The flood loosed late last month when southwest Washington’s Condit Dam was breached has literally coated the lower White Salmon River in layers of various thickness of fine, dark sediment.
But researchers predict that the river’s own dynamics make it a prime candidate to clean itself and restore the coarser, gravelly river bed needed for native fish to spawn and rear.
(See CBB, Oct. 28, 2011 “Blast Drains Condit Dam’s Reservoir On White Salmon River; Dam Structure Removal Set For Spring 2012” http://www.cbbulletin.com/413585.aspx)
“If you look at the White Salmon now…. It’s hammered,” researcher Andrew Wilcox said. “If you go there now there’s a lot of mud.”
The University of Montana assistant professor is leading a research project aimed at assessing how the river “responds” to the breaching of the dam and a return to a free flowing state.
“It’s a beautiful natural experiment,” Wilcox said of the opportunity to monitor how the river moves large pulses of sediment that have the potential to snuff out aquatic life.
The blasting of a tunnel through the base of Condit allowed the release of sediment that had been collecting since the dam was completed in 1913. It was estimated that between 1.6 million to 2.2 million cubic yards of sediment would be discharged into the White Salmon River immediately following tunnel’s opening.
Wilcox and one of his graduate students will monitor the lower White Salmon over the next two years to see how well it refreshes itself. The study focuses on sediment transport, or the lack thereof, as well as channel evolution, and habitat response.
The researchers will try to use the data gathered there as well elsewhere to develop a better understanding of how ecosystems respond to such events. That information could be used in planning such events in the future. The study is being funded by the National Science Foundation.
Wilcox has been involved in similar research following the breaching of Marmot Dam on the Sandy River in northwest Oregon in 2007 and the Milltown Dam in western Montana in 2008.
“Reservoirs tend to trap sediment that is fine,” Wilcox said. When the sediment is released it tends to settle into the cobbled river bottoms that salmon and steelhead prefer for spawning, and changes the depth of pools where fish seek shelter. The study aims to monitor when, where and how that sediment is deposited, and how soon the river might mend itself.
“How long do the changes last?” is a key question, he said.
“It is a system that is steep and confined and has a high transport capacity,” Wilcox said of the White Salmon. The slack water in the lowest part of the river “has less capacity to clear.”
The best thing to do is hope for a wet winter.
“It’s supposed to be a La Nina year,” Wilcox said. If the snowpack builds and strong flows develop in the spring, much of the sediment and at least some of the logs dislodged from the reservoir bottom should be swept downriver.
“I’m not going to say the system will be recovered by next summer” but the spring freshet should send it well on its way, Wilcox said.
The lower White Salmon River remains off limits as it has been since before the Oct. 26 breach, which quickly drained 1.8-mile-long Northwestern Lake. The dam is located 3.3 miles upstream from the river’s confluence with the Columbia River.
The river and its banks remains an unsafe place both above the dam in the reservoir reach and below the dam, according to PacifiCorp, which owns the dam. PacifiCorp, local law enforcement and experienced river experts are unanimous in urging the curious to stay away.
“Everyone saw the force of the river last Wednesday,” said Tom Hickey, PacifiCorp’s project manager. “Now downstream wherever the river narrows, there are logjams. In the former reservoir above the dam, the river is cutting through the sediment creating unstable slopes and moving debris such as buried logs as expected.
“Transported sediment is also building up in downstream areas. Working with our contractors, we have plans in place to deal with these obstructions, and they all require that everyone stay out of harm’s way and a safe distance from the river,” Hickey said.
The company’s options for clearing debris include using cranes and yarders or in some instances explosives to remove barriers. The entire area from the Northwestern Lake Road Bridge to the mouth of the White Salmon River continues to be an active construction zone and a dangerous place to be.
“We are still a long way from anyone attempting to boat the White Salmon River within the project area or downstream,” said Thomas O’Keefe, Pacific Northwest stewardship director of American Whitewater. “Those of us who know the river well urge everyone to stay safe and out of this river area until next fall when PacifiCorp has had a chance to complete the channel restoration work and address the severe hazards affecting navigability."
PacifiCorp will continue to post updates on closures and restrictions in the Condit area as work proceeds. Go to www.pacificorp.com/condit for updates. Signs will remain posted in the immediate areas to remind the public about the closures.