Article

A new methodology for the assessment of large woody debris accumulations on highly modified rivers (example of two French Piedmont rivers)

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Abstract

Methodologies that have been developed to quantify large woody debris (LWD) have been largely tested and adapted for mountain streams of the Pacific Northwest, characterised by a very high density of LWD, composed of large pieces of wood. In French rivers, LWD studies have focused on larger systems presenting low density and discrete distributions of LWD accumulations, where existing methods could not readily be used. We thus propose an easy-to-use method to quantify LWD within such systems. After defining three representative types of LWD, the volume is obtained by representing each LWD accumulation by a simple geometric form in order to measure its height, width and length. A model is then built for the different accumulation types to estimate wood mass from the measured volume. Since the measured volume is a combination of air and wood, we quantified the proportion of air, which is, respectively, equal to 18, 90 and 93% for trunks, wood jams and shrubs. To understand variability in wood mass, we evaluated the influence of different factors on wood density (defined as the ratio between mass and volume). The main factor was found to be the water absorption capacity of the wood, whereas a lesser factor was the degree of wood decay. Most wood pieces were found to increase their mass by an average of 100% and more after only 24 h in contact with water. Moreover, the observed levels of water loss and water absorption during the first 24 h of removal or exposure to water imply major short-term variations in wood mass, which may have significant consequences for wood transport during flooding. © 1998 John Wiley & Sons, Ltd.

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... Review of methods to assess jam porosity Direct estimates of Φ j can be done by utilizing back-calculations of porosity from known WVs and JVs measured in the field (Thevenet et al., 1998;Manners et al., 2007;Sanhueza et al., 2019), laboratory, or through computer simulations (Equation 3). ...
... B. LIVERS ET AL. Time consuming to determine WV; not possible for some field situations Manners et al., 2007;Sanhueza et al., 2019;Thevenet et al., 1998 Livers and Wohl, 2016;Manners et al., 2007;Ravazzolo et al., 2015;Sanhueza et al., 2019;Thevenet et al., 1998 Complete box JV completely encloses all wood, organic matter, and void space; 0.9 porosity used to convert air-wood space (JV) to WV with Equation 1 or Equation 2; Figure 1(B) A 0.9 porosity specific to Thevenet et al., 1998; calibration curves needed to account for variability in LW density and jam types across regions or depositional processes Boivin et al., 2015;Thevenet et al., 1998 Best-fit box JV defined by a box, prism, or other simple geometric shape that best fits the jam but may not totally enclose all jam materials; convert to WV; a Figure 1(C) JV is subjective; pieces extending outside best-fit box must be accounted for appropriately to obtain total WV Dixon, 2016;Livers and Wohl, 2016;Scott and Wohl, 2018 Aerial extent aerial extent of jam measured in situ or using aerial imagery, multiplied by average estimate of jam thickness (JV); convert to WV; a Figure 1(E) Field estimation of jam thickness and porosity needed, cannot be completed remotely Boivin et al., 2015, Kramer andWohl, 2015;Ventres-Pake et al., 2019 3D modeling 3D outer geometry of jam (JV) generated from field surveys (e.g. prism and rod surveys with total stations or laser rangefinders, LiDAR, hand held cameras, structure from motion, unmanned aerial vehicles); convert to WV; a Figure 1(D) Equipment required can be more expensive than traditional field methods; field estimation o porosity needed; post-processing can be time consuming Sanhueza et al., 2019;Spreitzer et al., 2019 Note: WV, wood volume; JV, jam volume; LW, large wood (>10cm diameter and 1m length). ...
... B. LIVERS ET AL. Time consuming to determine WV; not possible for some field situations Manners et al., 2007;Sanhueza et al., 2019;Thevenet et al., 1998 Livers and Wohl, 2016;Manners et al., 2007;Ravazzolo et al., 2015;Sanhueza et al., 2019;Thevenet et al., 1998 Complete box JV completely encloses all wood, organic matter, and void space; 0.9 porosity used to convert air-wood space (JV) to WV with Equation 1 or Equation 2; Figure 1(B) A 0.9 porosity specific to Thevenet et al., 1998; calibration curves needed to account for variability in LW density and jam types across regions or depositional processes Boivin et al., 2015;Thevenet et al., 1998 Best-fit box JV defined by a box, prism, or other simple geometric shape that best fits the jam but may not totally enclose all jam materials; convert to WV; a Figure 1(C) JV is subjective; pieces extending outside best-fit box must be accounted for appropriately to obtain total WV Dixon, 2016;Livers and Wohl, 2016;Scott and Wohl, 2018 Aerial extent aerial extent of jam measured in situ or using aerial imagery, multiplied by average estimate of jam thickness (JV); convert to WV; a Figure 1(E) Field estimation of jam thickness and porosity needed, cannot be completed remotely Boivin et al., 2015, Kramer andWohl, 2015;Ventres-Pake et al., 2019 3D modeling 3D outer geometry of jam (JV) generated from field surveys (e.g. prism and rod surveys with total stations or laser rangefinders, LiDAR, hand held cameras, structure from motion, unmanned aerial vehicles); convert to WV; a Figure 1(D) Equipment required can be more expensive than traditional field methods; field estimation o porosity needed; post-processing can be time consuming Sanhueza et al., 2019;Spreitzer et al., 2019 Note: WV, wood volume; JV, jam volume; LW, large wood (>10cm diameter and 1m length). ...
Article
Porosity, 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 modelled 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.
... Accumulation porosity is an important parameter for the assessment of jam formations, from monitoring to modelling (Manners et al., 2007;Boivin and Buffin-Bélanger, 2010), and varies significantly across studies. While a few studies have estimated log jam porosity to be in a range of 13 to 90% (Thevenet et al., 1998;Sanhueza et al., 2019), most studies revealed porosity parameters between 25 and 70% (Livers et al., 2015;Dixon, 2016). Log geometry governs porosity of accumulation skeletons, while the packing matrix varies with the aspect ratio (e.g. ...
... Although the importance and need for volumetric measures of LW accumulations have been frequently addressed in literature (Harmon et al., 1986;Lienkaemper and Swanson, 1987;Gurnell et al., 2002;Webb and Erskine, 2003;Manners and Doyle, 2008;Dixon and Sear, 2014;Wohl and Scott, 2017;Martin et al., 2018), accurate assessment methods available for the estimation of LW volume and accumulation porosity, are limited to date (Spreitzer et al., 2019b). Conventional volumetric methods often consider manually obtained measurements of individual logs (Cordova et al., 2006;Andreoli et al., 2007;Manners et al., 2007;Brown et al., 2014;Dixon and Sear, 2014;Tonon et al., 2018), or entire accumulations by means of a 'rectangular' approach, measuring the bounding-box of the accumulation body in form of a parallelepiped (Thevenet et al., 1998;Andreoli et al., 2007;Boivin et al., 2015). These methods provide an initial, rough estimation of bulk volume, yet they are not effective for complex log formations, nor applicable and safe for accumulations in rugged environments or non-wadable streams. ...
... Mapping of LW accumulations, including volumetric assessment and porosity estimates, is challenging due to the complex nature of jam formations, typically comprising a LW skeleton (Manners and Doyle, 2008), and void spaces which can be empty or filled with OFM and sediments (Thevenet et al., 1998;Linstead, 2001). Therefore a robust image-based methodology, leading to a high quality point cloud model, will provide a high level of detail in surface texture and geometries (Westoby et al., 2012;Dikovski et al., 2014;Micheletti et al., 2015), and can significantly increase the success rate of Structure from Motion (SfM) photogrammetry for LW applications. ...
... Step 1, field surveys: This step consisted of two tasks: (1) field surveys (performed from 29 March to 1 April 2016) to identify and accurately georeference LW pieces and WJ; measure the diameter and length of each log, both as a single element or a jam-forming log; and quantify WJ dimensions (i.e., length, width, and height) as a solid parallelepiped (i.e., Piégay 1993;Thévenet et al. 1998); and (2) a UAV survey (carried out on 31 March 2016) to obtain high resolution RGB imagery covering the study area. ...
... where V is the volume of each LW (m 3 ), D is the diameter (m), and L is the length (m). In addition, taking advantage of the field data, the volume of each WJ was calculated as: (a) the volume of a solid parallelepiped (Piégay 1993;Thévenet et al. 1998); and (b) the sum of the volume of every LW within each WJ Ravazzolo et al. 2015a). ...
... Specifically, for this study the air volume is on average~13.3%; to adjust to wood volume the WJ volumes derived from the GIS analyses must be adjusted by a factor of 0.8824. Air volume is much lower than the 90% mentioned by Thévenet et al. (1998) when WJ volumes are calculated assuming the shape of LW accumulations as solid parallelepipeds. However, it is important to emphasize that the air volume can be partially or totally filled by fine wood and/or organic material that might represent a relevant component of the riverine environment. ...
Article
Fluvial wood is recognized as one of the key elements of riverine environments. Its importance, role, and potential related risks are widely considered and analysed. Still, to characterize and measure wood elements in the field, a large investment in terms of time and cost is normally required. These activities are often carried out in complex and potentially dangerous environments. In this context, the use of Unmanned Aerial Vehicles (UAVs) provides a powerful alternative technology to traditional approaches. In this work, we propose a novel approach combining UAV surveys with Structure from Motion (SfM) photogrammetry to quantify fluvial wood. The proposed methodology was tested in the Blanco River (southern Chile), which was severely affected by the Chaitén volcanic eruption in 2008 that delivered large quantities of wood to the channel. An area of about 1.2 ha was surveyed using UAV and field measurements. A comparative analysis between the traditional fieldbased and UAV surveys was carried out to quantify the accuracy of the latter and to better understand the strengths and potential limitations of the proposed methodology. Results showed that differences between the two methodologies were about 13% for both single large wood elements and wood jam volumes. Moreover, a sensitivity analysis applied to 12 different scenarios allowed us to define the measurement precision achieved using the orthomosaics and DEMs. Our results showed that the proposed approach is effective in terms of field and laboratory activities, saving around half the time. This study demonstrates that the combination of UAV and SfM can yield accurate results, covering large areas in less time and providing a powerful tool for performing repeated surveys and thus acquiring relevant information for wood budgets and wood dynamics in rivers.
... Density is also subject to marked variations due to water absorption and wood decay and in particular high moisture content can cause wood to become heavier than water and sink to the riverbed where it tends to be buried by sediments (Curran, 2010). Thévenet et al. (1998) provide a detailed characterisation of the evolution of wood density over time as a consequence of wetting and drying cycles and show that piece mass can double over 24 hours due to water absorption. ...
... It is worth noting that the variety of piece shapes and the tendency to jam formation imply that simple metrics (such as piece diameter and length) are generally poorly suited to compute wood storage volume. Thévenet et al. (1998) proposed a wood-air box model based on the measurement of piece/jam size along three orthogonal axes and the estimation of wood to air ratios for logs, jams and shrubs. This approach has been applied to various European rivers (Gurnell et al., 2000a;Wyżga and Zawiejska, 2005). ...
... The present study does not cover the investigation of wood density as a driver of element mobility and therefore the same type of wood was used for all model runs. Thévenet (1998) provides reference wood density values measured on the Ain and Drôme Rivers (France). The most common tree species observed at these field sites (Salix sp., Alnus glutinosa, Populus nigra) are typical of European piedmont rivers (Dufour et al., 2007;Francis, 2007). ...
... Keller and Swanson, 1979). It is an active component of floodplain dynamics (Collins et al., 2012;Wohl, 2013), fluvial styles (Keller and Swanson, 1979;Hickin, 1984;Piégay, 1993;Piégay and Marston, 1998;Sear et al., 2010), fluvial habitats (Carlson et al., 1990;Thévenet et al., 1998;Mossop and Bradford, 2004;Floyd et al., 2009;Langford et al., 2012), and fluvial hazards (Lyn et al., 2003;Piégay et al., 2005;Ruiz-Villanueva et al., 2013;Ruiz-Villanueva et al., 2014;Lucia et al., 2015;Comiti et al., 2016). (Ruiz-Villanueva et al., 2014) While the influence of individual pieces of LW or LW jams on fluvial dynamics, especially in smaller rivers, has been the focus of numerous studies, LW budgeting has been increasingly applied to river reaches and river systems since the early 2000s because it encompasses the significant components of the LW dynamics (e.g. ...
... LW exported (E) from the watershed since 1963 was estimated using a spatio-temporal analysis of changes in LW raft surfaces in the delta using historical and recent aerial images (aerial photographs from 1963 to 2004; Landsat 7 imagery for 1999 to 2011; and GeoEye satellite images for 2012 to 2013). To obtain wood volume, estimated LW raft surfaces were multiplied by an estimated average raft thickness of 1.68 m (standard error of 0.06 m) (Boivin et al., 2015) and divided by the proportion of air-wood volume measurements proposed by Thévenet et al. (1998) and validated by Boivin et al. (2015) as appropriate for this region. ...
... where ρ w is the proportion of air in the wood volume measurements (LWJ porosity). Thévenet et al. (1998) proposed a proportion of air in the wood volume of 89.50% ± 0.91% from measurements on two rivers in France. This proportion factor was adopted after validation and regional calibration in the field accomplished by measuring the porosity of LWJ on SJR and in other rivers of the Gaspé Peninsula (Boivin and Buffin-Bélanger, 2010b). ...
Article
Large wood (LW) is a ubiquitous feature in rivers of forested watersheds worldwide, and its importance for river diversity has been recognized for several decades. Although the role of LW in fluvial dynamics has been extensively documented, there is a need to better quantify the most significant components of LW budgets at the river scale. The purpose of our study was to quantify each component (input, accumulation, and output) of a LW budget at the reach and watershed scales for different time periods (i.e., a 50-year period, decadal cycle, and interannual cycle). The LW budget was quantified by measuring the volumes of LW inputs, accumulations, and outputs within river sections that were finally evacuated from the watershed. The study site included three unusually large but natural wood rafts in the delta of the Saint-Jean River (SJR; Québec, Canada) that have accumulated all LW exported from the watershed for the last fifty years. We observed an increase in fluvial dynamics since 2004, which led to larger LW recruitment and a greater LW volume trapped in the river corridor, suggesting that the system is not in equilibrium in terms of the wood budget but is rather recovering from previous human pressures as well as adjusting to hydroclimatic changes. The results reveal the large variability in the LW budget dynamics during the 50-year period and allow us to examine the eco-hydromorphological trajectory that highlights key variables (discharge, erosion rates, bar surface area, sinuosity, wood mobility, and wood retention). Knowledge on the dynamics of these variables improves our understanding of the historical and future trajectories of LW dynamics and fluvial dynamics in gravel-bed rivers. Extreme events (flood and ice-melt) significantly contribute to LW dynamics in the SJR river system.
... Imprecision in calculating large wood volumes is magnified when large wood jams are present because many wood pieces are not visible and the spacing between pieces is difficult to measure [Livers et al., 2015]. Therefore, some researchers have applied a wood-air box model to estimate volume [Piégay and Marston, 1998;Thévenet et al., 1998;Gurnell et al., 2000;Wyzga and Zawiejska, 2005;Wyzga et al., 2015], whereas others have made a distinction between a large wood accumulations of two to four pieces and jams containing more than four pieces [Moore et al., 2002]. In some very large rivers (drainage areas from 30,000 to 500,000 km 2 ) and deltas, large wood may accumulate in very extensive wood rafts [Sedell and Froggatt, 1984;Triska, 1984;Sedell et al., 1988;Wohl, 2011;Boivin et al., 2015]. ...
... A similar analysis by Boivin et al. [2015] used adjustments in a 3 km long wood raft at the mouth of the Saint-Jean River to estimate minimum wood delivery from the catchment. They used information from aerial photos, field measurements, and wood volume calculations using the method of Thévenet et al. [1998]. The raft volume (≈25,000 m 3 between 1963 and 2013) combined with wood storage in the channel (≈5950 m 3 ) compared favorably with estimated wood recruitment between 1963 and 2004 (≈27,000 m 3 ± 400 m 3 ). ...
... A common value of 500 kg m À3 has been widely used in the literature . However, wood density varies quite widely as a function of several factors, including tree species, wood type (i.e., early and latewood), tree age, decay status, and water sorption [Thévenet et al., 1998;Millington and Sear, 2007;MacVicar et al., 2009;Curran, 2010;Shmulsky and Jones, 2011], but unlike more general forest assessments, wood density has only rarely been accurately quantified in fluvial systems studies Abbe and Brooks, 2011]. ...
Article
Full-text available
Large wood is an important physical component of woodland rivers and significantly influences river morphology. It is also a key component of stream ecosystems. However, large wood is also a source of risk for human activities as it may damage infrastructure, block river channels, and induce flooding. Therefore, the analysis and quantification of large wood and its mobility is crucial for understanding and managing wood in rivers. As the amount of large-wood-related studies by researchers, river managers, and stakeholders increases, documentation of commonly used and newly available techniques and their effectiveness has also become increasingly relevant as well. Important data and knowledge has been obtained from the application of very different approaches and has generated a significant body of valuable information representative of different environments. This review brings a comprehensive qualitative and quantitative summary of recent advances regarding the different processes involved in large wood dynamics in fluvial systems including wood budgeting and wood mechanics. First, some key definitions and concepts are introduced. Second, advances in quantifying large wood dynamics are reviewed, in particular how measurements and modeling can be combined to integrate our understanding of how large wood moves through and is retained within river systems. Throughout, we present a quantitative and integrated meta-analysis compiled from different studies and geographical regions. Finally, we conclude by highlighting areas of particular research importance and their likely future trajectories, and we consider a particularly under-researched area so as to stress the future challenges for large wood research.
... Large wood are currently perceived as an essential part of the river ecosystem and of channel morphology in forested watersheds (Gurnell et al., 2002;Montgomery et al., 2003;Hassan et al., 2005). In most cases, LW are beneficial and necessary for aquatic ecosystems (Keller and Swanson, 1979;Gregory et al., 2003;Beckman and Wohl, 2014), and rivers with LW have been shown to have a higher biodiversity than those without (Thévenet et al., 1998;Nakamura et al., 2012). ...
... where ρ w is the proportion of air in wood-volume measurements (LWJ porosity) representing a ratio of open volume to volume filled with wood (Monzyk et al., 1997;Thévenet et al., 1998;Manners et al., 2007;Manners and Doyle, 2008). Thévenet et al. (1998) proposed a proportion of air-in-wood volume of 89.50% ± 0.91% from 53 LWI and 58 LWJ measurements on two rivers in France. ...
... where ρ w is the proportion of air in wood-volume measurements (LWJ porosity) representing a ratio of open volume to volume filled with wood (Monzyk et al., 1997;Thévenet et al., 1998;Manners et al., 2007;Manners and Doyle, 2008). Thévenet et al. (1998) proposed a proportion of air-in-wood volume of 89.50% ± 0.91% from 53 LWI and 58 LWJ measurements on two rivers in France. This proportion factor was adopted after validation and regional calibration in the field that was done by measuring the porosity of LWJ in SJR and in other rivers of the Gaspé Peninsula (Boivin and Buffin-Bélanger, 2010). ...
Article
Abstract Semi-alluvial rivers of the Gaspé Peninsula, Québec, are prone to produce and transport vast quantities of large wood (LW). The high rate of lateral erosion owing to high energy flows and noncohesive banks is the main process leading to the recruitment of large wood, which in turn initiates complex patterns of wood accumulation and reentrainment within the active channel. The delta of the Saint-Jean River (SJR) has accumulated large annual wood fluxes since 1960 that culminated in a wood raft of > 3-km in length in 2014. To document the kinetics of large wood on the main channel of SJR, four annual surveys were carried out from 2010 to 2013 to locate and describe > 1000 large wood jams (LWJ) and 2000 large wood individuals (LWI) along a 60-km river section. Airborne and ground photo/video images were used to estimate the wood volume introduced by lateral erosion and to identify local geomorphic conditions that control wood mobility and deposits. Video camera analysis allowed the examination of transport rates from three hydrometeorological events for specific river sections. Results indicate that the volume of LW recruited between 2010 and 2013 represents 57% of the total LW production over the 2004–2013 period. Volumes of wood deposited along the 60-km section were four times higher in 2013 than in 2010. Increases in wood amount occurred mainly in upper alluvial sections of the river, whereas decreases were observed in the semi-alluvial middle sections. Observations suggest that the 50-year flood event of 2010 produced large amounts of LW that were only partly exported out of the basin so that a significant amount was still available for subsequent floods. Large wood storage continued after this flood until a similar flood or an ice-breakup event could remobilise these LW accumulations into the river corridor. Ice-jam floods transport large amounts of wood during events with fairly low flow but do not contribute significantly to recruitment rates (ca. 10 to 30% early). It is fairly probable that the wood export peak observed in 2012 at the river mouth, where no flood occurred and which is similar to the 1-in 10-year flood of 2010, is mainly linked to such ice-break events that occurred in March 2012.
... Our estimation of the wood volume trapped in rafts followed the method developed by Piégay (1993) and Citterio (1996) and was applied to measurements from aerial Thévenet et al. (1998). This estimated average thickness was used because of the difficulty of accessing the delta and safely measuring raft thickness. ...
... Having an estimate of the wood volume allows a better comparison with the other wood volume estimations (input and output). Thévenet et al. (1998) proposed a proportion of air-in-wood volume of 89.50% ± 0.91% from several field measurements, and this proportion factor was thus adopted. ...
... representing a ratio of open volume to volume filled with wood (Monzyk et al., 1997;Thévenet et al., 1998;Manner et al., 2007;Manners and Doyle, 2008). Thévenet et al. (1998) proposed a proportion of air-in-wood volume of 89.50% ± 0.91% from 53 LWI and 58 LWJ measurements on two rivers in France. ...
Thesis
Full-text available
This thesis is an analysis of the dynamics of large wood in river by a multi-scale large wood budget approach in a semi-alluvial river of cold regions: the Saint-Jean River, Gaspé. The study of the spatial and temporal variability of the dynamics of large wood was carried out through a methodological approach combining four years of field and by analyzing historical documents. The rivers of the Gaspé Peninsula produce annually and carry large amounts of large wood. This production comes from the high specific power of rivers and by banks composed of noncohesive sediment and having a generally dense riparian forest tree. Until 2015, the Delta of the Saint-Jean River had several very large jams. These jams are put in place since the 1960s, they represent a unique opportunity to quantify and apply a wood budget and to identify key variables related to the dynamics of large wood at multiple spatial and temporal scales. In the first chapter, we described the function and the temporal evolution of large wood jams in the delta of the Saint-Jean River and presented the dynamics of large wood in the watershed. This chapter shows that the Saint-Jean River is characterized by high dynamics of large wood that promote large jams in the delta and along the fluvial corridor. Our results show that almost all large wood in river is produced by lateral migration and by the influence of the morphology. The density of trees in riparian areas is very high, which favors a major recruitment of large wood to the system. For the accumulations in the river corridor, two areas accumulate the majority of wood and these first results show a significant mobility, which can fluctuate substantially from year to year. With this chapter, we confirm that the case of the Saint-Jean River is a unique study site to apply and validate a large wood budget and to quantify the various components and key factors in the dynamics of large at the watershed scale. In the second chapter, we analyzed the interannual variability of the dynamics of large wood and quantified the effect of low-recurrence hydro-meteorological events. To document the interannual variability of large wood in the Saint-Jean River, 4 annual surveys were made between 2010 to 2013 to locate and describe more than 1000 large wood jams and over than 2000 individual large wood along a river corridor of 60 km long. The intense hydrometeorological event in December 2010 resulted in a major flood in the area, causing significant lateral migration in the Saint-Jean River. The results indicate that the recruitment of large wood between 2010 and 2013 represents 57% of the total production for the period 2004 and 2013 and large wood volumes accumulated along the river corridor are 4 times higher in 2013 than in 2010. In terms of mobility, video analysis of three different events showed that the intensity of the transport (number of large wood per minute) can be higher to ten times during an event with mechanical ice-breakup, compared to an open water.hydroclimatic event. In the third chapter, we conducted an analysis by large wood budget and analysis of eco-hydromorphological trajectory over more than 50 years. We quantified each component (input, output and accumulated) of a large wood budget at multiple spatial and temporal scales. We used the volumes of data accumulated in the delta of the Saint-Jean River since 1963 to close an analysis of large wood budget. These analyzes demonstrated and quantified the large variability of a large wood budget at multiple spatial and temporal scales. At the interannual scale or decadal, scale, the dynamics of large wood have periods when the input, storage and mobility of large wood differ according to eco-hydromorphological contexts. The eco-hydromorphological trajectory suggests an increase in river dynamics due to a significant change in the hydrology, resulting in higher production and mobility of large wood and increased in volumes accumulated in the corridor of the Saint-Jean River since the last decade.
... Usually, volume of wood, rather than mass, is required for budgeting or flux estimations. Wood volume (V wood ) is often estimated based on the geometrical shape of the wood (Thévenet et al., 1998). To directly quantify wood volume and compute wood budgets, different techniques have been used, such as repeat estimates of the amount of wood deposited along a given reach, or direct counts of wood pieces at a given location. ...
... This is due to the fact that unlike in forestry research, wood density is infrequent assessed in aquatic studies. Wood density varies as a function of several factors including tree species, wood type (proportion of early to late wood), tree age (and proportion of heartwood to sapwood), decay status, and water sorption (Thévenet et al., 1998;Millington and Sear, 2007;MacVicar et al., 2009;Curran, 2010;Shmulsky and Jones, 2011). Environmental conditions and processes in rivers are very different than those in forests, where most of the data about wood density is obtained. ...
... Despite the abundant literature on wood properties, especially for manufacturing processes (Forest Products Laboratory-USDA, 2010;Shmulsky and Jones, 2011), and studies of wood in forests (Harmon et al., 2008), few studies have been published regarding instream wood physical characteristics. As an example, Thévenet et al. (1998) analyzed wood slices from instream wood collected at the Ain River, to estimate the ability to absorb water and test how the age, decay stage, density or size of samples influence the sorption process. Díez et al. (2002) analyzed small branches of several species to quantify wood breakdown in a first order stream in the Iberian Peninsula. ...
... Citterio (1996) ha comparato due fiumi francesi, il fiume Ain, un fiume pseudo meandriforme pedemontano, con il Drome, un fiume braided, e riscontrato che il primo fornisce quasi 40 t all'anno di detrito legnoso per km di lunghezza del fiume, rispetto il secondo che ne fornisce 12 t/anno. Fiumi meandriformi di pianura forniscono molto meno legname che nelle omologhe sezioni pedemontane, in quanto il tasso di erosione è molto basso, raggiungendo spesso solo pochi cm all'anno nelle sponde esterne (Thevenet et al., 1998). ...
... Il rilievo tradizionale consiste nel determinare il volume del LW utilizzando strumenti quali la cordella metrica ed il cavalletto forestale. Le dimensioni da determinare sono: altezza (h), lunghezza (L), larghezza (w); (Thevenet et al., 1998). La formula così utilizzata conterrà dei vuoti e dei pieni, da considerare applicando eventualmente un coefficiente di riduzione. ...
... La formula così utilizzata conterrà dei vuoti e dei pieni, da considerare applicando eventualmente un coefficiente di riduzione. Per due fiumi francesi, rispettivamente braided e wandering, Thevenet et al., (1998) ...
Thesis
Full-text available
Corso di laurea magistrale in Scienze Forestali e Ambientali Bilancio del materiale legnoso lungo un fiume a fondo ghiaioso interessato da eruzione vulcanica. Il caso del Rio Blanco (Cile)
... Both, laser scanning as well as SfM photogrammetry are capable of producing highly accurate 3D replicates (digital twin models) of topography (Goetz et al., 2018, Backes et al., 2020 and objects (Cunliffe et al., 2016, Sylvain et al., 2019, Moyano et al., 2020, Swayze et al., 2021, given that the surveyed scene is behaving static (mind vegetation in windy conditions or turbulent water). Accordingly, SfM photogrammetry represents a well-suited alternative to the more expensive laser scanning technology (Wallace et al., 2016, Anderson et al., 2019, as well as to traditionally applied LW mapping methods, such as the parallelepiped approach (Thevenet et al., 1998, Boivin et al., 2017, discrete point and transect sampling (Böhl andBrändli, 2007, Ritter andSaborowski, 2012), or manual measurement of individual LW elements (Wyżga et al., 2015, Tonon et al., 2018. With the transition from traditionally applied LW mapping practices over to better performing techniques, such as SfM photogrammetry, a whole new level of detail can be acquired within a single field survey, potentially benefitting LW research substantially. ...
... Consequently, V 2.5D claims more space than V 3D (Fig. 12). Although the 2.5D approach is associated with limitations in most computer aided modelling applications (Remondino, 2011, Reichinger et al., 2012, Zhang et al., 2019, it represents a valuable tool for bulk volume estimation in LW research (Sanhueza et al., 2019, Spreitzer et al., 2019, and a significant improvement to previously applied bulk volume estimates, such as the parallelepiped approach (Thevenet et al., 1998, Boivin et al., 2017, and visual estimates (Dixon, 2016;Scott et al., 2019, Livers et al., 2020. ...
Article
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Quantification and assessment of large wood (LW) accumulations in fluvial systems is still considered difficult due to the complex nature of wooden deposits. Although knowledge about volumetric measures and porosity parameters of LW accumulations is crucial for the prediction of hydraulic and geomorphic effects, it has not yet been possible to obtain accurate measurements. These limitations are mainly based on a lack of applicable sensing technologies available in the past. In the present study, a close-range aerial surveying technique (Structure from Motion (SfM) photogrammetry) is applied for generating 3D replicates (digital twin models) of wooden deposits, enabling their volumetric assessment. In addition, manually conducted volumetric measurements of corresponding prototype LW accumulations help to improve and calibrate the SfM-derived estimates. For the first time, precise porosity parameters for LW accumulations, ranging from 52.5 to 83.2%, are provided. In addition, a novel parameter – the packing arrangement – is used, which describes the structural alignment of individual elements in the LW accumulation and benefits porosity estimates based on the applied 2.5D and 3D photogrammetric approach. Accordingly, randomly and loosely organised LW accumulations allow for a high penetration depth of the 3D approach, resulting in a more accurate estimate of the actual porosity, as the 3D volumetric estimate approaches the solid wood volume of the corresponding LW accumulation. An empirical approach has been developed for future approximation of LW accumulation porosity, without the need of knowing the solid wood volume. With the present work a significant improvement of our understanding in employing a non-intrusive sensing technique is provided, linked with manually conducted field measurements of the solid wood volume of LW accumulations. Our study contributes to an improved data acquisition and processing plan, which represents a further important step towards a systematic assessment framework that is urgently needed by river managers and engineers to better evaluate and manage LW in fluvial systems.
... Methodological limitations restrict current understanding of LW dynamics (Thevenet et al., 1998;Peterson et al., 2015;Steeb et al., 2017). In this paper we focus specifically on the potential of SfM photogrammetry as a technique for assessing LW accumulation volume. ...
... The same is required for assessing wood inputs from natural forest disturbance such as fire, landslides and avalanches, or heavy storm events. This is the current focus of numerous LW studies (Thevenet et al., 1998;MacVicar et al., 2009;Ruiz-Villanueva et al., 2014b;Steeb et al., 2017;Sanhueza et al., 2018), however, the mass and volume of wood still remains rarely described (Ruiz-Villanueva et al., 2019). Although a broad variety of volumetric surveying methods for LW sources exists; including LiDAR (Kasprak et al., 2012;Atha and Dietrich, 2016), aerial photogrammetry (Boivin et al., 2017;Sanhueza et al., 2018) and manually conducted measurements (Piegay, 1993;Boivin et al., 2015), precise quantification of LW sources remains challenging. ...
... Each piece of LW (length > 1 m and diameter > 10 cm; Wohl et al., 2010) deposited during the flood along the studied reaches was assigned to a class relative to its mid-length diameter and length (Marcus et al., 2002;Daniels, 2006;Lucía et al., 2015;Rickli et al., 2016); i.e., seven classes were distinguished from < 10 to > 40 cm in diameter and nine classes from < 2 to > 16 m for length. Log volume was calculated as solid cylinders (Thévenet et al., 1998). Wood accumulations (i.e., wood jams) were also measured. ...
... Wood accumulations (i.e., wood jams) were also measured. The wood volume of each jam was calculated geometrically through its area and height (measured in the field), considering a 50-80 % range in porosity (Thévenet et al., 1998). In the tributary catchments where large quantities of wood were deposited, mainly along the Sädelgrabe fan, the extension of wood deposits and the size of accumulations prevented the measurement of individual pieces. ...
Article
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On 24 July 2014, an exceptionally large flood (recurrence interval ca. 150 years) caused large-scale inundations, severe overbank sedimentation, and damage to infrastructure and buildings along the Emme River (central Switzerland). Widespread lateral bank erosion occurred along the river, thereby entraining sediment and large wood (LW) from alluvial forest stands. This work analyzes the catchment response to the flood in terms of channel widening and LW recruitment and deposition, but also identifies the factors controlling these processes. We found that hydraulic forces (e.g., stream power index) or geomorphic variables (e.g., channel width, gradient, valley confinement), if considered alone, are not sufficient to explain the flood response. Instead, the spatial variability of channel widening was first driven by precipitation and secondly by geomorphic variables (e.g., channel width, gradient, confinement, and forest length). LW recruitment was mainly caused by channel widening (lateral bank erosion) and thus indirectly driven by precipitation. In contrast, LW deposition was controlled by channel morphology (mainly channel gradient and width). However, we also observed that extending the analysis to the whole upper catchment of the Emme River by including all the tributaries and not only to the most affected zones resulted in a different set of significant explanatory or correlated variables. Our findings highlight the need to continue documenting and analyzing channel widening after floods at different locations and scales for a better process understanding. The identification of controlling factors can also contribute to the identification of critical reaches, which in turn is crucial for the forecasting and design of sound river basin management strategies.
... In the reaches featuring LW jams, their average height was measured in the field for the subsequent computation of LW jam volume through the jam areas determined from aerial photos, as will be described later in the text. Where LW deposits could not be detected from the aerial photos (i.e., covered by the canopy of remaining trees or for the shadows as in most of the Pogliaschina channel network) their size was assessed in the field by measuring the different dimensions of a geometric form (generally with a parallelepiped form) that enclosed the LW jam (Thévenet et al., 1998). ...
... The wood volume of each jam was calculated geometrically through its area and height (measured in the field), considering a 80-90 % range in porosity. The lower value in this range was observed in LW jams in Chilean creeks (Andreoli et al., 2007), whereas the higher one in French piedmont rivers (Thévenet et al., 1998). In case of single LW elements visible in the orthophotos, each of them was digitized as a line, and log length was associated to the horizontally projected line length. ...
Article
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Understanding and modelling the dynamics of large wood (LW) in rivers during flood events has spurred a great deal of research in recent years. However, few studies have documented the effect of high-magnitude flash floods on LW recruitment, transport and deposition. On 25 October 2011, the Magra river basin (north-western Italy) was hit by an intense rainstorm, with hourly rainfall rates up to 130 mm h−1 and event rain accumulations up to 540 mm in 8 h. Such large rainfall intensities originated flash floods in the main river channels and in several tributaries, causing severe damages and loss of lives. Numerous bridges were partly or fully clogged by LW jams. A post-flood survey was carried out along the channels of two catchments that were severely and similarly affected by this event, the Gravegnola (34.3 km2) and Pogliaschina (25.1 km2). The analysis highlighted a very relevant channel widening in many channel reaches, which was more marked in the Gravegnola basin due to highly erodible material forming the slopes adjacent to the fluvial corridor. Large wood recruitment rates were very high, up to 1270 m3 km−1, and most of it (70–80 %) was eroded from the floodplains as a consequence of channel-widening processes, while the rest came from hillslopes processes. Overall, drainage area and channel slope are the most relevant controlling variables in explaining the reach-scale variability of LW recruitment, whereas LW deposition appears to be more complex, as correlation analysis did not evidence any statistically significant relationship with the tested controlling variables. Indeed, in-channel LW displacement during the flood has been mostly limited by the presence of bridges, given the relatively large width attained by channels after the event.
... The assessment of the wood volume of such accumulations might be challenging and uncertainty 664 might be high (Spreitzer et al., 2020;Thevenet et al., 1998). Some of the observed wood volumes 665 ...
Preprint
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Different models have been used in science and practice to identify instream large wood (LW) sources and to estimate LW supply to rivers. This contribution reviews the existing models proposed in the last 35 years and compares two of the most recent GIS-based models by applying them to 40 catchments in Switzerland. Both models, which we call here empirical GIS approach (EGA) and Fuzzy-Logic GIS approach (FGA), consider landslides, debris flows, bank erosion, and mobilization of instream wood as recruitment processes and compute volumetric estimates of LW supply based on three different scenarios of process frequency and magnitude. Despite being developed following similar concepts and fed with similar input data, the results from the two models differ markedly. In general, estimated supply wood volumes were larger in each of the scenarios when computed with the FGA and lower with the EGA models. Landslides were the dominant process identified by the EGA, whereas bank erosion was the predominant process according to the FGA model. These differences are discussed and results compared to available observations coming from a unique database. Regardless of the limitations of these models, they proved extremely useful for hazard assessment, and the design of infrastructure and other management strategies.
... This not only causes dissipation of flow energy (Radecki-Pawlik et al., 2016) but also allows plastic objects to be braced against the upstream jam side and to accumulate in the lee of a jam. As wood jams are formed of wood pieces of different size and orientation (Manners et al., 2007), they are porous structures (Spreitzer et al., 2020) with the porosity ranging from 13% to 90% (Thevenet et al., 1998). The flow of floodwater through a jam induces negative pressure acting on plastic objects braced against its upstream side, which causes that they adhere the jam and cannot be readily detached by water flowing around the wood accumulation. ...
Article
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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.
... Trees which have fallen into a stream notably affect fluvial processes (Gurnell et al. 2002). The type of woody debris (after Thévenet et al. 1998), its volume, and the place of its deposition in a channel, influence the distribution and sizes of channel forms (Gregory et al. 1985). ...
Article
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Strong wind events frequently result in creating large areas of windthrow, which causes abrupt environmental changes. Bare soil surfaces within pits and root plates potentially expose soil to erosion. Absence of forest may alter the dynamics of water circulation. In this study we attempt to answer the question of whether extensive windthrows influence the magnitude of geomorphic processes in 6 small second- to third-order catchments with area ranging from 0.09 km ² to 0.8 km ² . Three of the catchments were significantly affected by a windthrow which occurred in December 2013 in the Polish part of the Tatra Mountains, and the other three catchments were mostly forested and served as control catchments. We mapped the pits created by the windthrow and the linear scars created by salvage logging operations in search of any signs of erosion within them. We also mapped all post-windthrow landslides created in the windthrow-affected catchments. The impact of the windthrow on the fluvial system was investigated by measuring a set of channel characteristics and determining bedload transport intensity using painted tracers in all the windthrow-affected and control catchments. Both pits and linear scars created by harvesting tend to become overgrown by vegetation in the first several years after the windthrow. The only signs of erosion were observed in 10% of the pits located on convergent slopes. During the period from the windthrow event in 2013 until 2019, 5 very small (total area <100 m ² ) shallow landslides were created. The mean distance of bedload transport was similar ( t -test, p =0.05) in most of the windthrow-affected and control catchments. The mapping of channels revealed many cases of root plates fallen into a channel and pits created near a channel. A significant amount of woody debris delivered into the channels influenced the activity of fluvial processes by creating alternating zones of erosion and accumulation.
... This may explain why studies largely concerned with coniferous trees, which tend to break into near-cylindrical pieces, have readily applied threshold size metrics. However, the difficulties of applying threshold sizes to irregularly-shaped wood pieces prompted Thevenet et al. (1998) to define a wood-air "box" to quantify the outer dimensions of whole uprooted trees and shrubs as well as tangled wood jams that are characteristic wood forms of the bars and margins of rivers bordered by broadleaf tree species. The three dimensions of the enclosing box coupled with an estimate of the wood to air ratio of different wood accumulation or piece styles allowed wood length, diameter, volume and weight to be determined indirectly. ...
Chapter
This article explores the character and role of wood in fluvial systems. Following descriptions of the key characteristics of wood that affect its role and how it is measured, the quantities and styles in which wood is retained in fluvial systems are considered. This leads to discussions of wood budgets and wood mobility in fluvial systems and, finally, to relationships between wood and landforms. Throughout, discussions and descriptions focus on “small,” “medium” and “large” rivers where size relates to the ratio of wood piece length to channel width. The article concludes by drawing together some common aspects of wood and geomorphology across rivers with different physical and wood characteristics and then highlighting some areas that require more research attention.
... >1 m in length and > 10 cm in diameter (Thevenet, Citterio, & Piégay, 1998). This definition although arbitrary, is commonly used for convenience (Wohl et al., 2010) and is applied to this review. ...
Article
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The influence of naturally occurring in-channel large wood (LW) on the hydraulics, hydrology and geomorphology of rivers is well documented. To inform management and better understand naturally occurring or artificially placed LW, hydraulic and hydrological models are applied to predict the possible benefits and drawbacks for habitat, sediment management and flood risk mitigation. However, knowledge and guidance on appropriate representation in models, needed to underpin realistic predictions, is lacking. This could lead to unrealistic expectations of the effectiveness of LW for different river management goals. To date, seven types of LW representation in hydraulic and hydrological models have been applied, the range partly reflecting the variety of LW, model types, scales and purposes. The most common approach is by altering channel roughness to represent flow resistance. Although qualitatively the effects of LW have been captured using models, to date quantitative validation, as well as transferable knowledge to help a priori parameterization of LW representations, remain limited. Therefore, additional empirical investigations and robust model validation are required to inform defensible LW representations for specific purposes and scales in numerical models coupled with better accounting of input uncertainty to improve confidence in predictions. Future studies should also consider a greater range of artificial and natural LW features, settings, larger spatial scales and better account for temporal variability of flow, morphology and LW configuration.
... Table S1 summarizes which measurements were collected in each basin. Within each reach, we quantified wood volume in wood jams (accumulations of 3 or more pieces touching one another) using a census approach, measuring the length, width, and height of a rectangular prism that best fit the jam (i.e., these geometric measurements did not correspond to flow direction) and visually estimating the porosity (Thevenet et al., 1998). Although this method is not as accurate as dismantling jams to measure every wood piece (e.g., Manners et al., 2007), our consistency in this method (i.e., only a single person made all estimates using consistent methodology) likely minimizes systematic bias. ...
Preprint
Wood in rivers creates habitat, shapes the morphology of valley bottoms, and acts as a pool of organic carbon (OC). Effective riverine wood management depends on a robust understanding of the spatial distribution of wood throughout river networks. This motivates the analysis of wood load in relation to both reach- and basin-scale processes. We present wood load data coupled with precipitation, forest stand characteristic, land use, and geomorphic data across four basins in the Rocky, Cascade, and Olympic Mountains of the western USA. We compare basins with differing land use within the same climatic region and basins in differing climates and statistically model intra-basin wood load variability. Wood load is a function of metrics that generally describe river corridor spatial heterogeneity, metrics that describe wood storage patterns, and, at a broader scale, metrics that relate to wood supply. From this, we generate a conceptual model to describe controls on wood load across spatial scales. We use this model to propose that spatial heterogeneity and wood storage pattern together determine reach-scale wood trapping efficiency. Trapping efficiency in turn regulates how wood supply to valley bottoms determines wood load. We also find that wood in an undisturbed basin stores significant amounts of OC, and that wood load restoration has the potential to restore significant amounts of OC to valley bottoms. This conceptual model of wood load controls may serve as a framework to guide wood load modeling and restoration at multiple scales.
... Table S1 summarizes which measurements were collected in each basin. Within each reach, we quantified wood volume in wood jams (accumulations of 3 or more pieces touching one another) using a census approach, measuring the length, width, and height of a rectangular prism that best fit the jam (i.e., these geometric measurements did not correspond to flow direction) and visually estimating the porosity (Thevenet et al., 1998). Although this method is not as accurate as dismantling jams to measure every wood piece (e.g., Manners et al., 2007), our consistency in this method (i.e., only a single person made all estimates using consistent methodology) likely minimizes systematic bias. ...
Article
Wood in rivers creates habitat, shapes the morphology of valley bottoms, and acts as a pool of organic carbon (OC). Effective riverine wood management depends on a robust understanding of the spatial distribution of wood throughout river networks. This motivates the analysis of wood load in relation to both reach- and basin-scale processes. We present wood load data coupled with precipitation, forest stand characteristic, land use, and geomorphic data across four basins in the Rocky, Cascade, and Olympic Mountains of the western U.S. We compare basins with differing land use within the same climatic region and basins in differing climates and statistically model intrabasin wood load variability. Wood load is a function of metrics that generally describe river corridor spatial heterogeneity, metrics that describe wood storage patterns, and, at a broader scale, metrics that relate to wood supply. From this, we generate a conceptual model to describe controls on wood load across spatial scales. We use this model to propose that spatial heterogeneity and wood storage pattern together determine reach-scale wood trapping efficiency. Trapping efficiency in turn regulates how wood supply to valley bottoms determines wood load. We also find that wood in an undisturbed basin stores significant amounts of OC and that wood load restoration has the potential to restore significant amounts of OC to valley bottoms. This conceptual model of wood load controls may serve as a framework to guide wood load modeling and restoration at multiple scales.
... In case of LW jams, the respective area of the jam was digitized and the height was estimated from field observations. The wood volume of each jam was calculated geometrically by its area and height, considering an 80-90% range in porosity (Thévenet et al., 1998;Andreoli et al., 2007). The porosity values were not validated with field measurements. ...
Article
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This work presents a post-event survey study, addressing the geomorphic response and large wood budget of two torrents, Grimmbach and Orlacher Bach, in southwestern Germany that were affected by a flash flood on May 29, 2016. During the event, large amounts of wood clogged and damaged a bridge of a cycling path at the outlet of the Grimmbach, while the town of Braunsbach was devastated by discharge and material transported along the Orlacher Bach. The severity of the event in these two small catchments (30.0 km2 and 5.95 km2, respectively) is remarkable in basins with a relatively low average slope (10.7 and 12.0%, respectively). In order to gain a better understanding of the driving forces during this flood event an integrated approach was applied including (i) an estimate of peak discharges, (ii) an analysis of changes in channel width by comparing available aerial photographs before the flood with a post-flood aerial surveys with an Unmanned Aerial Vehicle and validation with field observations, (iii) a detailed mapping of landslides and analysis of their connectivity with the channel network and finally (iv) an analysis of the amounts of large wood recruited and deposited in the channel. The morphological changes in the channels can be explained by hydraulic parameters, such as stream power and unit stream power, and by morphological parameters such as the valley confinement. This is similar for LW recruitment amounts and volume of exported LW since most of it comes from the erosion of the valley floor. The morphological changes and large wood recruitment and deposit are in the range of studied mountain rivers. Both factors thus need to be considered for mapping and mitigating flash flood hazards also in this kind of low range mountains.
... g cm −3 , and they showed that the in situ density of LW pieces was regulated by their water content in a stream in Mississippi, USA. Thevenet et al. (1998) also reported that variation of the in situ density of LW pieces was explained principally by varying degrees of water absorption. Although their findings are consistent with our results for the in situ density of SW pieces (Figs. 5 and 6), they did not explicitly demonstrate the effects of depositional environments on the in situ density of instream wood. ...
Article
In cooperation with large instream wood (LW) within logjams, small instream wood (SW) can control downstream flux of sediment and particulate organic matter and can play an important role for stream ecosystems. However, information regarding the density and moisture content of SW—which affects wood transport, wood decay, and mass loading—is limited. Here we investigated the SW properties, i.e., density under field conditions (in situ density), basic density, volumetric water content, and depositional environment of SW sampled from five logjams and their backwater areas in two headwater streams (second- and third-order streams) surrounded by mixed broadleaf-conifer forests in western Japan. The in situ density ranged from 0.49 to 1.25 g cm− 3, and pieces with densities > 1.0 g cm− 3 accounted for 45% of all samples. Additionally, the in situ density of SW closely related to the volumetric water content (r² = 0.76) rather than the basic density as an index of solidity or decay condition of wood. The SW that was partially submerged in water had a higher volumetric water content than SW exposed to air. These results indicate that a nonfloating transport cannot be ignored as an important mechanism for SW movement and that in situ density depends not on the solidity of the wood but on water sorption by SW. However, waterlogged SW should be well decayed because it has a lower basic density than air-exposed and sediment-buried SW. We conclude that the moisture conditions of the depositional environment can affect subsequent transport and decay processes of SW. Moreover, most waterlogged and sediment-buried SW, because of its high in situ density (> 1.0 g cm− 3), may contribute to clogging between the channel bed and LW that initiate a logjam during future movements.
... It is essential in woody debris estimation to quantify wood mass volume by identifying wood/air volume ratio in the different types of accumulated material; isolated wood pieces, jams of logs, branches, root boles and twigs and shrubs and whole trees. An appropriate approach for estimation of woody debris accumulation mass, calculation of the density index for woody debris and air proportion estimation in log jams and shrubs derived from aerial photography were developed by Thévenet et al. [55] and presented by Piégay et al. [56] or Wyžga and Zawiejska [57]. ...
Article
This paper presents the template for high-resolution mapping of a river landscape by Unmanned Aerial Vehicle (UAV) technology with the following five steps: (i) reconnaissance of the mapped site; (ii) pre-flight field work; (iii) flight mission; (iv) quality check and processing of aerial data; and (v) operations above the processed layers and landforms (objects) mapping (extraction). The small multirotor UAV (HiSystem Hexakopter XL) equipped with Sony NEX 6 camera with standard 16-50 mm lens provided image capture and workflow design applications. Images were processed by Agisoft PhotoScan software and georeferencing was ensured with 20 Ground Control Points (GCP) and 18 check points certifying accuracy assessment. Three imaging methods for 3D model creation of the study area were used: (i) nadir, (ii) oblique and (iii) horizontal. This minimized geometric error and captured topography under treetop cover and overhanging banks.
... It was assumed the main trunk of individual wood pieces and their major stems were cylinders and the total volume of each wood piece could be expressed as the sum of the main trunk and the different stems. This method is similar to that applied by Thevenet et al. (1998) in defining irregular shaped wood pieces. The orientation of wood respect to the riverbank was recorded into one of three categoriesparallel to the flow (0-30°), partially angled (>30-60°) or perpendicular to the riverbank (>60-90°). ...
Article
It is hypothesized that the organization of wood within the Barwon–Darling River, Australia; a large low-gradient dryland river, differs to current models of wood in rivers. Current models are dominated by studies in high-energy systems where wood is highly mobile and non-uniform in their distribution. Large wood in this system is not highly mobile because of low-stream powers, high-wood densities and a low ratio of wood size to bankfull widths. This study analyses the organization of 7142 pieces along 210 km of the Barwon–Darling River, SE Australia. The majority of pieces (72%) were <10 m in length and of this >50% were complex in character. Most pieces (98%) were attached to the bank, distributed relatively uniformly and correlated to the riparian zone. Pieces were either completely (25.9%) or partially aligned (36.4%) to the flow suggesting passive realignment. The primary driver of wood alignment was related to its size, secondary influences were height above the river bed (a correlate of stream energy) and river channel geomorphology. Thus, large wood is not actively transported, rather pieces remain where they fall and then passively realign as a result of wood size, height in the channel and river channel geomorphology.
... Instream large wood is defined as living or dead wood >1m length and >10cm diameter (Thevenet et al., 1998). Naturally occuring wood jams, comprising multiple wood pieces of varying size and arrangement, can be highly complex in structure and vary according to channel style and dimensions (Gurnell et al., 2002). ...
Article
• Large wood is a powerful geomorphic agent in rivers, providing important habitat functions for a range of aquatic organisms, but has been subject to a long history of removal. • Internationally, approaches to river restoration are increasingly incorporating large wood features, but generally favour simple flow deflectors (e.g. single logs, stripped of branches and anchored in place) over more complex structures that more accurately mimic natural wood jams. • This paper explores channel response to wood‐based restoration of an overwidened lowland chalk stream that incorporated whole felled trees. Hydraulics, sediment, topography and vegetation data were assessed for a 3 year period for two restored reaches: an upstream reach where pre‐restoration baseline data were obtained, and a downstream reach restored before data collection. • Where pre‐restoration data were available, the introduction of wood jams generated sediment deposition within jams leading to the development of vegetated marginal ‘benches’ and bed scour in adjacent areas of flow convergence. Patterns were less clear in the downstream reach, where restoration design was less ambitious and outcomes may have been affected by subsequent restoration work upstream. • The results indicate that reintroduction of large wood (whole trees), can promote channel and habitat recovery from overwidening in lowland rivers, creating important ecological benefits through the provision of structurally complex marginal habitat and associated food resources. Longer‐term assessments are required to establish whether the trajectories of change are persistent. • The work emphasizes the effectiveness of restoration approaches that aim to ‘work with nature’. The ambitious design, incorporating structurally complex wood jams, was also low‐cost, using materials available from the river corridor (existing riparian trees). Furthermore, ecosystem engineering effects were amplified by the colonization of wood jams by aquatic vegetation. The approach should, therefore, be transferable to other lowland rivers, subject to wider catchment constraints.
... However, if we select the data to include only trunks with rootwads, the percentages reverse to 42% deciduous and 58% coniferous. Figure 2. c This is the air-wood rootwad volume which is the volume of a box that completely encloses the rootwad [Thevenet et al., 1998]. d Proportions based on only pieces with rootwads and may more accurately represent recruitment because deciduous are more likely to break and contribute more large pieces per tree to overall wood loads. ...
Article
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This study presents a case study of large wood transport on the great Slave River in northern Canada with the objective to better understand the processes of and variability in pulsed wood fluxes from large forested catchments. We use a varied approach, integrating field characterization of wood, historical anecdotes, repeat aerial imagery of stored wood, and time-lapse imagery of moving wood, for a robust analysis and synthesis of processes behind pulsed wood flux, from yearly uncongested export to rare congested wood floods. Repeat monitoring of known sites of temporary storage with new or historic imagery proved to be a very useful tool for constraining wood flux histories. Pulsed wood export on the Slave River is not an artefact of episodic recruitment from major up-basin disturbances, but rather reflects decadal- to half-century-scale discharge patterns that re-distribute wood recruited from channel migration and bank slumping. We suggest that the multi-year flow history is of paramount importance for estimating wood flux magnitude, followed in declining importance by the yearly sequence of peaks and the magnitude and characteristics of the rising limb of individual floods. This article is protected by copyright. All rights reserved.
... Air-wood box method (Thevenet et al., 1998) Wood volume=air-wood volume*0.10 ...
Conference Paper
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Measuring the volume of wood in logjams and accumulations is important for ecological applications and wood and carbon budgets. Porosity is difficult to estimate. We compare methods to estimate porosity and wood volumes of logjams across three field sites: the Colorado Rocky Mountains in the USA, Northern Canada, and interior Alaska.
... Wood jams occurring in the river consisted not only of logs but they were heterogeneous mixtures of logs, branches, root boles, and twigs, sometimes with a considerable addition of fine organic matter and inorganic sediment (see Fig. 6a below). As the volume of wood contained in wood jams and shrubs and trees cannot be easily measured, we used the method developed by Thévenet et al. (1998) that involves measuring the volume of wood deposits and multiplying it by wood mass estimates for particular types of wood deposits (50, 100 and 500 kg m −3 for shrubs and trees, jams, and logs, respectively). Wood deposits were recorded in 100-m river segments, for which river width was determined based on the measurements performed at each end of every segment. ...
Chapter
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Applicability, advantages and limitations of a range of methods applied to determine large wood dynamics in Kamienica Stream and the Czarny Dunajec River, Polish Carpathians, are discussed. Results of a 6-year-long monitoring suggest an increased rate of wood recruitment to Kamienica Stream caused by recent bark beetle infestation of the spruce forests in the valley. However, both monitoring of wood transport and wood inventories indicate that the mobility of large wood in the stream is low and can increase only during major floods. Thus flood hazard to downstream valley reaches potentially resulting from the considerable amounts of large wood stored in the upper stream reach is limited. In the Czarny Dunajec, wood inventories, a tracking experiment with logs tagged with radio transmitters, and numerical modelling indicated high potential for wood transport in the narrow river reaches formed by channelization or channel incision, and high potential for wood deposition in the wide, multi-thread channel. Vegetative regeneration of living willow wood considerably reduces its remobilization by subsequent floods. Efficient transport of large wood along narrow river reaches implicates that during floods substantial amounts of wood may be delivered from distant sources to the channel sections located downstream of the narrow reaches. Wide, multi-thread reaches operate as natural wood traps, considerably limiting further transfer of wood to vulnerable sites/reaches.
... Wood recruitment, accumulation, and reentrainment patterns have been explored at the reach scale, shedding some light on large wood kinetics and fluxes. However, these measurements are not sufficient to provide information on the real wood flux (Thévenet et al., 1998) because, most of the time, the field data result from one or several past events and data at the single-event scale is not available. To obtain measurements of wood flux, Moulin and Piégay (2004) and Seo et al. (2008) characterized the output of wood using archived reservoir wood extraction series. ...
... Wood density is used to calculate the initial motion and it influences the way logs move (floating or by traction). Wood density varies as a function of several factors including tree species, wood type (proportion of early to late wood), tree age (and proportion of heartwood to sapwood), decay status, and water sorption (Thevenet et al., 1998;Millington and Sear, 2007;MacVicar et al., 2009;Curran, 2010;Shmulsky and Jones, 2011). ...
Conference Paper
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In recent years the improvements in computational capacity and the advances in numerical modelling techniques have produced a significant increase in the type of river processes that can be studied with the support of numerical models. Water quality and sediment transport are some of these processes, and it also applies to the case of wood transport. In the last five years several publications have proven the utility of numerical modelling of wood transport for predicting and better understanding wood dynamics, analyzing the influence of wood on flow conditions, and the interactions with infrastructures, and for including this phenomenon in the flood risk assessment. Besides these studies, numerical modelling of wood in rivers is still challenging, and different strategies can be used. We present and discuss some details of numerical strategies used in the simulation of wood transport within a 2D hydrodynamic model based on the finite volume method.
... Second, little is known about LWD processes in channels with instability caused by system-wide degradation through knick point migration processes although there have been studies concerning the input of LWD and LWD -channel interaction caused by landsliding events (Lisle, 1995). Third, most studies have been conducted in upland areas (Robinson and Beschta, 1990;Nakamura and Swanson, 1993) although there are exceptions (Piégay, 1993;Thevenet et al., 1998). Finally, most studies have been undertaken in isolated reaches, and only a few investigations such as those by Gregory et al. (1993) and Piégay et al. (1999) have covered basin-wide debris processes. ...
... The most accurate way to quantify wood in a jam is to dismantle the jam and systematically measure its contents (Manners et al., 2007), but this is neither feasible for extremely large jams nor desirable in most cases, given the numerous important physical and ecological function that jams can perform. Jams have been characterized by approximating each jam as a geometric form, measuring the external dimensions, and estimating porosity of the jam (e.g., Thevenet et al., 1998). Jams have also been characterized by measuring or counting all visible and accessible individual pieces within the jam and assuming that this represents a minimum volume of LW within the jam (e.g., . ...
Article
Nearly 50 years of research focused on large wood (LW) in rivers provide a basis for understanding how wood enters rivers; how wood decays, breaks, and is transported downstream; and how at least temporarily stable wood influences channel geometry, fluxes of water, sediment, and organic matter, and the abundance and diversity of aquatic and riparian organisms. Field-based studies have led to qualitative conceptual models and to numerical stimulations of river processes involving wood. Numerous important gaps remain, however, in our understanding of wood dynamics. The majority of research on wood in rivers focuses on small- to medium-sized rivers, defined using the ratio of wood piece size to channel width as channels narrower than the locally typical wood-piece length (small) and slightly narrower than the longer wood pieces present (medium). Although diverse geographic regions and biomes are represented by one or a few studies in each region, the majority of research comes from perennial rivers draining temperate conifer forests. Regional syntheses most commonly focus on the Pacific Northwest region of North America where most of these studies originate. Consequently, significant gaps in our understanding include lack of knowledge of wood-related processes in large rivers, dryland rivers, and rivers of the high and low latitudes. Using a wood budget as an organizing framework, this paper identifies other gaps related to wood recruitment, transport, storage, and how beavers influence LW dynamics. With respect to wood recruitment, we lack information on the relative importance of mass tree mortality and transport of buried or surficial downed wood from the floodplain into the channel in diverse settings. Knowledge gaps related to wood transport include transport distances of LW and thresholds for LW mobility in small to medium rivers. With respect to wood storage, we have limited data on longitudinal trends in LW loads within unaltered large and great rivers and on fluctuations in LW load over time intervals greater than a few years. Other knowledge gaps relate to physical and ecological effects of wood, including the magnitude of flow resistance caused by LW; patterns of wood-related sediment storage for diverse river sizes and channel geometry; quantification of channel-floodplain-LW interactions; and potential threshold effects of LW in relation to physical processes and biotic communities. Finally, knowledge gaps are related to management of large wood and river corridors, including understanding the consequences of enormous historical reductions in LW load in rivers through the forested portions of the temperate zone; and how to effectively reintroduce and manage existing LW in river corridors, which includes enhancing public understanding of the importance of LW. Addressing these knowledge gaps requires more case studies from diverse rivers, as well as more syntheses and metadata analyses.
... ANOVA, chi-squared tests or t-tests are the tools most commonly used to assess whether the measurements are biased by operators or by methods. For example, Thévenet et al. (1998) measured geometric volumes of wood jams composed of both wood pieces and air as the product width × height × length. Before determining a linear model linking wood mass and air-wood volume, it was necessary to confirm that there was no estimator bias. ...
Chapter
This chapter reviews statistical tools and illustrates their use to answer geomorphological questions, and also overviews their advantages and limits. Application of statistical tools in fluvial geomorphology has the advantages of reducing subjectivity, eliminating assumptions, facilitating comparison between different spatial and temporal datasets of large sizes and refining data collection. Bivariate statistics, and regressions in particular, have been one of the most popular statistical tools in geomorphology. They focus on the relationship, or correlation, between two variables. Probabilities are useful to generate models in which the variables of interest are categorical, such as indicator variables of events (e.g. occurrence of peak flows). One of the most basic tools dealing with probabilities is the logistic or multinomial models. To develop more realistic descriptions of fluvial morphological systems, process-response systems, time and space trends and size effects, requires the collection of sufficient data and more thought about their relevance.
... Here, each distinct wood deposit could be classified into one of the following categories: (i) "logs," being isolated, unbranched wood pieces N 1 m in length and 10 cm in diameter ( Fig. 2A); (ii) wood jams, which were heterogeneous mixtures of logs, branches, root boles, and twigs, sometimes with a considerable addition of fine organic matter and inorganic sediment (Fig. 2B); and (iii) "shrubs and whole trees," i.e., isolated and uprooted shrubs or trees with a large branch-to-trunk volume and three-dimensional structure (Fig. 2C). As the volume of wood contained in the two last types of deposits cannot be easily measured, the amount of wood stored in the river was assessed using the method developed by Thévenet et al. (1998) and allowing estimation of the mass of wood contained in the three types of wood deposits. This method was previously applied in the studies on two Alpine braided rivers, the Drôme (Piégay et al., 1999) and the Tagliamento (Gurnell et al., 2000a(Gurnell et al., , 2000b, which similar to the Czarny Dunajec drain deciduous riparian forests. ...
... lpejskich rzekach Drôme (Piégay i in. 1999) i Tagliamento (Gurnell i in. 2000). Umożliwia ona oszacowanie masy kłód, zwałów oraz krzewów i całych drzew przy znanej objętości tych form depozycyjnych drewna. W Finzbachu i Kamienicy zmierzono objętość kłód, a następnie obliczono ich masę, posługując się współczynnikiem gęstości właściwej 500 kg/ m 3 (Thévenet i in. 1998). ...
Article
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This study aims at determining whether the inverse relation between wood quantity per unit river area and channel width, recognised in streams of small and medium width, typifies also wide mountain rivers. This is done by comparing wood distribution for Finzbach and Kamienica Streams, 14 and 9 m in width on average, and the Czarny Dunajec River with mean width of 52 m. In both streams, the values of total wood storage were unrelated to channel width, whereas the increase in channel width was reflected in a pronounced decline in specific wood storage. In the wide Czarny Dunajec, a marked trend of increasing total wood storage with the increase in river width was observed. The width-related variation in total wood storage in the river was so high that it overcame the influence of increasing channel area on calculated values of specific wood storage, and this parameter also increased with increasing river width. The contrasting patterns of wood storage observed in the watercourses point to different mechanisms governing wood retention in the channels narrower and wider than the height of trees growing on their banks. Słowa kluczowe: gruby rumosz drzewny, depozycja drewna, ciek górski, szerokość koryta, całkowity ładunek drewna, jednostkowy ładunek drewna
... But large woody debris is also an important component of river systems, contributing to geomorphic processes (bank stabilisation, sediment retention, water flow processes, Gregory & Davis, 1992;Piegay et al., 2003;Gautier et al., 2000), and habitat diversity, and providing food resource and shelter for benthic macrofauna, fish and specialist mammals like beaver (Johnston & Naiman, 1987;Tabacchi et al., 2000). The amounts of coarse woody debris were, however, still modest compared with ancient forests (Harmon et al., 1986;Thevenet et al., 1998;Vandekerkove et al., 2009) and probably the Ain valley (Piegay & Gurnell, 1997;Lassettre et al., 2007), although a quantification of the woody debris along and within the river is lacking in the upper Moselle valley. ...
Article
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In this paper we present the woodland dynamics of the Moselle valley, upstream from Nancy in north-eastern France. The Moselle flow regime has been partly preserved, although the valley underwent extensive land-uses in the past, with two periods of abandonment of agriculture practices since the 1870s. In the 2377 hectares of the Natura 2000 zone, the surface areas of all woodland patches of more than 0.1 ha were quantified by GIS (Arcview 3.3R), on the scale of 1:50.000 from aerial photographs from 1950 and 2003. One hundred and thirty-six phytosociological surveys were performed on vascular plants, and abundance - dominance was estimated by eye using the phytosociological scale. Human impact (cuttings, plantations, presence of ancient orchards) was evaluated by field trip. Woodlands were separated into two categories of conservation: high (i.e. natural character of forest architecture) and low (with human impacts). From these data, we quantified the surface areas of each forest community defined by phytosociology, as well as their conservation value. Fallopia x bohemica Chrtek & Chrtkova and Impatiens glandulifera Royle were tested with regard to the following factors: forest type, shape (perimeter), size (surface area), and age (more or less than 50 years old), and the frequency of flooding. Data were analysed using the KruskallWallis test. The total forest surface was 546.6 ha, split into 397 patches of various areas (ranging from 0.1 to 16.6 ha). On the current wooded forest surface, 11.1% was less than 50 years old. Four forest types were identified: willow bush (Salicetum triandrae) and willow tree (Salicetum albae) forest communities, both on river banks close to the river; ash-alder (Pruno-Fraxinetum) on more elevated sites; and marsh alder (Alnetum glutinosae) in old channels. The total species richness was 126. Ash-alder patches were the richest in species, and the most complex in architecture when not influenced by human activities. Communities of high conservation value were found in all forest types but in lower proportion than those of lower conservation value (28.4 versus 71.6%, respectively). Compared with other floodplain forests of similar ecology in the Rhine plain, the woodlands of the upper Moselle valley were more fragmented, but more natural because of the lack of recent silvicultural activities. Their relative youth explains why they lack native species of trees and some geophytes that are typical of mid- or late successional stages. Willow forests showed greater invasion by exotic species, and younger forests were invaded to a greater extent than forests over 50 years old by Fallopia x bohemica Chrtek & Khrtkova and Impatiens glandulifera Royle. The increase of woodlands in willow stands can be considered as a sign of modestly successful recovery from long-term deforestation. Of course, these fallows will never return to pristine old-growth forests. They could be defined as "feral" or " dedomesticated" landscapes because succession processes will take different courses and different lengths of time compared with natural processes. Such "dedomesticated" landscapes would however provide interesting evolutionary perspectives for the long term and suggest the interest of research in the context of changing uses. Forests should be therefore allowed to continue their expansion so that the entire range of natural habitats, as well as novel habitats, are re-created and full functional links can be established between terrestrial and aquatic communities.
... Durante la campaña de toma de datos de campo, además de la clasificación de cada una de las acumulaciones identificadas, se midieron sus dimensiones geométricas (altura H J , ancho B J , y largo L J ) asumiendo una forma de paralelepípedo sólido (Thevenet et al. 1998). El volumen de cada acumulación leñosa se estimó a partir de sus dimensiones geométricas (V J = H J *B J *L J ) sin considerar su porosidad. ...
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This work reports on the geomorphic role of large wood pieces and jams in a third order mountain stream located in Southern Tierra del Fuego (Argentina), and draining an old-growth nothofagus forested basin not influenced by beaver damming activity. Even if the in-stream number of wood pieces (2,300) is comparable to that observed in other climatic areas, the slow growth of the nothofagus forest causes a lower wood abundance in terms of volumetric load (121 m3 ha–1). Due to the relatively small dimensions of the large wood pieces located inside bankfull edges (83% of the total surveyed pieces), almost the 70% of them demonstrated to have been transported by rain and 6% derived from bank erosion or landslides. Wood jams exert a significant influence on the channel morphology, being responsible for the creation of 30% of pools. The geomorphic influence of LW jams is also exerted by a considerable sediment storing capacity (about de 1.750 m3). The LW-forced pool volume is strongly and positively correlated to the height of the LW jam. The results confirm that dead wood pieces, especially when organized in jams, play an important geomorphic role also in sub-Antarctic streams. The amount of large wood pieces quantified in the study site represents eference values for the assessment of the geomorphic effects of beaver activity in other Tierra del Fuego streams.
Conference Paper
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Conference Paper
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River wood-debris are a major hazard to lives and infrastructures, because tons of wood material can travel nearing the speed of the flood-flow. If post-event mapping, detection and numerical simulation have made important progress, it is still impossible to detect the wood-debris as they travel, due to poor visibility conditions (rain, night…). The present work aims to solve this issue by adapting Ground Penetrating Radar as an electromagnetic imaging method for in-flow wood de-bris detection. Laboratory test over a water circulation flume using a 800 MHz nominal frequency antenna sampling at 100 Hz a set of single wood logs of 20 cm length has shown that the method had the potential to detect moving wood debris, and that it could “see” underneath to the flume floor. The experiments resulted in the ability to count wood debris travelling underneath the an-tenna, and instantaneous velocity were obtained with velocities ranging from 0.307 to 0.352 m/s, which slightly higher than the averaged velocity measured from video, due to the acceleration time when wood was introduced in the flume.
Technical Report
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Following the major and consecutive floods of 2010 and 2011, the managers of the Port-Daniel wildlife reserve observed the presence of a major large wood jam obstructing the channel in the downstream portion of the Port-Daniel River. The general objective was to analyze the dynamics of large wood in river in order to assess its impact on the geomorphological trajectory of the stream and on the salmon migration.The historical monitoring of the minor bed was carried out from temporal sequences of aerial photographs (1964, 1975, 1986 and 2001), orthophotographs (2004 and 2016), satellite imagery (2010, 2013, 2018) and UAV (2019). The modifications observed in the planimetric geometry of the minor bed made it possible to characterize the processes and morphological adjustments (lateral migration, avulsion, meander overlap) and to quantify the erosion (calculation of recession rates, eroded surface) for each period. The assessment of the woody balance was carried out over approximately 15 km of the river corridor of the Port-Daniel River. The large wood budget was made from LW inputs (estimated from surfaces eroded over time and volumetric density), LW in transit (measured in the river corridor in summer 2019) and output volumes (measured in the deltaic zone). Analysis of the results then made it possible to make a diagnosis based on the hydrogeomorphological characteristics in order to assess the geomorphological trajectory of the Port-Daniel River. The LW budget of the Port-Daniel River does not in any way indicate that the wood present in the river corridor, including the major jam observed following the 2010 and 2011 floods, constitutes a restriction for salmon migration. Salmon. In addition, analyzes and field observations have shown that the formation of these massive large wood jams contributed to the reconstruction of the alluvial plain and for channel stabilization.
Article
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Large wood is a key component of river channels that affects numerous hydrological, physical and geomorphological processes. It promotes a diversity of benthic habitats in-channel and has shown to support more abundant and diverse benthic macroinvertebrate assemblages in previous ecological studies. However, the effects of large wood on the structural and functional diversities of hyporheic invertebrates are less well studied, and simultaneous examination of these diversity metrics on hyporheic and benthic compartments of the stream bed has not been conducted previously. Therefore, this study investigates the taxonomic and functional diversities of hyporheic and benthic invertebrate assemblages around natural accumulations of large wood in a British lowland river. Taxonomic and functional diversities were partitioned (into alpha, beta, and gamma diversities) and examined in reaches with and without large wood (control). We found that functional diversity is often decoupled from taxonomic diversity, demonstrating a functional redundancy of the macroinvertebrate assemblage for both hyporheic and benthic zones. Moreover, the highest functional variability at alpha-scale was observed in large wood habitats, which suggests that taxonomic diversity is enhanced by the small-scale environmental heterogeneity around large wood. To this end, this study contributes empirical evidence of functional and structural responses of invertebrates to large wood accumulation. Such information could be used to better understand the ecological implications of restoration works in lowland rivers and guide more effective management strategies.
Thesis
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Sur la rivière Mont-Louis, les volumes de bois mort semblent en augmentation depuis quelques décennies. La présence de bois mort en rivière est reconnue pour ses effets sur l’écoulement de l’eau, la dynamique sédimentaire et le développement de la morphologie fluviale. L’objectif général qui oriente cette recherche vise à documenter les effets mutuels de la dynamique fluviale et la dynamique du bois mort à l’échelle d’un tronçon de cours d’eau d’environ 12 km. La distribution et l’évolution interannuelle des volumes de bois mort sont mises en relation avec la segmentation du cours d’eau en tronçons homogènes. Par la suite, les effets de trois embâcles géomorphologiquement actifs sur la topographie locale du lit du cours d’eau sont documentées afin de mettre en évidence les ajustements morphologiques mis en place par les rivières à lit graveleux en présence de bois mort. Enfin, la trajectoire hydrogéomorphologique du cours d’eau eau est analysée, et mise en relation avec la série temporelle des débits maximaux, l’occupation du sol et l’évolution des superficies boisées. Les résultats mettent en évidence que la distribution du bois mort est largement conditionnée par le style fluvial du cours d’eau. Quatre tronçons homogènes ont été définis, de l’amont vers l’aval, des tronçons linéaire, divagant, à méandres stables et estuarien. Les volumes de bois produits et accumulés sont largement supérieurs au sein du tronçon divagant, alors que les autres agissent à titre de zone de transport. Les relevés topographiques ont permis de montrer que même les petits embâcles de bois peuvent influencer la dynamique sédimentaire. L’analyse des superficies boisées et des débits historiques montrent que les sources de bois sont en augmentation depuis les années 1980 et que des périodes de crues majeures sont généralement suivies de périodes de débits moyen ou faible. Il est donc proposé que de grands volumes de bois sont recrutés durant les périodes de crues et que les crues moyennes les dispersent en de nombreux embâcles de petits volumes et que l’effet morphologique du bois est maximal lors de ces périodes de débits moyens. L’utilisation de la trajectoire écogéomorphologique est finalement mise de l’avant comme un nouvel indicateur permettant de projeter les ajustements morphologiques du cours d’eau en présence de bois mort.
Article
Large wood (re)introduction can deliver multiple benefits in river restoration, but there is a dearth of the detailed and longer‐term post‐project monitoring and evaluation required for improving best practice. We present findings from an academic partnership approach to post‐project evaluation, based on successive MSc research projects on restored large wood in the Loddon catchment, UK. Field and modelling data reveal: (i) key differences in large wood features between restored and natural reaches; (ii) increased hydraulic retention and changes to mesohabitats associated with large wood; (iii) differences in macroinvertebrate community composition around large wood but a lack of site‐level effects; (iv) interactions between macrophytes and large wood that may be specific to restored reaches; (v) a need for further field and modelling studies to inform the accurate representation of large wood in hydraulic models. Some key challenges in partnership working are identified to aid planning and effectiveness of future collaborations.
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The aim of this paper is to present the possibilities of UAVs (Unmanned Aerial Vehicles) as photogrammetry payload carriers for data acquisition and fluvial landform identification and mapping. The manual and automatic classification of the Belá River riparian zone for landscape object identification and the analyses of the point cloud density after vegetation filtration was performed. The HEXAKOPTER XL including the Sony NEX 6 camera with 16 – 50 mm lens for landscape monitoring features was used. Data was processed in Agisoft PhotoScan software. The RMSE (root mean square error) of aligned images was 60.121 mm (x coordinate), 43.7584 mm (y coordinate) and 29.46 mm (z coordinate). The resulting point cloud was semiautomatic classified in the software Terrasolid – Terrascan (Microstation), in the following six classes: high vegetation (over 5 m), medium vegetation (from 1.5 m to 5 m), small vegetation (from 0.2 m to 1.5 m), topographic surface and water surface. Orthophotomosaic was classified in ArcGIS software by supervised Maximum Likelihood Classification (MLC). Here training site signatures identified the five land cover categories (water area, bar surface, vegetation, Large Woody Debris – LWD and bare surface). The classification of photogrammetric derived point clouds increases the accuracy elevation model, but on the other hand, does not capture the real terrain and topography under the vegetation.
Method
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A line-transect method for quantifying the volume of large wood in streams. See: Handbook for evaluating rehabilitation projects in rivers and streams
Article
A great variety of terms and threshold values are used in the German literature to name and define wood in streams and rivers, limiting the comparability of results and complicating communication between various disciplines. It therefore seems necessary to unify the use of terms that refer to wood in streams. The nomenclature of wood in streams presented in this paper has been developed on the basis of comprehensive discussions with stream ecologists, hydraulic engineers, foresters and anglers. That large 'dead wood' should be named 'Totholz' in German was beyond dispute. Congruent with common international threshold values, 'dead wood' is classified in two sub-classes called 'fine wood' (1 cm ≤ ∅ < 10 cm) and 'coarse wood' (∅ ≥ cm). Thus the diameter of 'dead wood must always exceed 1 cm. Material less than 1 cm in diameter belongs to the class 'litter'. 'Litter' can also be further broken down into two sub-classes: 'loopings' (woody material, ∅ < 1 cm) and 'leaves' (non-woody material). The 'leaves' classification is not defined by diameter, and thus includes material over 1 cm in diameter. 'Dead wood' in streams can be described and named unambiguously using the nomenclature presented and the 'influence zones' defined by Robison and Beschta (1990a).
Article
Heavy downpours and continuous rainfall accelerate denudation processes on slopes as well as erosion and accumulation processes on the valley bottoms [Zietara 1968, Słupik 1981, Starkel 1996, Gil 1998, Cebulak i in. 2008]. The intensity of floods and their geomorphological effects depend not only on the amount and duration of rainfall, but also on its intensity and spatial extent. Based on observations of precipitation L. Starkel [1976, 1986] distinguished three types of rainfall: local downpours, continuous rainfall and rainy seasons. The heavy downpours overlapping with continuous rains that can last for several days are a frequent phenomenon. Such a situation took place in May 2010 in southern Poland. The paper presents the role of rainfall and floods in relief transformation of a small catchment on the example of the Suszanka stream. The study was conducted in the catchment of the Great Suszanka (Suszanka), situated in the southern part of the Beskid Średni Mts. (Polish Carpathians). Total area of Suszanka catchment is 15.7 km 2. The Suszanka stream originates on the slopes of Mt łysina (897 m a.s.l.) and joins the Raba river close to Pcim, at 330 m a.s.l. It has three left-bank tributaries (a stream without name, Średnia Suszanka and Mała Suszanka). In the upper reach, the Suszanka stream is deeply incised into the Magura Flysch with numerous bedrock steps [Wojcik, Raczkowski 1994, Margielewski i in. 2010]. In the more resistant material, the width of the bed is between 0.5 and 4 m and the width increases to about 55 m downstream. In the widest part of stream, braided channel occurs. The effects of rainfall from 15-18 May 2010 was studied on the basis of field survey conducted in May and June 2010, and air photo analysis (1:26 000, 2009), in order to compare selected reaches of the Suszanka stream with the situation in 2009, prior to the flood, and after the flood (2010). The flood wave had culmination of about 2 m, which caused transformation of the Suszanka stream channel. In the upper section of the stream downcutting occurred, exposing rocky bottom. In the middle and lower reach of the stream lateral erosion dominated, causing rejuvenation of past erosion undercuts and leading to the origin of new ones. The total length of bank undercuts along the Suszanka stream was 455.08 m on the right side and 839.12 m on the left side. The longest stretch of continuous left bank undercutting reached 305 m. Gravel bars were also simultaneously incised and built-up in the middle part of stream. Area of gravel bars was transformed. The flood water changed single-tread channel into the braided one. At the low water level dry channels within the gravel bars area could have been seen. During the flood the Suszanka stream destroyed roads, bridges and other technical infrastructure.
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Abundance of woody debris was manipulated in a small Illinois stream to determine the importance of this material to fish. When a stream reach was divided along midchannel, and debris was added to one side, but removed from the other, fish and benthic invertebrates were usually more abundant on the side with woody debris than on the cleared side. In further experiments during a low-flow year (1980), debris removal was followed by rapid decreases in water depth and occurrence of benthic organic litter, and increases in current velocity and proportion of sand bottom. These changes were less apparent in unaltered reaches during 1980, and in all reaches during 1981, which was a high-flow year. Artificial debris was colonized by many invertebrates, including chironomids, trichopterans, and ephemeropterans. Most large fish (age 2+) avoided reaches without debris, whereas some smaller fish (such as johnny darter) preferred them; preferences for reach treatments were stronger in 1980 than in 1981. The adaptive significance of associations between fish and woody debris appeared more closely related to the advantages of camouflage than those of increased food availability or protection from strong currents. Extensive removal of woody debris may disrupt structure and function in small streams, especially low-gradient ones. If the biological integrity of stream resources is to be maintained despite agricultural and urban uses, less disruptive management protocols will need to be employed.
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Numbers of juvenile coho salmon in streams are reduced substantially in winter compared to those that occur in summer. Most of this reduction occurs early in autumn and onset of the first seasonal freshets. Stream sections containing adequate winter habitat in the form of deep pools, log jams, and undercut banks with tree roots and debris lost fewer fish during freshets and maintained higher numbers of coho in winter. These features provide shelter and reduce stream velocities. Microhabitats occupied by coho juveniles in winter after logging were unchanged from those described before logging - all micro habitats were characterized by low water velocities (= or <0.3 m/s). Up to 48% of the coho population inhabiting stream sections with adequate shelter remained there by midwinter. This percentage was typical of stream sections where at least some trees remained after logging. Streamside trees stabilized the banks and prevented their collapse.-from Authors
Article
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The ash-free dry mass of in-channel woody material was 6.5 kg/m2 of stream channel bottom in the 6th-order Ogeechee River and 5.0 kg/m2 in the 4th-order Black Creek. Most wood is located near the erosional bank in these meandering streams. These wood mass estimates are much higher than expected for middle-order streams and are similar to those from several small headwater streams in other regions. Due to their very low slopes (<0.02%), these streams appear to have insufficient stream power to move large wood material. Snag, or woody, habitat is the major stable substrate in these sandy-bottomed streams and is a site of high invertebrate diversity and productivity. In-channel snag surface area per square metre of channel bottom was 0.249-0.433 m2 in the Ogeechee and 0.191-0.379 m2 in Black Creek. With invertebrate biomass of 6.6 g dry mass/m2 of snag surface, this results in an invertebrate biomass of at least 1.88 g/m2 of channel bottom. Wood is also important to fishes, providing a rich source of invertebrate food, habitat and cover. Wood enhances the ability of a stream to process and conserve nutrient and energy inputs and has a major influence on the hydrodynamic behavior of the river.-from Author
Article
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Coarse woody debris (CWD) is an important component of temperate stream and forest ecosystems. This chapter reviews the rates at which CWD is added and removed from ecosystems, the biomass found in streams and forests, and many functions that CWD serves. CWD is added to ecosystems by numerous mechanisms, including wind, fire, insect attack, pathogens, competition, and geomorphic processes. Despite the many long-term studies on tree mortality, there are few published rates of CWD input on mass-area-1 time-1 basis. CWD is significantly transformed physically and chemically. Movement of CWD, especially in streams, is also an important but poorly documented mechanism whereby CWD is lost from ecosystems. Many factors control the rate at which CWD decomposes, including temperature, moisture, internal gas composition of CWD, substrate quality, size of CWD, and types of organisms involved. However, the importance of many of these factors has yet to be established in field experiments. CWD performs many functions in ecosystems, serving as autotrophic and heterotrophic habitat and strongly influencing geomorphic processes, especially in streams. It is also a major component of nutrient cycles in many ecosystems and is an important functional component of stream and forest ecosystems.
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Transfer of large woody debris (>10 cm diameter) from old-growth Douglas-fir (Pseudotsugamenziesii (Mirbel) Franco) forests into five first-to fifth-order stream reaches (drainage areas of 0.1 to 60.5 km2) has ranged from 2.0 to 8.8 Mg•ha−1•year−1 in 7- to 9-year study periods. Amounts of large debris in these streams range from 230 to 750 Mg•ha−1 with generally lower values in larger channels. The addition of woody debris is widely scattered in time and space and comes mainly from single trees rooted away from the streambank. We infer that wind is a major agent for entry of wood into these streams. Downstream movement of debris is strongly related to length of individual pieces; most pieces that moved were shorter than bankfull width.
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Unconfirmed Quercus prinus woody litter of three size classes (0-1, 1-3. and 3-5 cm diameter) was placed on forest floors of a control hardwood watershed and on mesic and xeric sites of a clear-cut watershed at Coweeta Hydrologic Laboratory, North Carolina. Exponential decay coefficients for mass loss on the control were ,1524, .1728, and .0912 yr~' for 0-1, 1-3, and 3-5 cm branches, respectively. Coefficients for 0-1, 1-3, and 3-5 cm branches were .1752, .0756, and .1644 yr"1 on the mesic site and .0456, .0948, and .0377 yr~' on the xeric site. The effect of site differences on decomposition rate was greater than the effect of diameter, although an inverse relationship be- tween diameter and decay coefficient is suggested. Time in the field, temperature, moisture, and microarthropod abundance also appeared to influence decomposition rate. Microarthropods dominated the animal community on decaying wood with oribatid mites and collembolans the most numerous. Microarthropod densities were highest on 0-1 cm twigs and lowest on 3-5 cm branches. Microarthropod densities were generally highest on the control, slightly de- pressed on the mesic site, and greatly depressed on the xeric site. Time in the field and state of decomposition both positively correlated with microarthropod abundance. Calcium concentration and total calcium exhibited transitory increases but little net change at the end of 1 yr in experimental branches. Total potassium decreased on all sites for 6 mo and for 12 mo on the control and xeric sites, with =60% remaining after 1 yr. Total potassium increased rapidly on the mesic site over the last 6 mo and reached 110% of the initial amount. Temperature, moisture, microbes, and microarthropods appeared to control nutrient dynamics. Woody litter dynamics were more important in terms of nutrient conservation on the clear-cut watershed than on the control and contributed to the resilience of the system. Removal or destruction of woody debris after clear-cutting would decrease the nutrient conservation properties of decaying wood and would probably contribute to watershed output of nutrients.
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ABSTRACT The influence of woody,debris on channel morphology,and aquatic habitat has been recognized,for many,years. Unlike sediment, however, little is known about how wood moves through river systems. We examined some dynamics of wood transport in streams ,through ,a series ,of flume ,experiments ,and ,observed ,three distinct wood ,transport regimes: uncongested, congested and semi-congested. During uncongested transport, logs move without piece-to-piece interactions and generally occupy less than 10per cent of the channel area. In congested transport, the logs move together as a single mass and occupy,more,than 33 per cent of the channel area. Semi-congested transport is intermediate between,these two transport regimes. The type of transport regime was most sensitive to changes in a dimensionless input rate, defined as the ratio of log ,volume ,delivered to the ,channel per second ,( Qlog) to discharge (Qw); this ratio varied between ,0·015 for uncongested,transport and 0·20 for congested,transport. Depositional fabrics within stable log jams varied by transport type, with deposits derived from uncongested and semi-congested transport regimes having a higher proportion of pieces oriented normal,to flow than those derived from congested,transport. Because wood,input rates are higher and channel dimensions decrease relative to piece size in low-order channels, we expect congested transport will be more common in low-order streams while uncongested,transport will dominate,higher-order streams. Single flotation models,can be used to model the stability of individual pieces, especially in higher-order channels, but are insufficient for modelling the more complex interactions that occur in lower-order streams. © 1997 by John Wiley & Sons, Ltd. Earth surf. process. landforms, 22, 669‐683 (1997)
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Abundance of woody debris was manipulated in a small Illinois stream to determine the importance of this material to fish. When a stream reach was divided along midchannel, and debris was added to one side, but removed from the other, fish and benthic invertebrates were usually more abundant on the side with woody debris than on the cleared side. In further experiments during a low-flow year (1980), debris removal was followed by rapid decreases in water depth and occurrence of benthic organic litter, and increases in current velocity and proportion of sand bottom. These changes were less apparent in unaltered reaches during 1980, and in all reaches during 1981, which was a high-flow year. Artificial debris was colonized by many invertebrates, including chironomids, trichopterans, and ephemeropterans. Most large fish (age 2+) avoided reaches without debris, whereas some smaller fish (such as johnny darter) preferred them; preferences for reach treatments were stronger in 1980 than in 1981. The adaptive significance of associations between fish and woody debris appeared more closely related to the advantages of camouflage than those of increased food availability or protection from strong currents. Extensive removal of woody debris may disrupt structure and function in small streams, especially low-gradient ones. If the biological integrity of stream resources is to be maintained despite agricultural and urban uses, less disruptive management protocols will need to be employed.
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An experiment was conducted in a small ice-free stream in southern Ontario to test the volitional responses of wild, stream-dwelling brook trout Salvelinus fontinalis and brown trout Salmo trutta to artificial cover during winter. Underwater observations indicated that both species preferred holding positions beneath submerged cover structures rather than under above-water structures or uncovered control forms. Trout used cover in riffle and pool habitats with similar frequency, probably due to the accumulation of organic debris on riffle structures that produced low-velocity pockets where fish often positioned themselves. Addition of cover to streams with stable flows is likely to enhance overwinter survival of trout.
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A functional account of log steps in forest streams is provided by field surveys of 163 kilometers of streams in the Central Oregon Coast range. Natural treefall, rather than silvicultural activities, accounts for the majority of log steps. During low-flow conditions, dissipation of potential stream energy by log steps amounts to 6 percent, approximately equal to that by falls. There are no statistical significant differences regarding spatial distribution of log steps between study basins with contrasting silvicultural and natural inputs of large woody debris. However, significant spatial differences are revealed between streams of various orders, a finding that points to channel flushing capacity and stream-adjacent topography as dominant controls on log step development. Application of thermodynamic principles to stream systems demonstrates that neither falls not log steps cause a statistically significant difference in equilibrium conditions of stream networks. The volume of sediment stored behind log steps in third-, fourth-, and fifth-order streams is 123 percent of the mean annual sediment discharge (suspended load and bed-load). Depriving some streams of log steps by stream clean-out or repeated harvest of stream-adjacent trees may initiate an episode of progressive erosion by not dissipating stream energy in excess of what is needed to transport imposed sediment supplies. Addition of log steps to streams with energy already sufficient to balance sediment inputs and outputs may only serve to accentuate progressive deposition. Function of large woody debris not incorporated as log steps must also be addressed in forest management decisions.
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The line-intersect technique was used to measure the loading of large woody debris in a 1 .8 km reach of the Thomson River, Victoria (catchment area of 3540 km 2). A debris census (measuring every item present) was done over 0 .775 km of this reach. The transect technique overestimated the actual loading revealed by the census. The loading of debris >0 .01 m in diameter for the total 1 .8 km reach was 0 .0172 m 3 m-2 , which is higher than that measured in many headwater streams in other parts of the world. The volume loading of debris measured from low level aerial photographs was only 4 .8% of the value estimated by the line-intersect technique. The line-intersect estimates were biased due to non-random orientation of debris in the stream (causing estimated errors of +8% for volume loading and +16% for surface area loading). It is recommended that to avoid this problem, when using the line-intersect transect technique in lowland rivers, each line should comprise at least two obliquely-angled transects across the channel. The mean item of debris (>0 .1 m in diameter) had a trunk basal diameter of 0 .45 m, a length of 7 .4 m, and volume of 0 .7 m3. The riparian trees and the in-channel debris were of similar dimensions. The debris tended to be close to the bed and banks and was oriented downstream by the flow at a median angle of 27°. Because of this orientation, most debris had a small projected cross-sectional area, with the median value being only 1 m 2. Thus, the blockage ratio (proportion of projected area of debris to channel cross-sectional area) was also low, ranging from 0 .0002 to 0.
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Beaver (Castor canadensis) impoundments are used to illustrate the effect of large animals on the boundary dynamics of patch bodies, volumetric landscape units which have surficial boundaries with upper and lower strata, and lateral boundaries with adjacent patches within the same stratum. Patch bodies created by beaver impoundments include the beaver pond, the aerobic soil beneath the pond, and the underlying anaerobic soil. Beaver herbivory in the riparian zone creates an additional patch body concentric to the pond. Beaver and water are the primary biotic and abiotic vectors mediating fluxes across lateral patch body boundaries; vegetation and microbes are the primary biotic vectors mediating fluxes across surficial patch body boundaries. Basin geomorphology affects the permeability of pond boundaries (i.e., their ability to transmit, energy and materials) by affecting the kinetic energy of water, the surface-to-volume ratio of the impoundment, and the movement of beaver between the pond and the riparian foraging zone. We suggest that: (1) permeability of lateral boundaries to abiotic vectors is a function of kinetic energy; (2) within-patch retention of particulate matter transferred by abiotic vectors across lateral boundaries is maximized by a decrease in kinetic energy; (3) lateral patch boundaries between safe refuge and a resource used by an animal vector are most permeable when they are narrow; and (4) total amount of energy and materials transferred across surficial boundaries is maximized by increasing surface area.
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Develops a standard way of measuring stream, riparian, and biotic conditions and evaluates the validity of the measurements recommended. Accuracy and precision of most measurements are defined. This report will be of value to those persons documenting, monitoring, or predicting stream conditions and their biotic resources, especially those related to impacts from land uses. -Authors
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Field surveys document the accumulation of large woody debris (LWD) into structurally distinctive jam types in the alluvial channel of the Queets River on the Olympic Peninsula of north west Washington. Calculations, field observations and historical evidence show that these jams can form stable structures controlling local channel hydraulics and providing refugia for riparian forest development over decades and possibly centuries. Distinctive spatial patterns of LWD, pools, bars and forested islands form in association with particular jam types. The deposition of 'key member' logs initiates the formation of stable bar apex and meander jams that alter the local flow hydraulics and thereby the spatial characteristics of scour and deposition leading to pool and bar formation. Historical evidence and the age structure of forest patches documents the temporal development of alluvial topography associated with these jam types. Bar apex jams, for example, are associated with a crescentic pool, an upstream arcuate bar and a downstream central bar that is the focus of forest patch development. Experimental and empirical studies in hydraulic engineering accurately predict channel scour associated with jams. Individual jams can be remarkably stable, providing long-term bank protection that creates local refugia for mature forest patches within a valley floor environment characterized by rapid channel migration and frequent disturbance. Processes controlling the formation, structure and stability of naturally occurring LWD jams are fundamental to the dynamics of forested river ecosystems and provide insights into the design of both habitat restoration structures and ecosystem-based watershed management.
Article
Removal of all organic debris dams from a 175-m stretch of second-order stream at the Hubbard Brook Experimental Forest in New Hampshire led to a dramatic increase in the export of organic carbon from this ecosystem. Output of dissolved organic carbon (<0.50 @mm) increased 18%. Fine particulate organic carbon (0.50 @mm-1 mm) export increased 632% and coarse particulate organic matter (>1 mm) export increased 138%. Measurement of the standing stock of coarse particulate organic matter on streambeds of the Hubbard Brook Valley revealed that organic debris dams were very important in accumulating this material. In first-order streams, debris dams contain nearly 75% of the standing stock of organic matter. The proportion of organic matter held by dams drops to 58% in second-order streams and to 20% in third-order streams. Organic debris dams, therefore, are extremely important components of the small stream ecosystem. They retain organic matter within the system, thereby allowing it to be processed into finer size fractions in headwater tributaries rather than transported downstream in a coarse particulate form.
Article
This paper reviews the form, function, and management of woody debris in streams, and reaches three major conclusions: (1) Large woody debris enhances the quality of fish habitat in all sizes of stream. Removal of most trees in the riparian zone during logging, combined with thorough stream cleaning and short-rotation timber harvest, h as altered the sources, delivery mechanisms, and redis- tribution of debris in drainage systems, leading to changes in fish population abundance and species composition. (3) There is an urgent need for controlled field experiments and long-term studies t hat focus on the protection of existing large woody debris in stream channels and the recruitment of new debris from the s urrounding forest. logjams that could block river navigation, water-based log transport, and the upstream passage of salmon and trout on their way to spawning grounds, but is now understood to play an important role in the crea- tion and maintenance of fish habitat throughout entire rivers. Although wood itself eventually enters the food web of the stream ecosystem as it gradually decays, the major importance of debris lies in its structural characteristics and the way these features influence channel hydraulics. Physical processes associated with debris in streams include the forma- tion of pools and other important rearing areas, control of sediment and organic matter storage, and modification of water quality. Biological properties of debris-created structures can include blockages to fish migration, provision of cover from predators and from high streamflow, and maintenance of organic matter processing sites within the benthic community. The locations and principal roles of woody debris change throughout the river system. In steep headwater streams where logs span the channel, debris creates a stepped longitudinal profile that governs the storage and release of sediment and detritus, a function that facilitates the biological processing of organic inputs from the surrounding forest, When the stream channel becomes too wide for spanning by large logs, debris is deposited along the channel margins, where it often forms the most productive fish habitat in main-stem rivers. In all but the smallest streams there is some degree of clump- ing, although the size and spacing of debris clumps generally increase in a downstream direction, Debris-related fish habitat can be found anywhere in small forested streams. In large rivers it is primarily Woody debris h as long been considered a potential source of
Article
Une forêt inondable, bien différente de celle observée dans la zone intertropicale, se développe sur les marges des cours d'eau des plaines alluviales de la zone tempérée. Un lien fonctionnel très fort existe notamment entre le chenal et les marges boisées des hydrosystèmes de piémonts et de plaines intra-montagnardes. Ces forêts constituent une mosaïque végétale extrêmement diversifiée et présentent des intérêts à la fois sociaux et économiques. La ripisylve organise le paysage de fond de vallée, modifie l'hydraulique et le transit des sédiments et de la matière organique. Ces forêts sont des milieux récents. Développées dès les XVIIIe et XIXe siècles sur les rivières intra-alpines, elles colonisent seulement entre 1945 et 1970, les marges des rivières de piémont à la suite de leur abandon par les communautés agricoles riveraines. Bien que ces espaces soient récents, ils apparaissent en danger. De plus en plus déconnectés, morcelés, ces milieux originaux risquent de n'être qu'éphémères à l'échelle du siècle. Zones humides à part entière, les forêts d'inondation méritent l'attention des gestionnaires. Leur conservation est de plus en plus affirmée. Des actions de réhabilitation sont mises en œuvre sur des tronçons particulièrement dégradés. Une politique d'entretien, organisée et sectorisée, se développe progressivement. Les interventions sont graduelles en réponse à la variation amont aval de la vulnérabilité et de la qualité écologique du corridor.
Article
Coarse woody debris (>0.2m in diameter, 1.5m long) was measured along undisturbed low-gradient stream reaches. Average debris length, diameter and volume per piece increased with stream size. Eighty percent of debris volume of the 1st order and the smaller 2nd order streams was suspended above or lying outside the bankfull channel, while <40% was similarly positioned in the 4th order stream. About 1/3 of all debris was oriented perpendicular to stream flow. Tree blowdown had a major influence on debris distribution along the smaller stream reaches. Debris jams and accumulations in the largest stream were formed from floated debris. -from Authors
Article
Publisher Summary This chapter reviews the rates at which Coarse Woody Debris (CWD) is added and removed from ecosystems, the biomass found in streams and forests, and many functions that CWD serves. CWD is an important component of temperate stream and forest ecosystems and is added to the ecosystem by numerous mechanisms, including wind, fire, insect attack, pathogens, competition, and geomorphic processes. Many factors control the rate at which CWD decomposes, including temperature, moisture, the internal gas composition of CWD, substrate quality, the size of the CWD, and the types of organisms involved. The mass of CWD in an ecosystem ideally represents the balance between addition and loss. In reality, slow decomposition rates and erratic variations in input of CWD cause the CWD mass to deviate markedly from steady-state projections. Many differences correspond to forest type, with deciduous-dominated systems having generally lower biomass than conifer-dominated systems. Stream size also influences CWD mass in lotic ecosystems, while successional stage dramatically influences CWD mass in boat aquatic and terrestrial settings. This chapter reviews many of these functions and concludes that CWD is an important functional component of stream and forest ecosystems. Better scientific understanding of these functions and the natural factors influencing CWD dynamics should lead to more enlightened management practices.
Article
The distribution and lignocellulolytic activity of the microbial community on a Douglas fir log (Pseudotsuga menziesii) was studied in a Pacific Northwest stream. Microbial colonization and lignocelluloytic activity was shown to be a surface phenomenon. Incubations of (¹⁴C)lignocelluloses and wood samples in a mineral salts medium showed no increase in ¹⁴COâ evolution over incubations in distilled water. Subsequent incubations revealed KNOâ was most favorable to decay. Decomposition of (¹⁴C)lignocelluloses was greatest when incubated in stream water collected from four different sources than in distilled water. Phosphate and nitrate additions alone and in combination to a stream water medium yielded increases in (¹⁴C)cellulose decay, whereas (¹⁴C)lignin decomposition responded only to both in combination. The organic nitrogen in the lignocellulose/wood sample mixture increases two-fold over the first 6 days. (¹⁴C)lignocellulose decomposition rates were greatest during the first 6 days, then diminished over the remaining 12 days, as did the rate of overall respiration. By 18 days, the ¹⁵N enrichments of the filtrate NHâ/sup +/, the organic fraction, and the inorganic nitrogen associated with the organic fraction had all increased to 20% ¹⁵N. Nitrogen fixation and denitrification measurements indicated insignificant gain/or loss of nitrogen from the incubations by these processes.
Article
With the use of a generalisation of the theory of single-stage line intersect sampling, estimators for population total per unit area and variance are derived for the case of line intersect three-stage sampling. In this case line intersect sampling is followed by two further stages of sampling: a sample from the intersecting first-order elements and a sample from the second-order elements that constitute the latter. Estimators for two types of two-stage sampling follow as special cases. The techniques developed may reduce costs or make sampling feasible in cases where single-stage line intersect sampling is impractical. Forest Sci. 20:129-133.
Article
A line sampling technique has been evolved for the assessment of logging waste remaining after clearfelling operations. The method was developed to obtain economically acceptable estimates of volume by reducing the amount of measurement of waste pieces required by conventional plot sampling. The method is described and the underlying theory presented. Its applicability is illustrated by the results of field trials carried out in the Kaingaroa State Forest, New Zealand, in connection with the sale of Pinus radiata to a large integrated pulp and paper plant.
Article
A method for estimating wood volume on the ground is described. It requires only a diameter tally of pieces intersected by a sample line, and application of a simple formula. Theory for the formula is presented, and practical application discussed. The effect of bias in orientation of wood pieces can be largely overcome by running sample lines in two or more directions. The method was demonstrated indoors with match splints scattered on a 54-inch square and tested on a 20-acre cutover area. It has potential value for measuring fuel quantities in fire research.
Article
Effects of logging on preferred winter habitats of juvenile salmonids in southeastern Alaskan streams were assessed by comparing the area of preferred winter habitat in 54 reaches of 18 streams. Three types of streams were sampled at each of six locations: a stream in a mature, undisturbed forest; a stream in a clear-cut area but logged on at least one bank; and a stream in a clear-cut area with strips of forest (buffer strips) along the stream bank. To identify preferred winter habitats, we classified stream areas in 12 of 18 streams into discrete habitat types and compared the density of salmonids within these habitat types with average density of the entire reach. Most wintering coho salmon (Oncorhynchus kisutch), Dolly Varden (Salvelinus malma), and steelhead (Salmo gairdneri) occupied deep pools with cover (i.e., upturned tree roots, accumulations of logs, and cobble substrate). Riffles, glides, and pools without cover were not used. Seventy-three percent of all pools were formed by large organic debris. Reaches in clear-cut areas without buffer strips had significantly less area of pool habitat than old-growth reaches. Buffer strips protected winter habitat of juvenile salmonids by maintaining pool area and cover within pools. In some cases, blowdown from buffer strips added large organic debris to the stream and increased the cover within pools.
Article
Coarse woody debris (CWD) has been examined in a section of the Ain, a sixth order piedmont river with an actively meandering channel and a wooded floodplain. The spatial distribution of CWD, its mass and forms of accumulation are controlled by the hydrodynamics and the retention capacity of the forest. A typology shows the relative importance of woody debris in the mosaic of patches and the essential role of the ecotonal zones. The mass of debris varies from 0001 t ha−1, to more than 200t ha−1, but is lower than those observed in certain American rivers. Most of the material is deposited in the margins and forms a narrow debris line.The restocking in woody debris is recent in Europe and tends to diversify the environment. This affects the researcher and the planner. The first considers this transit of material as a useful hydromorphodynamic and biodynamic tool which is easy to evaluate, and the second considers it as a restoring and generative vector, the ecological functions of which are recognized. Its effect is stronger today as the watershed area tends to be subjected to a decrease in agricultural activity.
Article
The behaviour and form of, and bedload sediment transport through, a 3.5 m wide forest stream have been monitored for nearly three years. Bedload transport is highly episodic and spatially variable, and is controlled less by water discharge than by sediment availability. Organic debris in the channel creates temporary base levels and sites at which coarse sediment may remain stored for long periods; collapse or disruption of log and debris jams makes sediment available for transport in only a small proportion of the runoff events that are actually competent to move the material. Even then, sediment travels only a short distance before being redeposited, frequently behind debris accumulations further downstream. Rates of sediment transport during a given runoff event can vary markedly over short distances along the stream, again depending on whether sediment was made available for transport by log jam collapse upstream. Organic debris is therefore a major constraint on the application of physical laws and theories to explaining sediment movement in, and the morphology of, this stream.
Article
Although river channel management now generally uses soft rather than hard engineering techniques the considerable research achieved for woodland river channels has not been completely collated with reference to management implications. Research results from 22 research papers show how debris dams have a significant influence upon the morphological, the process and the ecological aspects of channels; vary in their permanence, and differ in stability according to the overall organic matter budget. A summary diagram contrasts the impact of dams on river channel morphology, process and ecology before and after dam removal. Four major types of specific recommendation about the management of channels in woodland areas are identified from 29 research papers are that (1) management should be undertaken against a background knowledge of the behaviour of coarse, woody debris under natural conditions and that the organic matter budget should be disturbed as little as possible; (2) logging operations should minimize the amount of disturbance to, and disruption of, channel processes; (3) management should optimize the maintenance of habitat diversity and minimize the ecological disturbance to the channel; (4) in some areas specific management practices may require the introduction of new material into the channel. These recommendations are applied to the New Forest, southern U.K., which has a long history of clearance and management of coarse woody debris and where the requirements for clearance in relation to fish, drainage, and aesthetic impact can be achieved by minimizing the amount of removal of material from the river channel. In managing channels with debris dams in woodland areas, it is desirable to work with the river in a holistic basin context.
Article
The physical science of fluvial geomorphology is flawed because it ignores processes that are not easily quantifiable and physically or statistically manipulable. The influence of vegetation on river behaviour and fluvial geomorphology is a set of these processes. Vegetation may exert significant control over fluvial processes and morphology through five mechanisms: flow resistance, bank strength, bar sedimentation, formation of log-jams, and concave-bank bench deposition. Examples of these mechanisms, largely drawn from the Squamish River in British Columbia, are presented, and implications for future research are briefly discussed. La science physique de la géomorphologie fluviale manque de précision du fait qu'elle ne tient pas compte des processus qui ne sont pas facilement quantifiables et matériellement ou statistiquement traitables. L'influence de la végétation sur le régime des rivières et la géomorphologie fluviale constitue un ensemble de tels processus. La végétation peut exercer un contrôle significatif des phénoménes fluviaux et de la morphologie fluviale à partir de cinq mécanismes de base: la résistance au courant, la solidité des rives, les couches de sédimentation, la formation de barrages de détritus végétaux, et les dépôts sur les parties concaves des rives. Des exemples de ces mécanismes à partir de l'étude de la rivière Squamish en Colombie brittanique sont ici présentéd, et les implications en ce qui concerne la recherche future sont discutées.
Article
Examines the legislative framework and revised methods of management and impact assessment. Covers the physical and biological impacts of river channelization, as well as the repercussions downstream in the adjacent floodplain. Reviews revised procedures and designs which minimise harsh environmental impacts, and the prospects for environmentally sensitive river management. -from Publisher
Article
Thesis (M.S.)--University, of Washington, 1985. Includes bibliographical references (leaves [98]-102).
Measurement of turnover of biomass and nutrient elements from the woody component of forest litter on Walker Branch Watershed', East. Deciduous For
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Harris, W.F., Henderson, G.S., and Todd, D.E. 1972. 'Measurement of turnover of biomass and nutrient elements from the woody component of forest litter on Walker Branch Watershed', East. Deciduous For. Biome. Memo. Rep. 72-146. Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA.
La forêt d'inondation des rivières à haute énergie, un patrimoine écologique à gérer
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Piégay, H. 1996. 'La forêt d'inondation des rivières à haute énergie, un patrimoine écologique à gérer', Ann. Géogr., 590, 347 -368.
Large organic debris and anadromous fish habitat in the Coastal Redwood Environment: the hydrologic system
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Keller, E.A. and MacDonald, A. 1983. 'Large organic debris and anadromous fish habitat in the Coastal Redwood Environment: the hydrologic system', Technical Completion Report, University of California, Office of the Director, California Water Resources Center.
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Matson, K.G. and Swank, W.T. 1984. 'Carbon dioxide fluxes from conventional and whole tree harvested watersheds -effects of woody residue', Bull. Ecol. Soc. Am., 65, 123.
Quantification of submerged wood in a lowland Australian stream system
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Citterio, A. 1996. 'Dynamique de prise en charge et de dépô t des débris ligneux dans les systèmes Ain et Drô me', Mémoire de Maîtrise, Université Lyon III, France, 72 pp.
Les ripisylves et les crues dans la France de sud-est: de l'histoire à la gestion contemporaine
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Piégay, H., Bravard, J.P., and Dupont, P. 1994. 'Les ripisylves et les crues dans la France de sud-est: de l'histoire à la gestion contemporaine', in Socièté Hydrotechnique de France, 23ème journées de l'hydrauliqe: crues et inondations, Nîmes, France, 14 -16
Large woody debris in forested streams in the Pacific Northwest: past, present and future
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Bisson, P.A., Bilby, R.E., Bryant, M.D., Dolloff, C.A., Grette, G.B., House, R.A., Murphy, M.L., Koski, K.V., and Sedell, J.R. 1987. 'Large woody debris in forested streams in the Pacific Northwest: past, present and future', in Streamside Management: Forestry and Fishery Interactions Seattle, College of Forest Resources, University of Washington, pp. 143 -190.
Ecology of coarse woody debris in temperate ecosystems
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