Oregon State University on Wednesday disputed the findings of state geologists who said landslides from recently logged clearcuts on OSU land set in motion the mud-and-debris flow that deluged U.S. 30 and nearby homes.
University officials asked the state Department of Forestry to review its logging practices on the tract of land owned and managed by OSU's College of Forestry west of Clatskanie.
The College of Forestry will conduct its own examination of slides from clearcuts on the OSU land to tell how much they contributed to the later landslide last week.
But the Oregon Department of Geology and Mineral Industries released on its Web site a step-by-step diagram of events that led to the landslide. It shows that two small landslides from OSU clearcuts during heavy rains two weeks ago clogged a culvert just downstream.
That allowed mud and water to back up for a week behind an old railroad berm that finally burst, unleashing a much more catastrophic torrent below.
Aerial photos in the diagrams show that the railroad berm was much closer to the initial slides than identified earlier, and that, when it broke, mud and water cascaded more than a mile to reach the highway.
But OSU officials Wednesday questioned the conclusions, issuing a press release downplaying the possibility that their logging activities played a role. The question highlights the long-running controversy surrounding the role of logging in landslides and the difficulty of unraveling exactly why landslides happen.
The clearcuts involved were within the Blodgett Tract, 2,440 acres donated to the College of Forestry in 1929 and now logged to produce revenue for the college.
One of the clearcuts involved 58 acres and was logged in 1992, and now has young trees growing on it. The other involved 19 acres and was logged in 2004, state records show.
The ages are important because studies by the state Department of Forestry suggest that clear-cutting increases the risk of landslides within the 10 years after logging.
OSU officials now argue that no debris from the slide off the most recent clearcut - young enough that logging could have boosted slide risk - reached the culvert downstream. They say that indicates their logging probably had no bearing on the more catastrophic landslide that reached the homes and highway.
"The small slide (from the younger clearcut) had nothing to do with this," said OSU spokesman Dave Stauth. "Sometimes logging may play a role, and sometimes it does not play a role."
Stephen Hobbs, executive associate dean of the College of Forestry, also said it's unclear whether the slides from OSU land clogged the culvert, or if it was clogged already.
"I'm not sure we understand, and we may never fully understand, the sequence of events here," he said, noting he had not visited the site. "It's really important when these things happen that we do an assessment and see what can we learn from them."
Hobbs is in an unusual position, because apart from his role at OSU he is also chairman of the Oregon Board of Forestry. The appointed commission oversees the Oregon Department of Forestry. OSU is taking issue with earlier conclusions drawn by Department of Forestry geologists and others at the Department of Geology and Mineral Industries.
The Department of Forestry also is the state agency that regulates logging on land owned by OSU and other forest landowners.
Ted Lorenson, deputy state forester at the Department of Forestry, said there has been no pressure from Hobbs. "He's not the kind of person who would ever attempt to insinuate any influence on the department."
Lorenson said OSU asked the Department of Forestry to review OSU logging operations on the Blodgett Tract to make sure they complied with guidelines designed to minimize the risk of landslides and other erosion problems. ODF officials have said that they did, and that OSU is generally careful about its logging practices.
Lorenson said the ODF would also review its actions to determine whether its staff properly assessed the risk of slides from the lands logged by OSU. He said that would probably also involve ODF's own assessment of the events leading to the clogging of the culvert and the catastrophic slide that resulted. "Is this something we should have captured as a high landscape hazard or not?"
OSU notified the department before logging the most recent clearcut that the site had evidence of past slides. But the area, with slopes estimated at 36 to 65 percent, was not steep enough to trigger state rules designed to reduce risk of slides.
Even before last week's slide, the Department of Forestry was reviewing the rules, enacted after fatal slides during a major 1996 rainstorm. Assessments by ODF staff have suggested the rules may not be reducing the risk of slides as intended.
Lorenson and Jason Hinkle, an ODF geologist who has examined the slide west of Clatskanie, said that review may now be expanded to include issues that emerged from last week's slide.
"Some of the things learned from this storm will probably be rolled into that effort," said Hinkle, who is credited with evacuating people from homes hit by last week's Highway 30 slide. "Hopefully, we'll be in a better place when it's all done."
For instance, the department may look more closely at the risk of sediment from slides piling up behind old outdated culverts and causing a bigger torrent, as happened below the OSU land, Lorenson said.
Both Hinkle and Bill Burns, an engineering geologist with the Department of Geology and Mineral Industries, said Wednesday that it appeared to them debris from both the slides on OSU land contributed to what happened.
"From the helicopter and from the ground, it appeared both of them went in and made it to the main drainage and down the main drainage," Burns said.
Hinkle said, "From what I've seen from the upper end and lower end, it sure looked like material from both the slides reached the fill," behind the railroad berm.
They said it is difficult to tell which slide happened first and clogged the culvert, although a more careful study might help determine that.
Arne Skaugset, an OSU professor who has studied landslides and logging, said the Blodgett Tract has unusual geology, with very loose sediment where it's hard to find even a solid rock. He said it's difficult to know how accurately the past studies of landslide risk, conducted elsewhere in Oregon, apply to the OSU site.
He said that though logging increases risk of slides in the following decade, it's unclear how long it takes for that extra risk to disappear as trees grow back - their roots gaining strength and their branches slowing down deluges of rain that could trigger slides.The Oregonian
