Large Wood Dynamics Research Articles

The role of riparian buffer width on sediment connectivity through windthrow in a boreal headwater stream

Riparian buffers are commonly used to mitigate the negative effects of forestry operations near water, particularly sediment transport to streams. In Sweden, current practices typically involve 5-7 m wide riparian buffers along small streams. Historical forest management, which favored conifers up to the channel edge, has resulted in these narrow buffers having a simplified tree species composition and structure, making them prone to windthrow. While windthrow can contribute large wood (LW) to streams, windthrow also risks increasing sediment inputs if rootwads are exposed near stream edges. This disturbance affects sediment connectivity, or the movement of particles through the fluvial system, but the interaction between LW dynamics and sediment connectivity in small boreal streams is not well understood. We investigated sediment connectivity at the Trollberget Experimental Area in northern Sweden, where six 100 m stream reaches had either 5 m or 15 m wide riparian buffers. Pre-harvest and one-year post-harvest data on windthrow, hydrology, and sediment yields were collected. Forest harvesting increased sediment connectivity in the streams regardless of buffer width, indicating that buffers wider than 15 m are necessary to reduce sediment input impacts in small headwater streams. Windthrow affecting stream channels was more common in the 5 m buffers, leading to significantly higher deposition of very fine sediments (<250 μm) compared to the 15 m buffers. Coarse (>1 mm) and fine sediments (250 μm – 1 mm) were also higher in the 5 m buffers. We found that sediment connectivity in streams was closely linked to LW dynamics, negatively before harvest but positively after harvest. Before harvest, LW trapped sediment and prevented downstream transport, but after harvest, the increased sediment input overwhelmed this function. Our results highlight a trade-off between the recruitment of LW and minimizing sediment connectivity, two key objectives in riparian buffer management.

Influence of large wood dynamics on flow and channel morphology in a forest stream

The riparian zone is a dynamic ecosystem formed by the interaction of aquatic and terrestrial components of rivers and serves as a source of the large wood (LW). We aimed to understand the LW dynamics and the LW influence on river morphology, sediment distribution, and flow velocity within three reaches of a low-order stream. The study was performed in a segment (770 m in length) of the Perdizes stream, located in Aparados da Serra National Park, southern Brazil. We framed the study by focusing three issues: i) the processes explaining the LW dynamics in the Araucaria Forest biome; ii) the effects of LW on the flow velocity along the study reaches, and iii) the presence of LW affecting the sediment longitudinal connectivity. The methodology consisted of: (i) collection of hydrological data (rainfall, discharge, and streamflow velocity), (ii) Perdizes stream characterization by topo-bathymetric survey and river-flow simulation with HEC-RAS 5.0.7 1D. and (iii) detailed field surveys of LW and bed sediments. The LW descriptions were performed at four moments (July 10, 2019; November 19, 2019; July 24, 2020; and December 18, 2020). Abundant LW, mainly from araucaria (Araucaria angustifolia (Bertol.) Kuntze), was observed before meanders. A notable reduction in LW volume and an increased proportion of araucaria, compared to deciduous trees, were observed within the channel. Mass balance analysis indicated fluctuations in riparian vegetation biomass, emphasizing the connectivity between vegetation and the river. Streamflow velocity decreased in LW presence, from occurrence to the margin. Bed sediment diameters were consistently smaller in cross-sections with LW presence. The accumulation of smaller sediments with LW indicated partial downstream sediment disconnectivity. HEC-RAS simulations confirmed increased LW deposition in lower velocity zones. This understanding of fluvial dynamics contributes to effective natural environment management, especially in the Araucaria Forest context.

Long‐term dynamics of large wood in old‐growth and second‐growth stream reaches in the Cascade Range of Oregon

AbstractWe quantified temporal dynamics of wood storage, input, and transport over a 24‐year period in adjacent old‐growth and second‐growth forested reaches in Mack Creek, a third‐order stream in the Cascade Range of Oregon. The standing stocks of large wood in the old‐growth reach exceeded those at the second‐growth reach by more than double the number of wood pieces and triple the wood volume. Annual inputs of large wood were highly variable. Wood numbers delivered into the old‐growth reach were 3× higher and wood volume 10× greater than in the second‐growth reach. The movement of number and volume of logs did not differ significantly between the two reaches over time. Less than 2% of the logs moved in most years, and the highest proportion moved in the year of the 1996 flood (9% in old growth and 22% in second growth). Most of the large wood aggregated as jams in both reaches. The second‐growth reach lacked major jams, but 29% of the logs in the old growth were in full‐channel spanning jams. Long‐term observations of annual storage, input, and movement reveal the temporal dynamics of wood rather than static representations of the characteristics of wood. Input events and transport of wood in Mack Creek were episodic and varied greatly over the 24‐year study, which illustrates one of the major challenges and opportunities for understanding the cumulative dynamics of wood in streams.

SmartWood: field-based analysis of large wood movement dynamics using inertial measurement units (IMUs)

Wood plays an important ecological role in rivers. Yet challenges arise when large wood (LW) is mobilised and transported during floods. Due to a lack of quantitative data, movement behaviour of LW during floods is still not well understood to date. A proof-of-concept study was conducted at three Swiss rivers to test state-of-the-art sensor-tagged logs, so-called “SmartWood” and collect quantitative field-scale data about LW movement behaviour. The experiments utilised innovative inertial measurement units (IMUs), which have been developed at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) at ETH Zurich and implanted into wood logs (SmartWood) at prototype scale. Each IMU comprised three individual sensors (gyroscope, accelerometer, and magnetometer) and was equipped with an on-board processor, an AA battery (4.35 V), a memory (8 MB), and a Wi-Fi transmitter (100 m) for data transfer. After successful initial verification tests of the sensors, the IMUs were installed into debranched wood logs, measuring 4.35 m in length and 0.33 m in diameter. At the time of the field experiments, each SmartWood-log weighted between 170 and 220 kg, yielding a density of roughly 500 kg∙m−3. At the Limmat, Thur, and Grosse Melchaa Rivers in Switzerland, innovative yet discontinuous data were obtained. Results revealed consistent movement dynamics across all field sites. Specifically, we observed positive yaw movement during transport of SmartWood along the left river bank and negative yaw movement along the right river bank. Furthermore, interactions of SmartWood with channel boundaries, riparian vegetation, and objects (e.g., ferry dock) were registered and quantified, even when the SmartWood-log was transported out of sight of traditional sensing methods. The conducted field experiments enabled the initial testing of SmartWood in the field and exposed critical limitations of the IMUs and software algorithms for the reconstruction and analysis of floating LW dynamics. The gained knowledge and introduced sensing method will benefit the quantitative assessment of LW dynamics in rivers to maintain safety and functionality for instream structures (e.g., considering LW movement dynamics for the robust design of LW retention and guiding structures), but also river restoration projects and numerical models that rely on quantitative field-scale data.

A review of large wood dynamics relevant to hazard characteristics for built structures

Large wood exerts an influence on the topography and geomorphology of channels in areas of good vegetation development, and it is also an important component of riverine ecosystems. However, large wood may impact and damage buildings. The formation and failure of logjams can cause backwater rise, local scour, and the amplification of flow discharge, leading to more serious disasters. Therefore, quantifying the processes of large wood recruitment, entrainment, transport, deposition, accumulation and logjams failure is highly significant for the prevention of large wood hazards in channels. Based on existing research on large wood, this review provides a comprehensive analysis of large wood dynamics and hazards. First, the processes involved in large wood recruitment, entrainment, transport, and deposition are reviewed. Second, the results of large wood accumulation probability and the backwater rise, local scour, critical conditions of logjams failure and magnitude amplification of the flow discharge caused by large wood are analyzed comprehensively. Finally, large wood-related hazard mitigation measures are also introduced. Future research directions to improve the mitigation of hazards from large wood should concentrate on exploring quantification models for understanding how large wood impacts and accumulates on various built structures.

A high‐resolution inter‐annual framework for exploring hydrological drivers of large wood dynamics

AbstractRivers with alluvial bars store more wood than those without, supplied through channel shifting. However, wood dynamics (arrival or new deposits, departure or entrainment, and stable or immobile pieces) can vary substantially over time in response to critical hydrological drivers that are largely unknown. To evaluate them, we studied the dynamics of large wood pieces and logjams along a 12‐km reach of the lower Allier River using six series of aerial images of variable resolution acquired between 2009 and 2020, during which maximum river discharge fluctuated around the dominant flood discharge (Q1.5) that is potentially the bankfull discharge along this well‐preserved not incised reach. Individual wood departure was best correlated with water levels exceeding dominant flood discharge. The duration of the highest magnitude flood was best correlated with wood depositions, with shorter floods resulting in a higher number of deposits. Finally, most of the wood remained stable when river discharge did not exceed 60% of Q1.5 over a long period of time. Changes in inter‐annual wood budget (reach‐scale) depend on the duration over which discharge exceeded 60% of Q1.5. Hydrological conditions driving jam build‐up and removal were similar to those controlling individual wood piece dynamics. The results suggest that specific hydrological conditions influence the dynamics of large wood and log jams in the Allier River. Understanding the dynamics of large wood and its impact on river morphology is fundamental for successful river management and habitat restoration initiatives.

Snow Avalanches as a Driver of Large Wood Dynamics in Mountain Streams

AbstractSnow avalanches are thought to influence large wood dynamics within mountain streams, but studies that explicitly quantify their impact are minimal. In three headwater catchments of the Frying Pan River, Colorado, USA, we found that wood loads in stream reaches intersected by avalanche pathways ranged from 220 to 8,500 m3/ha and were significantly greater than in non‐avalanched reaches. Inter‐catchment differences in the number of avalanche occurrences were not reflected in control reach wood loads, suggesting that elevated loads may be restricted to the general vicinity of the avalanche pathway. However, the sizable wood volumes in avalanche reaches generated notable geomorphic impacts, indicating that avalanches can create hotspots of in‐stream geomorphic complexity and influence the overall habitat mosaic of the stream ecosystem. Loads in avalanche reaches were moreover significantly greater than literature values for similar streams and recruitment processes, emphasizing the importance of snow avalanches as a wood recruitment mechanism.

Transport Dynamics of Large Wood in a Stream Channel Affected by Spur Dikes

AbstractThe damage to river engineering structures induced by large‐wood (LW) jams is one of the significant problems in river management. For example, typical bridge damage in alluvial areas in Japan, such as wash away, is often caused by the accumulation of large wood materials. The densely transported large wood pieces are an important factor in the accumulation process. We investigated the influence of local flows generated by hydraulic structures on the initial stage of the concentration of large wood pieces. First, we experimentally investigated the flow structures generated by spur dikes in a 0.6 m wide channel and the trajectory of large wood pieces. Then, we numerically investigated the influence of external force on the transport mechanisms of large wood pieces. We employed a simplified Basset‐Boussinesq‐Oseen model to evaluate each term of the momentum equation of the particles and calculated the trajectories of the wood pieces previously observed experimentally. The results showed that the transported large wood pieces were concentrated in low‐vorticity regions of the water surface. This tendency was more prevalent in short pieces (10 mm) than in long pieces (40 mm) because the influence of the relatively small‐scale patterns of the pressure gradient of the surrounding water surface might be spatially averaged for long pieces. This tendency has not been explicitly elucidated in previous works; thus, this knowledge is expected to be key in controlling LW transport, such as detecting the possible regions where LW jams occur or designing efficient inlet sections of LW retention facilities.

Characterization of trajectories and drag coefficients of large wood in sharp river bends from flume experiments

AbstractThe transport of large wood (LW) has been a focus of research in the last decades because of its importance for river ecosystems, fluvial dynamics and flood protection. Riverine processes connected with the presence of LW have largely been based on laboratory experiments carried out in straight or weakly bended channels. The dynamics of LW in sharp river bends has received less attention, so there exist many open questions regarding how LW is transported through such channel parts. For this reason, this paper presents results of unique laboratory experiments designed to study the trajectories of single wooden dowels in sharp bends. Dowel trajectories were determined for four dowel sizes, two initial dowel orientations with respect to the main channel axis and three inlet positions. Information about the 3D velocity field in the bend were obtained from a previous study that used the same channel with identical hydraulic boundary conditions. Furthermore, a force‐balance analysis was developed for interpreting the dowel trajectory and drag coefficient of LW in sharp river bends. The experimental results show that the dowel length is the main parameter controlling dowel trajectory in a sharp bend, and indicate the role of inertial effects that drive the dowel drift along the bend. The obtained drag coefficients ranged between 0.35 and 1, which is in agreement with previous values for submerged, or semi‐submerged, fixed pieces of wood in straight river reaches.

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

AbstractDebris flow is one of the dominant processes distributing large wood (LW) within mountainous catchments. However, little has been reviewed on wood‐laden debris flow (WLDF), presumably owing to limited reviewable works. This article, therefore, navigates the international readers through 40 years of WLDF studies, most of which have been published only in Japanese. Firstly, we reviewed the historical development of Japanese WLDF particularly focusing on the 1980s and the 1990s. A series of post‐disaster fieldworks from the July 1982 Nagasaki flood to the July 1990 Kumamoto flood provided 32 catchment‐scale wood budgeting data; empirical relationships among drainage area, dominant tree species, sediment yield, and wood loads associated with single debris flow disasters were illustrated. Secondly, the characteristics of WLDF were summarized based on relevant previous studies on the recruitment, transport, and deposition processes of LW during debris flows. Thirdly, we discussed the connectivity between those Japanese WLDF studies and international LW studies by relating/contrasting their research approaches and spatiotemporal scales. In contrast to global LW research trends, Japanese WLDF studies have almost exclusively regarded LW as hazardous materials (i.e., “driftwood” or “woody debris”) that need to be retained upstream of the inhabited areas. Those practice‐oriented WLDF studies were concentrated on drainage areas of 10−2 to 100 km2, representing 1–6 orders of magnitude smaller spatial scales than those generally covered by existing international LW studies. Strongly motivated by engineering requirements, “dynamic” interactions between debris flows and LW during floods have also been physically presented, mainly based on unique laboratory experiments involving steep flume (&gt; 0.05) and mobile bed conditions. Finally, some future works for WLDF were briefly stated from practical and scientific perspectives. By “rediscovering” those WLDF studies domestically developed in Japanese debris flow channels since the 1980s, a more comprehensive understanding of LW dynamics in the river system may be achieved.

Large wood dynamics in a mountain river disturbed by a volcanic eruption

Volcanic eruptions can dramatically alter river basins and channel networks by delivering huge amounts of sediments into the channels and affecting the surrounding vegetated area. These disturbances modify the process chain of large wood (LW) recruitment, storage, and transport. We investigated the effects of the 2015 Calbuco volcanic eruption in southern Chile on the dynamics of LW along two reaches of the Blanco Este River, which drains the north-eastern flanks of the volcano. The two reaches, R1 and R2, were surveyed for almost four years, combining field and remote analyses to better comprehend LW dynamics. We framed our study around three research questions: i) what are the processes explaining the spatial and temporal variations of LW load into the active channel of the Blanco Este River? ii) can the longitudinal (dis)connectivity be considered a controlling factor rather than flood magnitude? iii) is it possible to infer a relationship between recruitment sources, and flood events, with LW load fluctuations? The abundance of individual LW pieces and wood jams (WJs) were always higher in the downstream reach (R2). LW source areas to R1 were limited to forested bank erosions, while in R2 LW was recruited from bank erosions with the addition of wood pieces entering in the main channel from a lateral affluent and from eroded old lahar deposits that re-connected this source to the active channel. WJs were highly unstable and there were not statistically significant relationships between LW fluctuations and water discharge. In the Blanco Este River, LW delivery and export can be classified as event-driven processes, but alternating periods with longitudinal (dis)connectivity led to events delivering wood into the channel which seemed to occur asynchronously with those exporting LW. Finally, LW load in R1 appeared to be in equilibrium, but this condition might change in the future since the area of upper forested streambanks is rapidly declining.

Engineered Large Wood Structures in Stream Restoration Projects in Switzerland: Practice-Based Experiences

The effects of large wood (LW) presence in streams on river ecology and morphology are becoming widely researched and nowadays their ecological benefits are undisputed. Yet LW presence in most Swiss plateau streams is poor mainly due to anthropological pressure on river ecosystems. The use of anchored, engineered LW structures under various forms in stream restoration projects is now state of the art. However, binding benchmarks for the equivalent naturally occurring instream LW quantities and complex LW structures do not yet exist. Therefore, hydraulic engineers often find themselves in a conflict between acceptable instream LW quantities for flood protection, quantities desirable from an ecological point of view and, last but not least, quantities accepted by the public based on the current ideologies of landscape design. In the first section, this paper treats the complexity of defining benchmarks for LW quantities in restoration projects. In the second section, we provide a qualitative practical insight into relevant questions when planning engineered LW structures, such as placement, anchoring, naturalness, and effectiveness from a hydraulic engineer’s point of view. The third part presents three examples of restoration projects with different dimensions where various engineered LW structures with different outcomes were built and introduced into active streams. Finally, the conclusion provides further possible measures to retain LW in streams and to restore more natural LW dynamics in rivers.

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

AbstractIn 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.

Dynamics of large wood added to Midwestern USA streams

AbstractLarge wood (LW) additions are commonly used to restore degraded streams, particularly in regenerating forests that have low LW recruitment due to past logging. While the short‐term effects of LW input on stream structure and function are well studied, the long‐term dynamics of added wood are less documented. We assessed the long‐term movement and condition of LW added to three small (mean discharge, 28–47 L s−1) midwestern USA streams. In 2004, 25 aspen logs (2.5 m L × 0.5 m D) were added to 100‐m treatment reaches of three replicate streams in northern Michigan, USA, that contained low prior LW abundance. We monitored log movement and evaluated factors contributing to that movement over 14 years. Across all three streams, 41 of the 75 added logs moved downstream, with a mean travel distance of 4.0 m (SD, 7.0 m; n = 75). However, all logs still remained within their original reaches. Most log movements occurred within the first 3 years following placement and were associated with high flow events. Individual log mobility was related to position in the channel; logs that were at least 70% submerged, and near horizontal in inclination, accounted for 83% of the single movements ≥0.5 m. In addition, after 14 years 32% of logs became part of aggregations and 86% displayed substantial decay. Our study suggests that restoration efforts that add LW to small, groundwater‐dominated streams can pose minimal risk to downstream reaches or human structures and may provide sustained ecological benefits to the ecosystem.

Application of computational modeling for large wood dynamics with collisions on moveable channel beds

This study aims to analyze model reproducibility on large wood collisions on moveable channel beds. Flume experiments were conducted to observe the responses of moveable bed change with the behavior of large wood, including wood collisions. In the experiments, we employed time intervals of 5 and 9 s in wood supply, which modified the collision patterns. Subsequently, we conducted simulations based on the experimental conditions. Herein, to analyze the wood collision effect in the simulations, we employed the dashpot-spring model in a large wood dynamics model. Subsequently, we compared the simulations with and without wood collision and discussed the reproducibility of the model. The results of the simulations and experiments revealed that the wood pieces exhibited diverse behaviors, including floating, sliding, deposition, plane rotation, rolling, collision, remobilization, jam formation, and causing local bed changes. In particular, the results indicate that model reproducibility is dependent on wood collision because this can actively alter wood deposition patterns. We also described the piping and tunnel erosion processes linked to wood collision and moveable beds and suggested the corresponding, suitable computational treatment. This study presents an experimental and modeling methodology on wood collision and the interaction between bed change and large wood. Thus, useful information for solving numerical difficulties linked to large wood dynamics, including wood collisions, is provided.

Numerical Modeling of Instream Wood Transport, Deposition, and Accumulation in Braided Morphologies Under Unsteady Conditions: Sensitivity and High‐Resolution Quantitative Model Validation

AbstractLarge wood promotes fundamental changes in river hydraulics and morphology, playing a relevant role in river ecology but also in flood hazard. Accurate predictions of large wood dynamics in terms of deposition patterns and travel distance are still lacking and only recently have numerical models been developed to this end. In this work we enhance the capabilities of the numerical model Iber‐Wood in reproducing large wood dynamics in shallow braided rivers and validate it by comparing simulations with the results of previous laboratory experiments. The flume experiments provide high‐resolution observations of wood travel distances and depositional patterns of wood. The comparison proves useful to improve the numerical simulation of (i) the interactions between wood pieces and the riverbed (e.g., when wood pieces are transported by dragging), (ii) wood pieces with roots, and (iii) the formation of wood jams (i.e., accumulations of greater than three wood pieces). A sensitivity analysis reveals the crucial role of bed topography, with limited effect played by drag and restitution coefficients. Taking advantage of a controlled environment with similar simplifying hypotheses, we combine the strengths of both physical and numerical modeling to explore the parameters that are most effective in controlling wood dynamics. We use the numerical model to explore the effect of unsteady flow conditions, with different wood supply input. The resulting wood depositional patterns, jam formation, and travel distances during floods may improve our understanding of some of the controls on biogeomorphic evolutionary trajectories of braided rivers.

Long-term monitoring of the recruitment and dynamics of large wood in Kamienica Stream, Polish Carpathians

Studies presenting long-term observations of the recruitment and mobility of large wood in mountain watercourses are scarce, but they can considerably contribute to the knowledge of river/riparian forest interactions and the assessment of flood hazard resulting from wood mobility during floods. Widespread dieback of riparian forest along the headwater course of Kamienica Stream in the Polish Carpathians, caused by bark beetle infestation of spruce trees, has raised concerns about potential increases of large wood recruitment to the stream and of the flood hazard to downstream valley reaches. In October 2009, 429 trees growing along three sections of the stream were tagged with numbered metal plates and monitored over 10 years to determine the timing and causes of their delivery to the channel and the lengths of their displacement during individual flood events. Moreover, in 2012 the mode of location of wood deposits and a degree of wood decay were determined in the second- to fourth-order stream reaches. The monitoring of tagged trees indicated that trees were recruited to the channel during highintensity meteorological and hydrological events, mostly as a result of bank erosion during floods or windthrow. With 22% of tagged trees recruited to the channel during 10 years, the rate of turnover of the riparian trees was estimated at 45 years. As the riparian area is overgrown with trees with ages up to ~160 years, the rate evidences substantial intensification of large wood recruitment to the channel in the recent period. Results of large wood inventory and the 10-year-long monitoring of tagged trees indicated variable mobility of large wood along the upper course of the stream. Wood mobility was negligible in the second-order stream reach, very small in the third-order reach, and greater, but still limited in the fourth-order reach. Wood is transported longer distances only during major floods. However, the advanced state of decay of most pieces leads to their disintegration during floods, precluding distant transport. Thus, large wood retained in the upper stream course does not constitute an important flood hazard to downstream, inhabited valley reaches.

Recent developments in the analysis of Large Wood dynamics in fluvial systems

Recent developments in the analysis of Large Wood dynamics in fluvial systems

Numerical simulation of large wood deposition patterns and responses of bed morphology in a braided river using large wood dynamics model

AbstractThis study discusses the reproducibility of a numerical model for simulating the morphodynamics involved in the transport of large pieces of wood in a braided river, considering the root wad effect and jam formation. The developed numerical model can simulate the behaviour of large pieces of wood using a two‐dimensional depth‐averaged Eulerian flow model that calculates the water flow and bed morphology. A Lagrange‐type wood transport model is used herein, and the applicability of the combined model is discussed through a comparison with obtained experimental results. From the simulation results, we calculate the total braiding index and estimate the deposition patterns of wood pieces for comparison with the experimental results. We then analyse the bed morphology responses and wood deposition patterns in terms of the root wad effect and input supply. Moreover, we discuss the advantages and limitations of the proposed model to predict the large wood dynamics considering the bed morphology. © 2019 John Wiley &amp; Sons, Ltd.

Computational modeling for large wood dynamics with root wad and anisotropic bed friction in shallow flows

Abstract This study developed a computational model for large wood deposition patterns in shallow flows considering the effect of a root wad based on laboratory experiments. We used the Nays2DH depth-averaged two-dimensional model of iRIC to simulate shallow flows. A newly developed large wood simulation model was combined with the shallow flow model. The laboratory tests were performed by changing several hydraulic parameters. In shallow water with a depth similar to the diameter of large wood, the root wad decreased the draft for wood motion (the depth at which large wood contacts the river bed) by lifting the head of large wood. The experimental results showed that the large wood tends to move toward the side walls and deposit on the bed after passing an obstacle. Computational results reasonably showed that the proposed coupling model reproduced the fundamental and physical aspects of the phenomena.