Journal
GEOMORPHOLOGY
Volume 246, Issue -, Pages 351-358Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.geomorph.2015.06.031
Keywords
Sediment pulse; Debris flow; Sediment wave; Large woody debris
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In 2001, a series of post-fire debris flows brought similar to 30,000 m(3) of sediment, deposited as fans, to the narrow valley floor of Sleeping Child Creek in western Montana (USA). In 2005, pebble-counts and surveys of the channel in proximity to six of the debris flow fans documented a regular sequence of fine-grained aggradation upstream of the fans, incision through the fans, and coarse-grained aggradation downstream of the fans. These measurements were repeated in 2012. We found that the delivery of large woody debris (LWD) over the intervening 7 years has been a dominant factor in the disposition of the debris-flow material. The amount of LWD in the study reach has increased by as much as 50% in the areas with a high burn severity, leading to the formation of large logjams that interrupt the flow of sediment along the streambed. Nearly all of the surveyed reaches have aggraded since 2005, including those that had initially begun incising through the debris flow deposits, and the streambed has become generally finer. We hypothesize that, over the next few decades, debris flow sediment not colonized and anchored by riparian vegetation will trickle out of the affected reaches as the logjams slowly degrade. (C) 2015 Elsevier B.V. All rights reserved.
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