree-related outages are due to the amount of tree exposure along the line outside the right of way,” he said “We did that on a statistical basis, so that we were actually able to make tree-related outages predictable based on wind speed.”
This year’s storms featured ice, not wind, but the underlying principles are similar, Guggenmoos said.
A tree-trimming program improves reliability in mid-level weather, but when conditions reach extremes, the best plans don’t help much. Windstorms take entire trees down, doing more damage to high-voltage transmission systems. Ice storms damage trees at the crowns, pulling down limbs and branches, which means a more localized effect at the level of distribution.
Guggenmoos has examined such effects on the East Coast and in New England, where storms, fallen trees and downed power lines come with winter. One big factor changes the dynamic between East and West: height. Our trees are taller.
In PSE’s service area, Guggenmoos found that 75 percent of the utility’s lines had trees adjacent to them. That’s a lot, but not as much as some areas of New England (in heavily forested Maine, the number climbs to 90 percent.)
However, in New England the average tree height hovers around 75 feet. In the Northwest, the average is 20 feet higher, with exceptional trees soaring 130 feet.
Height affects what Guggenmoos calls the arc of exposure: the taller the tree, the greater the potential damage. “When a thing like that comes down, it’s gonna be breaking poles, and it’s gonna be a long outage,” he said.
GROWTH NOT THE ISSUE
A common misconception about utility tree-trimming holds that tree growth is the chief cause of power-line damage. Guggenmoos found the opposite. Falling trees and limbs cause at least 85 percent of the damage in storms. Growth accounts for 15 percent at most.
Trees with falling potential are the real hazard (“tree failure,” Guggenmoos calls it) and that’s where the private property factor comes in. Cutting a tree on private property requires permission. Some owners won’t give it.
Utilities such as PSE can watch for hazardous trees, typically on a three-to-six-year cycle, but the hazards pay no attention to the calendar.
“There are always trees dying,” Guggenmoos said. “I call it the utility forest. Instead of it being a block, there’s this ribbon along the power lines. You’ve always got trees dying within that space. You can’t monitor all the trees that could conceivably hit your line in real time. It’s a matter of choice. Is it worth it to do annual inspections and removals, or is a three-to-four-year cycle adequate?”
Shifting to underground power lines is harder than it sounds. It works in new subdivisions, but in existing neighborhoods, it’s prohibitively expensive to dig and build.
Plus, it doesn’t help that much in power outages. Guggenmoos examined such efforts in the city of Baltimore, and found a different set of consequences: utility workers found it difficult to pinpoint the damage, and outages lasted longer as a result.
In the absence of easy solutions, the dilemma remains. If you want more reliable power, you’ve got to take down more trees, including those that people might prefer to keep.
“We know how to improve reliability and decrease storm damage,” Guggenmoos said. “We really have a societal issue.”
Sean Robinson: 253-597-8486
sean.robinson@thenewstribune.com
