3 January 2008
The New York Times today carries an interesting article here about destructive floods in Washington State resulting from a large storm in December. For me the interesting thing is an argument that appears to be raging as to whether the floods have resulted from measures to protect salmon fisheries, which have purportedly led to blockages forming in river channels, or from landslides and erosion that have resulted from logging. The stakes have been raised by this Seattle Times image (the image is well worth a look – there is actually a better version on the New York Times web page here).
So what to make of this. First, there is plenty of evidence that logging increases landsliding and erosion dramatically. It is clear that this slope has been recently deforested, and thus there is a logical link. The adjecant forested slopes appear to be unaffected by this level of landslides. The landslides themselves are shallow, which is exactly the type that trees stop so well. The landslides have certainly reached the channel and thus might well be responsible for releasing sediment associated with the floods. Note though that some nearby slopes without trees have not suffered landslides like this.
Whatever the cause, which is hard to determine from a single image, the need to change forestry practise in this area seems to me to be clear.