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Mon August 22, 2011
Elwha River dam removal historic, but not explosive
PORT ANGELES, Wash. – Seattle's Kingdome collapsed with a bang. Explosive demolition experts also brought down the cooling tower at the former Trojan nuclear plant. But if you're hoping for the same excitement from the upcoming destruction of two big hydropower dams on Washington's Elwha River, you'll be disappointed.
The history-making dam removal that begins in September will happen slowly and methodically.
The two hydropower dams blocking the Elwha River on the Olympic Peninsula are coming down to restore legendary fish runs. The upper dam on the Elwha will be the highest ever to be purposely removed.
Don Laford seems unfazed by the task. He's the Elwha project manager for the construction management company URS.
"Most all of demolition of the dam itself will be done with excavators fitted out with hydraulic concrete breakers," Laford says. "They'll break it into sections, dig it out, put it in trucks and haul it away. There actually is no dynamiting or blasting planned for the dam section itself."
That distant roar in the background is the river pouring down Elwha Dam's spillways. It's a thundering torrent now that the powerhouse intakes are shut off.
Tearing down both Elwha dams will open 70 miles of prime salmon spawning habitat, much of it in Olympic National Park.
Crane operator Andrew Seid is one of the first workers from the demolition contractor, Barnard Construction Co.,to arrive.
"I've done a little bit of demolition, but nothing this size," he says. "So it's interesting."
Seid hails from Boise. He considers himself lucky to get this assignment.
"It will definitely be something a lot of people will know about," Seid says. "So if I tell them in the future, 'Oh, yeah, I was on the Elwha project,' I'm sure it will be a big recognition for me."
Elwha Dam – completed in 1913 – is squat and broad. The other dam is tall and narrow. That upriver dam, Glines Canyon Dam – completed in 1927 – is 210 feet tall, nearly twice as high as its downriver sister.
At Elwha Dam, crews will build a temporary diversion upstream so they can deconstruct one side of that dam high and dry. Next the river will be shifted into the new gap while the other sections get torn down.
The other dam
Simultaneously, crews will chip away at Glines Canyon Dam using a different strategy. Don Laford compares it to nibbling kernels off a corncob, back and forth.
"The idea of the notches is to let the water out," he explains. "Then the water will drop and then they can go along the dam and take out the concrete either side of the notch. And then put another notch in and go down, down the line."
Teardown of the two dams is scheduled to take three years. That's much longer than Pacific Power estimates it will take to remove another big dam, this one on the White Salmon River in southwest Washington. Condit Dam is also nearly a century old and blocks fish passage.
This October, contractors plan to blow a hole in the base of the 125-foot tall dam. The lake behind it will drain in one big gush of muddy water, like poking a hole in the bottom of a rain barrel. Afterwards, Condit Dam can be briskly and methodically chopped up.
The Elwha dams have more sediment behind them. That necessitates a more deliberate approach says Olympic National Park spokesman Dave Reynolds.
"The crux of this project, especially with Glines Canyon, is the amount of sediment that is stored up behind that," he says. "That's the reason for the three year schedule."
Reynolds says it's not just the biggest dam removal in history, but also the biggest controlled release of sediment. What's more, the City of Port Angeles draws its drinking water from the Elwha River. There's also a fish hatchery and a low-lying Indian reservation to consider.
"It is a long drawn out process, but it's gotta be controlled or else we're going to be in deep trouble," Laford says.
If you want to watch the dam removal progress, there soon will be a new overlook trail and a pair of webcams.
On the Web:
- Dam removal kick-off events schedule
- Elwha River restoration
- Animation of Elwha Dam removal
- Animation of Glines Canyon Dam removal
- Condit Dam removal project
Copyright 2011 Northwest News Network