Wednesday, November 3, 2010

Debris Flow Risk

Two amazing warm sunny days in a row in November. I managed to get out in the field on both days; yesterday Whidbey Island and today a trip up the Nookasack River Valley in Whatcom County.

Tree clearing on alluvial fan

On the way up the Nooksak I took a look at the debris flow creek I posted about HERE and HERE. I was a bit surprised to see that land was being cleared adjacent to the creek on the alluvial fan. Large trees can do a very good job of stopping debris. The trees act a rake capturing logs within the debris flow. Hence removing large trees from an alluvial fan can significantly increase the run out distance of large wood increasing the risk to homes further down the fan that would otherwise not be at risk from large woody debris.
Large wood from debris flow stacked against trees. 

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