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

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

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

Citation: Ruiz-Villanueva, V., Piégay, H., Gurnell, A. A., Marston, R. A., & Stoffel, M. (2016). Recent advances quantifying the large wood dynamics in river basins: New methods and remaining challenges. Reviews of Geophysics. doi:10.1002/2015RG000514Large 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. ©2016. American Geophysical Union

Dating Torrential Processes on Fans and ConesMethods and Their Application for Hazard and Risk Assessment /

XXXII, 424 p.online resource

Investigation of earthquake impacts on protection structures like torrent barriers=Konzept zum nachweis der erdbebengefährdung von querschutzbauwerken in wildbächen

Protection structures with respect to settlement areas are for instance torrent barriers as often used in the mountains. In general, they can be classified in (a) sensitive and regular structures, or (b) according to their functionality in dispensing or defending structures etc. There are already numerous approaches regarding loading and combinations of loads acting on those varying types of structures, Nevertheless, earthquake impacts as loading situations on torrent barriers are only rarely investigated. Therefore, the objective of this paper is to investigate, whether neglecting loading situations resulting from earthquakes is justified. These investigations are based on a simplified dynamic method as generally used for reservoir structures of class III. Further on, the assessment is based on probability concepts as established in new design formats (e.g., JCSS model code) and the earthquake zone map

Possibilities and limitations of dendrogeomorphic time-series reconstructions on sites influenced by debris flows and frequent snow avalanche activity

Past debris-flow and snow avalanche activity was assessed for the Reiselehnrinne (Tyrol, Austria) using growth disturbances in growth-ring series of 372 Norway spruce (Picea abies (L.) Karst.) trees. Determination of events was performed by analyzing (a) the number and (b) intensity of growth disturbances within tree-ring series and (c) the spatial distribution of affected trees. Differentiation of debris flow from snow avalanche events was based on the intra-annual position of scars, callus tissues or tangential rows of traumatic resin ducts, and on the spatial distribution of trees with simultaneous reactions in the tree-ring series. We introduce a weighting factor to substantiate the dating of past process activity in a comprehensive way and to compare individual events as to their intensity and total number of tree-ring responses. The accuracy of the dendrogeomorphic assessment was then evaluated by comparing the reconstructed event frequency with chronologies available for the Reiselehnrinne. Comparison of tree-ring with historical data demonstrated clearly that the reconstructed event frequency contains the majority of past debris flow and snow avalanche events in the Reiselehnrinne, but that dating of events is not always possible, especially if they are clustered in time or have a limited spread on the cone

Frequency and spread of debris floods on fans: A dendrogeomorphic case study from a dolomite catchment in the Austrian Alps

Growth disturbances in tree-ring series have been regularly used to date debris-flow events in mountain environments. In contrast, no studies are available to date that have reconstructed debris floods by means of dendrogeomorphology. Therefore, the aim of this study was to determine the event frequency and the spread of debris floods in the Gratzental (Tyrol, Austria). The analysis of growth disturbances in the tree-ring series of 227 Picea abies (L.) Karst. and Larix decidua Mill. allowed the reconstruction of 37 events for the last 200 years. The lateral spread and preferable avulsion locations of reconstructed debris-flood events were assessed based on the dating of the events and the spatial position of trees affected by an event on the fan. Results show that the Gratzentalbach preferentially avulsed to the east, but affected trees were evenly spread over the fan. Reconstructed data illustrates the high potential of dendrogeomorphology for hazard assessment of debris floods

13th International INTERPRAEVENT Congress Lucerne, Switzerland 30 May - 2 June 2016, ISBN 978-3-901164-24-8

International audienc