the effects of large organic debris on sediment processes and stream morphology in vermont abstract research conducted on a small third order stream in the green mountains of vermont suggests that large organic debris lod has an important influence on areal sorting and storage of sediment spacing of pool riffle sequences and channel geometry large organic debris forms local base levels that trap over 26 cubic meters of sediment and cause over 14 percent of the vertical drop along a 412 meter study reach on tiger brook vermont the local base levels created by large organic debris accumulations are the most important control on sediment storage between large bedrock knickpoints along the study reach focusing fine grained sediment deposition in areas stable at low and moderate discharges the micro steps created by these lod local base levels dominate gradient and sediment storage at short time scales between the slowly evolving large bedrock macrosteps the relation that exists among the volumes of standing timber adjacent to the channel lod and sediment stored behind lod seems to indicate that large organic debris causes a negative feedback type mechanism where channel degradation leads to increased standing timber recruitment and large organic debris sediment storage sites

large wood recruitment processes and transported volumes in swiss mountain streams during the extreme flood of august 2005 abstract the extreme flood event that occurred in august 2005 was the most costly documented natural hazard event in the history of switzerland the flood was accompanied by the mobilization of 69 000 m3 of large wood lw throughout the affected area as recognized afterward wood played an important role in exacerbating the damages mainly because of log jams at bridges and weirs the present study aimed at assessing the risk posed by wood in various catchments by investigating the amount and spatial variability of recruited and transported lw data regarding lw quantities were obtained by field surveys remote sensing techniques lidar and gis analysis and was subsequently translated into a conceptual model of wood transport mass balance detailed wood budgets and transport diagrams were established for four study catchments of swiss mountain streams showing the spatial variability of lw recruitment and deposition despite some uncertainties with regard to parameter assumptions the sum of reconstructed wood input and observed deposition volumes agree reasonably well mass wasting such as landslides and debris flows were the dominant recruitment processes in headwater streams in contrast lw recruitment from lateral bank erosion became significant in the lower part of mountain streams where the catchment reached a size of about 100 km2 according to our analysis 88 of the reconstructed total wood input was fresh i e coming from living trees that were recruited from adjacent areas during the event this implies an average deadwood contribution of 12 most of which was estimated to have been in channel deadwood entrained during the flood event

stabilization of a gravel channel by large streamside obstructions and bedrock bends jacoby creek northwestern california jacoby creek bed width 12 m bankfull discharge 32 6 m 3 s contains stationary gravel bars that have forms and positions controlled by numerous large streamside obstructions bedrock outcrops large woody debris and rooted bank projections and bedrock bends bank projection width and bar volume measured in 104 channel segments 1 bed width long are significantly cross correlated at lags of 1 3 and 4 indicating the tendency for large obstructions and bends to form bars 3 to 4 bed widths downstream and 1 bed width upstream all of the 18 bars downstream of large obstructions or bends in the study reach were along the obstruction side of the channel or outside bank of the bend most of the pools 85 were next to large obstructions or in bends conversely 92 of large obstructions or bends had pools comparison of the volume of four bars with volumetric bar changes and volume of bedload transported during four high flow events suggests that rates of sediment transport were sufficient to cause major changes in bars during bankfull events the only important channel changes observed in 4 yr however have been associated with the movement of large woody debris and with changes in the angle at which the flow approaches an obstruction a general model is proposed that large obstructions and nonalluvial bends stabilize the form and location of gravel bars bars are stabilized by two related mechanisms 1 large obstructions and bends cause intense quasi steady secondary circulation in scour holes that terminate upstream bars at fixed locations obstruction width channel deflection scour hole width and bed width were measured at 26 obstructions these data show that obstructions wider than approximately one third of the bed form pools spanning the entire channel and thus terminating bars smaller obstructions form scour holes contained within a single bar 2 bars are deposited upstream of large obstructions and sharp bends because of backwater reductions in stream power bars are deposited downstream because flow energy is expended around obstructions and bends and because the flow expands downstream of constrictions that result from large obstructions the formation of bars and pools inherent in many gravel channels can thus be enhanced and fixed in position by flow structures set up around large obstructions and bends formed of resistant materials

distribution of bedrock and alluvial channels in forested mountain drainage basins mountain river networks often consist of both bedrock and alluvial channels1 5 the spatial distribution of which controls several fundamental geomorphological and ecological processes6 7 the nature of river channels can influence the rates of river incision and landscape evolution1 2 as well as the stream habitat characteristics affecting species abundance and aquatic ecosystem structure8 11 studies of the factors controlling the distribution of bedrock and alluvial channels have hitherto been limited to anthropogenic badlands12 here we investigate the distribution of channel types in forested mountain drainage basins and show that the occurrence of bedrock and alluvial channels can be described by a threshold model relating local sediment transport capacity to sediment supply in addition we find that valley spanning log jams create alluvial channels hospitable to aquatic life in what would otherwise be bedrock reaches the formation of such jams depends critically on the stabilizing presence of logs derived from the largest trees in the riverside forests suggesting that management strategies that allow harvesting of such trees can have a devastating influence on alluvial habitats in mountain drainage basins

log jam effects on bed load mobility from experiments conducted in a small gravel bed forest ditch abstract 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 c 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

pool spacing in forest channels 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 channel widths respectively forced pool riffle channels have high lwd loading typical pool spacing of 2 channel widths and slopes that overlap the ranges of free formed pool riffle and plane bed channel types while a forced pool riffle morphology may mask either of these low lwd loading morphologies channel slope provides an indicator of probable morphologic response to wood loss in forced pool riffle reaches at all study sites less than 40 of the lwd pieces force the formation of a pool we also find that channel width strongly influences pool spacing in forest streams with similar debris loading and that reaches flowing through previously clear cut forests have lower lwd loading and hence fewer pools than reaches in pristine forests

large wood sediment and flow regimes their interactions and temporal changes caused by human impacts in japan abstract water sediment and large wood lw are the three key components of dynamic river floodplain ecosystems we examined variations in sediment and lw discharge with respect to precipitation the presence of dams land and river use change and related channel incision and forest expansion on gravel bars and floodplains across japan the results indicated that unit sediment discharge and unit lw discharge were smaller in southern japan where precipitation intensity is generally much greater effective precipitation an index that takes current and antecedent precipitation into account was a strong predictor of discharge in small watersheds but not in larger watersheds however precipitation intensities related to unit sediment discharge in intermediate and large watersheds were smaller than those associated with unit lw discharge which we attribute to differences in particle shape and size and also transport mechanisms the relationship between river flow and discharge of sediment and lw lead us to posit that discharges of these components are supply limited in southern japan and transport limited in northern japan the cross sectional mean low flow bed elevation of gravel bed and sand bed rivers in japan decreased by 0 71 and 0 74 m on average respectively over the period 1960 2000 forest expansion on bars and floodplains has been prominent since the 1990s and trees apparently began to colonize gravel bars 10 to 20 years after riverbed degradation began forest recovery in headwater basins dam construction gravel mining and channelization over the past half century are likely the dominant factors that significantly reduced downstream sediment delivery thereby promoting channel incision and forest expansion changes in rivers and floodplains associated with channel incision and forest expansion alter the assemblages of aquatic and terrestrial organisms in riverine landscapes of japan and climate change may contribute to this change by intensified precipitation additionally regime shifts of water sediment and lw may continue or they may reach a dynamic state of quasi equilibrium in the future continued monitoring of these three components taking into account their geographic variation is critical for anticipating and managing future changes in river floodplain systems in japan and around the world

assessment of flow forces on large wood in rivers 1 large wood lw exerts an important influence on the geomorphology and ecology of streams and rivers the magnitudes of flow forces on lw are needed to support stream management activities and are typically computed using time mean lift and drag coefficients determined in laboratory flumes using small smooth cylinders herein we report measurements of forces on lw of varying complexity simple cylinder branching and complex root wad and surface bark roughness made in an outdoor grassed channel under steady and unsteady flows lw orientation relative to the primary flow direction and lw relative submergence were varied drag and lift coefficients for cylindrical unbranched lw followed patterns reported by others for metal cylinders in wind tunnels drag coefficients for cylindrical unbranched lw corrected for blockage effects ranged from 0 05 to 1 29 and lift coefficients ranged from 0 88 to 0 52 varying systematically with lw position relative to the channel bed and incident flow direction measured drag coefficients for the noncylindrical lw corrected for blockage effects ranged from 0 22 to 6 27 while lift coefficients varied from 3 65 to 30 84 systematic relationships between the relative submergence and orientation of branching lw and the drag and lift coefficients were not observed but coefficients were greatest for lw with few branches and converged on smaller values typical of blunt bodies as lw complexity increased for both simple and complex lw maximum lift and drag forces during the rising limb of unsteady flows were about 2 3 times greater than steady flow temporal mean values

effects of coarse woody debris and its removal on a channel affected by the 1980 eruption of mount st helens washington 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

changes in woody debris and bed material texture in a gravel bed channel abstract this study investigated the response of bed material texture under two distinct periods of log jam conditions in a 900 m study reach of carnation creek vancouver island bc a field program extending over seven flood seasons coupled with existing streamflow records channel maps and low altitude aerial photography provides observations of jam stability and permeability surface and subsurface grain size as well as bed material fluxes sediment supply calibre streambed stability and sediment exchange near jams all jams functioned as partial dams throughout the field program but the overall perturbation of sediment transfers decreased when two jams were breached bed material texture exhibited the largest differences over the study reach during a period when log jams exerted a stronger influence over the passage of water and sediment at individual gravel bars most adjustments in surface and subsurface grain size constituted less than a 20 change in percentile values larger changes occurred primarily in subsurface sediment temporal patterns in bed material texture exhibited variation between bars but downstream of breached jams surface sediment conformed to the expected fining trend while the subsurface sediment increased in size surface and subsurface sediments evolved in the same direction only 64 of the time and the different magnitudes of adjustment caused local armor ratios to vary over time results highlight that the temporal dynamism of large woody debris lwd should be coupled with spatial considerations for effective stream restoration and management of streambed sediment

neighborhood matters patterns and controls on wood distribution in old growth forest streams of the colorado front range usa abstract we surveyed wood characteristics along four headwater channel segments of the colorado front range with drainage areas of 8 82 km2 stream lengths surveyed range from 3025 to 8980 m and together include a total of 15 706 pieces of wood time since last disturbance in the form of a stand killing fire varied from 31 to 500 years individual pieces of wood were highly aggregated at length scales of 1 to 150 m trends among jams were more weakly developed but jams tended to be more segregated at lengths 300 m with jams along individual channels being aggregated segregated or random multiple linear regressions failed to produce highly predictive models to explain the response variables of wood load piece dimensions or characteristics of jams other than jam volume which correlated with drainage area and wood load but examination of downstream patterns suggests that local valley and channel geometry valley bottom width gradient and sequence of longitudinal channel changes exert a stronger influence on patterns of wood distribution than either time since last forest disturbance or progressive downstream trends associated with increasing drainage area the longitudinal sequences of wood recruitment sources forest stand age and channel geometry together exert an important control on reach scale wood load and aggregation wood loads in streams draining old growth 250 years forests of the colorado front range are low compared to old growth sites in other regions of the world which we interpret to reflect decreased retention of wood recruited to the streams

a new methodology for monitoring wood fluxes in rivers using a ground camera potential and limits abstract ground imagery which produces large amounts of valuable data at high frequencies is increasingly used by fluvial geomorphologists to survey and understand processes while such technology provides immense quantities of information it can be challenging to analyze and requires automatization and associated development of new methodologies this paper presents a new approach to automate the processing of image analysis to monitor wood delivery from the upstream rhone river france the genissiat dam is used as an observation window all pieces of wood coming from the catchment are trapped here hence a wood raft accumulates over time in 2011 we installed an axis 211w camera to acquire oblique images of the reservoir every 10 min with the goal of automatically detecting a wood raft area in order to transform it to wood weight t and flux t d the methodology we developed is based on random forest classification to detect the wood raft surface over time which provided a good classification rate of 97 2 based on 14 mechanical wood extractions that included weight of wood removed each time conducted during the survey period we established a relationship between wood weight and wood raft surface area observed just before the extraction r2 0 93 we found that using such techniques to continuously monitor wood flux is difficult because the raft undergoes very significant changes through time in terms of density with a very high interday and intraday variability misclassifications caused by changes in weather conditions can be mitigated as well as errors from variation in pixel resolution owing to camera position or window size but a set of effects on raft density and mobility must still be explored e g dam operation effects wind on the reservoir surface at this stage only peak flow contribution to wood delivery can be well calculated but determining an accurate continuous series of wood flux is not possible several recommendations are made in terms of maximizing the potential benefit of such monitoring

transport and deposition of large woody debris in streams a flume experiment abstract large woody debris lwd is an integral component of forested streams of the pacific northwest and elsewhere yet little is known about how far wood is transported and where it is deposited in streams in this paper we report the results of flume experiments that examine interactions among hydraulics channel geometry transport distance and deposition of floating wood these experiments were carried out in a 1 22 m wide 9 14 m long gravel bed flume using wooden dowels of various sizes as surrogate logs channel planforms were either self formed or created by hand and ranged from meanders to alternate bars floating pieces tended to orient with long axes parallel to flow in the center of the channel pieces were deposited where channel depth was less than buoyant depth typically at the head of mid channel bars in shallow zones where flow expanded and on the outside of bends we hypothesize that the distance logs travel may be a function of the channel s debris roughness a dimensionless index incorporating ratios of piece length and diameter to channel width depth and sinuosity travel distance decreased as the ratio of piece length to both channel width and radius of curvature increased but the relative importance of these variables changed with channel planform large pieces can move further than our debris roughness models predict if greater than 50 of the active channel area is deeper than the buoyant depth of the piece or if momentum is high enough to carry pieces across shallows our debris roughness model allows first order prediction of the amount of wood transport under various channel geometries

modeling entrainment of waterlogged large wood in stream channels 1 research has led to an understanding of how floatable wood provides physical complexity and habitat in streams but little is known about large wood that does not float because it is waterlogged mineralized or naturally heavier than water to better understand the dynamics of this largely unrecognized component of streams i derived a theoretical model for predicting entrainment of waterlogged logs then constructed prototype logs to simulate waterlogged wood and used them to measure log friction and critical flow velocities at log entrainment in an alluvial creek i then modeled critical velocities under the same conditions entrainment was observed the model underpredicted critical velocities by an average of 24 with a range of error from 8 to 69 sensitivity analyses indicated that reducing lift and drag coefficients improved the average error but not the error range lack of unique drag coefficients for prototype logs winnowing of bed material from around prototype logs during entrainment tests error estimating friction for logs approaching neutral buoyancy and the variability of flow velocity common in streams were probable causes of error observed critical velocities that entrained prototype logs averaged 0 70 m s 1 critical velocities and log friction increased with branch length bed roughness and log density but only friction increased with log length friction coefficients averaged 0 62 and increased with branch length and bed roughness this model and existing equations for predicting movement of buoyant large wood can be used to compute budgets for logs with a range of attributes in streams

regional thermal inertia mapping from an experimental satellite a new experimental satellite has provided for the first time thermal data that should be useful in reconnaissance geologic exploration thermal inertia a property of geologic materials can be mapped from these data by applying an algorithm that has been developed using a new thermal model a simple registration procedure was used on a pair of day and night images of the powder river basin wyoming to illustrate the method preliminary assessment of these satellite data suggests that they will be of significant use for resource exploration when used in conjunction with other geologic geophysical and geochemical data

log transport and deposition in incised channelized and multithread reaches of a wide mountain river tracking experiment during a 20 year flood abstract distance of large wood transport during floods and conditions for wood deposition in wide mountain rivers are still insufficiently understood tracking of logs tagged with radio transmitters was used to investigate differences in depositional conditions and the length of log displacement during a 20 year flood between channel reaches of different morphology in the czarny dunajec river polish carpathians during the rising limb of the flood logs were placed into the river at three locations at the beginning of an incised reach close to the beginning of a channelized reach and 1 km upstream from the beginning of a wide multithread reach the incised channelized and multithread reaches retained 12 5 33 and 94 of tagged logs introduced to these reaches respectively and of the logs retained in the multithread reach all were deposited in its upstream half significant differences in the length of displacement existed between the logs delivered to the river at the three locations with logs placed into the river at the beginning of the incised reach moving the longest distance and those delivered just upstream from the multithread reach moving the shortest distance before deposition one fourth of the logs were deposited in a low flow channel or on a channel margin one fifth on the floodplain and more than half on gravel bars after the flood river cross sections with deposited logs and a set of cross sections without any wood deposits were surveyed to collect data for one dimensional modelling of hydraulic conditions at the flood peak the cross sections with deposited logs were typified by significantly greater flow width and flow area and by significantly smaller mean flow depth mean velocity froude number mean bed shear stress and unit stream power principal component analysis of the hydraulic parameters in the analysed cross sections grouped the two types of cross sections in distinct clusters indicating that multithread cross sections differed in hydraulic parameters from all the other cross sections the experiment confirmed findings from the previous wood inventory and numerical modelling of wood transport and deposition in the river indicating that in a wide mountain river wood can be transported long distances in a narrow single thread channel it is however preferentially deposited in a wide multithread channel that functions as a natural wood trap preventing or considerably limiting further transfer of large wood to vulnerable sites therefore it is crucial to avoid channelization of multithread reaches that would eliminate their functioning as natural wood traps the hydraulic modelling provided a physical justification for the observed differences in wood behaviour between the distinct channel morphologies

effects on bedload transport of experimental removal of woody debris from a forest gravel bed stream experimental removal of woody debris from a small gravel bed stream in a forested area resulted in a four fold increase in bedload transport at bankfull discharge this was caused by increased transportability of sediment previously stored upslope of debris buttresses or in low energy hydraulic environments related to debris bank erosion delivered additional sediment to the channel and transport energy was increased by an inferred increase in the component of total boundary shear stress affecting grains on the bed increased transport following debris removal in may 1987 continued throughout the entire autumn storm season through late november 1987 indicating persistent adjustment of the stream bed and banks despite marked response to earlier flows as large as bankfull stream bed adjustments included development of a semi regular sequence of alternate bars and pools many of which were spaced independently of former pool locations

the geomorphic function and characteristics of large woody debris in low gradient rivers coastal maine usa abstract the role function and importance of large woody debris lwd in rivers depend strongly on environmental context and land use history the coastal watersheds of central and northern maine northeastern u s are characterized by low gradients moderate topography and minimal influence of mass wasting processes along with a history of intensive commercial timber harvest in spite of the ecological importance of these rivers which contain the last wild populations of atlantic salmon salmo salar in the u s we know little about lwd distribution dynamics and function in these systems we conducted a cross basin analysis in seven coastal maine watersheds documenting the size frequency volume position and orientation of lwd as well as the association between lwd pool formation and sediment storage in conjunction with these lwd surveys we conducted extensive riparian vegetation surveys we observed very low lwd frequencies and volumes across the 60 km of rivers surveyed frequency of lwd 20 cm diameter ranged from 15 50 pieces km 1 and wood volumes were commonly 3 km 1 moreover most of this wood was located in the immediate low flow channel zone was oriented parallel to flow and failed to span the stream channel as a result pool formation associated with lwd is generally lacking and

leaky rivers implications of the loss of longitudinal fluvial disconnectivity in headwater streams article i nfo naturally induced longitudinal disconnectivity in the form of channel spanning logjams creates backwaters along headwater streams that reduce velocity and transport capacity create at least temporary storage sites for finer sediment and organic matter and enhance biological processing and uptake of nutrients land uses that reduce wood recruitment and instream storage result in reduced stream complexity and in creased longitudinal connectivity in headwater rivers we examine three scales of naturally occurring longi tudinal disconnectivity in headwater streams of the colorado front range and the implications for channel process and form of historical alterations in disconnectivity basin scale disconnectivity at channel lengths of 10 2 10 3 m results from downstream alternations between steep narrowly confined valley segments with single thread channels and lower gradient wider valley segments with multi thread channels this variation in valley geometry likely reflects differences in average spacing between joints in bedrock outcrops which influences bedrock weathering and erosion greater volumes of wood stored in the wide valley seg ments correlate with more closely spaced channel spanning logjams and greater storage of fine sediments and organic matter reach scale disconnectivity at channel lengths of 10 1 10 2 m results from the presence of numerous closely spaced channel spanning logjams which cumulatively store substantial amounts of fine sediment and organic matter the backwater effects associated with an individual jam can result in the accumulation of up to 11 m 3 of fine sediment upstream from the jam of which as much as 21 is organic

assessment of transfer patterns and origins of in channel wood in large rivers using repeated field surveys and wood characterisation the isere river upstream of pontcharra france abstract 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 isere 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

the role of large wood in retaining fine sediment organic matter and plant propagules in a small single thread forest river abstract this paper investigates associations among large wood accumulations retained sediment and organic matter and the establishment of a viable propagule bank within a forested reach of a lowland river the highland water uk a wood survey within the 2 km study reach illustrates that the quantity of wood retained within the channel is typical of relatively unmanaged river channels bordered by deciduous woodland and that the wood accumulations jams that are present are well developed typically spanning the river channel and comprised of wood that is well decayed sediment samples were obtained in a stratified random design focusing on nine subreaches within which samples were aggregated from five different types of sampling location two of these locations were wood associated within and on bank faces immediately adjacent to wood jams and the other three locations represented the broader river environment gravel bars bank faces floodplain the samples were analysed to establish their calibre organic and viable plant propagule content the gravel bar sampling locations retained significantly coarser sediment containing a lower proportion of organic matter and viable propagules than the other four sampling locations the two wood related sampling locations retained sediment of intermediate calibre between the gravel bar and the bank floodplain samples but they retained significantly more organic matter and viable propagules than were found in the other three sampling locations in particular the jam bank samples areas of sediment accumulation against bank faces adjacent to wood jams contained the highest number of propagules and the largest number of propagule species these results suggest that retention of propagules organic matter and relatively fine sediment in and around wood jams has the potential to support vegetation regeneration further sediment retention and as a consequence landform development within woodland streams although this process is arrested by grazing at the study site these results also suggest that self restoration using wood is a potentially cost effective and far reaching river restoration strategy but that its full effects develop gradually and require the establishment of a functioning wood budget coupled with grazing levels that are in balance with vegetation growth

the complexity of the real world in the context of the field tradition in geomorphology abstract among the dominant twentieth century conceptual models of geomorphology that rely on insights resulting from field based research are stanley a schumm s formulations of complex response intrinsic thresholds river metamorphosis and spatial zonation of drainage basins schumm s research focused primarily on finer grained alluvial channels in lower relief environments as a result of his work most investigators now approach river process and form within a framework based on three fundamental assumptions first channel changes are abrupt and driven by crossing external and internal thresholds second channel change is likely to be asynchronous resulting in different portions of a river or a river network behaving in very different manners at a given point in time third different portions of a river network are dominated by distinct disturbance regimes and resulting suites of geomorphic processes and forms more recent research on resistant boundary mountain channels illustrates how field evidence demonstrates that river process and form are inherently nonlinear with spatial and temporal thresholds multithread channels can form within unconfined valley segments in mountainous river networks of the colorado front range but only in the presence of biotic drivers in the form of i old growth forest that facilitates the formation of closely spaced channel spanning logjams or ii beavers that build dams thresholds of channel and valley geometry govern the occurrence and persistence of jams and dams and these channel obstructions initiate specific nonlinear responses in valley and channel form when the biotic drivers are removed river metamorphosis occurs alluvial channels which are typically regarded as being relatively responsive to changes in water and sediment yield and substrate composition and channels with more resistant boundaries that typically respond to external changes over longer timespans exhibit nonlinear complex behavior in both cases the nonlinear behavior of rivers with numerous interdependent variables multiple internal and external thresholds and complex responses would be difficult to conceptualize and quantify in the absence of extensive field data one of the management implications of complex nonlinear behavior is that a one size fits all approach to managing rivers is inadequate field research initially focused on understanding specific examples of river process and form revealed underlying patterns that give rise to conceptual models broadly applicable within fluvial geomorphology

physical modelling of the combined effect of vegetation and wood on river morphology abstract the research reported in this paper employs flume experiments to investigate the potential effects of living vegetation and large wood on river morphology specifically aiming to explore how different wood input and vegetation scenarios impact channel patterns and dynamics we used a mobile bed laboratory flume divided into three parallel channels 1 7 m wide 10 m long and filled with uniform sand to reproduce braided networks subject to a series of cycles of flooding wood input and vegetation growth temporal evolution of river configuration in terms of the braiding index vegetation establishment and erosion and wood deposition amount and pattern was recorded in a series of vertical images the experiments reproduced many forms and processes that have been observed in the field from scattered logs in unvegetated dynamic braided channels to large wood jams associated with river bars and bends in vegetated stable single thread rivers results showed that the inclusion of vegetation in the experiments changes wood dynamics in terms of the quantity that is stored and the depositional patterns that develop vegetated banks increased channel stability reducing lateral erosion and the number of active channels this promoted the formation of stable wood jams where logs accumulated continuously at the same locations during subsequent floods reinforcing their effect on river morphology the feasibility of studying these processes in a controlled environment opens new possibilities for disentangling the complex linkages in the biogeomorphological evolution of the fluvial system and thus for promoting improved scientific understanding

modeling channel morphodynamic response to variations in large wood implications for stream rehabilitation in degraded watersheds abstract anthropogenic modification of forests has often decoupled streams from riparian ecosystems and altered natural wood recruitment processes extensive research has shown that large wood significantly impacts channel dynamics especially in small and intermediate sized forested streams where wood pieces are similar in length to channel width and many stream rehabilitation efforts now involve the addition of large wood to streams the primary objective of this research is to investigate the relation between large wood and reach scale channel morphology and hydraulics using a physical model in order to better inform stream rehabilitation programs and future modeling efforts four experiments each comprising numerous five hour runs were conducted using a froude scaled stream table with wood loads scaled to 0 m3 m2 0 011 m3 m2 0 016 m3 m2 and 0 022 m3 m2 the addition of large wood significantly decreased the reach averaged velocity in all experiments and was associated with decreased sediment transport and increased sediment storage in the reach increases in bed and water surface slope compensated for the loss of energy available to transport sediment and enabled the system to reach a new steady state within the equivalent of 6 to 9 years adding wood increased pool frequency as well as the variability in cross sectional depth while causing the reach to undergo a transition from a plane bed to a riffle pool morphology retention of fine sediment increased the availability of fish spawning substrate while increased water stage improved connectivity between the channel and the floodplain the changes in habitat complexity were generally related to the wood load added to the reach but were also dependent on the orientation and arrangement of the pieces these results demonstrate that wood may exert a primary control on channel morphodynamics and the availability of aquatic habitat in intermediate sized streams and suggest that the benefits from stream rehabilitation efforts are highly dependent on project scale the relatively long time needed to realize habitat benefits demonstrates that long term monitoring of rehabilitation projects is necessary

surface and aerodynamic roughness in arid and semiarid areas and their relation to radar backscatter coefficient surface roughness is a key parameter for surface atmosphere exchanges of mass andenergy only a few field measurements have been performed in arid or semiarid areaswhere it is an important control of the aeolian erosion threshold an intensive fieldcampaign was performed in southern tunisia to measure the lateral cover lc and theaerodynamic roughness length z0 over 10 sites with different surface roughnesses lcwas determined by combining field measurements of the geometry of the roughnesselements and simple assumptions on their shapes z0was experimentally determined fromhigh precision wind velocity and air temperature profiles the resulting data were found tobe in good agreement with the existing relationships linking the geometric and theaerodynamic roughness this suggests that for natural surfaces z0can be estimated onthe basis of the geometric characteristics of the roughness elements this data set wasthen used to investigate the capabilities of radar backscatter coefficients s0 to retrieve lcand or z0 significant relationships were found between s0and both lcand z0 thesar ers data set is in agreement with the sir c slr data set from greeley et al 1997 on the basis of these two data sets including data from different arid and semiarid areas north africa south africa north america we propose an empirical relationship toretrieve z0using radar observations in the c band from operational sensors

interactions between instream wood and hydrogeomorphic development within recently deglaciated streams in glacier bay national park alaska the physical and structural characteristics of instream wood were examined within five streams that represented 200 years of stream development following glacial recession within glacier bay national park alaska wood characteristics altered with watershed age as terrestrial succession progressed and wood was recruited into the riverine environment the influence of wood characteristics on the development of geomorphic diversity and hydraulic variability within the streams were assessed using detailed habitat mapping sediment analysis and hydraulic assessment using an acoustic doppler current profiler at a number of transects upstream downstream and adjacent to wood results show that the size complexity and orientation of wood accumulations are the main drivers in determining the degree of influence instream wood have on stream geomorphic and hydraulic complexity adjacent terrestrial vegetation must be of a sufficient stage of development in terms of size and maturity in order to elicit significant hydrogeomorphic changes to benefit aquatic biota such as fish macroinvertebrates and plants

using structure from motion photogrammetry to assess large wood lw accumulations in the field abstract river systems in forested catchments are strongly influenced by wood and sediment loading from both natural e g mass wasting and anthropogenic forestry sources in order to effectively manage impacts on property infrastructure and the broader ecosystem as well as to better assess the interactions between large wood lw channel morphology and flow hydraulics more efficient and accurate surveying techniques are required we present an evaluation of structure from motion sfm photogrammetry and point cloud based techniques for capturing the geometry and volume of lw in the field wood accumulations can be notoriously complex 3d objects with multi scalar features and thus difficult to quantify with photogrammetric methods we introduce a novel workflow to generate volumetric information of organic material accumulations using sfm and a suite of meshing algorithms the volumes of two accumulations are assessed individually using several meshing techniques and are compared with more conventional volume estimates results show volumetric variations of

rules of the road a qualitative and quantitative synthesis of large wood transport through drainage networks abstract 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

wood storage in three mountain streams of the southern andes and its hydro morphological effects this study analyses large wood lw storage and the associated effects on channel morphology and flow hydraulics in three third order mountain basins drainage area 9 12 km2 covered in old growth nothofagus forests ranging from the temperate warm chilean andean cordillera to the sub antarctic tierra del fuego argentina amount characteristics and dimensions of large wood 10 cm diameter 1 m long were recorded as well as their effects on stream morphology hydraulics and sediment storage results show that major differences in lw abundance exist even between adjacent basins as a result of different disturbance histories and basin dissection massive lw volumes i e 1000 m3 ha 1 can be reached in basins disturbed by fires followed by mass movements and debris flows potential energy dissipation resulting from wood dams is about a quarter of the total elevation drop in two streams with a gross sediment volume stored behind wood dams of around 1000 m3 km 1 which appears to be of the same order as the annual sediment yield finally the presence of wood dams may increase flow resistance by up to one order of magnitude copyright 2007 john wiley sons ltd