Geomorphic impacts of coarse woody debris within a recently burned mountainous hillslope

Authors: Jean Dixon, Montana State University, Kailey Adams*, Montana State University, Dave McWethy, Montana State University
Topics: Geomorphology, Geographic Information Science and Systems, Remote Sensing
Keywords: sediment yield, wildfire, sediment storage, coarse woody debris
Session Type: Poster
Day: 4/5/2019
Start / End Time: 8:00 AM / 9:40 AM
Room: Lincoln 2, Marriott, Exhibition Level
Presentation File: No File Uploaded

Wildland fires influence the geomorphology of mountainous systems. Removal of vegetation on hillslopes induces changes to sediment and flow routing, but surprisingly little is known about interactions between biotic materials that are added by fire (e.g., course woody debris CWD) and soil transport dynamics. In many systems fire events can result in large numbers of downed trees, producing volumes of CWD that would accumulate over decades or centuries via gap dynamics or other processes. Literature suggests downed trees store sediment at their upslope extent, and this storage capacity may be linked to morphologic variables such as hillslope gradient and aspect. However, few studies have quantified the role of logs in hillslope sediment storage, and the controlling factors are poorly understood. We report on research that uses high-resolution topographic data to quantify interactions between coarse woody debris and sediment transport dynamics at the hillslope-scale in a watershed in the northern Rocky Mountains. Within a small, headwater catchment in southwestern Montana, more than 6,000 logs were manually digitized from a 10-cm resolution orthophoto. Trigonometric relationships between logs and surrounding topography were then used to derive estimates of potential sediment storage. These data were combined with morphologic variables (e.g., slope, aspect, curvature) and burn severity data to quantify controls on log orientation and, consequently, potential volume of sediment stored. Understanding the relationship between fire-induced CWD and soil storage and transport will be increasingly important as the frequency, severity and extent of wildland fires in the western U.S. continue to increase.

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