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USGS Studies Document Changes in White Salmon River Post-Condit Dam; More Salmon, Steelhead Spawners
Posted on Friday, December 11, 2015 (PST)

At the time, PacifiCorp’s Condit Dam on Washington’s White Salmon River was one of the largest dams to be removed in the United States.

 

Its removal that opened up 33 miles of new habitat for salmon and steelhead spawning and rearing caused biologists to wonder if the fish that had been extirpated from the river when the dam was built would or could return.

 

They also wondered if the impact of removing the dam – it was done with explosives punching a 16-foot hole in the dam and releasing an immense amount of sediment – would ruin the 3 miles of habitat downstream of the dam where Columbia River tule fall chinook spawned, the only salmonid spawning in any numbers in the river prior to the dam’s removal October 26, 2011.

 

Two studies by the U.S. Geological Survey put those fears to bed. One study shows that the lower portion of the river is actually restoring itself faster than thought and that tule fall chinook are continuing to spawn in the river’s lower reaches. Roughly 1,700 tule spawners are estimated to have spawned in the White Salmon last fall.

 

“Salmon Habitat Assessment for Conservation Planning in the Lower White Salmon River, Washington” was published in May 2015 (http://pubs.usgs.gov/of/2015/1100/pdf/ofr2015-1100.pdf). The study area covers the lower six miles of the river, including three miles that was downstream of the dam where tule fall chinook spawned and the three miles of the former dam’s reservoir, known as Northwestern Lake.

 

“The lower White Salmon River continues to be used by salmon for spawning and rearing downstream of the former Condit Dam site and salmon and steelhead are using the newly accessible habitat upstream of the dam site as well,” the May study says. “The general trend for the last 2 years of spawning surveys was increasing numbers of returning Chinook salmon and increasing redd locations.”

 

The second study, published November 4, 2015, and titled “Effects of Dam Removal on Tule Fall Chinook Salmon Habitat in the White Salmon River, Washington,” http://onlinelibrary.wiley.com/doi/10.1002/rra.2982/abstract provides more information about how the White Salmon River is changing.

 

“As expected, dam breaching dramatically affected channel morphology and spawning habitat due to a large load of sediment released from Northwestern Lake,” the November study says. “Forty-two per cent of the project area that was previously covered in water was converted into islands or new shoreline, while a large pool near the mouth filled with sediments and a delta formed at the mouth.”

 

While the pool area that was Northwestern Lake decreased 68.7 percent in the study area, glides and riffles – features most conducive to spawning – increased 659 percent and 530 percent, respectively, the report says. Spawning habitat increased by 46.2 percent after dam breaching due to an increase in these glides and riffles.

 

Condit Dam since its construction in 1912-13 had blocked passage to the river’s upper reaches, confining spawning to the lower 3.3 miles of the river from its confluence with the Columbia River to the former dam.

 

Tule fall chinook salmon that have long frequented the lower White Salmon are one of 13 Columbia basin stocks that are listed under the federal Endangered Species Act. They are listed as threatened.

 

“Redd observations provided support that the study area is a migratory corridor for salmon and steelhead and that the lowest 2–3 miles had the highest concentration of documented fall Chinook salmon redds. The study area has potential for restoration/conservation areas to improve/conserve salmon habitat,” the May study concludes.

 

At the time it was breached, about 63.6 million cubic feet of sediment had collected behind the dam. It was “abruptly breached with an explosive blast with about a 16-ft-wide hole at the base of the dam that rapidly emptied the reservoir and much of the sediment consisting mostly of sand, silt, and clay,” according to the studies.

 

“The outflow of silt, sand, and gravel filled pools throughout the lower river, created gravel bars, and a delta at the confluence with the Columbia River,” the May study says.

 

It goes on to say that the river continues to change since the dam was breeched and may continue to be in a state of flux for some years. Natural processes are taking over, with large woody debris and gravel moving into the river’s lower reaches. “The amount of time these watershed processed take to reach equilibrium is unknown,” the study says.

 

A USGS survey in 2014 concluded that salmon habitat had improved already at that time in the lowest one mile of river “due to increased gravel recruitment, favorable velocities, and depths for spawning.”  It also found that that lowest river mile was still subject to some channel instability and the potential for gravel bars to change if and when a larger flood event occurs.

 

The USGS generally found habitat conducive to salmon spawning and rearing throughout the entire 6-mile study area. Still, areas along the former Northwestern Lake lacked “a properly functioning riparian corridor,” the May study says. However, revegetation projects by PacifiCorp and Yakama Nation Fisheries were underway last year.

 

Spawning surveys in 2013 by the Washington Department of Fish and Wildlife found spring and fall chinook spawning the mainstem river. While most of the spawning was in the lower two miles of river, they did find evidence of spawning in the area of the former lake and on the mainstem as far upstream as the confluence of Buck Creek (river mile 4.9) and Rattlesnake rapid (downstream of Husum Falls at river mile 7.6).

 

A 2014 survey found two to three times the number of spring chinook spawners upstream of the former dam (216 spawners) with some seen in Spring Creek at river mile 6.6. Tule fall chinook spawner abundance also was higher, with just under 10 percent of the total number of spawning tules found upstream below Steelhead Falls at river mile 2.6, according to the November report.

 

The Yakama Nation in 2014 found steelhead redds upstream of the former Northwestern Lake in Buck and Rattlesnake Creeks. There is also evidence that steelhead are spawning as far upstream as BZ Falls and Big Brother Falls at river mile 15.5. Both are upstream of Husum Falls, “indicating this is not a complete passage barrier for steelhead,” the May study says.

 

For more information on the 2014 spawning survey, see CBB, February, 13, 2015, “Salmon, Steelhead Spawning, Rearing In New White Salmon River Habitat Above Removed Condit Dam Site,” http://www.cbbulletin.com/433156.aspx

 

The dam was the only man-made impoundment between the Cascade Mountains’ Mount Adams and the Columbia River and its removal opened about 33 miles of new spawning and rearing grounds for steelhead and 15 miles of new habitat for salmon in the White Salmon River basin.

 

The dam’s owner, PacifiCorp, agreed to decommission and remove the project dam and water conveyance system in accordance with the 1999 Condit Hydroelectric Project Settlement Agreement and the related Federal Energy Regulatory Commission Surrender Order issued in December 2010. The private utility decided that it would be more economical to remove the dam than it would be to outfit the dam with salmon passage facilities that would be required by FERC to relicense the facility.

 

The White Salmon Working Group, which is a consortium of Yakama Nation, federal, state, and PacifiCorp biologists, has estimated the White Salmon River has enough spawning grounds to accommodate more than 600 steelhead spawners and 1,200 fall chinook. Bull trout, coho, lamprey and spring chinook could also benefit from a reconnected river.

 

Also see:

-- CBB, May 31, 2013, “A Year After Condit Dam Breaching, Natural Origin Salmonids Spawn In New Miles Of Upstream Habitat” http://www.cbbulletin.com/426822.aspx

 

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