Dynamics of large wood during a flash flood in two mountain catchments

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.

Section: Discussionmentioning

confidence: 98%

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

“…We reviewed available data concerning large wood exported during floods and the relationship between exported wood volume, flood magnitudes, and drainage basin characteristics (Figure ). Following the work by Rickenmann [], we updated his database from the original 34 events to 83, including recent events from France, Italy, and Switzerland [ Lange and Bezzola , ; MacVicar and Piégay , ; Badoux et al ., ; Lucía et al ., ; Steeb et al , 2016; data compiled by Seo et al [] from observations of wood volumes exported and stored in reservoirs in Japan, information from the Génissiat reservoir in France [ Moulin and Piégay, ]; and the large raft in the Saint‐Jean River in Canada [ Boivin et al ., ]. These last two sources were only used to provide an upper limit or maximum value of wood volume during the highest‐magnitude floods observed.…”

Section: Advances In Quantifying Large Wood Budgetingmentioning

confidence: 99%

“…Large wood, like sediment, remains relatively stable for most of the time within river corridors, with only the smaller and loose wood pieces able to move. However, large quantities of wood may be mobilized during infrequent, high‐magnitude flood events [ Mao et al ., ] and may induce potential hazards for human populations and infrastructure [ Comiti et al ., ; Badoux et al ., ; Lucía et al ., ]. The deposition of wood at critical locations (e.g., bridges) can cause a reduction of channel cross‐sectional area and related conveyance loss [ Gippel et al ., ; Beebe , ], thus inducing more frequent flooding.…”

Section: Introductionmentioning

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

205

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.

“…In this context, it is worth highlighting the added value of documenting extreme flood events deserving particular attention to assess recruited, transported, and deposited LW volumes and inferring the event‐related LW dynamics (Badoux et al ., , ; Rickenmann et al ., ; Lucía et al . a; Comiti et al . a; Steeb et al ., ).…”

Section: Introductionmentioning

confidence: 98%

Assessing and mitigating large wood‐related hazards in mountain streams: recent approaches

Mazzorana

J Flood Risk Management

Marchi

et al. 2017

Self Cite

The assessment and mitigation of floods in mountain streams, when large wood (LW) is transported, pose several challenges. The process chain consisting of flood propagation, LW recruitment, entrainment, transport, and entrapment triggers, at critical sections such as bridges, unexpected and exacerbated impacts to the exposed built environment. We provide a review on the recent advances in modelling LW dynamics during extreme river floods through computational approaches. Moreover, we describe how scaled flume experiments can enhance process understanding at critical flow sections such as bridges to address risk mitigation problems. Additionally, we present a framework based on Formative Scenario Analysis (FSA) to allow for expert knowledge integration and to subsequently derive consistent hazard process scenarios in steep mountain streams where the application of computational approaches is less reliable. Finally, we discuss how the application of the presented set of assessment methods can support integral flood risk management by explicitly considering LW dynamics since the effectiveness of mitigation critically depends on the acquired process understanding.