Wood Jams Research Articles

Wood jam characteristics influence but do not fully explain wood jam morphologic functions

In-stream wood jams alter their surrounding channel morphology, thus setting riverscape morphology and ecosystem function. While wood jams clearly scour pools, retain sediment, and influence bank erosion, there is a lack of observational evidence of how wood jam characteristics themselves control morphologic effects. Here, I analyzed field observations of hundreds of wood jams to test the hypothesis that wood jam characteristics can predict local morphologic effects such as sediment retention, bar forcing, and pool scour. I found mixed support for this hypothesis: While jam characteristics such as porosity, channel blockage ratio, thalweg occupation, and having rootwads and multiple trunks significantly predicted morphologic effect occurrence and magnitude, they only explained a small portion of the variance in those morphologic effects. While wood jam characteristics are relevant in controlling their overall morphologic functions, those functions are both inherently variable and likely affected by numerous other factors, such as reach-scale topography, the sediment transport capacity to supply ratio, and interactions with surrounding wood and vegetation. Wood function restoration may be more effective if it targets reach-scale objectives across dynamic wood jam assemblages, instead of individual jams.

Islands in the stream: Wood‐induced deposition and erosion in the river corridor

AbstractLarge wood causes and responds to deposition and erosion within a river corridor. We focus on the anastomosing, gravel‐bed Swan River and two meandering, gravel‐bed tributaries in northwestern Montana, USA to explore the temporal dimensions of deposition and erosion associated with channel avulsions and island formation and to introduce the concept of wood levees. Channel avulsion represents isolation of part of the existing floodplain and formation of an anastomosing channel planform, with wood‐induced deposition at the point of channel bifurcation. Islands form at a wood jam that migrates upstream with time as sediment accumulates in the lee of the jam. The island creates only a local interruption of the single‐channel planform. We use tree‐ring and 14C dating to constrain wood‐induced island ages. We interpret the three wood‐induced forms of deposition and erosion that we describe here as reflecting a temporal continuum. Wood levees have primarily non‐woody vegetation and may be transient relative to the other features. Tributary islands appear to persist from a decade to over a century. Tree ages of 100–200 years at the floodplain avulsion site and the characteristics of the secondary channels suggest that these wood‐induced avulsion features can persist for more than a century. Understanding the temporal dynamics of wood‐induced features and spatial variation in erosion and deposition provides insight into the dynamics and spatial heterogeneity of natural river corridors, with implications for river restoration.

Comment on “Momentum and Energy Predict the Backwater Rise Generated by a Large Wood Jam” by Follett, E., Schalko, I. and Nepf, H.

AbstractFollett et al. (2020a, https://doi.org/10.1029/2020gl089346) developed an analytical model to predict backwater rise by log jams, using the size and packing density of logs and the jam length, as well as river slope and bed roughness. We show that the model formulas can be rewritten using the Froude number instead of river slope and roughness, thus improving their applicability in engineering practice. The equation terms and results of Follett et al. (2020a, https://doi.org/10.1029/2020gl089346) are found to be similar to those of the empirically derived formula by Schalko et al. (2018, https://doi.org/10.1061/(asce)hy.1943‐7900.0001501). However, some differences are identified, calling for further study. Most notably, these distinctions pertain to the effect of accumulation porosity, with additional minor differences in the exponent of the Froude number. Lastly, model implications for some broader applications are explored, showing a methodology to calculate the representative log size for log mixtures, and the expected effect of log orientation on backwater rise.

Reply to Comment by Poppema and Wüthrich on “Momentum and Energy Predict the Backwater Rise Generated by a Large Wood Jam”

AbstractFollett et al. (2020, https://doi.org/10.1029/2020gl089346) demonstrated that a large wood jam can be modeled as a porous obstruction with momentum loss proportional to the number, size, and packing density of the logs and jam length. Poppema and Wüthrich (2024, https://doi.org/10.1029/2023gl106348) incorporated uniform flow Froude number, broadening the scope of our work. Here, we demonstrate that Froude number can be directly introduced to equations in the main body of Follett et al. (2020, https://doi.org/10.1029/2020gl089346), without requiring uniform flow. Based on this, we show that a managed increase in upstream depth is possible for conditions below a critical discharge, in which equilibrium upstream depth over uniformly distributed jams can be adjusted with inter‐jam spacing. This design could retain water in low flow conditions, allowing jams to act independently above critical discharge. Finally, we suggest that log orientation can be included in our model by varying both drag coefficient and frontal area perpendicular to the flow.

Large wood fluctuation and longitudinal connectivity conditions along a segment of the Blanco River (Chilean Patagonia)

Data collected between 2015 and 2022 was utilised to assess longitudinal connectivity and explain the temporal and spatial fluctuation of large wood (LW) along the Blanco River, which was severely affected by the 2008 eruption of the Chaitén Volcano in southern Chile. The study was performed along a ~ 10.6-km long segment, which was divided into two sub-segments (upper and lower). LW source areas were identified using information from previous research, complemented by the analysis of satellite images to cover the study period. LW fluctuation was studied for the period 2017–2022, using field data and images from an unmanned aerial vehicle along seven 80 m-long reaches located within the lower sub-segment of the river. Using the generated georeferenced orthomosaics and digital elevation models, LW and wood jams (WJs) locations, abundance, dimensions, volumes, and WJs stability were assessed, as well as wood deposition patterns. Streambank erosions and landslides were found to be the main LW sources. Considering wood sourcing, and the variations in the number of LW and WJs, in the dimensions of individual LW and WJs volume and deposition patterns as indicators, it was possible to infer the longitudinal connectivity conditions for the studied segment through time. The results showed that the upper and lower subsegments were poorly connected. However, changes in LW abundance over time, its dimensions and volumes, and the very low stability of WJs, and LW deposition patterns indicative of fluvial transport confirmed that the lower subsegment was longitudinally connected. The results also verified that the presence of LW did not affect water or sediment longitudinal connectivity along the fluvial system. The volume of individual LW and WJs showed a decreasing trend with time in all study reaches. As the bank erosions able to source LW to the channel are also reducing with time, pieces of wood deposited in the active channel may become the only way to sustain LW availability for the next few years. Things could change with the occurrence of an extreme and infrequent flood able to connect the upper and lower sub-segments and force the river to initiate a new phase of planform adjustments.

Widespread wood placement and regrading drive lateral connectivity and reworking of the channel and floodplain in a valley bottom reset to Stage 0

Valley bottom process reset, or the excavation of high surfaces and fill of incised channels combined with large wood addition, is a new method for creating multi-channel river-wetland corridors (also referred to as Stage 0 valley bottoms). Valley bottom process reset seeks to increase lateral flow and sediment connectivity, retain water and sediment, and kickstart geomorphic processes that may sustain aquatic and riparian habitat. This study uses this anthropogenic intervention to examine relationships among wood-induced hydraulic roughness, valley bottom topography, and geomorphic processes such as overbank flow and sediment transport, avulsion, sediment retention, and pool scour. Here, I present a 6-year case study of a two-phase valley bottom process reset along Deer Creek, Oregon. Kickstarting the floodplain reshaping processes required a substantial increase in roughness and hydrologic connectivity. The first phase of construction enhanced hydrologic but not sediment connectivity, failing to kickstart avulsion and floodplain reworking even during a likely 2- to 5-year recurrence interval flood. A second, more intensive phase of construction substantially reduced the threshold discharge necessary for overbank flow and floodplain reworking, as evidenced by the occurrence of these processes after only a <2-year recurrence interval flood. During this flood, a spatially distributed wood lattice rearranged into discrete jams that scoured pools, retained sediment, and drove geomorphically effective overbank flows. While valley bottom regrading likely contributed to these geomorphic effects, the spatial correlation between newly incised floodplain channels and areas of wood aggregation indicates wood's important role in driving floodplain reworking. I derive from these findings a conceptual model that details how wood drove floodplain reworking via two mechanisms: In-channel wood jams backwatered and constricted flow into the floodplain, and small wood jams formed in the floodplain forest further constricted flow through nascent channels to facilitate channel incision.

Shoal Destruction at Mancil Rock, Conecuh River, Alabama

Shoal Destruction at Mancil Rock, Conecuh River, Alabama Joann Mossa (bio) Lumber was an important component of the economy of the rural southeastern US in the late 1800s and early 1900s, and rivers provided less expensive routes than rail for floating either timber rafts or loose logs to major ports on the coast. However, obstacles and insufficient river depths throughout much of the year limited the use of rivers for this purpose. Army engineers documented conditions in these rivers and received appropriations from Congress to fund crews to clear out obstacles such as snags, rafts, wood jams, and overhanging trees in rivers across the United States (Wohl 2014). The annual reports of the Chief of Engineers describe the quantity of wood removed, but limited records exist for the rock, marl, clay shoals, islands, and boulders destroyed or modified to allow river transportation. One of many sites where Army engineers proposed work was the Escambia-Conecuh river system in Florida and Alabama (Chief of Engineers 1879). The Chief of Engineers (1879) described the Conecuh River as “impassable for boats, and even the transportation of timber and saw-logs during high-water is difficult.” Regrettably, the maps that accompanied this report could not be located. This issue’s cover photograph depicts the Conecuh River at Mancil Rock (spelled “Mansell” and “Mancell” in some reports), an altered calcareous shoal in Escambia County, southern Alabama (31.136856 °N,-86.836702 °W) (Figures 1 and 2). According to Clarke et al. (1966), the lithology of Mancil Rock is dolomite, composed of ~57.54 percent calcium carbonate, ~34.31 percent magnesium carbonate, and ~4.8 percent iron oxides and aluminum. The shoal remnants in the foreground connect to the right or north bank, water flows through the destroyed middle section, and the distant portion on the left or south bank lies under the shadows (Figure 2). According to Hiram Haines, Assistant Engineer, “the rocks belonging to the Eocene division of the Tertiary formation are exposed and form obstructions in the shape of shoals and heavy bowlders (sic)” (Chief of Engineers 1879). For a full improvement at Mancil Rock (section 15, township 2, range 12), Haines recommended removing 11,300 cubic yards of loose rock and 1000 cubic yards of solid rock totaling $7,650 (Chief of Engineers 1879). For partial improvement, he advised removing 750 cubic yards of loose rock and 100 cubic yards of solid rock totaling $575 (Chief of Engineers 1879). After several years of work on the Escambia, moving upstream annually, in 1887 Army engineers sent two parties totaling eleven men to work on the Conecuh River near Mancil Rock for several months (Chief of Engineers 1888). One crew removed ~3000 [End Page 127] Click for larger view View full resolution Figure 1. Maps of the Escambia and Conecuh rivers and study area, showing A) the location of the watershed within the region, B) the topography and drainage basin of the Escambia-Conecuh with some of its major tributaries, and C) a close-up of the topography of the Conecuh River near Mancil Rock with an arrow pointing to the location of the photograph. snags and logs from the channel and 275 overhanging trees from the banks and the other worked to excavate a channel through the “Mancell Rocks” and remove all rocks visible in the channel at low water. Despite this effort, later reports suggest that the changes at Mancil Rock were incomplete. As Cavanaugh (1906) described: “Mansell rock is a rock reef extending from the right bank toward the left bank so as to almost close the entire river” and “a cut of 600’ to 1000’ should be made.” Referring to 1887 efforts: “some work has been done toward cutting through this reef, but nothing has been accomplished so far.” Soon afterward, Congress appropriated $31,000 for the Conecuh River through the River and Harbor Act of March 2, 1907, small in proportion to the annual commerce reported on the Escambia-Conecuh of $2,500,000 (Chief of Engineers 1907). That year, the Corps staged two barges, a derrick barge and one for the storage of dynamite. Next, the Corps removed 1658 and 1563 cubic yards of rock and marl (Chief...

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.

A Faster Approach to Quantify Large Wood Using UAVs

Large wood (LW, log at least 1 m-long and 0.1 m in diameter) in river channels has great relevance in fluvial environments. Historically, the most used approach to estimate the volume of LW has been through field surveys, measuring all the pieces of wood, both as single elements and those forming accumulation. Lately, the use of aerial photographs and data obtained from remote sensors has increased in the study of the amount, distribution, and dynamics of LW. The growing development of unmanned aerial vehicle (UAV) technology allows for acquisition of high-resolution data. By applying the structure from motion approach, it is possible to reconstruct the 3D geometry through the acquisition of point clouds and then generate high-resolution digital elevation models of the same area. In this short communication, the aim was to improve a recently developed procedure using aerial photo and geographic information software to analyze LW wood stored in wood jams (WJ), shortening the entire process. Digital measurement was simplified using only AgiSoft Metashape® software, greatly speeding up the entire process. The proposed improvement is more than five times faster in terms of measuring LW stored in jams.

Trees, large wood and streams: Using archive survey data to inform changing interactions in a human‐impacted landscape

AbstractMonitoring is the key to understanding fluvial systems and a crucial foundation for assessing the outcomes of river restoration. The New Forest, southern England, was designated a National Park in 2005 in recognition of its highly valued landscape, which has been both positively and negatively impacted by over 1000 years of human management. Here we analyse archive field maps and tabulations extracted from walkover surveys that record the distribution and character of wood jams along ~59 km of New Forest streams in 1991. By integrating the 1991 archive survey data with other historical information, we analyse associations among stream channel characteristics, wood jams, riparian land cover, and stream and land management at that time. We reveal associations among these factors that reflect the imprint of centuries of grazing, forestry and stream management practices. Along ~10 km of one stream (the Highland Water), we analyse data collected during additional walkover surveys in 1997 and 2021, to track changes since 1991. We illustrate how a reduction in stream and wood management over recent decades and the restoration of some stream reaches in 2005 has resulted in overall increases in stream sinuosity and the number of wood jams. The walkover surveys on which our results are based provide an approach to characterizing the impacts of river corridor management in the New Forest landscape that are both cost and time effective and could be applied by non‐specialist volunteers (‘citizen scientists’) following appropriate training. Survey data of the spatial coverage achieved in 1991 are rare but need to be encouraged in the New Forest and farther afield to provide a robust framework into which more local, specialist surveys can be integrated, and from which the broad impacts of river corridor management approaches can be monitored.

First insight into the macroplastic storage in a mountain river: The role of in-river vegetation cover, wood jams and channel morphology

Macroplastic storage in mountain rivers remains unexplored and it is unknown how river morphology and different surface types of river areas modulate this process. Therefore, we sampled macroplastic debris stored on the surface of emergent river areas with different vegetation cover and on wood jams in a channelized, single-thread reach and an unmanaged, multi-thread reach of the Dunajec River in the Polish Carpathians. Total amounts of macroplastic debris retained in these reaches were then estimated on the basis of mean mass of macroplastic deposited on unit area of each surface type and the area of this surface type in a given reach. Exposed river sediments and areas covered with herbaceous vegetation stored significantly lower amounts of macroplastic debris (0.6 and 0.9 g per 1 m2 on average) than wooded islands and wood jams (respectively 6 g and 113 g per 1 m2). The amounts of macroplastic debris stored on wood jams exceeded 19, 129 and 180 times those found on wooded islands, areas covered with herbaceous vegetation and exposed river sediments. Wooded islands and wood jams covering 16.7% and 1.5% of the multi-thread reach stored 43.8% and 41.1%, respectively, of the total amount of macroplastic stored in that reach, whereas these surface types were practically absent in the channelized reach. Consequently, the unmanaged, multi-thread reach, 2.4 times wider than the neighbouring channelized reach, stored 36 times greater amount of macroplastic per 1 km of river length. Our study demonstrated that the storage of macroplastic debris in a mountain river is controlled by channel management style and resultant river morphology, which modulate river hydrodynamics and a longitudinal pattern of the zones of transport and retention of macroplastic conveyed by river flow.

Assessing woody vegetation recovery in the Rayas River following the eruption of the Chaitén Volcano in 2008

Abstract We studied the recovery of the woody vegetation in a segment of the Rayas River, which drains the Chaitén Volcano, in southern Chile. Data collection in the river corridor was performed to assess the regeneration rates of the colonizing vegetation within the river corridor, to investigate the site-specific regeneration modes (i.e. with respect to the different morphological units), to determine the species composition and to observe potential similarities with the regeneration process on hillslopes (i.e. outside the river corridor). We first performed a sampling of the shrub and tree vegetation regenerating in the Forest adjacent to the study segment. Further sampling efforts were executed on Islands, High bars, the Floodplain, and in association with Wood jams. Results show that 9 years after the volcano's last eruption, pre-eruption remnant Islands and the Floodplain exhibited abundant regeneration, with the highest density of recruits and species richness. In addition, a clear difference was observed between the river corridor and the forest, both in the characteristics of the plants that were regenerating as well as in the species composition. Finally, the vegetation that has re-established after the eruption has not yet acquired the capacity to play a stabilizing role in the fluvial corridor. New insights are provided on reforestation patterns at sites impacted by large infrequent disturbances.

First Insight into the Macroplastic Storage in a Mountain River: The Role of In-River Vegetation Cover, Wood Jams and Channel Morphology

First Insight into the Macroplastic Storage in a Mountain River: The Role of In-River Vegetation Cover, Wood Jams and Channel Morphology

Two-dimensional numerical experiment considering cohort size and wood jam characteristic on driftwood

Two-dimensional numerical experiment considering cohort size and wood jam characteristic on driftwood

Severely burned wood from wildfires has low functional potential in streams

Abstract More frequent and more severe forest fires mean more severely burned wood in streams. Instream wood provides habitat complexity, alters geomorphology, retains organic and inorganic material, promotes hyporheic flow and acts as substrate for biofilm and invertebrates. However, little is known about instream wood functions in fire‐prone biomes and how they combine with wood burning levels to guide postfire management efforts. Over 3 years, we tracked instream wood following forest fires in central Portugal. We examined for the first time the influence of burning level, season and a large suite of driving factors on the likelihood of four different functions having primary ecological consequences—retention of organic matter, serving as substrate for aquatic biota, being key pieces forming wood jams and deflecting flow including pool habitat formation. One of the main ecological functions of wood in rivers is to provide substrate for vegetation, periphyton, biofilm and oviposition. Our results show that this can be negatively affected when the wood is severely burned. Except for jam formation, the probability of each stream wood function changed markedly with season and the probability of non‐function was nearly twice as high in the Euro‐Mediterranean dry season than in the wet season. More anchored and decayed wood increased the probability of all functions, whereas the effect of submergence depended on the function. Challenging the ‘size paradigm’ that larger sized pieces provide more function, our data suggest that the effect of size is function‐specific. Synthesis and applications. We show how postfire stream restoration success can be maximized by selecting the most appropriate wood and taking advantage of attribute‐function relationships. We urge managers to refrain from removing wood or to selectively remove the most severely carbonized only, allowing the persistence of great potential to provide substrate for stream biota. The non‐attraction of severely burned wood as substrate can be compensated for by other wood with attributes enhancing this function, such as wood deeper within the bankfull area, and with large diameters. These results will help to inform successful management, as is increasingly asked from restoration ecology.

Large wood load fluctuations in an Andean basin

AbstractThe importance of monitoring and analysing wood fluxes in mountain environments is widely recognized. However, there is a lack of information related to the long‐term fluctuations in wood load and associated to the changes in large wood (LW) characteristics. The main aims of the research were to analyse (i) changes in wood characteristics, (ii) fluctuations in wood load, and (iii) the relationship between wood load and sub‐reach settings, proposing an ad hoc roughness index (RI). Repeated field surveys to measure wood load and LW characteristics during a 13‐year period were conducted within a 2.2 km‐long reach of the Rio Toro (Chile), which flows through the Malleco Forest National Reserve that was affected by wildfires in 2002 and 2015. Two spatial scales (i.e. study reach and sub‐reach) were considered. Irrespective of the adopted scale wood load fluctuated considerably, in both number and volume, with significant changes in LW characteristics (i.e. mean diameter and length). Moreover, a clear tendency to the aggregation in wood jams (WJs) was observed within the entire study reach. Based on our results, we conclude that 17 years after the first wildfire wood recruitment has started in the upper parts of the basin. Moreover, Generalized Linear Mixed Models (GLMM) analyses were carried out to investigate the relationship between RI and both number and volume of LW. Both models are characterized by high adjusted R2 of 74.9% and 72.8% for volume and number, respectively. This demonstrated that the RI can characterize the reaches in terms of tendency to deposition and trapping of wood. These results are promising, particularly in improving the knowledge related to potential deposition areas that can control wood load fluctuations, also permitting its management to be improved. © 2020 John Wiley &amp; Sons, Ltd.

Momentum and Energy Predict the Backwater Rise Generated by a Large Wood Jam

AbstractWood reintroduction is now considered an important aspect of stream restoration, due to ecohydraulic benefits associated with wood presence. Channel‐spanning wood jams create an upstream backwater, increasing flow heterogeneity, sediment deposition, and ecological productivity, but also flood risk. Backwater rise prediction is necessary to evaluate flood hazards in hydraulic models, improve design of engineered logjam projects, and compare jam effects across river systems. We present experimental results demonstrating that a jam can be modeled as a porous obstruction generating momentum loss proportional to the number, size, and packing density of the logs and the jam length. Energy and momentumconstraints are combined to predict backwater rise from unit discharge and a dimensionless structural parameter. This novel approach allows description of preexisting jams with a common metric. The model was used to demonstrate how backwater length, pool size, and upstream sediment deposition depend on jam structure and channel slope.

Porosity problems: Comparing and reviewing methods for estimating porosity and volume of wood jams in the field

AbstractPorosity, or void space, of large wood jams in stream systems has implications for estimating wood volumes and carbon storage, the impacts of jams on geomorphic and ecological processes, and instream habitat. Estimating porosity and jam dimensions (i.e. jam volume) in the field is a common method of measuring wood volume in jams. However, very few studies explicitly address the porosity values in jams, how porosity is calculated and assessed for accuracy, and the effect such estimates have on carbon and wood budgets in river corridors. We compare methods to estimate jam porosity and wood volume using field data from four different depositional environments in North America (jam types include small in‐channel jams, large channel‐margin jams, a large island apex jam, and a large coastal jam), and compare the results with previous studies. We find that visual estimates remain the most time‐efficient method for porosity estimation in the field, although they appear to underpredict back‐calculated porosity values; the accuracy of jam porosity, and thus wood volume, estimates are difficult to definitively measure. We also find that porosity appears to be scale invariant, dictated mostly by jam type, (which is influenced by depositional processes), rather than the size of the jam. Wood piece sorting and structural organization are likely the most influential properties on jam porosity, and these factors vary according to depositional environment. We provide a framework and conceptual model that uses these factors to demonstrate how modeled jam porosity values differ and give recommendations as a catalyst for future work on porosity of wood jams. We conclude that jam type and size and/or the study goals may dictate which porosity method is the most appropriate, and we call for greater transparency and reporting of porosity methods in future studies. © 2020 John Wiley &amp; Sons, Ltd.

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.

Effects of an engineered log jam on spatial variability of the flow field across submergence depths

AbstractEngineered log jams (ELJs) are commonly implemented in rivers to diversify fish habitat, but few studies have verified the hydraulic benefits of ELJs by assessing their effects on the spatial variability and turbulence structure of the flow field. This field and modelling study assessed the effects of an ELJ on various characteristics of the flow field with increasing submergence. A 2‐D hydrodynamic model was applied to simulate flow conditions of the Calapooia River, Oregon, with an ELJ installed at the upstream end of a meander. Output was analyzed using coherent flow structure identification, maps of turbulence measures, and wavelet analysis along linear transects. At the highest discharge (62% ELJ submergence), more and smaller coherent flow structures were identified than in the no ELJ model run, but the magnitudes of turbulence metrics were unaffected. At low flow (1% jam submergence), the presence of the ELJ did not affect the number of coherent flow structures identified and produced only small and localized effects on turbulence measures. Taken together, results indicate that the ELJ primarily affected the flow field by increasing the number of flow structures at higher discharges and submergence depths. However, these changes were small and local to the ELJ. The limited effects of this wood jam over limited spatial scales raise questions about the conditions under which such structures increase hydraulic diversity and highlight the need for more detailed understanding on spatial variability around habitat structures with complex shapes.