Geomorphic and stream flow influences on large wood dynamics and displacement lengths in high gradient mountain streams (Chile) |
| |
| Authors: | Andrés Iroumé Virginia Ruiz‐Villanueva Luca Mao Guillermo Barrientos Markus Stoffel Gastón Vergara |
| |
| Institution: | 1. Faculty of Forest Sciences and Natural Resources, Universidad Austral de Chile, Valdivia, Chile;2. Research Center for Assessment and Mitigation of Natural and Anthropogenic Risks (RiNA), Universidad Austral de Chile, Valdivia, Chile;3. Institute for Environmental Sciences, University of Geneva, Geneva, Switzerland;4. Department of Ecosystems and Environments, Pontificia Universidad Católica de Chile, Santiago, Chile;5. Graduate School, Faculty of Forest Sciences, and Natural Resources, Universidad Austral de Chile, Valdivia, Chile;6. Dendrolab.ch, Department of Earth Sciences, University of Geneva., Geneva, Switzerland;7. Institute of Statistics, Universidad Austral de Chile, Valdivia, Chile |
| |
| Abstract: | Understanding large wood (LW; ≥1 m long and ≥10 cm in diameter) dynamics in rivers is critical for many disciplines including those assessing flood hazard and risk. However, our understanding of wood entrainment and deposition is still limited, mainly because of the lack of long‐term monitoring of wood‐related processes. The dataset presented here was obtained from more than 8 years of monitoring of 1,264 tagged wood pieces placed in 4 low‐order streams of the Chilean mountain ranges and was used to further our understanding of key factors controlling LW dynamics. We show that LW displacement lengths were longer during periods when peak‐flow water depths (Hmax) exceeded the bankfull stage (HBk) than in periods with Hmax ≤ HBk and that these differences were significantly higher for smaller wood pieces. LW length and length relative to channel dimensions were the main factors governing LW entrainment; LW displacement lengths were inversely related to the ratio of piece length to H15% (i.e., the level above which the flow remains for 15% of the time) and to the ratio of H15% to bankfull width. Unrooted logs and LW pieces located at the bankfull stage travelled significantly longer distances than logs with attached rootwads and those located in other positions within the bankfull channel. A few large logjams were broken during the period of observation, and in all occasions, LW from these broken logjams did not travel over longer distances than other pieces of LW moved in the same periods and in the same stream segments. Most importantly, our work reveals that LW dynamics tend to be concentrated within a few reaches in each stream and that reaches exhibiting high wood dynamics (extensive entrainment, deposition, or repositioning of LW) are significantly wider and less steep than less dynamic reaches. |
| |
| Keywords: | channel morphology displacement length large wood dynamics mountain streams |
|
|
