A muffled roar and a puff of pulverized concrete preceded a rush of silt-laden water Wednesday as contractors set free southeast Washington’s White Salmon River by blasting a hole through the base of PacifiCorp’s Condit Dam.

The waters of Northwestern Lake and sediment that has long been collecting below the dam surged down through the 13-foot-high by 18-foot-wide drain tunnel created in the dam’s 90-foot wide base during August and September.

A video of the blast is available at http://whitesalmontimelapse.wordpress.com/

The hole allowed the draining of 1.8-mile-long Northwestern Lake in a matter less than two hours and restored long-blocked passage to upstream habitat for salmon, steelhead and other fish species.

Condit, which held back the 92-acre lake/reservoir, was equipped with fish ladders when first built in 1913, but the passage devices were twice washed out due to floods during the early life of the dam. A final attempt was made in 1925, when experiments were done on a newly designed fish elevator, without success.

Tribal leaders were among the 150 people gathered for the scheduled event. All hailed the prospects for rejuvenated fish populations in the upper basin. Condit is three miles upstream from White Salmon’s confluence with the Columbia.

“The White Salmon is sacred to the tribes because it flows from Pahto or Mt. Adams,” said Gerald Lewis, a member of the Yakama Nation Tribal Council and the chairman of the Columbia River Inter-Tribal Fish Commission. “This river system has always provided for our people. Now the White Salmon River can begin to heal and when that happens, those that depend on the river will also heal. The salmon and lamprey will return and our tribal members will be here to meet them.”

Tribal leaders from the Columbia River Inter-Tribal Fish Commission and its four member tribes (Umatilla, Yakama, Warm Spring and Nez Perce) celebrated the blast along with local officials and representatives of other entities long involved in talks that led to the breaching.

PacifiCorp, which owns the dam, and prime contractor JR Merit of Vancouver, Wash., along with the detonation crew from Kiewit Infrastructure West, also of Vancouver, surveyed the blast zone, took readings from sensing devices on the dam and flew over the area in a helicopter before declaring the breach event a success and the remaining structure safe.

“Condit has served our customers very well for nearly a century,” said Micheal Dunn, president and chief executive officer of PacifiCorp Energy, which operates 46 hydroelectric facilities in the West. “We are sad to lose this emission-free source of power.

“But we made a decision to work with our settlement partners to come to the most reasonable solution for everyone involved, especially the cost to our customers. For the next 11 months, we will proceed with the safe dismantling of the dam structure and work toward restoring the natural streambed of the area.”

The second largest dam to be removed in the United States for fish passage, the Condit breach comes 12 years after a 1999 legal settlement was reached over whether the dam should be removed, or fish passage provided. Demolition is under way at the 210-foot-tall Glines Dam on the Elwha River on Washington’s Olympic Peninsula. Condit is a 125-foot high, 471-foot long concrete gravity diversion dam.

The settlement agreement outlined a removal process for the dam that was less expensive than installing fish passage, as would have been required for the company to renew its federal license to operate the dam. The cost of decommissioning and removing Condit is currently estimated at about $33 million, including funds already spent during the planning process, according to PacifiCorp.

Settlement parties include: American Rivers, American Whitewater, Columbia Gorge Audubon Society, Columbia Gorge Coalition, Columbia River United, Federation of Fly Fishers, Friends of the Columbia Gorge, Friends of the Earth, Friends of the White Salmon, The Mountaineers, Rivers Council of Washington, The Sierra Club, Trout Unlimited, Washington Trout, Washington Wilderness Coalition, the Columbia River Inter-Tribal Fish Commission , the Yakama Nation, the U.S. Forest Service, the U.S. Department of the Interior, the National Marine Fisheries Service, the Washington Department of Ecology, the Washington Department of Fish and Wildlife and PacifiCorp.

Condit blocked access habitat historically used by coho, spring chinook and fall chinook salmon, steelhead and Pacific lamprey. Removal will open approximately 33 miles of new spawning and rearing grounds for steelhead and 15 miles for salmon

“This is a historic day for the White Salmon River,” said Paul Lumley, executive director for the Columbia River Inter-Tribal Fish Commission. “Today is the culmination of over 20 years of work and dedication by the tribes, federal agencies, and non-governmental organizations to ensure that salmon and lamprey are given every opportunity to survive in the White Salmon River.”

“Ecology and PacifiCorp have worked together for many years to make sure the decommissioning of Condit Dam is conducted in a way that minimizes the immediate impacts to the surrounding environment so that long-term habitat restoration can occur,” said Polly Zehm, Washington Department of Ecology deputy director.

“While there will be mud and debris for a short time, we are confident that opening up the river will restore an important salmon run and create new recreation and economic opportunities in the long run,” Zehm said.

An estimated 2.4 million cubic yards of reservoir sediment is expected to flush downstream, but removal was planned at a time when fish stocks are expected to be minimally affected.

In the spring of 2012, the dam structure will be removed along with the wood-stave flowline, surge tank and penstocks. Concrete from the dam will be broken into rubble and buried onsite; other materials will be salvaged or transported to the Klickitat County waste facility, according to PacifiCorp. The powerhouse will be left intact.

The temporary upstream dam (cofferdam) that was used during the initial construction of the dam will be removed from the White Salmon River as soon as practicable, after the breaching. PacifiCorp expects the full dam removal process to take approximately one year.

Meanwhile, in the fall of 2012, work will begin on re-vegetation of the former lake bottom with native trees and grasses, along with restoration of the wetlands, the power company says. Long-term monitoring and work to control invasive plants is also planned to ensure a successful restoration on the riverbanks and reclamation of Northwestern Lake.

Throughout this restoration, the former reservoir area and project area will remain closed to the public. PacifiCorp will continue to work closely with county officials and local residents on access restrictions and other safety measures as the project progresses.

“Our focus at all times is on safety,” said Dale Kuykendall, project manager, JR Merit. “The public needs to understand that the former reservoir and the mile-long stretch of river below the dam is an active work zone and they should refrain from trying to access the area.”