Physical modelling of large wood (LW) processes relevant for river management: Perspectives from New Zealand and Switzerland

Abstract

In the last 30 years, work on large wood (LW) has expanded and matured considerably, and river scientists, managers and practitioners now have a better appreciation of the role of LW in maintaining ecosystems, forming or stabilizing riverine landforms, and interacting with river morphodynamics. We have gained a better understanding of the hazards posed by the recruitment and transport of LW in the river channel and associated infrastructure. While LW dynamics have traditionally been studied in the natural river environment, innovations in laboratory techniques have enabled important advances in understanding LW process dynamics, using physical scale models, new sensors, scanners and sophisticated model boundary conditions. Current trends in LW laboratory research focus on (1) mobilization and transport of logs, (2) trapping and deposition of sediment in the presence of LW and(3) LW contribution to hydraulic flow resistance. Ultimately, a combined process understanding is needed to assess impacts upon infrastructure with erodible boundaries, such as bridge piers and LW retention racks. In this review, we present a critical analysis of emerging experimental work on LW obtained through physical modelling studies. We put recent experimental work in context with global LW management challenges. In particular, we set our work in context with the present environmental and engineering issues that confront catchment and natural resource managers in Switzerland and New Zealand. We show how improved physical models incorporating LW transport, accumulation and scouring processes are needed to contribute to more reliable hazard and risk assessment and improved river management in LW-prone systems.

Rediscovering wood‐laden debris flow studies: A perspective from Japan

“…However, existing models listed in table 3 of Gasser et al (2019), except for an empirical approach by Mazzorana et al (2009) and Rigon et al (2012), do not consider debris flows as LW recruitment processes; aside from those two works, we are only aware of a preliminary case study in Switzerland (Ruiz‐Villanueva & Stoffel, 2018) that incorporated debris flows in modeling LW recruitment. Similarly, LW transport and deposition processes during floods were recently summarized by Mazzorana et al (2018) and Friedrich et al (2022), mainly depending on resources from the European Alps, New Zealand, and flume experiments representing lower channel gradients typically < 0.05. Nevertheless, those synthetic analyses did not incorporate WLDF studies from the 1980s to the 1990s.…”

“…Recently, some review papers (Comiti et al, 2016; Ruiz‐Villanueva et al, 2016a; Swanson et al, 2021; Wohl, 2017) have synthetically analyzed international LW studies, outlining current achievements and future directions. Over the past decade, there have also been significant advances in classifying (Ruiz‐Villanueva et al, 2019), monitoring (Spreitzer et al, 2019b), experimenting (Friedrich et al, 2022), and modeling (Mazzorana et al, 2018) LW transport during floods.…”

Small-Scale Modeling of Flexible Barriers. II: Interactions with Large Wood

“…In this context, solid transport, especially of coarse elements (LW, gravel, and cobbles), can reach impressive volumes (Rickenmann et al 2015;Ruiz-Villanueva et al 2019). When reaching an urbanized area, LW tends to obstruct bridges and other hydraulic structures, and sediment to fill channel bed, both aggravating flood hazards (Badoux et al 2014;Ruiz-Villanueva et al 2014;Mazzorana et al 2018;De Cicco et al 2018;Friedrich et al 2022). Relevant strategies to prevent LW stopping and sediment deposition in critical areas is usually (1) to adapt the bottleneck sections, e.g., by removing piers of bridges or of dam spillways and by increasing their section (Schmocker and Hager 2011;Gschnitzer et al 2017;Bénet et al 2021), and/or (2) to trap the solid transport at dedicated structures, such as the debris basins, open check dams, racks, or flexible barriers (Comiti et al 2016;Piton and Recking 2016a, b;Mazzorana et al 2018;Wohl et al 2019;Bénet et al 2021Bénet et al , 2022.…”

The Effect of Large Wood Accumulations With Rootwads on Local Geomorphic Changes

“…Laboratory experiments are well‐suited to better study and capture the complex interactions between LW, sediment, flow, and infrastructure (Friedrich et al., 2021). However, physical modeling of LW processes that explicitly considers complex and realistic shapes still presents unexplored challenges.…”