In most of the U.S., landslides would be considered an odd and unlikely disaster to worry about. But as almost everyone who lives in the Columbia-Pacific region knows, around here they are an expensive, destructive and potentially dangerous part of everyday life for much of most years.
Although our own winter of 2012-13 wasnt that bad, the Pacific Northwest as a whole experienced a rainy season that was among the worst on record for landslides. A massive 200,000-cubic-yard hillside collapse on Whidbey Island in Puget Sound was sufficiently eye-catching to grab national headlines in March, while interruptions of passenger and freight rail service have been commonplace throughout the region.
In Pacific County, slides have closed all state highways at some point in recent years. Twenty years ago, one on KM Mountain between Naselle and Longview was fabulously costly to the local economy and dazzlingly expensive to fix. There have been many more in the years since, including one this winter on State Route 100 between Ilwaco and Cape Disappointment.
Whats going on? Is this a real trend, or looking for a story?
The usual suspect global warming certainly has been mentioned. In the Pacific Northwest, long-term trends are for wetter winters. In Washington the average annual precipitation has increased by about one-third of an inch each decade since the beginning of the 20th century, according to NPR.
Soils that have become saturated with rain are both heavier and weaker, their particles pushed apart by the water. They are prone to come tumbling down.
Placing known slide-prone areas off limits for building is sensible. Forest-practice rules must similarly keep pace with increasing precipitation, perhaps by adopting more conservative rules for acceptable grades and increasing setbacks anywhere near highways, homes or vital infrastructure like railways. Catchment walls, retaining walls and slide-detection fences are some of the other tools available to get ahead of landslides.
Property developers and homeowners are well advised to seek the advice of a qualified geotechnical engineer before upsetting the status quo of slopes. It is important to deal with these risks upfront openly and professionally before approving new subdivisions or other major changes in land use.
Avoiding landslides is expensive. Unfortunately, allowing them to happen can be much more so.