instream wood loads in montane forest streams of the colorado front range usa abstract although several studies examine instream wood loads and associated geomorphic effects in streams of subalpine forests in the u s southern rocky mountains little is known of instream wood loads in lower elevation montane forests of the region we compare instream wood loads and geomorphic effects between streams draining montane forest stands of differing age old growth versus younger and disturbance history healthy versus infested by mountain pine beetles we examined forest stand characteristics instream wood load channel geometry pool volume and sediment storage in 33 pool riffle or plane bed stream reaches with objectives of determining whether i instream wood and geomorphic effects differed significantly among old growth younger healthy and beetle infested forest stands and ii wood loads correlated with valley and channel characteristics wood loads were standardized to drainage area stream gradient reach length bankfull width and floodplain area streams flowing through old growth forests had significantly larger wood loads and logjam volumes pairwise t tests as well as logjam frequencies kruskal wallis test residual pool volume and fine sediment storage around wood than streams flowing through younger forests wood loads in streams draining beetle infested forest did not differ significantly from those in healthy forest stands but best subset regression models indicated that elevation stand age and beetle infestation were the best predictors of wood loads in channels and on floodplains suggesting that beetle infestation is affecting instream wood characteristics wood loads are larger than values from subalpine streams in the same region and jams are larger and more closely spaced we interpret these differences to reflect greater wood piece mobility in subalpine zone streams stand age appears to exert the dominant influence on instream wood characteristics within pool riffle streams in the study area rather than beetle infestation although this may reflect the relatively recent nature

coarse sediment movement in the vicinity of a logjam in a neotropical gravel bed stream wood influences channel morphology by increasing channel roughness altering flow hydraulics and decreasing sediment transport in most fluvial systems where it is present in many locations the collection of wood into jams leads to even greater interruption of sediment transport by means of sediment impoundment and the creation of low velocity backwater flow zones we examined tracer clast movement near a wood jam in a neotropical gravel bed stream in order to evaluate the effect of wood mobility and piece transience on the ability of the jam to impede sediment transport we found that the jam had minimal influence on the passage of any individual clast with tracer clast mobilization and travel distance being best predicted by flow magnitude and grain size rather than location relative to the jam the rate of clast passage through the jam did not correlate with either the piece retention rate of the jam or with the density of the jam the jam did however temporarily trap a sediment wedge during a period when fluvially imported wood pieces blocked flow under a key wood piece diverting flow to a secondary flow path these results suggest that there is an upper bound on the flows in which wood is able to disrupt sediment transport and unlike for bedrock roughness elements this bound is frequently crossed at our study site

input storage and distribution of large woody debris along a mountain river continuum the drome river france abstract large woody debris lwd input storage and distribution were studied along the drome river a french alpine river with an active shifting channel and a well developed riparian forest lwd input from the floodplain is low 669 6 mg year 1 between 1948 and 1971 and 569 3 mg year 1 between 1971 and 1991 based on estimates of average lwd mass per study plot a range of 766 2122 mg year 1 of lwd were stored within the active channel e g unvegetated bars and low flow channel 60 km course covering 492 ha lwd accumulations are mainly observed on gravel bars at a limited number of preferential sites they are relatively rare and are randomly distributed in the low flow channel consequently lwd location is mainly associated with the decrease of flow level in shallow sectors in the low flow channel lwd stop en route is primarily caused by in channel structures such as boulders or vegetated islets general geomorphological factors e g pattern slope etc provide less explanation of lwd distribution moreover the residence time of lwd accumulations on the drome river is short lwd storage 1 3 3 7 times the annual lwd input from the floodplain and their morphogenic role is negligible few of the accumulations are buried or characterized by vegetation shoots and associated pools

river stabilisation due to changing climate and vegetation during the late quaternary in western tasmania australia abstract the stanley river in western tasmania australia contains sub fossil rainforest logs within the channel and floodplain of the more than 85 radiocarbon dates obtained all but 3 date from 17 ka to the present and permit an interpretation of fluvial and related environmental changes over this period particular attention is focused on the interactive relationship between the river and its riparian rainforest following the last glacial maximum the stanley river was a laterally active gravel load system reworking most of its valley floor in the upstream reaches with ameliorating conditions at the end of the pleistocene climate became less seasonal and flow regimes less energetic huon pines already present in the catchment re asserted themselves in the form of dense tree cover along the river banks and floodplains with basal floodplain deposition shifting from gravels to coarse sands and granules by about 3 5 ka a further change in climate reduced stream discharges substantially as a result the channel reduced in size transported finer sediment became laterally stable and the floodplain accreted with overbank deposits of sand and silt huon pines falling into the channel formed obstructions of woody debris some surviving for 2 ka these have reduced stream power and boundary shear stress further contributing to channel stability generational sequences of huon pines on the river banks some extending back 1 2 ka are additional evidence of this stability since the pleistocene changing climate and the re establishment of dense riparian rainforest appear to have stabilised the river channels and floodplains of western tasmania

flow chutes in fowlers creek arid western new south wales australia evidence for diversity in the influence of trees on ephemeral channel form and process abstract this paper identifies a fluvial landform the flow chute from fowlers creek an ephemeral stream in western new south wales australia on this stream there are contrasting configurations of channel margin and channel bed vegetation channel associated vegetation in the most common type of channel reach large eucalyptus camaldulensis trees grow on the bed and banks and contribute to high channel roughness in some reaches of about 0 5 km length however no trees grow below mid bank height the bed remains completely unvegetated and the channel narrows to one third or less of the width of adjoining reaches immediately upstream and downstream the coarse end of the bedload grain size population is not represented in these narrow reaches indicating that the coarsest grains are efficiently moved through them overpassing finer sediments these reaches evidently experience higher flow speeds than the remainder of the channel are here termed flow chutes the bed material within them is often moved as dunes that remain upon flood recession each flow chute ends with a reverse bed slope and just downstream of the terminus the channel widens resulting in the deposition of coarse bed load in the form of gravel and cobble bars the reverse bed slope detains water in the flow chutes which remain as major pools or waterholes for months following flood events the large and apparently old trees lining the flow chutes imply that these channel features are stable over periods of 10 2 10 3 years in contrast with the behaviour of reaches with vegetated beds where bank erosion and local lateral channel migration and or widening are active flow chutes thus appear to be stable equilibrium fluvial landforms

morphology hydrology and evolution of the anastomosing ovens and king rivers victoria australia anastomosing channels form the characteristic stream pattern of the riverine plain of southeastern australia investigations of the ovens and king rivers in northeastern victoria show that the individual channels and reaches of channels vary markedly in channel morphology and age young channels have large bankfull flows low sinuosity large meander wavelength steep gradients and are unstable they are incised channels that are rapidly eroding their bed and banks old channels however have small bankfull flows high sinuosity small meander wavelength gentler gradients and are relatively stable the multiple channels develop by avulsion as individual channels become older and more sinuous they also become more hydraulically inefficient thus increasing proportions of flood discharge are displaced overbank this overbank flow concentrates in relatively straight flood plain depressions and it erodes a new channel which develops by both up and down valley incision down valley incision is initiated at outflow points and up valley incision is initiated where the overbank flow rejoins the main channel with time both channel segments join to form a new anabranch of the anastomosing channel system large anastomosing channel networks have been identified in ancient rocks by stratigraphers and sedimentologists on the basis of studies of the anastomosing ovens and king rivers it is very likely that these channel networks are composed of channels of different ages hence even at one stratigraphic level not all of the anabranches functioned simultaneously nevertheless as a result of anabranch incision which intersects older channels at depth a three dimensional network of paleochannels can form that permits fluid flow throughout the network

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

bridging the gaps an overview of wood across time and space in diverse rivers abstract nearly 50 years of research focused on large wood lw in rivers provide a basis for understanding how wood enters rivers how wood decays breaks and is transported downstream and how at least temporarily stable wood influences channel geometry fluxes of water sediment and organic matter and the abundance and diversity of aquatic and riparian organisms field based studies have led to qualitative conceptual models and to numerical stimulations of river processes involving wood numerous important gaps remain however in our understanding of wood dynamics the majority of research on wood in rivers focuses on small to medium sized rivers defined using the ratio of wood piece size to channel width as channels narrower than the locally typical wood piece length small and slightly narrower than the longer wood pieces present medium although diverse geographic regions and biomes are represented by one or a few studies in each region the majority of research comes from perennial rivers draining temperate conifer forests regional syntheses most commonly focus on the pacific northwest region of north america where most of these studies originate consequently significant gaps in our understanding include lack of knowledge of wood related processes in large rivers dryland rivers and rivers of the high and low latitudes using a wood budget as an organizing framework this paper identifies other gaps related to wood recruitment transport storage and how beavers influence lw dynamics with respect to wood recruitment we lack information on the relative importance of mass tree mortality and transport of buried or surficial downed wood from the floodplain into the channel in diverse settings knowledge gaps related to wood transport include transport distances of lw and thresholds for lw mobility in small to medium rivers with respect to wood storage we have limited data on longitudinal trends in lw loads within unaltered large and great rivers and on fluctuations in lw load over time intervals greater than a few years other knowledge gaps relate to physical and ecological effects of wood including the magnitude of flow resistance caused by lw patterns of wood related sediment storage for diverse river sizes and channel geometry quantification of channel floodplain lw interactions and potential threshold effects of lw in relation to physical processes and biotic communities finally knowledge gaps are related to management of large wood and river corridors including understanding the consequences of enormous historical reductions in lw load in rivers through the forested portions of the temperate zone and how to effectively reintroduce and manage existing lw in river corridors which includes enhancing public understanding of the importance of lw addressing these knowledge gaps requires more case studies from diverse rivers as well as more syntheses and metadata analyses

reconstructing dust storm frequency in china since 1617 ce using coral based estimates of sea surface temperature abstract dust storms occur frequently in arid and semi arid regions of china and other parts of the world exerting a considerable influence on air quality in densely populated areas instrumental observations of dust storms are only available over the past 50 to 60 years limiting our ability to understand dust storm variability over longer timescales however tropical sea surface temperatures have been reconstructed over the past four centuries using geochemical records from corals here we show that tropical pacific sea surface temperatures as recorded by corals can be used to reconstruct dust storm frequency at one year resolution based on the coral reconstructed annual sea surface temperature anomaly data from two regions the western pacific 25 n 25 s 110 155 e and the eastern pacific 10 n 10 s 175 e 85 w published by tierney et al 2015 we reconstructed the frequency of dust storms in northern china dsfcn for the period from 1617 to 1953 ce the reconstructed dsfcn variation can be divided into several distinct periods 1 dsfcn increased from 1617 to 1650 then 2 decreased from 1650 to 1675 3 remained unchanged from 1675 to 1755 4 increased again from 1755 to 1860 5 remained unchanged from 1860 to 1925 and finally 6 decreased rapidly from 1925 to 1995 we propose the following causal chain to explain the observed relationship between dsfcn and sst as tropical pacific ocean sst increases the siberian high weakens and the eastern asian trough strengthens as the air pressure difference weakens the east asian winter monsoon weakens and strong wind frequency decreases causing dsfcn to decrease as well the statistical results support this interpretation of the causal chain

palaeozoic landscapes shaped by plant evolution fluvial landscapes diversified markedly over the 250 million years between the cambrian and pennsylvanian periods the diversification occurred in tandem with the evolution of vascular plants and expanding vegetation cover in the absence of widespread vegetation landscapes during the cambrian and ordovican periods were dominated by rivers with wide sand beds and aeolian tracts during the late silurian and devonian periods the appearance of vascular plants with root systems was associated with the development of channelled sand bed rivers meandering rivers and muddy floodplains the widespread expansion of trees by the early pennsylvanian marks the appearance of narrow fixed channels some representing anabranching systems and braided rivers with vegetated islands we conclude that the development of roots stabilized the banks of rivers and streams the subsequent appearance of woody debris led to log jams that promoted the rapid formation of new river channels our contention is supported by studies of modern fluvial systems and laboratory experiments in turn fluvial styles influenced plant evolution as new ecological settings developed along the fluvial systems we suggest that terrestrial plant and landscape evolution allowed colonization by an increasingly diverse array of organisms

distribution recruitment and geomorphic significance of large woody debris in an alluvial forest stream tonghi creek southeastern australia the complex yet poorly understood interactions between riparian vegetation large woody debris and fluvial geomorphology in an anthropogenically undisturbed reach of an alluvial sand bed forest stream in se australia have been determined riparian vegetation exhibits lateral and vertical zonation of understorey and overstorey species the dominant riparian tree species tristaniopsis laurina water gum grows within the channel and on the floodplain within one channel width of the stream larger eucalyptus species only grow on the highest parts of the floodplain and on a low pleistocene river terrace a complete large woody debris lwd census conducted in the 715 m long study reach revealed that water gum comprises 17 6 of the total lwd loading which at 576 m 3 ha 1 is high for a stream with a catchment area of 187 km 2 although most lwd has a small diameter 0 1 0 3 m the greatest contribution to the total volume of lwd is by pieces with a diameter between 0 3 and 0 7 m a high proportion of lwd 10 4 has a blockage ratio greater than 10 the spatial distribution of lwd is random both longitudinally and within individual meander bends dominant recruitment processes of lwd vary by species t laurina trees are recruited to the channel by minor bank erosion and senescence while the eucalyptus species are predominantly recruited from the highest parts of the floodplain low river terrace by episodic windthrow during large storms multiple radiocarbon dates of outer wood of immobile lwd indicate a maximum residence time of 240f40 years bp for t laurina timber the high loading of lwd combined with the extensive root systems of riparian vegetation stabilize tonghi creek log steps form natural wooden drop structures with a mean height of 29 mm that were responsible for 20 5 of the total head loss under base flow conditions q 0 08 m 3 s 1 large woody debris is buried in the bed at depths of up to 2 3 m and is responsible for an estimated 49 of the 11 600 m 3 of sand stored in the study reach pools are spaced at 0 8 channel widths and 82 of pools are formed by scour over under around or beside lwd or by the impoundment of water upstream of debris dams due to the high density of hardwood timber species debris dams however do not readily form in tonghi creek as the timber is difficult to transport and lwd usually sinks to the bed of the stream despite the high degree of

late holocene development of a floodplain along a small meandering stream northern quebec canada this paper describes the activity of a small meandering stream and the development of its floodplain during the last 4600 years calendar years bp in the northern boreal zone of quebec three trenches were excavated across the floodplain s full width and permitted the interpretation of morphosedimentary units in relation to modern analogs chronological controls within trenches was provided by the dendrochronological and radiocarbon dating of buried tree trunks from 4600 to 2900 cal bp and from 1000 to 120 cal bp the channel migrated and constructed its floodplain at very slow rates mostly because of low flow velocities vegetated streambanks and the cohesive texture of marine sediments reworked by the channel vertical accretion rates were extremely variable on the floodplain with high rates proximal to the modern channel and low rates over distal also older portions of the floodplain following a major channel shift meander cut off or avulsion around 2900 cal bp channel migration appears to have been constrained to a narrow zone adjacent to the modern channel within this constrained zone the migrating channel has reworked its own sediments leading to a marked unconformity between 2900 1000 cal bp it is thought that underlying marine sediments protrusions and perhaps the forested banks protected older alluvial sediments from being eroded during the last three millenniums our study shows that small boreal floodplains may contain in a very small area abundant and diversified archives of their evolution

large wood recruitment and transport during large floods a review large wood lw elements transported during large floods are long known to have the capacity to induce dangerous obstructions along the channel network mostly at bridges and at hydraulic structures such as weirs however our current knowledge of wood transport dynamics during high magnitude flood events is still very scarce mostly because these are locally rare and thus unlikely to be directly monitored therefore post event surveys are invaluable ways to get insights although indirectly on lw recruitment processes transport distance and factors inducing lw deposition all aspects that are crucial for the proper management of river basins related to flood hazard mitigation this paper presents a review of the quite limited literature available on lw transport during large floods drawing extensively on the authors own experience in mountain and piedmont rivers published and unpublished the overall picture emerging from these studies points to a high catchment specific variability in all the different processes affecting lw dynamics during floods specifically in the lw recruitment phase the relative floodplain bank erosion vs hillslope landslide and debris flows contribution in mountain rivers varies substantially as it relates to the extent of channel widening which depends on many variables itself but also to the hillslope channel connectivity of lw mobilized on the slopes as to the lw transport phase within the channel network it appears to be widely characterized by supply limited conditions whereby lw transport rates and thus volumes are ultimately constrained by the amount of lw that is made available to the flow indeed lw deposition during floods was mostly in terms of volume observed at artificial structures bridges in all the documented events this implies that the estimation of lw recruitment and the assessment of clogging probabilities for each structure for a flood event of given magnitude are the most important aspects for the prediction of lw transport magnitude at any cross section along the river network finally the review discusses the optimal strategies to manage lw related hazard which should consider riparian vegetation and in channel dead wood as key components of river ecosystems and thus should interfere with lw as well as with sediment transport dynamics only for limited spatial and temporal scales

wood storage within the active zone of a large european gravel bed river wood storage within the active zone of the dynamic gravel bed fiume tagliamento italy was investigated at eight sites along the river s main stem the quantity nature and mode of wood storage revealed a number of trends related to active zone morphology cover type and distance from the river s source relatively small quantities of wood were stored on open gravel surfaces estimates ranged from 1 to 21 t ha 1 intermediate quantities were associated with established islands 24 186 t ha 1 and large quantities were associated with pioneer islands 293 1664 t ha 1 thus variations in the geomorphological style of the river which are associated with changes in these three cover types are reflected in variations in the amount of wood that is stored in different reaches in addition although wood was found in many locations within the active zone it was preferentially stored in three specific locations i bar crests the main open gravel location for wood accumulations and pioneer islands ii the margins and iii surfaces of established islands the proportion of the stored wood that was living sprouting increased downstream and was higher on the open gravel than in association with established islands there was a downstream gradient in the dominant type of wood accumulation individual logs predominated at the most upstream site thereafter on the open gravel whole shrubs and trees dominated the more confined sites in the headwaters and middle reaches whereas jams were the most frequent form of accumulation in the downstream reaches jams were the most frequent type of accumulation associated with established islands throughout the river in contrast to small streams where debris dams constitute the major type of wood accumulation complex patterns and trends of wood storage were revealed along the tagliamento although further studies are needed it is clear that erosion of woody vegetation its subsequent transport and deposition play a major role in structuring the geomorphological and ecological character of this relatively natural large european river system insight into the mechanisms underlying the observed spatial patterns will contribute to a better understanding of the dynamic processes involved and is essential for more effective management of river ecosystems

large wood lw 3d accumulation mapping and assessment using structure from motion photogrammetry in the laboratory abstract 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

mind the gap an absence of valley fill deposits identifying the holocene hypsithermal period of enhanced flow regime in southeastern australia the holocene sedimentary record in southeastern australia is present in a range of landscape settings such as upland swamps dells internally drained lake basins alluvial fans and mid catchmen

porosity and volume assessments of large wood lw accumulations abstract the formation of large wood lw accumulations during floods represents a major hazard for constricted river cross sections e g bridges and weirs as it affects flow hydraulics and sediment transport to better assess lw accumulations reliable strategies and techniques are required there are currently practical limits on monitoring accumulation configurations both laser scans and photogrammetric techniques can be used to scan the outer contours of lw accumulations but cannot practically assess the wood content and porosity details of the outer deposit are captured in high resolution but the core of the deposit remains occluded and estimation is necessary this becomes more challenging for deposits of increasing size relative to wood elements to develop a more efficient workflow for lw accumulation assessment in the field we performed a laboratory study to develop a relationship between the envelope volume of water worked lw jams during a single flood hydrograph and the volume of woody elements within explicitly accounting for porosity we used photogrammetric techniques now in common use for reconnaissance surveys of debris accumulations on wood accumulations scaled for the laboratory the study s aim is to develop a semi automated assessment method enabling efficient image acquisition processing and computation of lw accumulation volume using a multi camera array above the laboratory channel and applying structure from motion photogrammetry we developed 3d models for 16 experimental flow formed wood accumulations each with 50 individual wooden dowels no correlations were found between porosity and flow magnitude porosity was found to be similar for most deposits 66 as a result of this accumulation structure the envelope volume used in 3d and 2 5d photogrammetric methods tended to overestimate wood content by 3 and 2 6 respectively the results obtained here will contribute to a more reliable volumetric assessment for inventories of wood mass in river systems

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

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

the geomorphic and ecological effectiveness of habitat rehabilitation works continuous measurement of scour and fill around large logs in sand bed streams abstract geomorphologists ecologists and engineers have all contributed to stream rehabilitation projects by predicting the physical effect of habitat restoration structures in this study we report the results of a stream rehabilitation project on the snowy river se australia that aims to improve fish habitat and facilitate migration associated with scour holes around large wood in the streambed whilst engineering models allow us to predict maximum scour the key management issue here was not the maximum scour depth but whether the holes persisted at a range of flows and if they were present when fish actually required them this led to the development of a new method to continuously monitor scour in a sand bed using a buried pressure transducer in this study we monitored fluctuations in the bed level below three large logs 1 m diameter on the snowy river each log had a different scour mechanism a plunge pool a horseshoe vortex analogous to a bridge pier and a submerged jet beneath the log the continuous monitoring demonstrated a complex relationship between discharge and pool scour the horseshoe vortex pool maintained a constant level whilst contrary to expectations both the plunge pool and the submerged jet pool gradually filled over the 12 months filling was associated with the average rise in flows in winter and occurred despite several freshes and discharge spikes the plunge pool showed the most variation with bed levels fluctuating by over 1 m a key factor in pool scour here may not be the local water depth at the log but the position of the log in relation to larger scale movements of sand waves in the stream these results question assumptions on the relative importance of small floods or channel maintenance flows that lead to beneficial scour around large wood in sand bed streams further the continuous measurement of scour and fill around the logs suggested the presence of pool scour holes would have met critical requirements for australian bass macquaria novemaculeata during the migration period whereas less frequent monitoring typical of rehabilitation trials would have suggested the contrary the results of this study have demonstrated that geomorphic effectiveness is not always synonymous with biological effectiveness whilst physical models emphasise extreme changes such as maximum scour the key biological issue is whether scour occurs at the critical time of the life cycle continuous measurement of sand levels is an example of a geomorphic technique that will help to develop models that predict biologically meaningful processes not just extremes

mobility of large woody debris lwd jams in a low gradient channel abstract mobility of large woody debris lwd in low gradient channels is an important but often overlooked transport process the majority of studies on lwd have focused on its role in geomorphic and ecologic river processes when jams extend across the width of the channel they have the potential to retain sediment and alter the channel profile when jams obstruct only a portion of the channel they can re direct flow altering patterns of scour and deposition the boundary complexity created by lwd has a recognized role in riverine ecosystems which has led to programs of replacing lwd in channel corridors where it was previously removed although lwd jams are common in rivers around the world they have been studied most intensely in steep forested channel reaches where they are often found to be stable channel features it is not fully known how much of the information on lwd from steep forested channels will transfer to other channel types whereas it may be reasonable to assume that the ecological benefits of lwd are similar in low gradient channels research has shown that a much higher rate of lwd transport occurs in low gradient channels with jams mobilized on timescales of 10 0 10 2 years this study evaluates the distribution and mobility of lwd over 72 km of the san antonio river a low gradient channel in southeast texas lwd jam locations were identified for 2003 and 2007 using a combination of aerial photography and field mapping each jam was cataloged according to its location in the channel cross section and the amount of channel area blocked during the four year period all the lwd jams were mobilized including those jams extending across the channel width although easily mobilized 34 jams re form in the same locations creating 34 channel locations with persistent lwd jams data from the san antonio river are applied to two models developed to predict lwd mobility and transport distances to assess the applicability of each model to a low gradient channel the locations of stable or recurring lwd jams were matched to model results where predicted lwd transport distances were equal to measured lwd jam spacing model results showed good agreement with the mean and median spacing of lwd jams when given input parameters specific to the channel and wood species the ability to predict where lwd jams will persist over time in a low gradient channel has application in watershed management persistent lwd jams can exert a greater influence on channel morphology and may require active management