Condit Dam to be breached Wednesday
Safety a key consideration ahead of historic blast
Sunday, October 23, 2011
On the Web:
A video of the breaching of Condit Dam will be available Wednesday afternoon on www.columbian.com
Watching crews set dynamite and blow a hole in the bottom of a 125-foot-tall hydroelectric dam might sound like a fun way to spend a day.
But PacifiCorp is taking no chances as it makes final plans for the historic breaching of Condit Dam on Wednesday, and state, federal and tribal officials will be working overtime to prevent mishaps as the White Salmon River bursts through a 12-foot-by-18-foot tunnel . A huge surge of released water and sediment is expected to rush downstream to the river’s mouth and all the way to the Columbia River’s Bonneville Dam. The Army Corps of Engineers is lowering the water behind that dam by two feet to make room for the added volume.
Roads, waterways and airspace near the dam will be closed in the hours leading up to the breaching, which is scheduled for noon.
PacifiCorp spokesman Tom Gauntt announced the following closures:
Powerhouse Road, which provides access to the dam, will be closed to the public Wednesday, and Alternative Highway 141, which follows the river’s east bank, will be closed from 10 a.m. to 2 p.m. No parking will be allowed along Alternative 141, and police will patrol the mouth of the White Salmon at Underwood to keep people from parking along state Highway 14. Additional patrols will also be maintained along the riverbank and in adjacent areas that could provide access to the canyon.
Enforcement officers from the Columbia River Inter-Tribal Fish Commission will be patrolling the Columbia River to keep private boat traffic away from the mouth. The in-lieu tribal fishing area at the mouth of the river will also be closed and patrolled.
Private property owners along the White Salmon River above and below the dam have posted their property to warn any potential sightseers against trespassing. The bridge that crosses the river at what was until recently Northwestern Lake will be open to traffic, but the river upstream of the dam to the bridge is closed to boating of any kind.
“After the breach, the newly forming river channel will be extremely dangerous, with large amounts of debris and unstable banks,” Gauntt said. “This portion of the river will not be open for recreational boating until the fall of 2012.”
The Federal Aviation Administration will issue a temporary flight restriction in the immediate area of the dam Wednesday morning. PacifiCorp contractors will use the airspace to patrol the river canyon, the blast area near the dam and the stretch of river upstream to the former lake bed, checking to make sure no one has managed to sneak into the restricted area.
“They want to see specifically whether they can see anyone in the canyon,” Gauntt said. No one will be flying at the time the explosives are detonated, he stressed, because of concussive vibrations in the canyon. “Helicopters and explosions are not a good mix,” he said.
Contractors began drilling and dynamiting a tunnel through the 90-foot-thick base of the dam in August and have conducted more than a dozen blasts, boring deeper into the dam with each one. A 10-foot plug remains. That’s what will come out Wednesday, with the detonation of 700 pounds of dynamite.
“Overnight, the demolition experts will be up in the tunnel placing the charges and doing all the detonation preparations,” Gauntt said. On Wednesday morning, they’ll complete all their final safety checks. When they get the green light, they’ll step on the detonator.
It’s hard to predict how loud the blast will be, Gauntt said. It might be muffled by water. “It should be instantaneous as you and I understand it,” he said.
Soon after the all-clear, people will be able to walk on the dam. The water and most of the sediment are expected to move downstream within six hours. It could take longer, Gauntt said, “but the majority is fine silt and should move along pretty well.”
He hopes any kayakers who have thoughts of running the White Salmon through the hole in the dam so they can star in their own YouTube video will think again.
The river will be closed to rafting until next year. “We want to emphasize that it’s going to be a very unsafe environment in that former reservoir bed. The debris will be completely unknown, the riverbanks will be eroding, things will be falling down,” Gauntt said.
One of the closest views Wednesday will be that of Portland filmmaker Andy Maser, who has been given special access to the site by PacifiCorp to document the breaching. Maser has taken about 4,000 images, including underwater photos of fall chinook salmon spawning above the dam for the first time in 100 years, and posted many to the American Rivers website. “On breach day, we’ll capture close to 15,000 images” using two time-lapse cameras, he said. “The primary objective is to make the images available to environmental science educators.”
He’s excited to see, from his perch on the shore, what will happen when the river rushes through the hole in the dam.
“I’m curious to see what’s waiting below the lake and what the river looks like. Will all the water rush out? Maybe a tree could get stuck. There are so many unknown factors. Scientifically, it’s incredibly interesting. This is the first time this has ever been tried.”