Sunday, November 11, 2012

Stillman Creek 5 Years On

Little Mountain landslides (picture from DNR Forest Practices Board presentation)
In December 2007 a large storm dumped large quantities of rain on northeast Oregon and southwest Washington. The above picture was a rather infamous picture from that storm of some steep slopes in the Stillman Creek drainage southwest of Chehalis, Washington. The picture was on the front page of the Seattle Times. This site was one of tens of sites with landslides that took place in the area.

Little Mountain landslides (piture from DNR Forest Practices Board presentation) 

A PowerPoint presentation by the Department of Natural Resources to the Forest Practices Board regarding the harvest pictured above ended with a conclusion that the forest practice "application was correctly classified and processed by the DNR according to Forest Practice Rules."

The harvest was approved because there were errors and discrepancies in the application. The DNR does have maps showing potential unstable slopes based on the shape and steepness of the slope. A glance at that map indicates there were numerous potentially unstable slopes within the harvest. However, the only way that the DNR can make a determination of the slope stability is to do a site visit. Apparently they did not in this case. Hence, the DNR relies on the applicant.  
I pulled up an image from the other side of the mountain. Different harvest but in a way worse  results from the December 2007 storm. Clearly harvests were done on steep convergent topography and road construction across this terrain appears to have played a role as well. Again the slide locations were within areas that slope screening tools indicate as potentially unstable. 
Southwest side of Little Mountain (USGS), red dots are my own marks of landslides
The December 2007 storm was a big storm and was particularly intense within the area where these slides took place. Storms with that much rain should be expected to result in landslides. Indeed these same slopes and similar slopes have tolerated more typical winter storms without slope failures (or at least this level of failures). However, the frequency and magnitude of slides in recently harvested areas appears substantially greater within the are shown above.
I do not know what exactly was said at the Forest Practices Board meeting. This storm did cause some agency and land management angst and nearly 5 years on still is. Why? The policy established by Washington State Forest and Fish Law is that landslide delivery streams to streams should be at levels similar to natural levels. That should include large storms.
The above image implies that the current rules or rule implementation have not been working. The DNR statement in the PowerPoint presentation that the "application was correctly classified and processed by the DNR according to Forest Practice Rules" perhaps sums up how well policy is being met.

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