Management of Large Wood in Streams: An Overview and Proposed Framework for Hazard Evaluation

Earth Surf Processes Landf

Mazzorana

Castellet

et al. 2019

Self Cite

Inorganic sediment is not the only solid‐fraction component of river flows; flows may also carry significant amounts of large organic material (i.e. large wood), but the characteristics of these wood‐laden flows (WLFs) are not well understood yet. With the aim to shed light on these relatively unexamined phenomena, we collected home videos showing natural flows with wood as the main solid component. Analyses of these videos as well as the watersheds and streams where the videos were recorded allowed us to define for the first time WLFs, describe the main characteristics of these flows and broaden the definition of wood transport regimes (adding a new regime called here hypercongested wood transport). According to our results, WLFs may occur repeatedly, in a large range of catchment sizes, generally in steep, highly confined single thread channels in mountain areas. WLFs are typically highly unsteady and the log motion is non‐uniform, as described for other inorganic sediment‐laden flows (e.g. debris flows). The conceptual integration of wood into our understanding of flow phenomena is illustrated by a novel classification defining the transition from clear water to hypercongested, wood and sediment‐laden flows, according to the composition of the mixture (sediment, wood, and water). We define the relevant metrics for the quantification and modelling of WLFs, including an exhaustive discussion of different modelling approaches (i.e. Voellmy, Bingham and Manning) and provide a first attempt to simulate WLFs. We draw attention to WLF phenomena to encourage further field, theoretical, and experimental investigations that may contribute to a better understanding of flows in river basins, leading to more accurate predictions, and better hazard mitigation and management strategies. © 2019 John Wiley & Sons, Ltd.

Section: Implications For Hazards and River Managementmentioning

confidence: 99%

Characterization of wood‐laden flows in rivers

Earth Surf Processes Landf

Mazzorana

Castellet

et al. 2019

Self Cite

“…In the latter, preferential retention of large wood in wider river reaches leads to an increase in total and specific wood storage with increasing river width [ Wyzga et al ., ]. This propensity for large wood to be preferentially retained in the widest sections of mountain rivers can be used as a natural buffer attenuating transfer to intensively managed valley reaches [ Wyżga and Zawiejska , ; Wohl et al ., ].…”

Section: Advances In Quantifying Large Wood Budgetingmentioning

confidence: 99%

Recent advances quantifying the large wood dynamics in river basins: New methods and remaining challenges

Piégay

Gurnell

et al. 2016

Reviews of Geophysics

190

194

Large wood is an important physical component of woodland rivers and significantly influences river morphology. It is also a key component of stream ecosystems. However, large wood is also a source of risk for human activities as it may damage infrastructure, block river channels, and induce flooding. Therefore, the analysis and quantification of large wood and its mobility are crucial for understanding and managing wood in rivers. As the amount of large-wood-related studies by researchers, river managers, and stakeholders increases, documentation of commonly used and newly available techniques and their effectiveness has also become increasingly relevant as well. Important data and knowledge have been obtained from the application of very different approaches and have generated a significant body of valuable information representative of different environments. This review brings a comprehensive qualitative and quantitative summary of recent advances regarding the different processes involved in large wood dynamics in fluvial systems including wood budgeting and wood mechanics. First, some key definitions and concepts are introduced. Second, advances in quantifying large wood dynamics are reviewed; in particular, how measurements and modeling can be combined to integrate our understanding of how large wood moves through and is retained within river systems. Throughout, we present a quantitative and integrated meta-analysis compiled from different studies and geographical regions. Finally, we conclude by highlighting areas of particular research importance and their likely future trajectories, and we consider a particularly underresearched area so as to stress the future challenges for large wood research.

“…Consequently, to take advantage of the benefits of LW and to prevent its potential negative impacts in the case of floods, natural LW dynamics must be managed properly (Mao, Andreoli, Iroumé, Comiti, & Lenzi, ; Mazzorana et al, ; Wohl et al, ). However, our understanding of wood entrainment and deposition processes is still limited (Dixon & Sear, ; Schenk, Moulin, Hupp, & Richter, ) and largely restricted to a small number of field‐based (Ravazzolo, Mao, Picco, & Lenzi, ); laboratory (Welber, Bertoldi, & Tubino, ); or modelling (Ruiz‐Villanueva, Wyżga, Hajdukiewicz, & Stoffel, ) approaches, typically hampered by short measurement periods and a limited number of tagged logs.…”

Section: Introductionmentioning

confidence: 99%

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

Iroumé

Mao

et al. 2018

Hydrological Processes

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.