[ad#200-left]One would think that most industries would be learning from past failures in systems and techniques, however, there is always the chance that a major oversight can happen, particularly on steep and hazardous slopes, as residents and officials in Lewis County, WA found out last December.

The December storm triggered more than 730 landslides in the Upper Chehalis basin, according to a state aerial survey. Those slides dumped mud and debris into swollen rivers, helping fuel the floods that slammed houses, barns and farm fields downstream.

A disproportionate number of those landslides started on slopes that had been clear-cut.

The Seattle Times, using information from state aerial surveys, examined 87 of the steepest sites that had been clear-cut. Nearly half of them suffered landslides during the storm. Those sites represented less than 8 percent of the total acreage — both logged and forested in the Upper Chehalis and its tributary drainages. But the sites produced about 30 percent — 219 — of the landslides.

Seattle Times – Logging and landslides: What went wrong?


This is an example of inappropriate large scale land clearing practices on steep slopes with a previous history of failure. I point that out because this result is not necessarily indicative of clear-cut practices on milder slopes or different soil types, or for that matter of other methods of logging or land clearing that may be more selective in the removal of trees.

But what happened in this County is an example of a community watershed apparently unable to protect itself from the activities of a resource extraction company…

As a drinking-water source, Little Mill Creek would appear to rank high on the list of public resources that needed protection. Watershed plans noted the intake for the water-treatment plant had been damaged in a 1990 flood, and it was vulnerable to clogging from sediment.

Weyerhaeuser expanded logging around Little Mill Creek in the late 1990s as the second-growth forests, originally cut some 50 years before, reached maturity. “The logging was going to cause problems,” said Richard Eitel, manager of the water corporation, who told the company of his concerns. “But we don’t own the land, and I couldn’t see any way to overcome it.”

In talks with the water corporation, Weyerhaeuser officials discussed concerns about the logging. They believed they could head off problems with improved logging and road-building practices.

Seattle Times – Logging and landslides: What went wrong?

This discussion is relevant for all forestry areas as nearly all have the potential to impact downstream water quality. With climate change comes potentially wilder weather, with greater consequences to the environment.

Published by Mike Thomas

Mike Thomas P.Eng. ENV SP, is the author of UrbanWorkbench.com and Director of Engineering at the City of Revelstoke in the Interior of British Columbia, Canada.