Geomorphic and stream flow influences on large wood dynamics and displacement lengths in high gradient mountain streams (Chile)

Understanding large wood (LW;≥1 m long and≥10 cm in diameter) dynamics in riversis critical for many disciplines including those assessing flood hazard and risk. How-ever, our understanding of wood entrainment and deposition is still limited, mainlybecause of the lack of long‐term monitoring of wood‐related processes. The datasetpresented here was obtained from more than 8 years of monitoring of 1,264 taggedwood pieces placed in 4 low‐order streams of the Chilean mountain ranges and wasused to further our understanding of key factors controlling LW dynamics. We showthat LW displacement lengths were longer during periods when peak‐flow waterdepths (Hmax) exceeded the bankfull stage (HBk) than in periods with Hmax≤HBkand that these differences were significantly higher for smaller wood pieces. LWlength and length relative to channel dimensions were the main factors governingLW entrainment; LW displacement lengths were inversely related to the ratio of piecelength to H15%(i.e., the level above which the flow remains for 15% of the time) andto the ratio of H15%to bankfull width. Unrooted logs and LW pieces located at thebankfull stage travelled significantly longer distances than logs with attachedrootwads and those located in other positions within the bankfull channel. A few largelogjams were broken during the period of observation, and in all occasions, LW fromthese broken logjams did not travel over longer distances than other pieces of LWmoved in the same periods and in the same stream segments. Most importantly, ourwork reveals that LW dynamics tend to be concentrated within a few reaches in eachstream and that reaches exhibiting high wood dynamics (extensive entrainment, depo-sition, or repositioning of LW) are significantly wider and less steep than less dynamicreaches