Large Wood Debris Research Articles

Large wood debris that clogged bridges followed by a sudden release. The 2019 flash flood in Catalonia.

Study regionFrancolí River (Catalonia, Iberian Peninsula). Study focusThe aim is the reconstruction of the October 2019 flash flood, that was documented through extensive field work: rainfall (300 mm in just a few hours), flood marks, times of flood passage and witnesses' snapshots and reports, channel changes, log drift (20,000 trees) and woody debris at bridges, as well as large damage and six fatalities. The methods are: hydrological model built for the rainfall-runoff in the basin and the flood routing in the river, use of hydraulic principles such as flow at waterfalls, flow against obstacles (trees), etc. and finally 1D/2D free surface numerical models. New hydrological insightsThe uppermost 100 km2 produced discharges of 700 m3/s (up to 50 m3/s/km2, locally). Three bridges failed, but their cascading failure (when one failure triggers the next one downstream) was not proved. The main channel widened more than 10 times, dragging away soil and vegetation like a bulldozer. The resulting large wood debris that clogged two bridges worsened the inundation. An anomalous flow downstream, probably a surge of around 1090 m3/s, due to the failure of a woody jam at a narrow bridge, took two lives. Water Authority is now warning flood planners that vegetated, torrential basins may cause catastrophic floods in the valley towns, if their narrow bridges are sensitive to woody debris.

Large Wood Debris Contributes to Beach Ecosystems but Colombian Beachgoer’s Do Not Recognize It

Large Woody Debris (LWD) accumulation serves essential ecological functions and benefits society’s coastal ecosystems (e.g., beaches). Thus far, the ecosystem services perspective has paid little attention to LWD. Therefore, we aim to contrast social perceptions on LWD and its ecological significance in Puerto Velero beach, Caribbean, Colombia. In consequence, the contribution of LWD to the conformation and creation of Puerto Velero beach was analyzed, as well as how beachgoers perceive the importance of LWD and if they were willing to pay to remove LWD in this beach. To achieve this, a quantitative convergent approach was then proposed using GIS analysis and remote sensing to understand the contributions of LWD to the Puerto Velero beach ecosystem; and in addition, a survey was performed to determine how beachgoers perceived LWD and how they valued the phenomenon. Results indicate that LWD contributed to beach maintenance; nevertheless, most people neglected LWD values because of its lack of visual attractiveness. As such, ecosystem services targets become conflicted because people positively perceived ecosystem services provided by beaches, but they did not assign importance to the beach dynamics they deemed unattractive, regardless of their vast importance.

Assessing human perceptions towards large wood in river ecosystems following flooding experiences

AbstractLarge wood deposited in rivers provides ecological benefits for multiple trophic groups, but public perceptions of these deposits can be varied. In particular, flooding experiences linked to large wood debris could influence how the public and stakeholders view large wood deposited into the river ecosystem. Here, we assessed the perceptions towards large wood using groups of undergraduates, postgraduates and staff from a local university in Limpopo Province of South Africa. A survey was conducted using questionnaires, which were distributed online to a sample of 104 participants across these groups, using both visual (i.e. paired photographs of different river scenarios) and categorical questions. Large shares of respondents regularly used river systems recreationally (62.9%), with woodless systems perceived as being significantly more aesthetic, less dangerous and least in need of improvement. These perceptions, however, differed among university groups, with staff having stronger perceptions of aesthetics (median = 5.5, mean 5.4 ± 2.8), less dangerousness (median = 3.0, mean 4.2 ± 3.0) and naturalness (median = 6.0, mean 5.8 ± 2.6) towards systems with large wood. Correlation analyses indicated significant interrelatedness among perceptions of aesthetics, naturalness, danger and improvement needs. However, negative perceptions towards large wood in the river were generally not determined by any recent experience of flooding in the area, with large wood‐related dangers rather associated with leisure activities in rivers by students. These results highlight a need for passing on the knowledge of natural river systems with wood to people in Vhembe Biosphere Reserve and communities' scientists and assessing wider perceptions outside of the university context.

Closure to “Trapping Large Wood Debris in Rivers: Experimental Study of Novel Debris Retention System” by Diego Panici and Prakash Kripakaran

Closure to “Trapping Large Wood Debris in Rivers: Experimental Study of Novel Debris Retention System” by Diego Panici and Prakash Kripakaran

Discussion of “Trapping Large Wood Debris in Rivers: Experimental Study of Novel Debris Retention System” by Diego Panici and Prakash Kripakaran

Discussion of “Trapping Large Wood Debris in Rivers: Experimental Study of Novel Debris Retention System” by Diego Panici and Prakash Kripakaran

Experimental study of debris-induced scour around a slotted bridge pier

One of the most common problems for river engineers is the accumulation of waterborne debris upstream of the bridge piers. In addition to reducing the cross-sectional flow area, debris increases the drag force exerted to the pier and contributes to scour. Several studies have been carried out by previous researchers to examine the usefulness of different types of countermeasures. The effectiveness of these countermeasures is not well understood when debris accumulation occurs. In this study, the effect of debris accumulation on the efficiency of a bridge pier slot, as scour countermeasure, is investigated experimentally. A total of 54 experiments were carried out under different hydraulic and debris geometrical conditions. The results showed that slots were effective in protecting bridge piers against scouring in presence of debris. Depending on the debris shape, the reduction efficiency may increase or decrease for a slotted pier in presence of debris accumulation when compared to the standard pier conditions without debris accumulation. Except for the inverse pyramid shape, the maximum scour is generally more reduced due to sheltering effect when the debris is located on the bed. While debris accumulation can lead to a reduction of the slot efficiency, the slot can be considered a reliable countermeasure against scouring. The outcome of this study can help the design of new bridges affected by large wood debris accumulations.

Dynamic amplification responses of short span bridges considering scour and debris impacts

During extreme flooding events, bridges could experience large lateral displacements or even collapse due to either strong hydraulic forces or the effects of large waterborne debris, such as tree branches. The effects of waterborne debris on the structural behaviors of bridges include temporary accumulated dams and direct debris impacts. The additional lateral hydraulic forces and the acceleration of bridge scouring process due to temporary accumulated dams were investigated by researchers. Several debris impact force models were proposed to determine the loading effects applied on bridges. However, very few studies were conducted on the dynamic responses of bridges during flooding events considering the effects of large wood debris (LWD) as a combination of additional lateral hydraulic forces, foundation scour, and direct debris impacts. Therefore, the present study performed numerical analyses for bridges subjected to foundation scour and LWD impacts corresponding to flooding events. Besides, the effects of foundation scour and LWD impacts on the dynamic responses were simplified for bridge design purposes. Firstly, various short-span bridges with possible foundation scour depths due to debris accumulation were numerically simulated to obtain dynamic characteristics. Then, the hydraulic forces applied on the bridges were updated considering an extra blocking area due to debris accumulation. The collision forces due to floating woody debris were also introduced into the vehicle-bridge coupling system. Finally, the dynamic amplification factors (DAFs) with and without considering the effects of debris impacts were calculated and compared. It was found that the DAFs increase 20% at the maximum due to the effects of debris impacts. A modified factor was proposed to consider the effects. The reaction forces with and without the effects were also calculated to investigate the effects on the risk of deck unseating. Introducing possible debris impacts during flooding events into the dynamic analyses of bridges brings a more realistic estimation for the safety of bridges. The DAFs of bridges can be further taken as a guide for the supplements of design codes. The updated reaction forces would help to guide the risk mitigation of deck unseating.

Riverine large woody debris introduced for natural flood management leads to rapid improvement in aquatic macroinvertebrate diversity

Natural flood management interventions, such as Large Wood Debris (LWD) or engineered log jams, are being increasingly deployed throughout the UK and elsewhere. In addition to alleviating flood risk, it is anticipated that they may influence the ecology of freshwater river systems, including macroinvertebrate populations. This study explores macroinvertebrate assemblages, water quality parameters, and sediment size distribution in a headwater stream following the addition of LWD as part of a natural flood management scheme. The study area consists of 6 sites within the intervention zone where LWD log jams were implemented, with comparative control sites upstream and downstream (3 sites each). Macroinvertebrate communities, sediment size distribution, and water chemistry were sampled 3 and 10 months following the addition of LWD. Our findings revealed increased macroinvertebrate abundance and taxa richness in the LWD intervention zone versus control, with an increased BMWP score reflecting the increased taxa richness. Average Score Per Taxon, and water chemistry showed no change, revealing invertebrate changes to be independent of water quality. NMDS and hierarchical clustering analysis on invertebrate data showed a clear separation of communities where LWD was present from those with no LWD, while SIMPER analysis showed that LWD addition led to the rapid establishment of taxa (Hydraenidae, Rhyacophilidae, Scirtidae, and Elmidae) that were otherwise absent. Ten months after LWD addition, improved biodiversity was also found in areas below the intervention zone, suggesting the positive impacts of LWD extend downstream. LWD also altered sediments, with sites immediately upstream of LWD log jams having a greater percentage of fine sediment than those immediately downstream. These results suggest that biological complexity and niche availability increased within the in-channel zone as a result of introduced LWD, thus revealing wider aquatic habitat improvement potential of LWD for natural flood management. The use of LWD as an intervention for flood management is recommended for its additional benefits for ecosystem health.

Trapping Large Wood Debris in Rivers: Experimental Study of Novel Debris Retention System

AbstractLarge wood debris can cause critical damage to bridges and other riverine structures, and increase flood risk. Although their effects on hydrodynamic actions and flood levels have been inve...

NATURE-BASED DYNAMIC REVETMENT CONSTRUCTION AT NORTH COVE, WASHINGTON, USA

A dynamic revetment was constructed at North Cove, Washington, USA in December 2018 along a historically eroding 2-km shoreline reach of coastal barrier at the northern entrance to Willapa Bay. The revetment is composed of poorly sorted angular quarry rock ranging in size from pea gravel to small boulders as well as large wood debris and structures, a dune ridge, and native vegetation integrated with the revetment. The design, aim, and maintenance of the dynamic revetment is to simulate the functions of naturally forming cobble berms along composite beaches in the U.S. Pacific Northwest. The dynamic revetment continues to be adaptively constructed over time, enabling the testing of innovative design approaches and concepts that are rarely possible to do at full-scale in the field. The project provides a unique opportunity to explore nature-based engineering principles and design features.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/5w18tEjEePg

A practical method to assess risks from large wood debris accumulations at bridge piers

Accumulations of large woody debris can worsen scour at a bridge pier and thereby lead to structural damage. Accumulations can also increase the flood risk in adjacent areas. These consequences can cause disruption to local communities and even pose a risk to human life. Current methodologies acknowledge the existence of these effects of debris but do not provide a practical method, usable by engineers and practitioners, to assess the potential for debris accumulation at a bridge structure based on readily available data. This work aims to address this practical need by proposing a methodology based on direct and indirect observations. Using this methodology, a desk-based analysis can be performed to assess whether a bridge is prone to the formation of debris accumulations. Direct observations may include information from inspection reports, satellite imagery and tree removal works, while indirect observations may use information related to the geographical location of the bridge such as on other structures that share the watercourse or the presence of forested areas in its proximity. This methodology has been applied to local authority-owned bridges in Devon, UK. Results show that a large number of the structures (100 out of over 3000 bridges) are liable to debris accumulations. Direct observations served as primary evidence for over 80% of the bridges liable to debris accumulations. For many cases, direct observations existed to corroborate indirect observations suggesting that indirect observations can also be relied upon. The proposed methodology has also been applied to the prioritisation of bridge inspections for scour assessment. Results showed that many of the bridges prone to debris accumulations would need to be prioritised for scour inspections over other bridges in the aftermath of floods due to their significantly higher risk to scour in the presence of debris.

An experimental and theoretical analysis of floating wood diffusion coefficients

Wood transport during high flow events is here treated as an advective–diffusive phenomenon. A theoretical definition of the governing equation is first provided, highlighting the dependence of floating wood diffusion on the adoption of adequate diffusion coefficients. To estimate these coefficients, an experimental investigation on large wood debris was carried out in a channel presenting a weakly sinusoidal plant, employing regular cylinders with various sizes under different flow conditions. For each configuration, a consistent number of trajectories for the floating wood were acquired and processed through imaging techniques, allowing for a statistical analysis of the wood dynamics. The tests showed that floating logs travel at a velocity lower than the water surface one, not completely aligned to the flow direction and tend to disperse streamwise and transversely. Under the assumption that wood dispersion can be derived from the analysis of wood trajectories fluctuations, the longitudinal, transversal and angular diffusion coefficients were computed. Finally, a preliminary dimensional analysis is presented discussing the relevant spatial and temporal scales for these coefficients.

Formation, Growth, and Failure of Debris Jams at Bridge Piers

AbstractThe accumulation of large wood debris around bridge piers obstructs the flow, producing increased upstream water levels, large horizontal structural loadings, and flow field modifications that can considerably exacerbate scour. These effects have frequently been held responsible for the failure of a large number of bridges around the world, as well as for increased risk of flooding of adjacent areas. Yet little is currently known about the time evolution and processes responsible for the formation and growth of these debris piles. This paper is aimed at deciphering the whole life of debris accumulations through an exhaustive set of 570 experiments in which debris elements were individually introduced into a flume and accumulated at a pier model downstream. Our findings show that in all experiments, the growth of accumulations is halted at a critical stage, after which the jam is removed from the pier by the flow. This condition typically coincides with the time when the dimensions of the accumulations are maxima. The values of the accumulation maximum size display a clear dependence on flow characteristics and debris length distribution. On the other hand, other variables have shown much weaker effects on the geometry of the accumulations. For a given debris length, accumulations are wide, shallow, and long at low flow velocities but become narrower, deeper, and shorter with increasing velocities. A comparison of results of accumulations formed with debris of uniform and nonuniform size distributions has revealed that the former can be up to 2.5 times wider than the latter.

Electrical resistivity imaging of anastomosing river subsurface stratigraphy and possible controls of fluvial style change in a graben-like basin, Czech Republic

Subject to frequent channel avulsions due to the increased frequency of floods, rise of base level, and/or sediment overloading, anastomosing rivers are sensitive to external (climatic or tectonic) forcing in sedimentary basins. The Morava River, Czech Republic, shows a well-developed Holocene anastomosis, confined to the pull-apart type Upper Morava Basin (UMB). We studied the stratigraphy and aggradation rates of the UMB using electrical resistivity tomography (ERT), dipole electromagnetic profiling (DEMP), core data, and radiocarbon ages, with the aim of identifying factors triggering the anastomosis at the Pleistocene/Holocene transition. The ERT and DEMP proved to be excellent tools to visualize the shape and thickness of floodplain depositional units (abandoned meanders, scroll bars, etc.). The major geophysical surfaces identified are the base of the late Weichselian braided-stream deposits (OSL age = 34.53 ± 3.42 ka), interpreted as a palaeo-stream gradient of the Morava River, and their transition to Holocene floodplain deposits. In the late Weichselian, the river aggraded at an average rate of 0.2 mm/yr. The Holocene (oldest 14C age = 7.066 ± 0.072 ka) short-term aggradation rates reached up to 13.7 mm/yr, but the average long-term rates (~0.07 to ~0.4 mm/yr) are comparable to the late Weichselian. The stratigraphy and sediment ages indicate that the onset of anastomosis was not likely associated with accelerated basin subsidence. Possible controls of the anastomosis include upstream control by numerous tributaries, large wood debris in the floodplain forests, and changes in land use. The tectonic and geomorphic context of the UMB pull-apart basin probably favoured the development of the anastomosis.

Floods at the northern foothills of the Tatra Mountains — A Polish-Swiss research project

The present paper introduces the topical area of the Polish-Swiss research project FLORIST (Flood risk on the northern foothills of the Tatra Mountains), informs on its objectives, and reports on initial results. The Tatra Mountains are the area of the highest precipitation in Poland and largely contribute to flood generation. The project is focused around four competence clusters: observation-based climatology, model-based climate change projections and impact assessment, dendrogeomorphology, and impact of large wood debris on fluvial processes. The knowledge generated in the FLORIST project is likely to have impact on understanding and interpretation of flood risk on the northern foothills of the Tatra Mountains, in the past, present, and future. It can help solving important practical problems related to flood risk reduction strategies and flood preparedness.

A framework for managing runoff and pollution in the rural landscape using a Catchment Systems Engineering approach

Intense farming plays a key role in increasing local scale runoff and erosion rates, resulting in water quality issues and flooding problems. There is potential for agricultural management to become a major part of improved strategies for controlling runoff. Here, a Catchment Systems Engineering (CSE) approach has been explored to solve the above problem. CSE is an interventionist approach to altering the catchment scale runoff regime through the manipulation of hydrological flow pathways throughout the catchment. By targeting hydrological flow pathways at source, such as overland flow, field drain and ditch function, a significant component of the runoff generation can be managed in turn reducing soil nutrient losses.The Belford catchment (5.7km2) is a catchment scale study for which a CSE approach has been used to tackle a number of environmental issues. A variety of Runoff Attenuation Features (RAFs) have been implemented throughout the catchment to address diffuse pollution and flooding issues. The RAFs include bunds disconnecting flow pathways, diversion structures in ditches to spill and store high flows, large wood debris structure within the channel, and riparian zone management.Here a framework for applying a CSE approach to the catchment is shown in a step by step guide to implementing mitigation measures in the Belford Burn catchment. The framework is based around engagement with catchment stakeholders and uses evidence arising from field science. Using the framework, the flooding issue has been addressed at the catchment scale by altering the runoff regime. Initial findings suggest that RAFs have functioned as designed to reduce/attenuate runoff locally. However, evidence suggested that some RAFs needed modification and new RAFs be created to address diffuse pollution issues during storm events. Initial findings from these modified RAFs are showing improvements in sediment trapping capacities and reductions in phosphorus, nitrate and suspended sediment losses during storm events.

Temporal scour evolution at bridge piers: effect of wood debris roughness and porosity

Large wood debris transported by floods affects the scour morphology at bridge piers, thus increasing the bridge failure potential. The characteristic size and shape of the riparian vegetation includes various roughness and permeability conditions of the debris surface. The interaction between two-dimensional flow and rough debris accumulations increases the shear stress, the turbulence and consequently affects the scour evolution process at bridge piers. An experimental study on the bridge pier clear-water scour evolution in the presence of wood debris was conducted at the PITLAB research centre, University of Pisa, Italy. A debris accumulation is characterized by roughness, shape and porosity. Flow intensities range from 65 to 100% of the threshold velocity and included up to 18% of the total flow area. Flow depths were varied from 2.67 to 5.67 times the pier diameter. The effects of wood debris roughness and porosity were analysed in terms of scour temporal evolution and scour morphology.

Spatial patterning of habitat for Oncorhynchus mykiss in a system of intermittent and perennial streams

Abstract – The salmonid Oncorhynchus mykiss tends to inhabit forested or snow‐fed streams having cold reliable flows, but in the California chaparral they inhabit rain‐fed stream networks with extensive areas of intermittent flow. We hypothesised that hydrological mechanisms in such watersheds tend to spatially segregate spawning and over‐summering habitats, and tested the hypothesis using observations from a series of tributaries in a pristine watershed. Consistent with the hypothesis, reaches with suitably sized spawning gravels tended to occur in intermittent tributaries, and also the perennial mainstem (which was too warm for over‐summering). In early summer, juvenile O. mykiss (<10 cm) occurred at similar densities in the intermittent and perennial tributaries, but larger fish had greater densities in perennial tributaries. Large wood debris would be expected to mitigate the spatial segregation of habitats somewhat, but was scarce, though stream‐side outcrops appeared to partially compensate by forcing gravel bars in high‐gradient channels.

Influences of flooding and hyporheic exchange on floodplain plant richness and productivity

AbstractFlooding disturbance and associated fluvial processes are generally thought to be the primary controls on floodplain species richness patterns. We expanded this idea to include ground and surface water (hyporheic) exchange within alluvial flood plains. At the floodplain scale, we hypothesized that upwelling areas would be richer in species and support higher growth rates of woody plants. At reaches within each flood plain, we evaluated the mechanisms of flood duration, patterns in sedimentation and driftwood as influences. We found patterns of species richness within the shifting mosaic of floodplain wetland habitats to be incoherent with flood duration for large flood plains on the Flathead and Talkeetna Rivers. Rather, species richness was closely associated with hyporheic exchange at the floodplain scale and locally with alluvial particle size. Species richness was highest in areas of both flood plains characterized by upwelling groundwater. On annually scoured surfaces, richness was affected by large wood debris that reduced flow competence, allowing fine sediment deposition and plant establishment. Richness within upwelling and downwelling reaches was highest at sites with the finest alluvia.Growth rates of woody species used as indices of site productivity were also significantly higher at areas characterized by upwelling. We concluded that plant species richness was strongly controlled by hyporheic exchange at the floodplain scale and locally by the deposition of fine alluvia. This interpretation was not consistent with intermediate levels of flood disturbance. Indeed, areas of the flood plain least influenced by flow energy had the highest richness on both flood plains. Copyright © 2008 John Wiley & Sons, Ltd.

Large wood debris recruitment on differing riparian landforms along a Gulf Coastal Plain (USA) stream: a comparison of large floods and average flows

AbstractIn southeastern Coastal Plain streams, wood debris can be very abundant and is recruited from extensive forested floodplains. Despite importance of wood debris, there have been few opportunities to examine recruitment and redistribution of wood in an undisturbed setting, particularly in the southeastern Coastal Plain. Following extensive flooding in 1994, measurements of individual downed trees (species, dbh, orientation, distance from base‐flow channel and condition) were made across replicated riparian landforms in a Gulf Coastal Plain 5th‐order stream. Annually, the fate of these trees was determined and newly recruited trees were noted. More than 300 downed trees have been recorded. Recruitment varied across landforms with more constrained reaches having greatest mortality. Total tree mortality varied substantially across years. Generally, tree recruitment was greatest in years with substantial floods (1994 and 1998). For each riparian landform type, tree mortality was correlated with the maximum daily flow during the period preceding annual debris surveys. This relationship was particularly strong for sand ridges (r2 = 0.942) and low terraces (r2 = 0.915), but was significant for floodplains (r2 = 0.413). Greatest rates of debris recruitment per maximum daily flow were observed for sand ridges followed by low terraces. Flood characteristics also influenced debris recruitment. The 1994 flood was caused by a tropical storm and resulted in a rapid rise in streamflow. Much of the debris recruited during this flood was from toppled trees and was oriented parallel to the stream channel. In contrast, the 1998 flood was preceded by a wetter than average winter with more gradually rising flows and there was no relationship between riparian landform and debris characteristics. These results indicate that wood recruitment dynamics in Coastal Plain streams are complex. Wood recruitment rates are controlled by cyclical variations in climate interacting with riparian geomorphology. Infrequent high flows appear critical in the maintenance of the instream debris pool. Copyright © 2007 John Wiley & Sons, Ltd.