Monitoring Large Woody Debris dynamics in the Unuk River, Alaska using digital aerial photography

Abstract

Large Woody Debris (LWD) and changes in its accumulation pattern influence the morphology, flow characteristics, ecological attributes, and physical habitats along a river. Digital aerial photos were acquired for the Unuk River in Alaska during the spring of 2003 and 2004. Digital processing of aerial photos involved high-pass filtering on the second principal component image, followed by a low-pass filtering, thresholding, and color coding to map individual logs and large wood accumulations. This processing technique provided an effective classification of the LWD with an overall classification accuracy of 89%. In the selected test site, the 2004 images show a 23% decrease in LWD, which is attributed to the large-scale wash-over of the wood due to a known flooding event in October 2003. Large shifts in LWD have caused main channel shifts, channel splits, merging of split channels, and changes in locations of sand bars and pools, dislocating and redistributing known fish habitat. Copyright © 2006 by V.H. Winston & Son, Inc. All rights reserved.