OSO – The soggy, sagging hillside that has been threatening to close Highway 530 for several weeks also could pull the plug on one of Seattle’s main power sources.
Looming directly above the potential landslide are two parallel rows of giant metal towers connecting four main power lines from Ross Dam in Skagit County to Seattle.
Engineers are trying to figure out how to stabilize the hillside before a slide occurs.
Their worst-case fear is that a big landslide could take down both sets of power lines.
If so, it would temporarily cut off almost a third of Seattle’s electricity, forcing Seattle City Light to buy power from other providers on the open market, said Dan Williams, a spokesman for the Seattle utility.
Even if that happens, Seattle residents probably would not experience any power outages, Williams said.
“It would involve some cost” to buy more power, Williams said, “but not a loss of power.”
Seattle City Light crews have been preparing for the worst by erecting huge goalpostlike structures out of telephone poles on both sides of the road.
The crossbars would allow emergency crews to drape fallen lines over them if one or more of the towers were to collapse, Williams said.
Rod Siverson, a Seattle City Light manager, said the towers aren’t likely to fall.
While the hillside near the road has shifted more than 12 inches, causing the road to slump, the footings of the towers are up the hill, which has yet to move, Siverson said.
“There’s no imminent danger,” Siverson said. “However, there’s no real good way to measure slides like this. So just to be on the safe side, we have put up some poles as a safety precaution.”
Nature has taken down a Seattle City Light tower near Darrington at least once before, Siverson said.
“One went into the Sauk River,” Siverson said. “The river actually turned course and ate off the whole bank for quite a ways. The bank just disappeared. When I got out there, the tower was hanging off the side of the cliff and not much holding it up.”
In that case, Seattle City Light simply shifted all the power to the parallel set of lines until new towers could be erected, he said.
The same could occur on Highway 530 if only one of the two parallel lines falls, he said.
“We do have some redundancies in case we have to take lines out or towers out for maintenance,” Siverson said.
For safety reasons, the power lines are designed to shut off if they collapse, he said.
Meanwhile, consultants for the state Department of Transportation continue to work on a plan to stabilize the hillside to prevent a major slide. A preliminary report could be ready sometime this week, said Travis Phelps, a department spokesman.
Reporter Scott Morris: 425-339-3292 or smorris@heraldnet.com.
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