Logging andamp; landslides

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It's hardly a revelation that a hillside denuded of trees is more prone to landslides during a rainstorm than is a slope covered with a dense forest.

That's not politics it's geology.

But it seems that after certain slides there is, among some observers, a tendency to cast logging and in particular clearcuts, if any are available in the sole villain's role.

This is understandable.

When a glutinous stew of mud and boulders fouls a highway, for instance, it's natural that people look to blame someone for the mess.

We would, though, urge caution.

Logging can increase the odds of a landslide, but it is rarely if ever the only causal factor.

If the experts who study landslides set their focus too narrowly, they might miss other contributing factors which, if recognized, could be dealt with so as to reduce the risk of future slides.

A recent example is the mudslide that flowed across U.S. Highway 30 and inundated several homes near Portland on Dec. 11.

State geologists said debris slid down a clearcut slope and then plugged a culvert. Water pooled behind the culvert, and the pressure breached a wood-and-earthen berm, letting loose the muddy torrent that swept across the highway.

The landslide garnered an extra measure of media attention because Oregon State University owns the logged-over land. OSU's College of Forestry uses the property as an outdoor classroom, and the university put cash in its coffers by selling the logs.

The geologists present a convincing case, including diagrams showing the path the debris flowed from the clearcuts to the berm.

But they also acknowledge that the weather had something to do with the slide. Quite a lot, it seems to us.

The rainstorm that slogged into Oregon a week before the slide was even soggier, in parts of the nearby Coast Range, than was the infamous 1996 storm that spawned widespread flooding in Western Oregon.

The volume of rain is significant because the larger of the two OSU clearcuts was logged in 1992. Oregon Department of Forestry studies show that the risk of landslides on clearcut slopes is higher during the first decade after logging. Yet the clearcut slope didn't give way during the copious rains of 1996, just four years after logging. It failed 11 years later, when, based on the Forestry Department research, the risk ought to have been less.

Perhaps the researchers didn't consider the potential effects of exceedingly rare events such as this December's torrential downpours.

We suspect some logging critics will cite the Highway 30 slide as proof that Oregon's forestry laws, which are among the more stringent in the nation, are too lenient as regards clearcutting.

We're not convinced that's so, considering what happened earlier this month on OSU's land and, equally important, what did not happen there in 1996.

We wouldn't blame the researchers if they didn't delve too deeply into natural disasters. Maybe they figured they needn't bother pointing out what most people inherently know: That nature plays by no rules.

We're glad OSU officials decided to study the Highway 30 slide, and that they asked the Forestry Department to look into the causes.

But we don't think it's reasonable to regulate logging based on a worst-case scenario. If the government used that as its universal standard, then we ought to get busy moving most of downtown Portland. Who can say on what damp day the Willamette River will decide to carve itself a new channel through the Park Blocks.

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The Baker City Herald
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