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The raft of the Saint-Jean River, Gaspé (Québec, Canada): A dynamic feature trapping most of the wood transported from the catchment
... Galia et al. (2022) assessed spatiotemporal variations in large wood using satellite images and found that it was not possible to make direct comparisons of volume and frequency through time because of resolution differences across the images. Raft dynamics are easier to monitor using aerial photographs or satellite images because of the greater spatial extent of rafts compared with individual pieces (Boivin et al., 2015;Kramer & Wohl, 2015). Comiti et al. (2008b) used aerial RGB images to quantify wood storage within seven sub-reaches of braided/ wandering rivers in Italy, while Smikrud and Prakash (2006) used an automated method to map individual logs and wood accumulations to assess changes in wood distribution over two successive years. ...
... Moreover, to provide adequate management of large wood in large rivers, we need a good understanding of its dynamics from recruitment and through deposition and remobilisation phases. River discharge is the primary driver that governs wood transport (Gurnell et al., 2002), and multiple studies have shown a significant correlation between peak flow magnitude and wood export (Boivin et al., 2015;Moulin & Piégay, 2004;Ruiz-Villanueva et al., 2016a;Senter et al., 2017). However, the relationship appears to be nonlinear and slightly noisy (Boivin et al., 2015;MacVicar & Piégay, 2012), demonstrating the complex interactions that exist between the main channel, its margins and the alluvial plain in terms of wood exchange. ...
... River discharge is the primary driver that governs wood transport (Gurnell et al., 2002), and multiple studies have shown a significant correlation between peak flow magnitude and wood export (Boivin et al., 2015;Moulin & Piégay, 2004;Ruiz-Villanueva et al., 2016a;Senter et al., 2017). However, the relationship appears to be nonlinear and slightly noisy (Boivin et al., 2015;MacVicar & Piégay, 2012), demonstrating the complex interactions that exist between the main channel, its margins and the alluvial plain in terms of wood exchange. Kramer and Wohl (2017) suggested that a flow duration of near or just under bankfull discharge has the greatest influence on the transport distance of large wood. ...
Rivers with alluvial bars store more wood than those without, supplied through channel shifting. However, wood dynamics (arrival or new deposits, departure or entrainment, and stable or immobile pieces) can vary substantially over time in response to critical hydrological drivers that are largely unknown. To evaluate them, we studied the dynamics of large wood pieces and logjams along a 12‐km reach of the lower Allier River using six series of aerial images of variable resolution acquired between 2009 and 2020, during which maximum river discharge fluctuated around the dominant flood discharge (Q 1.5 ) that is potentially the bankfull discharge along this well‐preserved not incised reach. Individual wood departure was best correlated with water levels exceeding dominant flood discharge. The duration of the highest magnitude flood was best correlated with wood depositions, with shorter floods resulting in a higher number of deposits. Finally, most of the wood remained stable when river discharge did not exceed 60% of Q 1.5 over a long period of time. Changes in inter‐annual wood budget (reach‐scale) depend on the duration over which discharge exceeded 60% of Q 1.5 . Hydrological conditions driving jam build‐up and removal were similar to those controlling individual wood piece dynamics. The results suggest that specific hydrological conditions influence the dynamics of large wood and log jams in the Allier River. Understanding the dynamics of large wood and its impact on river morphology is fundamental for successful river management and habitat restoration initiatives.
... In Chile, the monitoring of two low-order gravel bed streams revealed estimated wood recruitment of 0.5 and 0.8 m 3 /km/year (Iroumé, Ruiz-Villanueva, & Salas-Coliboro, 2020), which is very low compared with what has been observed in two low-land gravel bed meandering rivers in France, where wood volumes of 17-36 m 3 /km/year and 58 m 3 /km/year were estimated on the Ain River (Lassettre et al., 2008) and the Allier River, respectively. In between these cases, the recruited wood volume in the large Saint-Jean River in Canada accounted for 12 m 3 /km/year with great differences between the river reaches (Boivin et al., 2015). ...
... In large river catchments (>300 km 2 ), it is very challenging to identify wood sources (e.g., contributing tributary) and the different recruitment processes that deliver the wood (Boivin et al., 2015). After instream wood is supplied, and transported through the stream network, as described in the previous section, it might be deposited, forming wood accumulations or logjams along the channel, on the floodplain, or in reservoirs and lakes. ...
... The amount of wood stored in rivers (also called wood load and measured in cubic metres of wood per hectare; e.g., Wohl et al., 2017) is a critical value to quantify the wood regime. Previous studies showed that the link between flood magnitude and transported wood is not so strong (Boivin et al., 2015;Moulin & Piegay, 2004;Senter et al., 2017), demonstrating that wood availability (wood stored within the channel reach), among other factors, is playing an important role. ...
Large wood drives both the form and function of gravel‐bed rivers draining forested basins. Previously overlooked benefits of wood in rivers are now widely recognized. Together with flow and sediment regimes, the wood regime controls rivers' physical and ecological integrity. Yet large quantities of wood transported during floods can pose additional hazards, potentially damaging infrastructures like bridges or dams and exacerbating flooding. However, unlike the water and sediment regimes intensively studied over the past decades, the instream wood regime or budgeting has been only recently defined and thus is still rarely quantified. The instream wood budget describes the cascading processes from supply or recruitment, entrainment, and transport to deposition, storage and decay (i.e., fragmentation or decomposition). These processes show high spatial and temporal variability but can be characterized by magnitude, frequency, timing, duration and mode. Instream wood budgeting is challenging, primarily because of the lack of observations, monitoring stations, and standardized protocols to acquire data. This contribution reviews the most recent advances to quantify the different instream wood budget components, notably the wood supply, and transfer. Case studies showing applications of biogeochemistry, videography, artificial intelligence, numerical modelling or tracking illustrate the current progress. Because critical challenges remain, we identify and describe some of them and discuss how the wood in riverine sciences may develop in the future.
... To better understand wood flux, specific trapping structures such as reservoirs or hydropower dams can be used to sample the flux over time interval windows (Moulin and Piégay, 2004;Seo et al., 2008;Turowski et al., 2013). Accumulations upstream of a retention structure can also be monitored where they trap most or all of the transported wood, as was observed by Boivin et al. (2015), to quantify wood flux at the flood event or annual scale. All these approaches allow the assessment of the wood budget and in-channel wood exchange between geographical compartments within a given river reach and over a given period (Schenk et al., 2014;Boivin et al., 2015Boivin et al., , 2017. ...
... Accumulations upstream of a retention structure can also be monitored where they trap most or all of the transported wood, as was observed by Boivin et al. (2015), to quantify wood flux at the flood event or annual scale. All these approaches allow the assessment of the wood budget and in-channel wood exchange between geographical compartments within a given river reach and over a given period (Schenk et al., 2014;Boivin et al., 2015Boivin et al., , 2017. ...
... As shown in Fig. 7.b, this module contains three main parts: (i) the column on the far left allows the operator to switch to another module (detection, learning, or performance), (ii) the central part consists of a video player with a configuration tab for extracting the data, and (iii) the right part contains the tools to generate, create, visualize, and save annotations. The tools allow rather quick coarse annotation, similar to what was done by MacVicar and Piégay (2012) and Boivin et al. (2015), while still allowing the possibility of finer pixel-scale annotation. The principle of this module is to associate annotations with the frames of a given video. ...
Wood is an essential component of rivers and plays a significant role in ecology and morphology. It can be also considered a risk factor in rivers due to its influence on erosion and flooding. Quantifying and characterizing wood fluxes in rivers during floods would improve our understanding of the key processes but are hindered by technical challenges. Among various techniques for monitoring wood in rivers, streamside videography is a powerful approach to quantify different characteristics of wood in rivers, but past research has employed a manual approach that has many limitations. In this work, we introduce new software for the automatic detection of wood pieces in rivers. We apply different image analysis techniques such as static and dynamic masks, object tracking, and object characterization to minimize false positive and missed detections. To assess the software performance, results are compared with manual detections of wood from the same videos, which was a time-consuming process. Key parameters that affect detection are assessed, including surface reflections, lighting conditions, flow discharge, wood position relative to the camera, and the length of wood pieces. Preliminary results had a 36 % rate of false positive detection, primarily due to light reflection and water waves, but post-processing reduced this rate to 15 %. The missed detection rate was 71 % of piece numbers in the preliminary result, but post-processing reduced this error to only 6.5 % of piece numbers and 13.5 % of volume. The high precision of the software shows that it can be used to massively increase the quantity of wood flux data in rivers around the world, potentially in real time. The significant impact of post-processing indicates that it is necessary to train the software in various situations (location, time span, weather conditions) to ensure reliable results. Manual wood detections and annotations for this work took over 150 labor hours. In comparison, the presented software coupled with an appropriate post-processing step performed the same task in real time (55 h) on a standard desktop computer.
... It allows us to calculate the change in wood deposition between flight dates and lateral outputs as a result of floodplain advancement. Boivin et al. (2015) estimated a wood raft volume in channel by using a planimetric analysis of aerial photos. Using decadal and annual intervals, this study aims to examine the accumulation of wood in a large raft of the Saint-Jean River and to conclude that the relationship between river discharges and wood volumes was not simple, explaining the river network can store or deliver wood in a variable manner during each of the flood events. ...
... Understanding the variability and the process-scale dynamics which control wood delivery and transport rate is also a critical challenge (Martin and Benda, 2001;Marcus et al., 2011;Schenk et al., 2014;Boivin et al., 2015). ...
... We observed that the second or the third peaks, even when more intense, carry lower amounts of wood (Table II-2). This result agrees with Moulin and Piégay (2004) who indicate that the deposited wood on floodplain from last event (such as: flood, wind and ice (Boivin et al., 2015)) is transmitted by the first rising of water depth. In addition, show that the sequence of peaks and the magnitude and characteristics of the rising limb of individual floods can decline the amount of wood during a flood. ...
Drift wood plays a significant role both on the ecology and morphology of a river. Therefore, quantifying the amount of wood in rivers is an important issue. During recent years, streamside video monitoring has been introduced as a feasible technique to evaluate the amount of wood in riverine environment. Beside many advances, there are still many questions needed to be address concerning this technique. Therefore, in this study, I focused on three major objectives. Firstly, I studied the relation between wood flux and flow discharge in order to create a model for predicting wood flux on invisible period of camera sight. Wood in-stream can show some different characteristics in some critical events, such as in two multi-peak floods, wood flux on the first peak of discharge is more than second one, and in a flood after a stronger windy day, wood flux can be activated by water elevation arise. In addition, the second major objective was implementation and validation the application of an automatic detection software. After training the software, it is used to extract wood flux automatically by its own surveillance. The third major objective was evaluating human-based uncertainties in video monitoring due to two limitations, first time limitation which results in sampling the videos and second limitation in visibility of the operator which results in bias between different operators. I expect the results of this thesis develop the application of streamside video monitoring technique for practical concerns.
... Understanding the variability and the process-scale dynamics which control wood delivery and transport rate is also a critical challenge (Martin and Benda, 2001;Benda et al., 2003;Marcus et al., 2011;Schenk et al., 2014;Boivin et al., 2015). Wood budgeting can be explored at different time scales. ...
... The high quality and frequency of the data, which is likely necessary in high gradient rivers, allowed them to compare LW dynamics with flood hydrograph and develop a quantitative relation between wood and water discharges. Other studies have implemented similar approaches (Boivin et al., 2015;Senter et al., 2017;Ruiz-Villanueva et al., 2019;Ghaffarian et al., 2020a) but overall the technique remains undersubscribed, and models of the wood flux as a function of the flow hydrograph remain poorly parameterized. ...
... We observed that the second or the third peaks, even when equal to or higher than the first, carry lower amounts of wood (Table 2). This result agrees with Moulin and Piégay (2004) who found that the deposited wood on channel edges that remained from the previous event (for example from smaller floods, wind and ice (Boivin et al., 2015)) is mobilized by the first increase of water depth. also showed that the sequence of peaks, flow discharge and the shape of hydrograph can influence the amount of wood during a flood. ...
Wood flux (piece number per time interval) is a key parameter for understanding wood budgeting, determining the controlling factors, and managing flood risk in a river basin. Quantitative wood flux data is critically needed to improve the understanding of wood dynamics and estimate wood discharge in rivers. In this study, the streamside videography technique was applied to detect wood passage and measure instantaneous rates of wood transport. The goal was to better understand how wood flux responds to flood and wind events and then predict wood flux. In total, one exceptional wind and 7 flood events were monitored on the Ain River, France, and around 24000 wood pieces were detected visually. It is confirmed that, in general, there is a threshold of wood motion in the river equal to 60% of bankfull discharge. However, in a flood following a windy day, no obvious threshold for wood motion was observed, which confirms that wind is important for the preparation of wood for transport between floods. In two multi‐peaks floods, around two‐thirds of the total amount of wood was delivered on the first peak, which confirms the importance of the time between floods for predicting wood fluxes. Moreover, we found an empirical relation between wood frequency and wood discharge, which is used to estimate the total wood amount produced by each of the floods. The data set is then used to develop a random forest regression model to predict wood frequency as a function of three input variables that are derived from the flow hydrograph. The model calculates the total wood volume either during day or night based on the video monitoring technique for the first time, which expands its utility for wood budgeting in a watershed. A one‐to‐one link is then established between the fraction of detected pieces of wood and the dimensionless parameter “passing time × framerate”, which provides a general guideline for the design of monitoring stations.
... As new technologies have evolved, indirect, remote methods have been developed to estimate wood loads with increasing detail and precision. Photographs (Kramer and Wohl, 2014;Benacchio et al., 2017), multispectral (Boivin et al., 2015) and Lidar (Abalharth et al., 2015;Atha and Dietrich, 2016) data sets captured from the ground , unmanned aerial vehicles (Sanhueza et al., 2019), helicopters (Moulin et al., 2011), aircraft and satellite platforms (Atha, 2014) have all been exploited. For example, aerial photographs, Landsat 7 and GeoEye satellite images were used in combination with field observations to quantify the size and budget of enormous wood rafts on the Saint Jean River Canada (Boivin et al., 2015(Boivin et al., , 2017a. ...
... Photographs (Kramer and Wohl, 2014;Benacchio et al., 2017), multispectral (Boivin et al., 2015) and Lidar (Abalharth et al., 2015;Atha and Dietrich, 2016) data sets captured from the ground , unmanned aerial vehicles (Sanhueza et al., 2019), helicopters (Moulin et al., 2011), aircraft and satellite platforms (Atha, 2014) have all been exploited. For example, aerial photographs, Landsat 7 and GeoEye satellite images were used in combination with field observations to quantify the size and budget of enormous wood rafts on the Saint Jean River Canada (Boivin et al., 2015(Boivin et al., , 2017a. Google Earth images and Lidar data have been used by Atha (2014) and Atha and Dietrich (2016) to detect sizes of large wood accumulations. ...
... They also identify "rafts" of wood (stable accumulations capable of plugging larger channels), sustained by the shear mass of wood (e.g. Boivin et al., 2015Boivin et al., , 2017a. ...
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.
... In previous studies, several methods have been applied to estimate LW volume in riparian zones and stream channels as a review of Ruiz-Villanueva et al. (2016) reveals. For LW accumulation assessment and wood-budgeting, Boivin et al. (2015) considered measurements of the 'air-wood' volume by applying a rectangular model with accumulation length, width and average height. Other volume assessing methods include developing scaling relationships relating wood accumulation to catchment size, the proportion of forest cover in the catchment upstream, forested river length (Uchiogi et al., 1996), and the density of landslide occurrence upstream (Rigon et al., 2008). ...
... Expressed as a volume, the upper bound error of 2.5 mm difference in elevation would result in a deviation of ±0.01 m 3 . Considering this magnitude of error, the SfM photogrammetry methodology presented here for volume computation represents an improvement from the previously applied volume estimate techniques, such as counting and measuring individual logs (Cordova et al., 2006;Brown et al., 2014;Dixon and Sear, 2014), or applying a rectangular model for air-wood volume estimation (Boivin et al., 2015). ...
... There are time and cost benefits to be gained from the rectangular (parallelepiped) approach to estimate volumes directly in the field (Boivin et al., 2015), which can be obtained within a few minutes after measuring the three axes. In contrast, it takes about 21 h to acquire data and execute SfM volume computations (Table 2), although with significant gains in volume accuracy. ...
... The anastomosed style is essentially found in the delta where overbank deposits of fine sediments and rafts generated avulsions occur frequently ( Figure 1C). Previous studies have described the annual and decadal components of the LW wood budget and examined several aspects of the LW dynamics [10,11,12] in the SJR, including the evolution of the large raft from which we sampled trees to estimate their residence time in the watershed. ...
... On average, one sample was extracted every 3 linear meters but, because extracting was realized using large machinery in a difficult and moving working environment, the exact position of each large wood was estimated with a precision of between 25 to 50 meters. This accuracy is sufficient to identify the year of arrival in the raft, considering that each major flood brings more than 50 to 200 linear meters of wood in the mouth of the SJR [10]. Figure ...
... Because the surface of samples was smooth and non-eroded, we assumed that the wood recruitment year (Y R ) corresponds to the crossdated year of death (i.e. the outermost tree ring). The wood accumulation year (Y A ) was determined by analyzing the raft evolution from aerial photos (1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004), satellite images (1999-2014) and five years surveys (2010 to 2014) [10,11,12]. Using these images, it was possible to determine the most probable year that each LW was accumulated within the delta [10,12] based on the extraction location ( Figure 1F). ...
The Saint-Jean River (SRJ) in Eastern Canada is prone to the formation of very large rafts of wood. Managers of the SJR suspected these jams to influence salmon migration and carried out a dismantling operation to remove large wood accumulated in a 1.2 km long wood raft. This operation became a great opportunity to address key issues relating to large wood dynamics in a fluvial system: residence time and flood contribution to wood recruitment and transport. During the dismantling, we systematically sampled 319 trees from which year of death could be estimated from dendrochronology and year of accumulation in the raft could be obtained from satellite and aerial photos. These two dates allowed us to quantify the residence time for 262 datable large wood (LW) within the fluvial system, to examine the peak years of LW recruitment and to correlate the raft growth rate with hydrometeorological conditions since 1993. The results also emphasized four types of LW flood related to wood dynamics: 1) an erosive flood that produces a large amount of wood in river, 2) a mobilizing flood that carries large quantities of wood, 3) a flood mix that both recruits and transports large quantities of wood, and 4) an ice-breakup flood.
... The purpose of our study was to quantify all the components of a LW budget at both the reach and the watershed scales for two time periods, i) a 50-year period at a decadal scale, and ii) a four-year period at an interannual scale. The LW budget was quantified by measuring the volumes of LW inputs, LW accumulations, and LW outputs at the reach and watershed scales using three unusually large but natural wood rafts in the delta of the Saint-Jean River (SJR; Québec, Canada) (Boivin et al., 2015). Three questions motivated the research: i) what was the LW budget on SJR over the last 50 years and how did it evolve interannually?; ii) what are the potential geomorphic and hydrological factors disrupting wood transfers within reaches and within the watershed that could explain the difference between LW input and LW output?; and iii) if the LW budget is not at equilibrium at an interannual level, is it so at a decadal one? ...
... For example, sediment loads influence LW mobility and retention by modifying river morphologies such as concave eroded banks or large central bars in the river corridor. LW dynamics are also influenced by the occurrence of storms (Golladay et al., 2007;Comiti et al., 2016) and ice flood events (Boivin et al., 2015;Boivin et al., 2017). All discharges and fluxes are influenced by hydrometeorological characteristics and previous events because of LW availability in the fluvial corridor. ...
... All discharges and fluxes are influenced by hydrometeorological characteristics and previous events because of LW availability in the fluvial corridor. Two similar events occurring close together in time do not have the same magnitudes of LW discharges (Moulin and Piégay, 2004;Boivin et al., 2015): ...
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.
... Furthermore, most large wood studies focus on headwater rather than lowland rivers [Wohl, 2016;Seo et al., 2010]. In the recent wood literature, some of the largest rivers are the Queets River, Washington [Collins et al., 2012], Sacramento River, California [MacVicar et al., 2009], A ın River, France [MacVicar and Pi egay, 2012], Tagliamento River, Italy [Ravazzolo et al., 2015], Saint-Jean River, Gasp e Penninsula, Qu ebec [Boivin et al., 2015[Boivin et al., , 2016, and Lower Roanoke River, South Carolina [Schenk et al., 2014]. For perspective, the Slave River in northern Canada described in this paper has a drainage area 10-100 times larger, is 10-100 times wider, and has maximum and average flows 10-100 times greater than these rivers. ...
... Wood-initiated, mid-river, vegetated islands and log rafts are not unique to the Slave River. This process and resulting landforms have been well documented elsewhere on other large rivers draining forested catchments in North America, Europe, and Africa [Hickin, 1984;Triska, 1984;Jacobson et al., 1999;Gurnell and Petts, 2002;Collins et al., 2012;Boivin et al., 2015]. ...
... Known temporary trapping sites that have high turnover of wood, such as channel constrictions, channel spanning jams, and mid-channel bars and islands, are ideal locations to study wood transport through time and can be analyzed with historic imagery or actively monitored with time-lapse cameras. Other ideal locations are sites of continued and permanent deposition such as log rafts [Boivin et al., 2015], lakes and reservoirs [Moulin and Pi egay, 2004;Seo and Nakamura, 2009], and delta fronts [Kramer and Wohl, 2015]. ...
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.
... Large wood, channel-spanning jams, and wood rafts can be very efficacious at trapping wood and when present are commonly the dominant entrapment site for fluvially transported wood (Pettit et al., 2006;Millington and Sear, 2007;Warren and Kraft, 2008;Beckman and Wohl, 2014;Dixon and Sear, 2014;Wohl, 2014a;Boivin et al., 2015;Jackson and Wohl, 2015) and smaller coarse particulate matter (Jochner et al., 2015). Higher amounts of wood in storage, especially as jams, have been related to higher amounts of wood recruited during floods (Johnson et al., 2000), lower wood export rates (Bertoldi et al., 2014;, and longer residence times (Wohl and Goode, 2008). ...
... The downstream movement of logs can by tracked with GPS (e.g., Ravazzolo et al., 2015b) or by actively following radio tags during flooding via boat or aircraft (e.g., Schenk et al., 2014). • Monitor change in storage at known retention sites at varying timescales (e.g., Wohl and Goode, 2008;Moulin et al., 2011;Bertoldi et al., 2013;Schenk et al., 2014;Boivin et al., 2015). • Use wood characteristics to fingerprint wood source. ...
... • Use remote sensing techniques to assess change on larger spatial and longer temporal scales (e.g., Bertoldi et al., 2013;Atha, 2014;Ulloa et al., 2015;Kramer et al., in press). • Conduct stratigraphic and/or other analysis of wood deposited in basins and floodplains to obtain long-term (decade to millennial scale) records of wood flux from watersheds (Guyette et al., 2008;Seo et al., 2008;Seo and Nakamura, 2009;Fremier et al., 2010;Boivin et al., 2015;Kramer and Wohl, 2015). • Use already existing data from unconventional sources. ...
To effectively manage wood in rivers, we need a better understanding of wood mobility within river networks. Here, we review primarily field-based (and some numerical) studies of wood transport. We distinguish small, medium, large, and great rivers based on wood piece dimensions relative to channel and flow dimensions and dominant controls on wood transport. We suggest further identification and designation of wood transport regimes as a useful way to characterize spatial-temporal network heterogeneity and to conceptualize the primary controls on wood mobility in diverse river segments. We draw analogies between wood and bedload transport, including distinguishing Eulerian and Lagrangian approaches, exploring transport capacity, and quantifying thresholds of wood mobility. We identify mobility envelopes for remobilization of wood with relation to increasing peak discharges, stream size, and dimensionless log lengths. Wood transport in natural channels exhibits high spatial and temporal variability, with discontinuities along the channel network at bankfull flow and when log lengths equal channel widths. Although median mobilization rates increase with increasing channel size, maximum mobilization rates are greatest in medium-sized channels. Most wood is transported during relatively infrequent high flows, but flows under bankfull can transport up to 30% of stored wood. We use conceptual models of dynamic equilibrium of wood in storage and of spiralling wood transport paths through drainage networks, as well as a metaphor of traffic on a road, to explore discontinuous wood movement through a river network. The primary limitations to describing wood transport are inappropriate time scales of observation and lack of sufficient data on mobility from diverse rivers. Improving models of wood flux requires better characterization of average step lengths within the lifetime travel path of a piece of wood. We suggest that future studies focus on: (i) continuous or high-frequency monitoring of wood mobility; (ii) monitoring changes in wood storage; (iii) using wood characteristics to fingerprint wood sources; (iv) quantifying volumes of wood buried within river corridors; (v) obtaining existing or new data from unconventional sources, such as citizen science initiatives, and (vi) creating online interactive data platforms to facilitate data synthesis.
... Methods to ascertain wood mobility generally rely on field campaigns to measure logs and log jam characteristics along a reach or an entire stream length (Comiti et al., 2006(Comiti et al., , 2008Lassettre and Kondolf, 2012;Ravazzolo et al., 2015;Boivin et al., 2015). All pieces larger than a defined size are counted, measured, and described in order to understand where they were recruited and how long they have been stored in the channel. ...
... Such field observations are time-consuming when long reaches are surveyed but also because they must be repeated to examine LW mobility. Aerial (Lassettre et al., 2008;Moulin et al., 2011;Atha, 2013) and satellite (Boivin et al., 2015) imagery analysis appears to complement these field measurements; but riparian tree cover often prohibits the use of remotely sensed images because it partially or completely overhangs the channel width. To overcome this, Atha (2013) used aerial LiDAR to acquire workable imagery even with dense forest cover. ...
... Observed wood delivery from extraction versus peak flows: The wood weight extracted in the Génissiat dam reservoir is very significantly related to the peak flow as the sum of the Arve and Valserine rivers discharge ( Fig. 16A; R 2 = 0.91). This result is very significant compared to the one of Boivin et al. (2015) or even Moulin and Piégay (2004), who showed more complex relationships, for which the large range of variability was interpreted in terms of wood trapping within the reach, inducing a lag between wood input and output and explaining effects of flood position within the series. ...
... Neither the Leung (2019) nor the DeMott et al. (2021) studies examined porosity of large-wood deposits. The thickness and porosity of a given wood accumulation cannot be derived with confidence from imagery alone, even though previous remote sensing studies have made these estimates using sphere approximations (e.g., Sanhueza et al., 2019;Ulloa et al., 2015) or using estimates of wood height (or thickness) and porosity (e.g., Boivin et al., 2015;Livers et al., 2020;Livers & Wohl, 2021). Finally, we note that DeMott et al. (2021), who reported their Elwha River wood measurements as areas for possibly the same reasons as listed above and were nonetheless able to draw convincing conclusions from their data regarding wood distributions in the middle reach. ...
... There was no evidence of any channelspanning log jams, nor observable hydraulic backwater effects (cf. Livers & Wohl, 2021) associated with wood accumulations and no evidence of wood rafts that completely blocked the active channel (Boivin et al., 2015). Only a negligible (estimated <1%) amount of wood was detected in the channel, presumably undergoing active transport at the time of survey (and could possibly be further isolated and studied by finding wood pixels surrounded by water pixels). ...
Large wood is an integral part of many rivers, often defining river‐corridor morphology and habitat, but its occurrence, magnitude, and evolution in a river system are much less well understood than the sedimentary and hydraulic components, and due to methodological limitations, have seldom previously been mapped in substantial detail. We present a new method for this, representing a substantial advance in automated deep‐learning‐based image segmentation. From these maps, we measured large wood and sediment deposits from high‐resolution orthoimages to explore the dynamics of large wood in two reaches of the Elwha River, Washington, USA, between 2012 and 2017 as it adjusted to upstream dam removals. The data set consists of a time series of orthoimages (12.5‐cm resolution) constructed using Structure‐from‐Motion photogrammetry on imagery from 14 aerial surveys. Model training was optimized to yield maximum accuracy for estimated wood areas, compared to manually digitized wood, therefore model development and intended application were coupled. These fully reproducible methods and model resulted in a maximum of 15% error between observed and estimated total wood areas and wood deposit size‐distributions over the full spatio‐temporal extent of the data. Areal extent of wood in the channel margin approximately doubled in the years following dam removal, with greatest increases in large wood in wider, lower‐gradient sections. Large‐wood deposition increased between the start of dam removal (2011) and winter 2013, then plateaued. Sediment bars continued to grow up until 2016/17, assisted by a partially static wood framework deposited predominantly during the period up to winter 2013.
... Neither the Leung (2019) nor the DeMott et al. (2021) studies examined porosity of large-wood deposits. The thickness and porosity of a given wood accumulation cannot be derived with confidence from imagery alone, even though previous remote sensing studies have made these estimates using sphere approximations (e.g., Sanhueza et al., 2019;Ulloa et al., 2015) or using estimates of wood height (or thickness) and porosity (e.g., Boivin et al., 2015;Livers et al., 2020;Livers & Wohl, 2021). Finally, we note that DeMott et al. (2021), who reported their Elwha River wood measurements as areas for possibly the same reasons as listed above and were nonetheless able to draw convincing conclusions from their data regarding wood distributions in the middle reach. ...
... There was no evidence of any channelspanning log jams, nor observable hydraulic backwater effects (cf. Livers & Wohl, 2021) associated with wood accumulations and no evidence of wood rafts that completely blocked the active channel (Boivin et al., 2015). Only a negligible (estimated <1%) amount of wood was detected in the channel, presumably undergoing active transport at the time of survey (and could possibly be further isolated and studied by finding wood pixels surrounded by water pixels). ...
Large wood is an integral part of many rivers, often defining river-corridor morphology and habitat, but its occurrence, magnitude, and evolution in a river system are much less well understood than the sedimentary and hydraulic components, and due to methodological limitations, have seldom previously been mapped in substantial detail. We present a new method for this, representing a substantial advance in automated deep-learning-based image segmentation. From these maps, we measured large wood and sediment deposits from high-resolution orthoimages to explore the dynamics of large wood in two reaches of the Elwha River, Washington, USA, between 2012 and 2017 as it adjusted to upstream dam removals. The dataset consists of a time series of orthoimages (12.5-cm resolution) constructed using Structure-from-Motion photogrammetry on imagery from 14 aerial surveys. Model training was optimized to yield maximum accuracy for estimated wood areas, compared to manually digitized wood, therefore model development and intended application were coupled. These fully reproducible methods and model resulted in a maximum of 15% error between observed and estimated total wood areas and wood deposit size-distributions over the full spatio-temporal extent of the data. Areal extent of wood in the channel margin approximately doubled in the years following dam removal, with greatest increases in large wood in wider, lower-gradient sections. Large-wood deposition increased between the start of dam removal (2011) and winter 2013, then plateaued. Sediment bars continued to grow up until 2016/17, assisted by a partially static wood framework deposited predominantly during the period up to winter 2013.
... Satellite imaging covers large spatial extents, and is low cost to access, but at the expense of spatial and temporal resolution, where wood may be difficult to distinguish at coarse (>1 m) spatial resolutions (Marcus et al., 2002) due to the influence of mixed pixels (Lu & Weng, 2007). However, very high-resolution (VHR) satellites respectively)] now provide imagery at spatial resolutions where wood may be more easily captured in the landscape (Atha, 2014;Boivin et al., 2015). This work focuses on classification of LW in satellite imagery. ...
... Several studies quantifying wood distribution using satellite imagery relied on manual digitization techniques to identify wood. For example, Atha (2014), using imagery hosted in GoogleEarth, manually tracked the distribution of individual logs in the Queets River, Washington, DC. Boivin et al. (2015Boivin et al. ( , 2017 manually delineated the extent of a wood raft and created a LW budget in the St. Jean River in Quebec, Canada using a GeoEye image. Schenk et al. (2018) manually quantified the distribution of LW before and after a large flood in the Missouri River, USA. ...
Wood researchers increasingly rely on remote sensing products to augment field information about wood deposits in river corridors. The availability of very high resolution (<1 m) satellite imagery makes capturing wood over greater spatial extents possible, but previous studies have found difficulty in automatically extracting wood deposits due to the challenge in distinguishing wood from spectrally similar corridor features such as sand. We also lack knowledge on the spectral properties of different wood deposit types in multiple depositional environments. In this work, we explore image classification workflows for four wood deposit types in three North American environments: in‐channel jams deposited in the Tatshenshini River in Alaska, USA; a wood raft on the Slave River in Northwest Territories, Canada; and wood deposited along a lakeshore and coastal embayment in the Mackenzie River Delta in Northwest Territories, Canada. We compare classification results of object‐based and pixel‐based image analysis with supervised (Support Vector Machine (SVM)) and unsupervised (ISO Clustering) classifiers. We evaluate several accuracy assessment parameters and achieve overall classification accuracies of 65‐99%, showing automated image classification is a possible approach for analyzing wood across larger areas. We also find that wood sensitivity in the classification ranged 0‐95% indicating some techniques are better suited to wood capture than others. We find that supervised classification produced more accurate wood maps, though there is large variation in classification outcomes across environments related to spatial arrangement of wood in the landscape. We discuss the influence of depositional environment on classification and provide recommendations for designing a wood classification work‐flow.
... The export of wood per unit catchment area is the highest from medium-sized catchments and decreases towards both smaller and larger ones (Seo et al., 2008;Seo and Nakamura, 2009). Individual floods may differ significantly in their effects on wood budget, thus causing wood recruitment, remobilization and transport or mixed effects (Boivin et al., 2015(Boivin et al., , 2017a. ...
... We also did not detect the exponential trends in LW depletion usually reported for fluvial environments (Ruiz- Villanueva et al., 2016a), finding a linear trend instead. Moulin and Piégay (2004) and Boivin et al. (2015Boivin et al. ( , 2017a, who conducted LW budgeting studies, reported the combination of extreme hydrological events, LW input by bank erosion and geomorphic configuration of the river channel as significant factors of LW dynamics and the resultant LW budget. Similarly, the highest LW dynamics were linked to extreme flood events in the studied river reach. ...
This study examined the large wood (LW) load and transport during the non‐flood period (2009–2018) following major floods that occurred in 2002 and 2006 within the inter‐dam reach of the Dyje River (Czech–Austrian border). The LW load was examined in 36 river corridor segments scattered within the reach in the 2009–2018 period. Two whole reach surveys (2011 and 2019) on LW frequency and distribution were conducted, and the export of LW to the downstream reservoir was analysed between June 2013 and December 2018.
In the period of non‐flood discharges, the recruitment and depletion of LW were highly variable processes in space and time, leading to a considerable change in the total LW quantity. Whereas the total number of LW pieces decreased, the total LW volume increased because of the increasing dimensions of newly recruited pieces. The annual variability in the quantity of newly recruited pieces was better explained by the variation in the maximum annual discharges (y = 41.043ln(x) + 3.2737, R² = 0.5352) than by the variability in the number of days with wind gusts > 17.2 m/s (y = 1.5004x + 82.096, R² = 0.118). The land use change with the abandonment of human settlements after World War II and the progressive expansion of forest was the major historical factor driving the increased recruitment of LW to the river corridor.
While the 2006 (> 100‐year RI) flood brought approximately 1,250 LW pieces to the reservoir, the 2013 (1.5‐year RI) flood delivered 45 pieces. The long‐term average monthly input of LW to the reservoir was 7.7 pieces. The exceptional low‐magnitude flood of 2013, which occurred at the beginning of the monitoring period, was shown to be a threshold above which the number of LW pieces floated to the dam significantly increased.
... 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). ...
... Determining the spatial boundaries of the best-fit box (e.g. average versus maximum length, width, and height of the jam) or other shape can vary from person to person in the field, and reproducibility of this method is thus challenging (Scott et al., 2019), whereas reproducibility of complete boxes by different field technicians can be quite good, with statistically insignificant margins of error (Boivin et al., 2015). The FIGURE 1. Illustrations of jam components and differing measurement techniques. ...
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.
... 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. ...
... The 2.5D model approach was shown to provide a reliable and efficient tool for bulk volume estimation (Pix4Dmapper, 2018), and outperforms conventional approaches of rough volumetric estimates based on log count and measurements (Cordova et al., 2006;Tonon et al., 2018), as well as the air-wood rectangular approach introduced and used by Piegay (1993), Boivin et al. (2015) and Lucía et al. (2015). The 3D PSR model approach considered some of the accessible overhanging void spaces (Carrea et al., 2015), resulting in somewhat more accurate volume computation than 2.5D Pix4D. ...
... Some studies have focused on assessing LW volumes along channels (Van Wagner, 1968;Uchiogi et al., 1996;Benda and Sias, 2003;Rigon et al., 2008), and only a small number have endeavoured to evaluate the volume of existing log jams. Those that focused on LW accumulation volume applied a parallelepiped approach (Boivin et al., 2015) or geometric measures of length and diameter as well as number of individual logs, or wood pieces (Cordova et al., 2006;Brown et al., 2014;Dixon and Sear, 2014;Ruiz-Villanueva et al., 2016; and calculated a volume based on cylindrical approximations. These methods do not consider any irregularities in shape, and in many cases volume estimates are based on a line intersection technique introduced by Warren and Olsen (1964), leading to a rough estimation of LW volume rather than a precise measurement. ...
... However, it provides a good approximation and would be useful for first-order assessment of porosity characteristics across a population of LW deposits, both in the field as well as in the laboratory. Our porosity estimation approach has great potential for field applications and the improvement of recent SfM photogrammetry studies (Sanhueza et al., 2019;Spreitzer et al., 2019), as there are no visual estimates or manual calculations involved (such as a parallelepiped approach (Boivin et al., 2015;Livers et al., 2015;Scott et al., 2019), and the introduced 3D approach is a major advance for the development of semi-automated and automated methods, which allow for accurate LW accumulation volume and porosity assessment. The porosity results correspond to expected values, ranging from 30 to 50% (Dixon, 2016). ...
A Structure from Motion (SfM) photogrammetry-based methodology for precise mapping of large wood (LW) accumulations in fluvial systems is presented. The technique may be useful for routine inventory and rapid volume estimation of complex LW structures that tend to divert or obstruct flow in rivers. Our methodology is validated by means of laboratory experiments, ranging from elementary to complex arrangements of LW components and organic fine material (OFM). Seven experimental setups were used as the basis for (i) manual approximations of 2.5D and 3D geometric reference volumes, (ii) 2.5D volume models based on mesh geometry, (iii) a closed (‘watertight’) 3D mesh from an unorganized point cloud and (iv) estimates of porosity. A commercially available SfM photogrammetry software package, Pix4Dmapper, was used for point cloud and simplified mesh generation. In order to obtain more precise volumes, 3D surface models are required. Accordingly, we generated 3D watertight mesh models of the unorganized point cloud using the screened Poisson Surface Reconstruction (PSR) technique. The Pix4D volume tool (2.5D) resulted in an overestimation (2.9 to 52.7%) of the geometric volume (3D), due to the convex hull approximation of the geometry normal to the surface plane. PSR (3D) resulted in more precise volumes, showing deviations from the geometric volume (3D) in a range of −15.9 to +10.6%, as the algorithm could capture concavities and involuted surfaces on the accumulation. Assuming that the difference between 3D and 2.5D volume models represents many of the voids visible within or on the surface of the deposit, this volume can be used as an estimate of porosity. Our assessment suggests that image-based SfM methodology is well-suited for further investigations in LW research, due to its time and cost efficiency in comparison with other conventional surveying techniques. The methodology can be used to generate high quality point cloud and mesh models of log jam formations; these may be used by river managers and researchers to quantify accumulation volume and thus gain a better understanding of LW composition and the influence of wood geometry on hydraulic flow conditions.
... Wood recruitment to a river corridor can be quantified using at least two approaches. Direct measurements commonly cover only short periods such as a single large storm or flood (e.g., Comiti et al. 2016) or at most a few decades (Boivin et al. 2015). Numerical models typically focus on either forest dynamics over decades to centuries and the resulting magnitude and frequency of wood recruitment or on the potential for recruitment during a single storm or flood in relation to factors such as volume of standing wood and processes that recruit that wood to the river corridor (e.g., landslides; Mazzorana et al. 2011). ...
... Feedback loops are particularly important in creating nonlinear behavior in river corridors, including alternative states mediated by the presence or absence of wood (supplemental text 3; Collins et al. 2012. Multiyear monitoring of storage from ground-based measurements or airborne imagery can show the potential variability in magnitude, duration, and mode of wood storage at one location and can inform transport dynamics by tracking wood that is imported into the storage zone, remains in storage, or is exported downstream (Boivin et al. 2015; figure 4). This type of monitoring may be particularly effective at identifying feedback loops and thresholds. ...
The natural wood regime forms the third leg of a tripod of physical processes that supports river science and management, along with the natural flow and sediment regimes. The wood regime consists of wood recruitment, transport, and storage in river corridors. Each of these components can be characterized in terms of magnitude, frequency, rate, timing, duration, and mode. We distinguish the natural wood regime, which occurs where human activities do not significantly alter the wood regime, and a target wood regime, in which management emphasizes wood recruitment, transport, and storage that balance desired geomorphic and ecological characteristics with mitigation of wood-related hazards. Wood regimes vary across space and through time but can be inferred and quantified via direct measurements, reference sites, historical information, and numerical modeling. Classifying wood regimes with respect to wood process domains and quantifying the wood budget are valuable tools for assessing and managing rivers
... Wood recruitment to a river corridor can be quantified using at least two approaches. Direct measurements commonly cover only short periods such as a single large storm or flood (e.g., Comiti et al. 2016) or at most a few decades (Boivin et al. 2015). Numerical models typically focus on either forest dynamics over decades to centuries and the resulting magnitude and frequency of wood recruitment or on the potential for recruitment during a single storm or flood in relation to factors such as volume of standing wood and processes that recruit that wood to the river corridor (e.g., landslides; Mazzorana et al. 2011). ...
... Feedback loops are particularly important in creating nonlinear behavior in river corridors, including alternative states mediated by the presence or absence of wood (supplemental text 3; Collins et al. 2012. Multiyear monitoring of storage from ground-based measurements or airborne imagery can show the potential variability in magnitude, duration, and mode of wood storage at one location and can inform transport dynamics by tracking wood that is imported into the storage zone, remains in storage, or is exported downstream (Boivin et al. 2015; figure 4). This type of monitoring may be particularly effective at identifying feedback loops and thresholds. ...
... Quantification of wood storage is relatively simple, whereas wood transport 128 dynamics are less so, as highlighted by predictive wood mobility analyses that yielded 129 models explaining 47% (Wohl and Goode, 2008) and 39% (Merten et al., 2010) of data 130 variability. 131 Wood export quantities have been correlated with peak annual discharge (Moulin 132 and Piégay, 2004;Boivin et al., 2015;Senter et al., 2017) and watershed area (Seo et 133 al., 2008;Ruiz-Villanueva et al., 2016b). The depositional nature of reservoirs provides 134 ideal locations in which to study wood export patterns and characteristics (Moulin and 135 Piégay, 2004;Seo et al., 2008;Senter et al., 2017) in a manner analogous to sediment 136 budget studies (Dendy and Bolton, 1976). ...
... Hydrographic peaks smaller 1027 than annual í µí± 3456 events will mobilize and export wood at lower rates than flood events 1028 (Moulin and Piégay, 2004;Senter et al., 2017). Wood discharge monitoring has been 1029 achieved using still image analysis (Moulin and Piégay, 2004;Kramer and Wohl, 2014;1030Boivin et al., 2015Benacchio et al., 2017) and video monitoring at-a-station (MacVicar 1031MacVicar et al., 2009MacVicar and Piégay, 2012;Boivin et al., 2017;Senter et al., 2017). These 1032 studies reveal semi-continuous to continuous real-time transport processes; data which 1033 are necessary to obtain further insights into associations between wood discharge, 1034 water discharge, and watershed processes. ...
Abstract Wood export from a watershed is a function of peak annual discharge, but one hydrologic relationship alone does not fully explain observed variability. Consideration of physical processes that influence the amount of wood available for transport is needed. However, wood recruitment, storage, mobilization, breakage, and transport rates and processes remain difficult to quantify. A theoretical wood transport equation focused on variations in discharge was the motivation for investigation into watershed-specific wood export rates. Herein, multiplicative coefficients categorized by water year type are developed, paired with the equation, and validated to provide a new method for prediction of wood export at the watershed scale. The coefficients are defined as representing a broad suite of watershed processes that encompass spatio-temporally variable scales. Two complementary data sets from the 1,097 km2 mountainous North Yuba River, California watershed were used. Wood surveys above New Bullards Bar Reservoir yielded a wood availability estimate of 250,000–300,000 m3 along the channel network. Annual wood export into the reservoir was field-surveyed in 2010, 2012, and 2013, and estimated in seven years via remotely sensed images over the 30-year study period of water years 1985–2014. Empirical, watershed-scale wood export rates ranged from 0.3-5.6%. Comparison of predicted quantities using the new DVWP (discharge variations and watershed processes) wood export equation to observed wood export quantities resulted in an aggregate error rate of ± 10%. When individual wood export quantities were compared, predicted to observed varied by 0.5–3.0 times. Total wood export of 59,000–71,000 m3 was estimated over the 30-year period, yielding a rate of 1.8 to 2.2 m3/year/km2. Wood export predictive capabilities at the watershed scale may help water resource and regulatory agencies plan for wood transfers to augment downstream ecosystems.
... Wood export quantities have been correlated with peak annual discharge (Moulin 132 and Pi?gay, 2004;Boivin et al., 2015;Senter et al., 2017) and watershed area (Seo et 133 al., 2008;Ruiz-Villanueva et al., 2016b). The depositional nature of reservoirs provides 134 ideal locations in which to study wood export patterns and characteristics (Moulin and 135 Pi?gay, 2004;Seo et al., 2008;Senter et al., 2017) in a manner analogous to sediment 136 budget studies (Dendy and Bolton, 1976). ...
... ???? 3456 events will mobilize and export wood at lower rates than flood events 1028 ( Moulin and Pi?gay, 2004;Senter et al., 2017). Wood discharge monitoring has been 1029 achieved using still image analysis ( Moulin and Pi?gay, 2004;Kramer and Wohl, 2014;1030Boivin et al., 2015Benacchio et al., 2017) and video monitoring at-a-station (MacVicar 1031(MacVicar et al., 2009MacVicar and Pi?gay, 2012;Boivin et al., 2017;Senter et al., 2017). These 1032 studies reveal semi-continuous to continuous real-time transport processes; data which 1033 are necessary to obtain further insights into associations between wood discharge, 1034 ...
The dynamics that move wood through and out of watersheds are complex and not yet fully understood. In this study, climatic conditions, hydrologic responses, and watershed processes were explored to better understand variations in wood export using aerial imagery, event-based video monitoring, and field measurements from the 1097 km² mountainous Mediterranean climate North Yuba River, California, watershed and its reservoir near the downstream outlet. Over a 30-year study period, 1985–2014, volumetric estimates of annual wood export into the reservoir, available for a subset of years, were used to investigate watershed-scale, wood export dynamics. Variations in annual peak discharge explained 79% of the variance in interannual wood export, with 84% of total observed wood export (ca. > 10,000 m³ of wood per event) delivered by years with discharge events of 19-year, 21.5-year, and 60-year flood recurrence intervals. Continuous video monitoring conducted during snowmelt season periods in 2010 and 2011 yielded wood discharge observations at minima 15% of statistical bankfull flow, while maximum daily discharge explained 55% of observed daily wood piece variation. No statistically significant wood discharge differences were found in snowmelt season observations, likely caused by domination of the hydrograph by diurnal pulses within the seasonal cycle. Wood piece sizes in upstream watershed locations were found to be significantly longer but not significantly larger in diameter than those observed in transport or measured in the reservoir, an indication that more downstream fining of length than diameter may occur during transport. A conceptual model and functional framework are introduced in support of a watershed-scale explanation of wood export, transport, and storage processes applicable to large, Mediterranean-climate, mountain watershed settings.
... Wohl & Scott (2017), for example, distinguished channel-spanning wood jam steps and backwater sediment wedges (e.g., Short et al., 2015) in steep channels from more widespread channel aggradation associated with wood-induced increases in bed hydraulic roughness (e.g., Brooks et al., 2003). Other studies have documented wood rafts and associated floodplain sedimentation in large, low-gradient rivers (e.g., Boivin et al., 2015;Triska, 1984). We can conceptualize these interactions between large wood and sediment to include six basic forms of wood-induced deposition in river corridors, which can be paired with wood-induced erosion in river corridors ( Figure 1). ...
Large wood causes and responds to deposition and erosion within a river corridor. We focus on the anastomosing, gravel‐bed Swan River and two meandering, gravel‐bed tributaries in northwestern Montana, USA to explore the temporal dimensions of deposition and erosion associated with channel avulsions and island formation and to introduce the concept of wood levees. Channel avulsion represents isolation of part of the existing floodplain and formation of an anastomosing channel planform, with wood‐induced deposition at the point of channel bifurcation. Islands form at a wood jam that migrates upstream with time as sediment accumulates in the lee of the jam. The island creates only a local interruption of the single‐channel planform. We use tree‐ring and ¹⁴ C dating to constrain wood‐induced island ages. We interpret the three wood‐induced forms of deposition and erosion that we describe here as reflecting a temporal continuum. Wood levees have primarily non‐woody vegetation and may be transient relative to the other features. Tributary islands appear to persist from a decade to over a century. Tree ages of 100–200 years at the floodplain avulsion site and the characteristics of the secondary channels suggest that these wood‐induced avulsion features can persist for more than a century. Understanding the temporal dynamics of wood‐induced features and spatial variation in erosion and deposition provides insight into the dynamics and spatial heterogeneity of natural river corridors, with implications for river restoration.
... Organic carbon stock in river corridors (active channel(s), floodplain, hyporheic zone) occurs primarily in the form of floodplain soil (here, soil refers to all floodplain sediment and includes litter and duff created by particulate organic matter smaller than large wood), downed dead wood pieces >10 cm in diameter and 1 m in length (hereafter, large wood), and living riparian vegetation (Sutfin et al., 2016). Active channels can contain substantial quantities of large wood (Triska, 1984;Wohl, 2014;Boivin et al., 2015), but the majority of carbon in most river corridors is found in the floodplain (e.g., Sutfin et al., 2016;Scott and Wohl, 2020). River restoration has traditionally been focused on the active channel but is gradually broadening to include an explicit focus on hydrologic connectivity within the river corridor. ...
Restoration aimed at rewetting the valley floor has the potential to increase organic carbon stock in the form of floodplain soil carbon, downed wood, and riparian vegetation. The primary goal of stream restoration is typically to restore habitat or maintain balance between natural ecosystem function and human land use. Although many benefits result from stream restoration, the carbon sequestration potential of different restoration approaches in diverse geographic settings has not yet been quantified. We investigate the carbon storage potential of restored stream segments (known as treatment segments) relative to otherwise analogous degraded and reference segments. We develop a conceptual framework to identify the conditions that maximize carbon storage in relation to characteristics of the river corridor and specific restoration practices and propose response surfaces for carbon storage. We illustrate application and quantification of the conceptual framework using data from a pilot study of treatment, degraded, and reference stream segments along two streams in Oregon, United States. The conceptual model is designed to help managers identify levels of hydrologic connectivity, channel and floodplain dynamics, floodplain vegetation, and other variables that may optimize carbon storage at a treatment site.
... As transport capacity increases, logjams are more likely to be composed of pieces transported to a site with persistent, locally reduced transport capacity, such as the head of a bar or vegetated island or the mouth of a secondary channel Bertoldi et al., 2013;Gurnell et al., 2000;Schenk et al., 2014;Wohl et al., 2018). Logjams are less likely to span the entire bankfull channel as channel width increases relative to wood piece size, although naturally occurring wood rafts composed of thousands of individual wood pieces occur in a few places today (Boivin et al., 2015;Kramer & Wohl, 2015) and were more widespread historically (Triska, 1984;Wohl, 2014). Consequently, the size of wood accumulations that are commonly the focus of management and that are capable of creating channel-spanning logjams and backwater pool storage typically occur in channels ≤25 m wide (e.g., Bilby & Ward, 1989;Wohl & Scott, 2017). ...
Plain Language Summary
Logjams are accumulations of three or more large wood pieces in streams and stream environments. Logjams can obstruct flow and create frictional resistance in small stream channels, creating many physical and beneficial ecological effects in stream environments. This includes, but is not limited to, temporary storage of water, sediment, and organic matter, which translates to habitat and nutrient availability for aquatic organisms. Despite these benefits, deforestation and active wood removal from stream environments have significantly reduced the size and abundance of logjams throughout the temperate latitudes, contributing to the loss of ecological integrity and the simplification of stream channels. Stream restoration projects are increasingly using engineered logjams (ELJs), which are less likely to span a stream channel than naturally occurring logjams. Limited understanding of how logjam characteristics relate to specific effects constrains our ability to evaluate whether ELJs have comparable effects to natural logjams. We systematically evaluate characteristics and effects of 183 logjams in unaltered headwater Southern Rocky Mountain streams. We find that channel‐spanning logjams have significantly greater effects, such as pool and organic matter volume storage, than non‐channel‐spanning logjams, and recommend considering channel‐spanning ELJs in restoration projects in small streams to maximize retention.
... As transport capacity increases, logjams are more likely to be composed of pieces transported to a site with persistent, locally reduced transport capacity, such as the head of a bar or vegetated island or the mouth of a secondary channel Bertoldi et al., 2013;Gurnell et al., 2000;Schenk et al., 2014;Wohl et al., 2018). Logjams are less likely to span the entire bankfull channel as channel width increases relative to wood piece size, although naturally occurring wood rafts composed of thousands of individual wood pieces occur in a few places today (Boivin et al., 2015;Kramer & Wohl, 2015) and were more widespread historically (Triska, 1984;Wohl, 2014). Consequently, the size of wood accumulations that are commonly the focus of management and that are capable of creating channel-spanning logjams and backwater pool storage typically occur in channels ≤25 m wide (e.g., Bilby & Ward, 1989;Wohl & Scott, 2017). ...
... Il a été observé sur la rivière Saint-Jean que les embâcles de bois dans l'embouchure ont engendrés des avulsions à chaque période de dix ans. La présence de bois en rivière a permis l'accumulation de sédiments, causant ainsi une aggradation du lit qui a engendré la création d'un nouveau chenal principal(Boivin et al., 2015). L'embouchure de la rivière Port-Daniel se comporte d'une façon similaire en réponse à la présence de bois, particulièrement entre 2004 et 2016 où quelques apports considérables en bois sont arrivés dans le segment estuarien. ...
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.
... Other wood rafts were described on the rivers of the Pacific Northwest, including those in Oregon's Willamette Valley and Washington's Puget Sound lowlands (Sedell and Luchessa 1981;Collins et al. , 2003, and in diverse forested regions of the United States (Wohl 2014) where mass recruitment could occur during tornadoes, microbursts or other intense winds capable of blowing down large numbers of trees, and debris flows and landslides. Although uncommon, wood rafts still occur today (Webster et al. 2002;Erskine et al. 2012;Martín-Vide et al. 2014;Boivin et al. 2015). Buried wood in channels and floodplains record long-term accumulation of wood along stream corridors (Guyette et al. 2008;Davies et al. 2014). ...
Large wood and beaver dams are fundamental components of forested stream ecosystems but can also create hazards. We present guidelines for identifying stream segments that maximize environmental benefits while minimizing hazards. We focus on lesser gradient stream segments, although wood can be ecologically beneficial anywhere in a river network. Stream segments can be targeted for field-based evaluation using checklists for scenarios of either retention or reintroduction for logjams or beaver dams. We also present the Wood Jam Dynamics Database and Assessment Model, which incorporates a machine-learning-based statistical analysis to predict wood jam dynamics and provides a standardized survey protocol for wood jams.
... Toutefois, la littérature disponible semble confirmer certaines observations relatives à la dynamique du bois mort dans l'estuaire de la rivière Mont-Louis. rivière Saint-Jean est caractérisée par un delta où s'est accumulé un embâcle de plus de 3 km de long, ce qui contraste avec la quantité de bois retrouvé dans l'estuaire de la rivière Mont-Louis (Boivin et al., 2017a ;Boivin et al., 2017 b ;Boivin et al., 2015). (Boivin et al., 2017a ;2017 b ;2015 ;Lawrence et al., 2013 ;Fremier et al., 2010 ;Seo et al., 2010 ;2008, Martin et Benda, 2001, celle du tronçon (Martin et al., 2016 ;Iroumé et al., 2015 ;Davidson et Eaton, 2013 ;Nagayama et al., 2012, Curran, 2010 et celle du site (Ravazzalo et al., 2015 ;Keller et Swanson, 1979). ...
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.
... Although most contemporary studies of wood in rivers focus on small to mediumsized rivers, even the largest rivers historically had substantial quantities of wood (Triska 1984;Montgomery et al. 2003;Wohl 2014a). Large wood continues to influence some large rivers with less alteration of land cover in the drainage basin (e.g., Martín-Vide et al. 2014;Boivin et al. 2015;Kramer et al. 2017). ...
This work is designed to broaden the scope with which many people regard a river. Rivers are commonly regarded from a very simplistic perspective as conduits for downstream flows of water. In this context, it may be considered acceptable and necessary to engineer the channel to either facilitate such flows (e.g., channelization, levees) or limit flows and store water (e.g., water supply reservoirs, flood control). The book presents the concept of a river as a spatially and temporally complex ecosystem that is likely to be disrupted in unexpected and damaging ways by direct river engineering and by human activities throughout a drainage basin.
Viewing a river as a complex ecosystem with nonlinear responses to human activities will help to promote a more nuanced and effective approach to managing river ecosystems and to sustaining the water resources that derive from rivers. In this context, water resources refers to ecosystem services including water supply, water quality, flood control, erosion control, and riverine biota (e.g., freshwater fisheries). Chapters in this book draw extensively on existing literature but integrate this literature from a fresh perspective. General principles are expanded upon and illustrated with photographs, line drawings, tables, and brief, site-specific case studies from rivers around the world.
... Existing syntheses of wood loads in diverse rivers commonly include data from moderate to large rivers in Europe and North America (e.g., Piégay, 2003;LeLay et al., 2013;Ruiz-Villanueva et al., 2016), which typically have a long history of management that might be expected to result in wood loads below the natural range of variability. The presence of contemporary (Boivin et al., 2015) or historical (Triska, 1984) wood rafts on large rivers suggests that contemporary assumptions of an inverse relationship between wood load and channel size may be heavily influenced by the long history of anthropogenic modification of forest and river characteristics in moderate to large rivers of the temperate zone. ...
Instream large wood in forested rivers creates diverse physical and ecological effects and is a vital component of river process and form. The majority of research on wood in rivers has been conducted within a limited geographic range, raising questions about the applicability of resulting insights. We analyze data from 438 river segments in old-growth or unmanaged forests and 250 river segments in lightly managed forests representing diverse environments. We evaluate whether drainage area, channel width, and channel slope influence instream wood load in unmanaged forests across bioclimatic regions. Here we show that, without accounting for variations across regions, these numeric variables do not correlate significantly with wood loads. When accounting for the influence of all available potential influences on wood load in unmanaged forest rivers, bioclimatic region, drainage area, and channel width are the dominant predictors of wood load, and the relationship between wood load and channel width differs between regions. Combining data across bioclimatic regions, unmanaged rivers have significantly greater wood loads than lightly managed forests. Splitting data by bioclimatic region, unmanaged rivers in the northern dry conifer and northern wet conifer regions have significantly greater wood loads than lightly managed forests, but wood loads in the northern wet deciduous region do not differ between unmanaged and lightly managed forests. Our findings suggest that (i) bioclimatic region is a critical factor in predicting and understanding wood dynamics in rivers, (ii) even historic or relatively light levels of timber harvest and wood removal can create persistent differences in wood loads, and (iii) substantial variation in wood load among river segments within a bioclimatic region suggests that riparian forest and river management should focus on processes that maintain wood loads capable of creating desired physical and ecological effects rather than specified volumes of wood.
... Although most contemporary studies of wood in rivers focus on small to mediumsized rivers, even the largest rivers historically had substantial quantities of wood (Triska 1984;Montgomery et al. 2003;Wohl 2014a). Large wood continues to influence some large rivers with less alteration of land cover in the drainage basin (e.g., Martín-Vide et al. 2014;Boivin et al. 2015;Kramer et al. 2017). ...
People have been altering the environment since prehistory. Archeological records and the stratigraphy of valley bottoms suggest that prehistoric alteration of native upland vegetation for grazing and crops resulted in enhanced sediment yields to river corridors, as well as associated changes in channel dimensions and planform and channel-floodplain connectivity (e.g., Mei-e and Xianmo 1994; Stinchcomb et al. 2011). The magnitude of these changes varied through time and space. Examples of intensive vegetation clearing and valley-bottom aggradation come from diverse regions. In the southeastern United States, nineteenth century row-crop agriculture led to floodplain deposition of more than a meter of sediment (Jackson et al. 2005). In southeastern Australia, nineteenth century land clearance caused channel and floodplain aggradation (Brooks and Brierley 1997). In southern Poland, land clearance for agriculture during the late seventeenth to nineteenth centuries triggered increased sediment yields that changed meandering rivers into braided channels (Latocha and Migoń 2006). Conversely, twentieth century declining resource use, regrowth of upland vegetation, and erosion of channels occurred in mountainous regions of western and central Europe (Latocha and Migoń 2006).
... Although most contemporary studies of wood in rivers focus on small to mediumsized rivers, even the largest rivers historically had substantial quantities of wood (Triska 1984;Montgomery et al. 2003;Wohl 2014a). Large wood continues to influence some large rivers with less alteration of land cover in the drainage basin (e.g., Martín-Vide et al. 2014;Boivin et al. 2015;Kramer et al. 2017). ...
The previous chapter reviewed a long list of human activities that have directly and indirectly altered process and form in river ecosystems, with an associated loss of ecosystem services. Management in many river basins now focuses on trying to restore some balance between existing, typically consumptive or homogenizing uses of river resources versus restoration of diversity, sustainability, and river ecosystem health. None of the latter three terms is easy to define. Diversity refers to variety but, as discussed in Chap. 2, there are multiple ways to define physical or biotic diversity and no particular metric is consistently better in all situations or for all purposes. Sustainability in an ecological context typically refers to the ability of ecosystems to remain diverse and productive. In a physical context, sustainability may refer to the ability of a system to continue functioning or providing natural resources. River health also has multiple potential definitions. Even using the relatively simple definition in Chap. 1, that river health is the degree to which a river ecosystem matches natural conditions, requires understanding natural conditions. On the one hand, use and understanding of words matters and people may use similar words but have different objectives or desired outcomes. On the other hand, diversity, sustainability, and river health are now widely used and there is at least broad consensus on the meaning of these words. So, what is being done to protect and restore river corridors? This chapter reviews the development of river restoration during the latter twentieth century and early twenty-first century; discusses particular concepts used in restoration; and presents specific examples of watershed-scale restoration.
... Although most contemporary studies of wood in rivers focus on small to mediumsized rivers, even the largest rivers historically had substantial quantities of wood (Triska 1984;Montgomery et al. 2003;Wohl 2014a). Large wood continues to influence some large rivers with less alteration of land cover in the drainage basin (e.g., Martín-Vide et al. 2014;Boivin et al. 2015;Kramer et al. 2017). ...
This chapter reviews the different physical components of the river corridor, the physical processes that create and maintain those components, and the interactions between physical processes and living organisms. Among the critical aspects of physical processes and physical-biotic interactions are transfers of matter and energy and the occasional disturbances that reconfigure the river ecosystem and the processes occurring within the ecosystem. Individual rivers and segments of rivers respond differently to these disturbances and the nature of the response is characterized by how much the river ecosystem changes and how quickly the ecosystem recovers from change.
Large wood (LW) is widely recognized as a significant driver of geomorphic and ecological processes in river systems, but research on LW has been focused largely on low‐order streams in high‐gradient catchments. By comparison, there have been relatively few studies examining the channel‐scale distribution of LW in higher‐order, low‐gradient river systems, such as those in the Coastal Plain of the Southeast US. Here, a field survey of LW in three Coastal Plain rivers in Alabama and North Carolina was conducted. Total wood loads were calculated, LW characteristics were examined, and Ripley's K analysis was used to investigate the channel‐scale spatial distribution of LW in the study rivers for all pieces and for subsets based on stability and decay class. Results indicate that the range of LW loads in the study rivers (9.6–20.8 m ³ per 100‐m channel length) is generally in line with loads reported for other temperate forested sites. Over half of the surveyed LW pieces were oriented perpendicular to the channel, and substantial proportions (36%–44%) were pinned, favoring the formation of jams. Ripley's K analysis showed that, on two of the three study rivers, LW was significantly clustered at short distance intervals, with higher degrees of clustering for pinned pieces, indicating the concentration of these pieces in jams. Older LW pieces (as indicated by decay class) were generally more clustered than new ones, potentially indicating the role of transport in moving pieces with longer residence time to favorable deposition locations during mobilizing flows.
In this article, we track the evolution of fluvial biogeomorphology from the middle of the 20th century to the present. We consider the emergence of fluvial biogeomorphology as an interdisciplinary research area that integrates knowledge drawn primarily from fluvial geomorphology and plant ecology, but with inputs from hydrology and landscape ecology. We start by assembling evidence for the emergence of the field of fluvial biogeomorphology with a keyword search of the Web of Science and a detailed analysis of papers published in two scientific journals: a geomorphology journal—Earth Surface Processes and Landforms; a multidisciplinary river science journal—River Research and Applications. Based on this evidence, we identify three distinct time periods in the development of fluvial biogeomorphology: the ‘early years’ before 1990; the transitional decade of the 1990s; and the period of rapid expansion and diversification in themes, methods and investigation scales since 2000. Because the literature is vast, we can only summarize developments in each of these time periods, but we refer to recent in‐depth reviews and conceptual perspectives on relevant topics. Thus, rather than a full and deep review, we present an annotated bibliographic overview of the development of fluvial biogeomorphology, whereby the text describes broad trends but is supported by tables of citations that can deliver greater detail. We end with a brief consideration of likely future developments.
Plain Language Summary
The Arctic is warming rapidly, and this can increase landscape erosion. Consequently, carbon can be transferred into rivers and transported toward the Arctic Ocean. To date, work has tracked finer material dissolved in river water and the size of sand grains but has missed large pieces of wood that fall or slide into rivers. Wood is an important carbon‐rich material that may break down differently from the finer carbon pools, however, the amount of wood stored in Arctic river deltas has not been measured before. We also don't know the age of wood in those deposits. Here we study the Mackenzie River Delta, where river‐sourced wood is common and deposits extensive. We use very high‐resolution satellite images which show individual pieces of wood and use a machine learning technique to map wood across the delta. We also visited the deposits to measure their size and collected samples for radiocarbon dating. We find the wood is very young compared to other carbon pools carried by the river, and that the stocks of carbon are regionally important. Our work calls for further work to understand this overlooked carbon pool in river deltas and coastal regions of the Arctic.
Large active channels usually store more wood than channels with a narrow flow because of the availability of large unvegetated bars for wood deposition and inner functioning that usually supplies more wood through channel shifting. However, the dynamics of the wood supply (wood input, output, or stability) can vary substantially over time and the drivers are largely unknown. To explore them, we studied the temporal variability of large wood pieces and logjams along a 12-km reach of the lower Allier River using six series of aerial images of variable resolution acquired between 2009 and 2020, during which maximum river discharge fluctuated around the biannual (Q2) flood magnitude. We show that the wood budget was controlled by specific hydrological conditions. Wood output was best explained by water levels exceeding bankfull discharge (Q1.5). The duration of the highest magnitude flood (over bankfull discharge) was the best predictor of wood inputs, with shorter floods resulting in higher input rates. Finally, most of the wood remained stable when the river discharge did not exceed 60% of the bankfull discharge over a long period of time. Hydrological conditions driving jam build-up and removal were similar to those controlling individual wood piece dynamics. A succession of floods of similar (relatively low ~ Q2) magnitude and decreasing flood duration since 2016 have probably reinforced the filtering effect of wood obstacles, leading to positive feedback, which has been strengthened by riparian vegetation colonisation of the active channel.
Popularnonaukowa monigrafia zagadnień związanych z bilansem, rolą i ochroną martwych drzew w w ekosystemach, głównie (ale nie tylko) leśnych. Przedstawia m. in. zagadnienia:
Co to jest drewno. Jakich rozmiarów dorastają i jak długo żyją drzewa?
Pochodzenie, bilans i cechy martwego drewna, w lasach, poza lasem: w parkach, zadrzewieniach i innych środowiskach; w wodach. Martwe drewno na żywym drzewie – Mikrosiedliska nadrzewne. Znikający krajobraz ekotonów leśnych i lasów pastwiskowych.
Etapy i konsekwencje zamierania drzew. Jak martwe drzewa „ożywają”: kolonizacja martwych drzew i martwego drewna
Zamierające i martwe drewno jako środowisko życia. Organizmy zwiąane z martwym drewnem.
Funkcje ekosystemowe martwego drewna: Leśne „paliwo”, magazynowanie materii organicznej, akumulacja węgla i azotu, magazynowanie wody, rola martwych drzew w odnowieniu lasu, ochrona przed erozją, rola w procesach glebowych, rola w ciekach.
Rola martwego drewna w ochronie lasu i ochronie przyrody. Rola w leśnictwie i świadomość leśników. Martwe drewno jako składnik chronionych ekosystemów i wskaźnik ich stanu. Ochrona gatunkowa zwiążanych z martwym drewnem zwierząt, roślin i grzybów, w tym gatunków reliktowych.
Rozległe zaburzenia – niechciany dar przyrody?
Martwe drewno a zagadnienia bezpieczeństwa.
Martwe drewno w nauce i gospodarce.
Metody jakościowej i ilościowej oceny martwego drewna.
„Drugie Zycie Drzewa”, autorstwa J.M. Gutowskiego, A. Bobca, P. Pawlaczyka i K. Zuba ukazało się po raz pierwszy w 2004 r. Obecne II wydanie (2022 r.) jest znacznie zmienione i rozbudowane, stosownie do obecnej wiedzy na temat ekologicznej roli martwych drzew. Wiedza ta przez 18 lat jakie minęły od I wydania, wzrosła niepomiernie: w 2021 r. internetowe wyszukiwarki literatury naukowej znajdowały ok. 40 tys. publikacji na ten temat. Blisko połowa z nich pochodzi z ostatniego dziesięciolecia.
Do autorów II wydania dołączyli: Michał Ciach i Anna Kujawa. W szczególności szeroko zostały opisane zagadnienia związane z rolą tzw. drzew biocenotycznych i mikrosiedlisk nadrzewnych w lasach. Zupełnie nową treść i jakość uzyskały rozdziały opisujące grzyby, porosty i śluzowce oraz ich związki z martwym drewnem. O nowe zagadnienia i treści został rozszerzony rozdział „Martwe drewno w ochronie lasu i ochronie przyrody”, który zaktualizowano też do obecnego stanu prawnego. Znacznie szerzej przedstawiono rolę martwego drewna w wodach. Zaktualizowano oraz uzupełniono, przede wszystkim o nową literaturę, również pozostałe rozdziały publikacji. Znacznie rozbudowano materiał ilustracyjny. Nowe wydanie liczy ponad 340 stron, dodatkowo na większym formacie, co oznacza ok. dwukrotnie większą objętość od wydania I.
Książka w wersji elektronicznej (pdf) jest dostępna także na stronach wydawcy (The book is available at the publisher website): https://www.wwf.pl/sites/default/files/2022-03/drugie-zycie-drzewa-03-2022.pdf
Rivers historically transported unquantified volumes of driftwood to the ocean. Driftwood alters coastal sediment dynamics and provides food and habitat for diverse organisms. Floating driftwood supports open-ocean organisms. Sunken wood sustains seafloor communities. Centuries of deforestation, flow regulation, and channel engineering have substantially reduced riverine large wood fluxes to the oceans. Here, we use contemporary records of wood flux to reservoirs and coastal regions to estimate the magnitude of potential contemporary global wood fluxes. We estimate that 4.7 million m3 of large wood could enter the oceans each year (the 95% prediction interval range is ~300,000 to 70 million m3). This represents an upper bound for contemporary wood fluxes to the oceans because of wood removal from rivers and reservoirs and a lower bound for historical wood fluxes because of deforestation and river engineering. Substantial reduction of this wood flux likely negatively affects coastal and marine environments.
Les processus glaciels sont un paramètre fondamental de la dynamique des rivières. Ceux-ci affectent notamment la morphologie du lit et du chenal des cours d'eau, dont la rivière l'Acadie. S'écoulant du sud au nord sur 84 km, la rivière l'Acadie est un affluent de la rivière Richelieu située en Montérégie, au Québec. Celle-ci présente des problèmes récurrents d'inondations hivernales ayant de lourds impacts sur les milieux habités des villes de Chambly et Carignan. La recherche présentée ici a pour objectif d'acquérir des connaissances sur le régime d'embâcles de glace par leur spatialisation au sein du bassin versant de la rivière l'Acadie. Suivant une approche hydrogéomorphologique, une caractérisation des propriétés du bassin versant, de la rivière puis des berges de la rivière l'Acadie a été effectuée afin de spatialiser l'activité glacielle le long de celle-ci. Par la suite, la fréquence des événements d'embâcles de glace aux endroits ciblés a été établie à l'aide des cernes d'arbres et des archives documentaires pour comprendre la synergie entre les phénomènes d'embâcles et les autres processus se déroulant sur la rivière. Les résultats ont démontré comment la morphométrie et l'hydrographie du bassin versant, l'omniprésence de l'agriculture et des infrastructures civiles ainsi que l'héritage de la dernière glaciation quaternaire favorisent l'activité glacielle sur la rivière. De plus, l'étude des berges et des impacts glaciels a permis de localiser, différencier et expliquer les processus d'embâcles dominant les trois secteurs situés en aval de la rivière. En somme, il a été possible d'évaluer la signature du régime glaciel sur les berges et de comprendre l'évolution longitudinale de l'activité glacielle le long de cette rivière.
Wood in rivers plays a major role both ecologically and morphologically. In recent decades, due to human activities in the river channels and along the riparian zone, wood obstruction and jamming has exacerbated flooding hazards and infrastructure damage. Therefore, it is necessary to quantify the wood flux and discharge in rivers to improve wood hazard management. Among the various methods for monitoring the wood flux in a river, the streamside videography technique is effective given its high temporal and spatial resolution. Previous work monitored the wood discharge (m³/s) using this technique in the Ain River (France) during three floods (MacVicar & Piégay, 2012), and the same method is implemented on the Isère River (France) to obtain the statistics of wood discharge for two floods. Comparison between the two sites supports the generalization of both the monitoring technique and the link between wood discharge and flood characteristics. We first show that the maximum wood discharge is observed at bankfull discharge, and we confirm the three stage model proposed by (MacVicar & Piégay, 2012). Additionally, transverse distributions of the number of wood pieces and corresponding wood length appear to be similar for different flood magnitudes on each site. As a technical contribution, the use of the same technique on two sites allows for recommendations on key decisions related to the location and implementation of the equipment. Both statistical and technical contributions can be used by decision makers to implement this monitoring technique, acquire the wood transport parameters, and evaluate the potential wood hazards at local scale or along a river.
Fallen trees and their remains, i.e. woody debris, are an important element of the majority of the world’s river ecosystems. They are particularly significant for the functioning of river ecosystems in forest biomes, as they influence the formation of river channel morphological structures and natural habitats, initiate and maintain microhabitats for water organisms, and affect material and energy transfer along the river continuum. However, woody debris is also a problem in river management. Individual fallen tress do not block streamflow significantly, yet accumulation of debris can form woody jams, mainly on poorly designed hydrotechnical objects, which leads to flash flooding and destruction of riverside infrastructure. Such problems can be mitigated by technical measures (debris racks, stabilising logs on banks and in the river channel). Despite the issues, modern management of river ecosystems should take into account the management of woody debris and ensure its adequate amount in a river. Adding deadwood to rivers and maintaining its natural resources is applied in the majority of river restoration projects.
Ważnym elementem większości ekosystemów rzecznych świata są powalone do rzeki drzewa i ich szczątki, czyli tzw. rumosz drzewny. Są one jednym z kluczowych elementów dla funkcjonowania większości ekosystemów rzecznych, a szczególnie wszystkich rzek płynących w strefie klimatycznej lasów, wpływając znacząco na kształtowanie się morfologii koryt rzecznych, rozwój siedlisk przyrodniczych, powstawanie i utrzymywanie się mikrosiedlisk istotnych dla organizmów wodnych, przepływ materii i energii w continuum rzecznym. Rumosz drzewny stanowi jednak też element problemowy w zarządzanie rzekami. Piętrzenie wody na pojedynczych zwalonych drzewach nie jest zwykle znaczące, ale znoszone przez wodę fragmenty drzew mogą tworzyć zatory, zwłaszcza na źle zaprojektowanych konstrukcjach hydrotechnicznych, a to może skutkować gwałtownymi wezbraniami i zniszczeniami przyrzecznej infrastruktury.
Problemy takie można minimalizować środkami technicznymi (łapacze rumoszu, stabilizacja kłód na brzegach i w korycie). Mimo pewnych problemów, współczesne ekosystemowe zarządzane rzekami powinno uwzględniać zarządzanie rumoszem drzewnym i zapewnienie jego odpowiedniej ilości w rzece. Uzupełnianie ilości martwych drzew w rzece i utrzymanie zasobów kształtujących się w sposób naturalny są elementami większości przedsięwzięć rewitalizacji rzek.
Key words: deadwood in water courses, river wood, coarse woody debris, woody jams, river bed dynamics, rivers maintenance, rivers restoration
Słowa kluczowe: martwe drewno w ciekach, gruby rumosz drzewny, zatory z rumoszu drzewnego, dynamika fluwialna koryta rzecznego, utrzymanie rzek, rewitalizacja rzek
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.
When and whence does wood enter large mountain alluvial rivers? How stable through time are characteristics and quantities of wood deposited in a reach? These simple questions related to the complex practice of wood budgeting are explored on the Isère River in France. We hypothesise that (i) the wood originates from the riparian zone all along the alluvial reach and that (ii) the characters and quantity of wood in the reach can vary through time according to flood occurrence and provenance. In order to validate these hypotheses, two complementary approaches were performed: (i) wood pieces were surveyed along 190. km river length and taxonomy, in-channel wood macromorphology, and dendrochemistry were used to infer wood origin (local vs. upstream, respective subbasin contributions) and transport conditions; (ii) wood movement was monitored using both tracking techniques in specific sampling plots and with an experiment orchestrated using wood placement coupled with a significant artificial flood. Surveys were done over a period of 3. years so as to include two distinct sampling events to explore wood deposition and mobilisation within a channel network under different flood conditions. One of the subbasins, the Arly River, underwent a 1-in-30-year flood in 2004, allowing us to assess its effect on in-channel wood quantity and characteristics.Results confirm that wood is primarily introduced by erosion from river banks but they are not always as close as expected from the sites of deposition. Temporal variability of wood introduced, deposited, and transferred downstream is also significant in terms of abundance and origin as shown by dendrochemical and macromorphological signatures. The types of wood observed along the channel length changes through time. Large flood signature can be detected from wood characteristics and uplands make a slight contribution. But in average, wood characteristics do not change much (no significant difference between years and tributaries in wood characteristics based on discriminant analysis). Data suggest that the interannual variability is fairly low, so that the diversity of wood characteristics is maintained by the complex and multiple sources of wood in the network. Further research is needed to better understand such patterns and to study physical breakage in space and time to better infer distance between sources and depositional zones.
Despite the abundance of large wood (LW) river studies there is still a lack of understanding of LW transport dynamics on large low gradient rivers. This study used 290 radio frequency identification tagged (RFID) LW and 54 metal (aluminum) tagged LW, to quantify the percent of in-channel LW that moves per year and what variables play a role in LW transport dynamics. Aluminum tags were installed and monitored on LW in-transit during the rising limb of a flood, the mean distance traveled by those pieces during the week was 13.3 river kilometers (km) with a maximum distance of 72 km. RFID tagged LW moved a mean of 11.9 km/yr with a maximum observed at 101.1 km/yr. Approximately 41% of LW low on the bank moves per year. The high rate of transport and distance traveled is likely due to the lack of interaction between LW floating in the channel and the channel boundaries, caused primarily by the width of the channel relative to length of the LW. Approximately 80% of the RFID tags moved past a fixed reader during the highest 20% of river stage per year. LW transport and logjam dynamics are complicated at high flows as pieces form temporary jams that continually expand and contract. Unlike most other studies, key members that create a logjam were defined more by stability than jam size or channel/hydrologic conditions. Finally, using an existing geomorphic database for the river, and data from this study, we were able to develop a comprehensive LW budget showing that 5% of the in-channel LW population turns over each year (input from mass wasting and fluvial erosion equals burial, decomposition, and export out of system) and another 16% of the population moving within the system. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.
Channel-spanning logjams completely span the active channel and create longitudinal discontinuities of the water surface and stream bed across at least two-thirds of the channel width. These jams disproportionately affect channel process and form relative to smaller jams that do not span the entire channel width. We analyze a spatially extensive dataset of 859 channel-spanning jams distributed along 124 km of 16 distinct rivers on the eastern side of Rocky Mountain National Park, Colorado, USA, with drainage areas spanning 2.6 to 258 km2 and diverse valley geometry and forest stand age. We categorized valley geometry in terms of lateral confinement (confined, partly confined, or unconfined), which correlates with gradient. Jams exhibit substantial downstream variability in spacing at channel lengths of 102–103 m. The number of jams within a reach is explained by a statistical model that includes drainage area, valley type (lateral confinement), and channel width. Longitudinal spacing of jams drops substantially at drainage areas greater than ~20 km2, although jam spacing exhibits tremendous variability at smaller drainage areas. We interpret the lack of jams at larger drainage areas to reflect increasing transport capacity for instream wood. We interpret the variability in jam spacing at small drainage areas to reflect local controls of valley geometry and associated wood recruitment and fluvial transport capacity. Our results suggest that management of instream wood designed to facilitate the formation of channel-spanning jams can be most effectively focused on smaller drainage areas where these jams are most abundant in the absence of management that alters instream wood recruitment or retention. Unmanaged streams in the study region with drainage area
Field surveys of stream channels in forested mountain drainage basins in southeast Alaska and Washington reveal that pool spacing depends on large woody debris (LWD) loading and channel type, slope, and width. Mean pool spacing in pool-riffle, plane-bed, and forced pool-riffle channels systematically decreases from greater than 13 channel widths per pool to less than 1 channel width with increasing LWD loading, whereas pool spacing in generally steeper, step-pool channels is independent of LWD loading. Although plane-bed and pool-riffle channels occur at similar low LWD loading, they exhibit typical pool spacings of greater than 9 and 2-4 channels widths, respectively. Forced pool-riffle channels have high LWD loading, typical pool spacing of
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.
During the May 18, 1980, eruption of Mount St. Helens, Washington, a pyroclastic surge introduced large volumes of coarse woody debris (CWD) and fine grained sediment to Clearwater Creek, approximately 15 km northeast of the summit. Effects of controlled CWD removal on sediment storage, substrate, and pool frequency and volume were measured in four reaches, each with three 200-m segments, from 1982 to 1990. In each reach the upstream segment served as a control with no debris removal, and CWD was totally and selectively removed from the other two segments. Unique among similar experiments are the large size and volume of CWD and the large inputs of fine grained sediment. Except for segments of two reaches that received debris torrents, the Clearwater channel thalweg scoured until 1985. In three reaches, total debris removal caused additional scour and coarsening of the bed surface compared to segments with no or partial debris removal. Pools contracted from 1982 to 1985 and expanded afterward, especially in control segments. Total debris removal apparently caused pools to become shallower and, in segments of low sinuosity, decreased the frequency of major pools. Habitat complexity decreased after total debris removal, as indicated by a decrease in the standard deviation of residual depth and an increase in the size of substrate patches.
The distribution of large woody debris (LWD) was studied along the concave outer bend of three meanders in the Ain River, 195 km long tributary of the upper Rhône River. The Ain River is a sixth-order channel dominated by a gravel-cobble bed substrate that meanders through a floodplain covered largely by riparian forest vegetation. The mass of LWD was measured in a 15-meter wide forest band along the three meander bends, with total loads calculated to be 56.1 t.ha-1 at the Mollon study site compared with 22.9 and 21.5 t.ha-1 at the study sites of Bublane and Blyes, respectively. The distribution of LWD within any one meander concavity was dependent on three main variables: 1) the position of the concavity in relation to the main flow axis; 2) the height of the bank; 3) the presence and position of overbank flow channels in the concavity. The type of vegetation community along the channel margin is not discriminating allowing to conclude that the LWD are mainly coming from upstream the bends rather than locally. The relative influence of each variable contrasted between the three study sites. The total LWD deposited along concavities was most strongly controlled by meander bend geometry. The supply areas for LWD, located a few kilometers upstream from the study sites, were also found to influence total LWD along concavities.
Findings from this study are applicable to managing instream large woody debris as part of ongoing efforts to restore alluvial forests along French rivers.
A 1-km reach of Brierly Brook, Nova Scotia, was studied from 1995 to 2004 to determine if the addition of artificial structures mimicking large woody debris could enhance Atlantic salmon populations. In 1995, digger logs (which mimic fallen trees) and deflectors (which narrow the channel) were constructed in a 250-m section of the brook devoid of woody debris (Old Restored Site). In 2003, 5 more digger logs and defectors were built in a previously unrestored section of the stream (New Restored Site). A third control site was left unchanged. Physical changes caused by the structures were monitored at the New Restored Site. Densities of juvenile and spawning Atlantic salmon were also monitored. At all sites, woody debris structures in the brook were important and effective in creating complex salmonid habitat. The structures narrowed the channel, scoured pools and undercut banks. They created habitat that parr used for summer and winter refuge and adult spawners used for cover and resting during upstream migration and spawning. The structures caused gravels to accumulate that spawning adults used to build redds and fry used for shelter. The reaches with structures had higher spawning densities than reaches without them; spawning increased in the New Restored Site relative to the control site. The absence of woody debris may be a bottleneck for salmonid populations in streams of the Atlantic Northeast. For streams with a small or immature riparian zone and little woody debris in the channel, woody structures may be an effective tool for restoring salmonid populations. Copyright © 2008 John Wiley & Sons, Ltd.
Wood load, channel parameters and valley parameters were surveyed in 50 contiguous stream segments each 25 m in length along 12 streams in the Colorado Front Range. Length and diameter of each piece of wood were measured, and the orientation of each piece was tallied as a ramp, buried, bridge or unattached. These data were then used to evaluate longitudinal patterns of wood distribution in forested headwater streams of the Colorado Front Range, and potential channel-, valley- and watershed-scale controls on these patterns. We hypothesized that (i) wood load decreases downstream, (ii) wood is non-randomly distributed at channel lengths of tens to hundreds of meters as a result of the presence of wood jams and (iii) the proportion of wood clustered into jams increases with drainage area as a result of downstream increases in relative capacity of a stream to transport wood introduced from the adjacent riparian zone and valley bottom. Results indicate a progressive downstream decrease in wood load within channels, and correlations between wood load and drainage area, elevation, channel width, bed gradient and total stream power. Results support the first and second hypotheses, but are inconclusive with respect to the third hypothesis. Wood is non-randomly distributed at lengths of tens to hundreds of meters, but the proportion of pieces in jams reaches a maximum at intermediate downstream distances within the study area. We use these results to propose a conceptual model illustrating downstream trends in wood within streams of the Colorado Front Range. Copyright © 2009 John Wiley & Sons, Ltd.
During the past decade, research on large in-stream wood has expanded beyond North America's Pacific Northwest to diverse environments and has shifted toward increasingly holistic perspectives that incorporate processes of wood recruitment, retention, and loss at scales from channel segments to entire watersheds. Syntheses of this rapidly expanding literature can be facilitated by agreement on primary variables and methods of measurement. In this paper we address these issues by listing the variables that we consider fundamental to studies of in-stream wood, discussing the sources of variability in their measurement, and suggesting more consistency in future studies. We recommend 23 variables for all studies of in-stream wood, as well as another 12 variables that we suggest for studies with more specific objectives. Each of these variables relates either to the size and characteristics of in-stream wood, to the geomorphic features of the channel and valley, or to the ecological characteristics of the riparian zone adjacent to the study reach. The variables were derived from an overview of those cited in the literature and from our collective field experiences. Copyright © 2010 John Wiley & Sons, Ltd.
Recent research has elucidated the positive ecological roles of large wood (LW) in fish-bearing channels. However, where logjams
increase local flooding and bank erosion, LW has negative impacts on public safety and property protection. Although our understanding
of reach-scale processes and patterns has increased dramatically in recent years, only a few studies have integrated this
knowledge at the watershed scale. Here we review variations in LW dynamics along a gradient of watershed sizes. In small watersheds,
a massive amount of LW, resulting from forest dynamics and hillslope processes, remains on the valley floor. These pieces
may persist for several decades and are eventually transported during debris flows. In intermediate watersheds, LW is dominantly
recruited by bank erosion from adjacent riparian areas. These pieces are continuously transported downstream with LW pieces
that are supplied from the upstream watershed by floods because these channels have a greater width and depth than the length
and diameter of the pieces, as well as a high stream power. This leads to fragmentation of the LW pieces, which increases
their transportability. In large watersheds, LW pieces are frequently recruited at locations where the channel is adjacent
to riparian forests. Floated LW pieces can accumulate along channels with wide floodplains. Storage in floodplains can lead
to more rapid decay than in an anaerobic environment, resulting in the subsequent removal of LW pieces from the system. Our
review presents a generalized view of LW processing at the watershed scale, and is relevant to ecosystem management, disaster
prevention and the identification of knowledge gaps.
KeywordsEcosystem management-Disaster prevention-Large wood dynamic-River systems-Watershed scale
Bien que les utilisateurs de prises d'eau ne soient pas responsables des entrées de bois dans les hydrosystèmes fluviaux, l'évolution de la législation et la demande sociale d'une protection accrue de l'environnement poussent les exploitants à reconsidérer leur gestion des corps flottants qui s'accumulent contre les barrages. Longtemps perçus comme une nuisance susceptible d'occasionner des pertes de charge, les bois flottants peuvent être valorisés, notamment dans le cadre du compostage et du chauffage. Mais cette valorisation reste tributaire de son insertion dans une filière dont le succès repose sur l'implication des différents acteurs à l'œuvre dans les territoires locaux de l'eau.
Le bois mort aggrave les conséquences des crues en s'accumulant au droit d'ouvrages, mais aussi en favorisant les sapements de berge et les débordements sur les propriétés riveraines. Face à ces problèmes, les gestionnaires préconisent un entretien sectorisé reposant des objectifs clairs afin de préserver les embâcles là où ils sont écologiquement intéressants. La construction d'ouvrages de rétention, lorsque des enjeux aval existent, ainsi que l'adaptation des infrastructures au transfert de flottants peuvent également être préconisés. Une campagne de sensibilisation des citoyens pourrait être aussi effectuée afin que ceux-ci perçoivent plus positivement ces structures naturelles.
Large organic debris in streams flowing through old-growth redwood forests in California significantly influence channel form and fluvial processes in small to intermediate size streams. The role of large organic debris is especially important in controlling the development of the long profile and in producing a diversity of channel morphologies and sediment storage sites. The residence time for the debris in the channel may exceed 200 yr.-from Authors
The paper discusses the role of large organic debris on channel form, fluvial processes, and development and maintenance of anadromous fish habitat for streams flowing through an old-growth redwood forest. Specifically considered are: how the large organic debris affects channel width, depth, and slope; diversity of anadromous fish habitats such as pools, riffles and bars; areal sorting of bedload material; erosion-deposition patterns; and the instream residence time for large organic debris.
A large river, in relation to wood dynamics, has a width several times greater than the height of the trees in its riparian area. Large rivers undergo particular physical and biological processes related to wood that vary according to their condition (pristine or managed) and their locations in the landscape (upland area or downstream, tropical or temperate climates). In this chapter, several topics are developed to illustrate how large wood plays a significant role in the functioning of large rivers: production and transfer of wood, interactions between wood and channel geometry (accumulation sites, trapping efficiency, effects of wood on channel forms), and interactions between wood and human activities and management (effects of wood on fish resources, damages associated with the wood, restoration and maintenance strategies). Bank erosion, wind, beavers, floodplain forest clearing by overbank flow, meteorological events (snow, wind), and humans (dump areas, residuals of timber harvest) are the main vectors of wood introduction to large rivers. The amount of wood stored in the channel is usually low compared to what is introduced annually. Wood is mainly located at the edge of the floodplain (islands, concave banks, side channels), but differences exist in accumulation sites, according to the channel pattern and geometry. The effects of wood on island formation as well as its effects on meander cut-off have been observed but are variable from one river to another according to the size of the wood and the character of the floodplain. Fish abundance and diversity are influenced by wood structures, even in rivers with low amounts of wood. Wood obstructions and their associated geomorphic facies provide rearing sites and habitats for aquatic invertebrates. Because the amount of wood in large rivers is usually low, it rarely increases flooding risks locally. Wood affects navigation where unobstructed channels are favored; wood transport has then a cost because it must be removed. When the wood in rivers is enhancing fish resources, there is a need to define a balance between the ecological benefit of the wood and the need for removing it for safety purposes. In the 1980s, research was focused on habitat questions at a local spatial scale, linking hydraulic and geomorphic conditions, and characters of fish species. A research priority is now necessary to understand wood mobility and its downstream impacts.
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.
Wood has been falling into rivers for millions of years, resulting in both local effects on channel processes and integrated influences on channel form and dynamics over a wide range of spatial and temporal scales. Effects of stable pieces of wood on local channel hydraulics and sediment transport can influence rates of bank erosion, create pools, or initiate sediment deposition and bar formation. At larger spatial scales, changes in the supply of large wood can trigger changes in both river-reach morphology and the interaction between a river and its floodplain. Over long time scales, wood-rich rivers may retain more sediment and have lower sediment transport rates and steeper slopes than comparable wood-poor channels. Most geomorphic effects of wood in rivers arise from large, stable logs that catalyze changes in the routing and storage of both smaller wood and sediment. The size of a log relative to the channel provides a reasonable gauge of the potential stability of in-channel wood. Channels with a high supply of large, potentially stable wood may experience substantial vertical variability in bed elevation independent from external forcing (e.g., climate variability, temporal variations in sediment supply, or tectonic activity). In some river systems, changes in the wood regime, as described by the size and amount of wood supplied to a river, can result in effects as great as those arising from changes in the sediment supply or the discharge regimes. Consequently, an understanding of the geomorphic effects of wood is crucial for assessing the condition and potential response of forest channels.
Following some definitions, this chapter explores wood retention in fluvial systems. Retention is then placed in the context of wood mobility and budgets. The role of wood in landform development from patch to landscape scales is explored not only through the direct impact of wood accumulations on flow hydraulics and associated erosion and deposition of sediment but also by considering interactions between wood and riparian vegetation. The chapter concludes by drawing together key aspects of wood and geomorphology and then briefly highlights the importance of wood for stream ecosystems and as a key component in river restoration.
The San Antonio River Delta (SARD), Texas, has experienced two major avulsions in the past 80 years, and a number of other historical and Holocene channel shifts. The causes and consequences of these avulsions – one of which is ongoing – were examined using a combination of fieldwork, geographic information system (GIS) analysis, and historical information to identify active, semi-active, and paleochannels and the sequence of shifting flow paths through the delta. The role of deposition patterns and antecedent morphology, large woody debris jams, and tectonic influences were given special attention. Sedimentation in the SARD is exacerbated by tectonic effects. Channel aggradation is ubiquitous, and superelevation of the channel bed above the level of backswamp areas on the floodplain is common. This creates ideal setup conditions for avulsions, and stable, cohesive fine-grained banks favor avulsions rather than lateral migration. Flood basins between the alluvial ridges associated with the aggraded channels exist, but avulsions occur by re-occupation of former channels found within or connected to the flood basins. Large woody debris and channel-blocking log-jams are common, and sometimes displace flow from the channel, triggering crevasses. However, a large, recurring log-jam at the site of the ongoing avulsion from the San Antonio River into Elm Bayou is not responsible for the channel shift. Rather, narrow, laterally stable channels resulting from flow splits lead to accumulation of wood. Some aspects of the SARD avulsion regime are typical of other deltas, while others are more novel. These includes avulsions involving tributaries and subchannels within the delta as well as from the dominant channel; tectonic influences on delta backstepping and on channel changes within the delta; avulsions as an indirect trigger for log-jam formation (as well as vice-versa); and maintenance of a multi-channel flow pattern distinct from classic anastamosing or distributary systems. Copyright © 2012 John Wiley & Sons, Ltd.
The Pilcomayo River flows south-eastwards from the Bolivian Andes across the Chaco Plains, setting the border between Argentina and Paraguay. It flows down along 1000 km, in principle, to finally join the Paraguay River. It spills over the plains during the rainy season from January to March. The sediment load of the Pilcomayo is one of the largest in the world: 140 million tons per year, which is mostly wash load from the upland Andes. The mean concentration of suspended sediment is 15 g/l. The maximum recorded concentration is as high as 60 g/l. The river has built a large fan covering a surface of 210,000 km2, with many abandoned channels. Today, it is a river prone to avulsion, raising border disputes between the two lowland countries, Argentina and Paraguay. Moreover, the very special feature of Pilcomayo River is that it does not actually flow into the Paraguay River. Very far upstream of the mouth in the Paraguay the channel blocks itself with sediment and wood debris forcing water and sediment to spread across the plains. Moreover, the point of blockage has moved hundreds of kilometers upstream throughout the 20th century. Many environmental issues arise because of this collapse (channel discontinuity), not the least of them is the migration of fish. The future of the river concerns Bolivia and the two lowland countries.
Responses by fish assemblages to individual restoration actions among a suite of channel modifications are not well understood. We investigated whether increasing woody debris abundance, without significant change to channel morphology, would increase native fish abundance and species richness in a sediment-disturbed river channel (Glenelg River, Victoria, Australia). We conducted a Before–After, Control-Impact design experiment at twelve locations containing either a high (n = 6) or low (n = 6) quantity of large woody debris (LWD). We added small woody debris (SWD) to half (n = 6: 3 high, 3 low LWD densities) of the locations to increase woody debris complexity without the impacts on channel morphology associated with LWD manipulations. Fish species richness and abundance was quantified using electrofishing surveys before (4 sampling trips) and after (3 sampling trips) SWD addition. Fish species richness was not associated with high or low quantities of LWD or with types of woody debris (LWD or SWD). Addition of SWD altered fish assemblage composition but the effect depended on LWD quantity. SWD additions to locations with low LWD quantities increased abundance of two, wood-affiliated species: Philypnodon grandiceps and Gadopsis marmoratus. SWD additions to locations with high LWD quantities increased abundance of P. grandiceps and Galaxias olidus. Fish body size was important in detecting a response to added SWD because for two species, only certain size classes responded: adults of P. grandiceps (>50 mm TL) and juveniles of G. marmoratus (<123 mm TL). Fish assemblages responded positively to increased density of SWD through local increases in abundance, despite channel sedimentation. Unlike LWD, SWD is relatively cheap to place in rivers because it does not require heavy machinery and can be obtained without tree mortality. The use of SWD to assist in habitat restoration, especially for small species of native fish and juvenile fish, should be considered as a strategy in river restoration.
The importance of large woody debris (LWD) in forested stream ecosystems is well documented. However, little is known about LWD in northern boreal forest streams. We investigated the abundance, characteristics, and function of LWD in 13 small tributary streams of the upper Yukon River basin, Yukon Territory, Canada. LWD abundance was similar to values reported from temperate regions, whereas LWD size and total volume were well below values for the Pacific Northwest. LWD formed 28% of the pools, which provide important habitat for juvenile chinook salmon (Oncorhynchus tshawytscha Walbaum). The median diameter of pool-forming pieces was 17 cm, and ring counts on fallen riparian trees indicated that pool-forming pieces were likely 70200 years old when downed. Juvenile chinook salmon density was correlated with LWD abundance in our study reaches. We conclude that despite differences in climate and forest type, LWD in Yukon streams and LWD in temperate regions appear to perform a similar function in creating fish habitat. Resource managers should consider the relatively slow tree growth and thus potentially long recovery times following human disturbances in these watersheds.
The role of wood in the formation and maintenance of complex dynamic floodplain surfaces is important and to date has received relatively limited attention compared to in-channel habitat processes. This paper explores the role of logjams as important agents of channel:floodplain interaction. We draw on a specific case study as well as examples from the literature to show that although the processes of interaction differ, the resulting dynamic floodplain patchwork is a common feature of rivers with logjams. In addition, we contend that the presence of logjams is an important factor in the evolution and maintenance of multiple channel patterns in both montane and lowland river environments. These observations have important implications for the definition of reference targets for river restoration.The specific results of this research show:1)The presence of a range of types of multiple channel network dissecting the floodplains of low order channels that are strongly associated with the presence of logjams.2)The relatively rapid formation of floodplain channels following logjam formation.3)The dynamic nature of logjams within headwater channels on both seasonal and annual timescales that lead to a highly dynamic habitat mosaic on the floodplain surface.4)An increased frequency of overbank flooding and high rates of floodplain sediment accumulation upstream of logjams and along floodplain channel networks that create the complex topography observed in the case study forested floodplains.
Bed-load transport experiments have been conducted in a steep gravel-bed open ditch. This initially straight ditch has been neglected for many years and looks at present like a second-order natural stream channel. The channel flows through a spruce forest and several log-jams have produced chutes and pools, creating supplementary roughness. The total shear stress has been evaluated using the slope-hydraulic radius product, and the ratio between grain and bed-form shear stresses has been calculated using different methods. The shear stress has also been evaluated from the shear velocities, and this gives a good evaluation of the grain shear stress. Additional experiments have been conducted with marked pebbles to estimate particle mobility and to improve the motion equations. Equations such as θc = a(Di/D50)b)b, defined by Andrews, apply in these cases but the values of a and b are lower than those produced by this author. In a second stage of experimentation, we have destroyed the log jams resulting in a diminution of the roughness and critical shear stress (when the total shear stress is used), an increase of the grain shear stress, and thus greater bed particle mobility for the same discharge. It emerges from these experiments that the log-jams contribute to the reduction of bed-load evacuation and explain the very weak bed-load discharge measured by a bed-load trap (0.3 t · km−2 yr−1).
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.
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.
The creation of cutoffs and of oxbow lakes is a well-known phenomenon of meandering rivers, but views on the extent to which they are inherent in meander behaviour have varied. Assumptions of meander behaviour have shifted from those of stability and equilibrium to recognition of gradual evolution and increased complexity of form. Alternative explanations of cutoff occurrence are discussed here in relation to a remarkable set of cutoffs that occurred in one reach of the River Bollin, UK, for which long-term historical evidence of meander evolution existed and which has been monitored for change and processes over the last 20 years. The cutoffs occurred during the high floods of winter 2000–2001. A series of hypotheses is examined, including the occurrence of floods and effects of hydrological changes. Although the flood events actually caused the cutoffs, the long-term pattern accords with ideas of chaotic behaviour and sinuosity of a river reaching a critical state at which clustering of meander cutoffs takes place. It is suggested that the occurrence of the cutoffs can be explained as inherent in meander behaviour.
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.
Total debris loading for a particular channel reach represents the relation between rates of debris entering and leaving the reach and is primarily a function of the following interrelated variables: number and size of trees in the vicinity of the channel, rate of decomposition, geology, valley-side slope, landslide activity, channel width, discharge, and upstream drainage. The study of large organic debris in streams is pertinent to two interrelated management problems brought about by road building and timber harvesting in northwestern California: (1) reduction of sediment pollution and (2) restoration and enhancement of anadromous fish habitat. In the management of streams to maximize production of anadromous fish in the coastal redwood environment, the role of large organic debris should be considered. -from Authors
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.
Stream channel development in forested areas is profoundly influenced by large organic debris (logs, limbs and rootwads greater than 10 cm in diameter) in the channels.
In low gradient meandering streams large organic debris enters the channel through bank erosion, mass wasting, blowdown, and collapse of trees due to ice loading. In small streams large organic debris may locally influence channel morphology and sediment transport processes because the stream may not have the competency to redistribute the debris. In larger streams flowing water may move large organic debris, concentrating it into distinct accumulations (debris jams). Organic debris may greatly affect channel form and process by: increasing or decreasing stability of stream banks; influencing development of midchannel bars and short braided reaches; and facilitating, with other favourable circumstances, development of meander cutoffs.
In steep gradient mountain streams organic debris may enter the channel by all the processes mentioned for low gradient streams. In addition, considerable debris may also enter the channel by way of debris avalanches or debris torrents. In small to intermediate size mountain streams with steep valley walls and little or no floodplain or flat valley floor, the effects of large organic debris on the fluvial processes and channel form may be very significant. Debris jams may locally accelerate or retard channel bed and bank erosion and/or deposition; create sites for significant sediment storage; and produce a stepped channel profile, herein referred to as ‘organic stepping’, which provides for variable channel morphology and flow conditions.
The effect of live or dead trees anchored by rootwads into the stream bank may not only greatly retard bank erosion but also influence channel width and the development of small scour holes along the channel beneath tree roots. Once trees fall into the stream, their influence on the channel form and process may be quite different than when they were defending the banks, and, depending on the size of the debris, size of the stream, and many other factors, their effects range from insignificant to very important.
Previously undocumented deposits are described that store suspended sediment in gravel-bedded rivers, termed ‘fine-grained channel margin’ (FGCM) deposits. FGCM deposits consist of sand, silt, clay, and organic matter that accumulate behind large woody debris (LWD) along the margins of the wetted perimeter of the single-thread, gravel-bed South River in Virginia. These deposits store a total mass equivalent to 17% to 43% of the annual suspended sediment load. Radiocarbon, 210Pb and 137C dating indicate that sediment in FGCM deposits ranges in age from 1 to more than 60 years. Reservoir theory suggests an average turnover time of 1·75 years and an annual exchange with the water column of a mass of sediment equivalent to 10% to 25% of the annual sediment load. The distribution of ages in the deposits can be fitted by a power function, suggesting that sediment stored in the deposits has a wide variety of transit times. Most sediment in storage is reworked quickly, but a small portion may remain in place for many decades. The presence of FGCM deposits indicates that suspended sediment is not simply transported downstream in gravel-bed rivers in agricultural watersheds: significant storage can occur over decadal timescales. South River has a history of mercury contamination and identifying sediment sources and sinks is critical for documenting the extent of contamination and for developing remediation plans. FGCM deposits should be considered in future sediment budget and sediment transport modeling studies of gravel-bed rivers in agricultural watersheds. Copyright © 2010 John Wiley & Sons, Ltd.
In‐channel large woody debris (LWD) promotes quality aquatic habitat through sediment sorting, pool scouring and in‐stream nutrient retention and transport. LWD recruitment occurs by numerous ecological and geomorphic mechanisms including channel migration, mass wasting and natural tree fall, yet LWD sourcing on the watershed scale remains poorly constrained. We developed a rapid and spatially extensive method for using light detection and ranging data to do the following: (i) estimate tree height and recruitable tree abundance throughout a watershed; (ii) determine the likelihood for the stream to recruit channel‐spanning trees at reach scales and assess whether mass wasting or channel migration is a dominant recruitment mechanism; and (iii) understand the contemporary and future distribution of LWD at a watershed scale. We utilized this method on the 78‐km‐long Narraguagus River in coastal Maine and found that potential channel‐spanning LWD composes approximately 6% of the valley area over the course of the river and is concentrated in spatially discrete reaches along the stream, with 5 km of the river valley accounting for 50% of the total potential LWD found in the system. We also determined that 83% of all potential LWD is located on valley sides, as opposed to 17% on floodplain and terrace surfaces. Approximately 3% of channel‐spanning vegetation along the river is located within one channel width of the stream. By examining topographic and morphologic variables (valley width, channel sinuosity, valley‐ side slope) over the length of the stream, we evaluated the dominant recruitment processes along the river and often found a spatial disconnect between the location of potential channel‐spanning LWD and recruitment mechanisms, which likely explains the low levels of LWD currently found in the system. This rapid method for identification of LWD sources is extendable to other basins and may prove valuable in locating future restoration projects aimed at increasing habitat quality through wood additions.
Effects of coarse woody debris (CWD) on channel morphology and sediment storage were investigated at five sites, representative of first-order to fifth-order streams. In the steep and bedrock-confined stream (first-second order), interaction between the channel and CWD was limited, except where breakage upon falling produced CWD pieces shorter than channel width. Channel widening, steepening and sediment storage associated with CWD were observed predominantly in third- to fifth-order streams. Variation in channel width and gradient was regulated by CWD. In the fifth-order stream, most of the CWD pieces derived from the riparian forest interacted directly with the channel without being suspended by sideslopes. In this system CWD promoted lateral channel migration, but sediment storage was temporary, with annual release and capture.
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.
1. Large wood forms an important component of woodland river ecosystems. The relationship between large wood and the physical characteristics of river systems varies greatly with changes in the tree species of the marginal woodland, the climatic and hydrological regime, the fluvial geomorphological setting and the river and woodland management context.
2. Research on large wood and fluvial processes over the last 25 years has focussed on three main themes: the effects of wood on flow hydraulics; on the transfer of mineral and organic sediment; and on the geomorphology of river channels.
3. Analogies between wood and mineral sediment transfer processes (supply, mobility and river characteristics that affect retention) are found useful as a framework for synthesising current knowledge on large wood in rivers.
4. An important property of wood is its size when scaled to the size of the river channel. ′Small′ channels are defined as those whose width is less than the majority of wood pieces (e.g. width < median wood piece length). `Medium' channels have widths greater than the size of most wood pieces (e.g. width < upper quartile wood piece length), and `Large' channels are wider than the length of all of the wood pieces delivered to them.
5. A conceptual framework defined here for evaluating the storage and dynamics of wood in rivers ranks the relative importance of hydrological characteristics (flow regime, sediment transport regime), wood characteristics (piece size, buoyancy, morphological complexity) and geomorphological characteristics (channel width, geomorphological style) in `Small', `Medium' and `Large' rivers.
6. Wood pieces are large in comparison with river size in `small' rivers, therefore they tend to remain close to where they are delivered to the river and provide important structures in the stream, controlling rather than responding to the hydrological and sediment transfer characteristics of the river.
7. For `Medium' rivers, the combination of wood length and form becomes critical to the stability of wood within the channel. Wood accumulations form as a result of smaller or more mobile wood pieces accumulating behind key pieces. Wood transport is governed mainly by the flow regime and the buoyancy of the wood. Even quite large wood pieces may require partial burial to give them stability, so enhancing the importance of the sediment transport regime.
8. Wood dynamics in `Large' rivers vary with the geometry of the channel (slope and channel pattern), which controls the delivery, mobility and breakage of wood, and also the characteristics of the riparian zone, from where the greatest volume of wood is introduced. Wood retention depends on the channel pattern and the distribution of flow velocity. A large amount is stored at the channel margins. The greater the contact between the active channel and the forested floodplain and islands, the greater the quantity of wood that is stored.
The study of accumulations of dead wood within the fluvial environment has been mainly undertaken in mountain streams and rivers within the Northwestern United States, and particularly in hydrosystems which have experienced little riparian vegetation cutting or disturbance by man. Appraisals of the spatial variability in the physical character of accumulations of dead wood has mainly highlighted the volumes of large woody debris (LWD) accumulations and the local channel morphological properties induced by their presence. The spatial variability in the accumulation and processing of organic material forms one of the central concepts of the River Continuum Concept, which characterises the occurrence and processing of organic material, of which LWD is an important component, according to a longitudinal gradient along a river's course. Some studies have extended the concept by illustrating the importance of the lateral dimension, particularly in large rivers with extensive floodplains, and by relating the occurrence of dead wood to fluvial morphodynamics. However, to date there has been no synthesis of the relationship between LWD and the geomorphic pattern of the river channel.
A quantitative framework is developed for analyzing the mass budget of in-stream woody debris. Wood budgets are necessary for defining the relative importance of different recruitment processes over short and long periods, for designing spatially explicit simulation models, and for estimating the range of variability. The framework is used to analyze century-long patterns of large woody debris in streams that are governed by episodic forest death (fire and wind), forest growth and chronic mortality, bank erosion, mass wasting, decay, and stream transport. Simplified mathematical expressions are used to represent climatic, hydrologic, geomorphic, and biotic processes. Results are expressed in terms of time series and probability distributions. Predictions include that in areas of longer fire rotation (500 years) toppling of fire-killed trees comprises only 15% of the long-term wood budget yet chronic stand mortality that affect the large standing forest biomass ensures continuous large volumes of wood in streams. In contrast, toppling of fire-killed trees in forest environments with shorter fire rotations (150 years) comprise about 50% of the wood budget and indicates that field observers have a significantly higher chance of encountering low wood volumes in streams. Wood recruitment by bank erosion should increase irregularly downstream and bank erosion recruitment should exceed mortality recruitment at a bank erosion rate of approximately 5 cm per year. Recruitment from debris flows represents the single largest point source of woody debris to streams. The rarity of debris flows, in conjunction with a 3% per year annual decay rate, limits the contribution of wood from debris flows to about 12% of the long-term wood budget. Fluvial transport of wood promotes an increase in both inter-jam spacing and jam volume downstream. The proportion of woody debris transported into a reach in comparison to lateral recruitment approaches an asymptotic maximum of 50% when tree height approaches channel width. The relationships among process rates, their spatial variance across landscapes, and the resulting probability distributions of long-term patterns of wood abundance are proposed as a set of general theoretical principles. New data on wood supply and storage at the network scale are needed to fully test the predictions made in this analysis.
Large wood maintains in-channel and floodplain habitats by influencing the biophysical character of the river corridor. Large wood dynamics in a river corridor are a product of watershed wide processes and also of local recruitment, transport, and storage. This complexity of scales added to the logistical constraints in taking measurements limits our understanding of large wood dynamics through the watershed. To begin to unravel this issue, we compiled a data set of the volume of large wood deposited annually into 131 reservoirs across Japan and compared large wood export to flow discharge and watershed characteristics (watershed size, latitude, channel slope, percent forest, and forest type). We found that large wood was predominately transported during peak flow events. Large wood export increased logarithmically with watershed area. The decreasing export rate of large wood per watershed area is interpreted as a combination of annual export variability in upper watersheds, a non-significant increase in large wood recruitment along the longitudinal gradient (potentially human influenced), the increase in long-term storage on adjacent large floodplains, and significant decay/fragmentation downstream. Watersheds < 10–20 km2 had a highly variable large wood export pattern, conforming generally to previously published work that suggest transport limitation in smaller watersheds. The data suggest the existence of an export threshold (∼ 75 km2) where large wood export is no longer related to watershed size. Export across all watershed sizes was controlled by watershed characteristics (slope, percent forested, etc.) and peak discharge events. The connection with upstream watersheds and laterally with the floodplain increases the net flux of large wood through downstream transport and retransport of buried logs. Identifying rates of large wood transport from watershed connectivity as a potential key input process will improve our basic understanding of geomorphic and ecological patterns within the watershed. These results highlight the importance of understanding the local- and watershed-scale dynamics of large wood in creating and maintaining more heterogeneous riparian and aquatic habitat along the river corridor.
Dynamique de prise en charge et de dépôt des débris ligneux dans les systèmes Ain et Drome. Mémoire de Maîtrise
- A Citterio
Citterio, A., 1996. Dynamique de prise en charge et de dépôt des débris ligneux dans les
systèmes Ain et Drome. Mémoire de Maîtrise. Université Lyon III, France (72 pp.).
Bilan forestier régional, basé sur les connaissances-Gaspésie-Les Îles
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Côté, M., Théau, J., Langis, M.-H., Fortin, S., 2008. Bilan forestier régional, basé sur les
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Les activités forestières à Gaspé (1700-1950). Recherche documentaire
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Cégep de la Gaspésie et des Îles.
Stream Channel Morphology: Comparison of Logged and Unlogged Wa-tersheds in the Queen Charlotte Islands. (M.Sc. thesis) Department of Geography Cutoffs galore!: Occurrence and causes of multiple cutoffs on a meandering river
- D Hogan
Hogan, D., 1985. Stream Channel Morphology: Comparison of Logged and Unlogged Wa-tersheds in the Queen Charlotte Islands. (M.Sc. thesis). Department of Geography, University of British Columbia, Vancouver, Canada, p. 206. Hooke, J.M., 2004. Cutoffs galore!: Occurrence and causes of multiple cutoffs on a meandering river. Geomorphology 61, 225–238.
Longitudinal distribution of erosion rates (m 2 /km) and cumulative curves (%) for the eroded surfaces and the wood volume input into the river system
- Fig
Fig. 9. Longitudinal distribution of erosion rates (m 2 /km) and cumulative curves (%) for the eroded surfaces and the wood volume input into the river system.
Effect of large organic debris on channel morphology and sediment storage in selected tributaries of Redwood Creek Les barrages face à la problématique des bois flottants: collecte, traitement et valorisation
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Keller, E.A., Macdonald, A., Tally, T., Merrit, N.J., 1985. Effect of large organic debris on channel morphology and sediment storage in selected tributaries of Redwood Creek. Geomorphic Processes and Aquatic Habitat in the Redwood Creek Drainage Basin: U.S. Geological Survey Professional Paper. Le Lay, Y., Moulin, B., 2007. Les barrages face à la problématique des bois flottants: collecte, traitement et valorisation. La Houille Blanche 3, 96–103.