Thursday, Aug. 21, 2008

Landslide spills into Columbia River (w/video, photos)

By John Trumbo, Herald staff writer

A huge landslide that fell from a clay bluff south of Ringold sent a white plume of silt into the Columbia River on Wednesday that was visible for miles and as far downstream as Kennewick's Columbia Park.

The collapse and sloughing off of the soft earth covered an area larger than several football fields beginning about 200 feet above the river, near the orchards of Alton Haymaker and Ed Skelton off Cottonwood Drive in the Sagemoor Road area of Franklin County.

Mark Nielson, manager of the Franklin County Conservation District, said seepage from irrigation in the Columbia Basin Irrigation District likely triggered what he called the "bluff slumping."

Other than the instability of the bluff, Nielson said major concerns are water quality and what the turbidity plume in the river could do to salmon habitat.

Nielson said he first heard about the landslide from Skelton, who he said called it "the big one."

The slide traveled down the slope more than 500 feet before two fingers of debris entered the river, where current began pulling the white clay into the main channel just north of Johnson Island.

Skelton told the Herald that slides along the river have occurred repeatedly in that area. He pointed out several sites of past slides visible from his apple and cherry orchards just south of the recent slide.

"There's no question it is from irrigation," said Skelton, who is continuing the family orchard business his father started in the 1950s.

Much of the orchard, including Skelton's two-story home, is in the potential slip-and-slide zone, he said.

"I could lose quite a bit" he said, noting that a geologist once told him the high bluff had an angle of repose, or natural slope, that would end up in the river if the right amount of seepage from irrigation occurred. And that angle would take in much of his property, Skelton said.

Haymaker and his wife Joan, who live about a half-mile east of the river, were unaware of the recent slide. But Haymaker said the sloughing of the cliff has been a concern for decades.

"I've been fighting it for years," he said.

River ecologist Dennis Dauble, who works in the energy and environment directorate at the Pacific Northwest National Laboratory in Richland, said there have been bluff slumps along the Columbia River before. But this one is notable for its size and that it was "a blowout."

Dauble said most slides in that area that are triggered by irrigation soaking the soil move slowly, "but this was faster."

He estimated the turbidity plume covered 10 percent to 20 percent of the river's width, which he said "can significantly reduce the productivity of algae and the insects that reside there."

That compromised productivity means less food for fish. Dauble said the plume will continue until river flows get high enough to move the sediment downstream.

Nielson said slumping from the bluffs has been a longtime concern of the conservation district.

"I was hired 20 years ago just to look at this issue. One concern was if there could be enough volume (in a slide) to move the channel onto the Hanford site. We concluded that would not be likely to happen," he said.

But that did happen about six years ago on a side channel about five miles upstream from this week's event, said Dauble. The amount that tumbled into the water blocked boat passage, he said, but did not affect the Hanford site.