valley scale morphology drives differences in fluvial sediment budgets and incision rates during contrasting flow regimes abstract high resolution topographic surveys using lidar and multibeam sonar can be used to characterize and quantify fluvial change this study used repeat surveys to explore how topographic change fluvial processes sediment budgets and aggradation and incision rates vary across spatial scales and across two contrasting decadal flow regimes in a regulated gravel cobble river a novel method for quantifying digital elevation model uncertainty was developed and applied to a topographic change detection analysis from 2006 2008 to 2014 during this period which had four modest 3 5 year floods most sediment was laterally redistributed through bank erosion and channel migration erosion primarily occurred in the floodplain 97 000 m 3 terraces 80 000 m 3 and lateral bars 58 000 m 3 while deposition occurred in the adjacent pools 73 000 m 3 fast glides 48 000 m 3 and runs 36 000 m 3 in contrast significantly higher magnitude and longer duration floods from 1999 to 2006 2008 caused sediment to be displaced longitudinally with the upstream reaches exporting sediment and the downstream reaches aggrading the river maintained floodplain connectivity during both periods despite different processes dominating the type of connectivity larger floods promoted overbank scour and avulsion while smaller floods promoted bank erosion and lateral migration this study explores and illustrates how the geomorphic response to contrasting flood regimes in a nonuniform river is highly dependent on which landforms are controlling hydraulics

monitoring and modelling particle and reach scale morphological change in gravel bed rivers applications and challenges this paper focuses on developments in topographic data acquisition including airborne remote sensing digital photogrammetry differential gps and laser profiling e g lidar technologies that allow rapid acquisition of high resolution and high precision topographic data sets over a range of spatial scales these developments have offered new opportunities for investigating spatial and temporal patterns of morphological change in gravel bed rivers and have contributed to revitalization in three key areas 1 morphometric estimates of sediment transport and sediment budgeting 2 boundary conditions for numerical models including computational fluid dynamics and cellular modelling 3 three dimensional characterisation of morphology that is independent of flow stage the potential is clear but there remain a number of significant challenges including quality control and the effects of error on specific applications and morphologies this paper presents results from two investigations representing field and laboratory analyses of gravel bed river morphology at different spatial scales and for different applications case study 1 is concerned with monitoring and modelling morphological change in a large braided gravel bed river using ground based gps survey and digital photogrammetry derived from airborne imagery case study 2 is an investigation of the mechanisms for infiltration of fine sediment into gravel bed rivers which applies close range laser altimetry in flume experiments to derive very high resolution digital elevation models dems that are used to quantify and analyse changes in bed texture these case studies highlight the strengths and weaknesses of specific technologies and approaches to analysis of channel and floodplain morphology and change and suggest key areas that remain to be fully resolved in particular the critical need to define a specific threshold level of detection associated with each acquisition method and for different fluvial settings e g bar surface sub aqueous zone is emphasised

effects of lateral confinement in natural and leveed reaches of a gravel bed river snake river wyoming usa this study examined the effects of natural and anthropogenic changes in confining margin width by applying remote sensing techniques fusing lidar topography with image derived bathymetry over a large spatial extent 58 km of the snake river wy fused dem s from 2007 and 2012 were differenced to quantify changes in the volume of stored sediment develop morphological sediment budgets and infer spatial gradients in bed material transport our study spanned two similar reaches that were subject to different controls on confining margin width natural terraces vs artificial levees channel planform in reaches with similar slope and confining margin width differed depending on whether the margins were natural or anthropogenic theeffects of tributaries also differed between the two reaches generally the natural reach featured greater confining margin widths and was depositional whereas artificial lateral constriction in the leveed reach produced a sediment budget that was closer to balanced although our remote sensing methods provided topographic data over a large area net volumetric changes were not statistically significant due to the uncertainty associated with bed elevation estimates we therefore focused on along channel spatial differences in bed material transport rather than absolute volumes of sediment to complement indirect estimates of sediment transport derived by morphological sediment budgeting we collected field data on bed mobility through a tracer study surface and subsurface grain size measurements were combined with bed mobility observations to calculate armoring and dimensionless sediment transport ratios which indicated that sediment supply exceeded transport capacity in the natural reach and vice versa in the leveed reach we hypothesize that constriction by levees induced an initial phase of incision and bed armoring because levees prevented bank erosion the channel excavated sediment by migrating rapidly across therestricted braidplain and eroding bars and islands

flood driven topographic changes in a gravel cobble river over segment reach and morphological unit scales regulated rivers generally incise below dams that cut off sediment supply but how that happens and what the consequences are at different spatial scales is poorly understood modern topographic mapping at meter scale resolution now enables investigation of the details of spatial processes in this study spatial segregation was applied to a meter scale raster map of topographic change from 1999 to 2008 on the gravel cobble regulated lower yuba river in california to answer specific scientific questions about how a decadal hydrograph that included a flood peak of 22 times bankfull discharge affected the river at segment reach and morphological unit scales the results show that the river preferentially eroded sediment from floodplains compared to the channel and this not only promoted valley wide sediment evacuation but also facilitated the renewal and differentiation of morphological units especially in the channel at the reach scale area of fill and mean net rate of elevational change were directly correlated with better connectivity between the channel and floodplain while the mean rate of scour in scour areas was influenced by the ratio of slope to bankfull froude number a ratio indicative of lateral migration versus vertical downcutting hierarchical segregation of topographic change rasters proved useful for understanding multiscalar geomorphic dynamics this article is protected by copyright all rights reserved

geomorphic effectiveness a linear concept in a non linear world geomorphic effectiveness has been an influential concept in geomorphology since its introduction by reds wolman and john miller in 1960 it provided a much needed framework to assess the significance of an event by comparing event magnitude to the resultant geomorphic effects initially this concept was applied primarily in river channels under the linear assumption that geomorphic responses to similarly sized flood events will be consistent numerous authors have since attempted to quantify a direct proportional relationship between event magnitude and different forms of geomorphic response in a variety of geomorphic settings in doing so these investigations applied an array of metrics that were difficult to compare across different spatiotemporal scales and physiographic and geomorphic environments critically the emergence of other geomorphic concepts such as sensitivity connectivity thresholds and recovery has shown that relationships between causes events and geomorphic effects responses are often complex and non linear this paper disentangles the complex historical development of the geomorphic effectiveness concept and reviews the utility of various metrics for quantifying effectiveness we propose that total energy joules is the most appropriate metric to use for quantifying the magnitude of disturbance events cause and volumetric sediment flux associated with landform modification is the most appropriate metric for quantifying geomorphic effects while both metrics are difficult to quantify they are the only ones which facilitate comparison across a range of spatiotemporal scales comparability in a variety of geomorphic environments flexibility the geomorphic effectiveness concept can continue to be useful provided that geomorphologists use flexible and comparable metrics today geomorphologists are better prepared to consider the influence of non linear processes on determinations of geomorphic effectiveness allowing investigators to not only determine if a disturbance event was effective but also to explain why or why not copyright

three dimensional reconstruction of fluvial surface sedimentology and topography using personal mobile laser scanning high resolution quantification of fluvial topography has been enabled by a number of geomatics technologies hyperscale surveys with spatial extents of 1 km2 have been widely demonstrated by means of terrestrial laser scanning tls and structure from motion sfm photogrammetry recent advances in the development and integration of global navigation satellite system gnss inertial measurement unit imu and lightweight laser scanning technologies are now resulting in the emergence of personal mobile laser scanners mls that have the potential to increase data acquisition and processing rates by 1 2 orders of magnitude compared to tls sfm and thus challenge the recent dominance of these technologies this investigation compares a personal mls survey using a leica pegasus backpack that integrates velodyne puck vlp 16 sensors and a multi station static tls survey using a riegl vz 1000 scanner to produce digital elevation models dems and surface sedimentology maps the assessment is undertaken on a 500 m long reach of the braided river feshie comparison to 107 independent real time kinematic rtk gnss check points resulted in similar mean error me and standard deviation error sde for tls me 0 025 m sde 0 038 m and personal mls me 0 014 m sde 0 019 m direct cloud to cloud c2c comparison between a sample of tls and personal mls observations 2 8 million points revealed that c2c distances follows a sharply decreasing burr distribution a 2 35 b 3 19 rate parameter s 9 53 empirical relationships between sub metre topographic variability and median sediment grain size 10 100 mm demonstrate that surface roughness from personal mls can be used to map median grain size differences between tls and personal mls empirical relationships suggest such relationships are dependent on survey technique personal mls offers distinct logistical advantages over sfm photogrammetry and tls for particular survey situations and is likely to become a widely applied technique

landscape scale geomorphic change detection quantifying spatially variable uncertainty and circumventing legacy data issues abstract repeat surveys of high resolution topographic data enable analysis of geomorphic change through digital elevation model dem differencing such analyses are becoming increasingly common however techniques for developing robust estimates of spatially variable uncertainty in dem differencing estimates have been slow to develop and are underutilized further issues often arise when comparing recent to older data sets because of differences in data quality airborne lidar data were collected in 2005 and 2012 in blue earth county minnesota 1980 km2 and the occurrence of an extreme flood in 2010 produced geomorphic change clearly observed in the field providing an opportunity to estimate landscape scale geomorphic change initial assessments of the lidar derived digital elevation models dems indicated both a vertical bias attributed to different geoid models and localized offset strips in the dem of difference from poor coregistration of the flightlines we applied corrections for both issues and describe the methods we used to discern those issues and correct them we then compare different threshold models to quantify uncertainty poor quantification of uncertainty can erroneously over or underestimate real change we show that application of a uniform threshold often called a minimum level of detection overestimates change in areas where change would not be expected such as stable hillslopes and underestimates change in areas where it is expected and has been observed such as channel banks we describe a spatially variable dem error model that combines the influence of slope point density and vegetation in a fuzzy inference system vegetation is represented with a metric referred to as the cloud point density ratio that assesses the complete point cloud to describe the density of above ground features that may hinder bare earth returns we compare the significance of spatially variable versus spatially uniform dem errors on change detection by thresholding the dem of difference at a 95 confidence interval 2 results indicate significant geomorphic change in relatively predictable locations such as erosion on the outside and deposition on the inside of bends final totals indicated net erosion of 2 625 100 2 389 000 m3 in the county between 2005 and 2012 of this 39 was generated from bluffs 1 from ravines and the remainder came from banks and floodplain areas

flow recession as a driver of the morpho texture of braided streams braiding has been widely studied in humid temperate climates though rarely in arid environments morpho texture of braided streams refers to the morphological textural organization in a braid cell stream section including bars anabranches and chutes that may strongly relate to different processes and hydrological regimes the objective of this study is to compare the morpho texture of braided streams governed by diverse flow recessions in different climates measurements were conducted in the wadis ze elim and rahaf southeast hyper arid israel in the mediterranean barranca de los pinos central spain and in humid temperate braided systems the la bleone river haute provence france and in the saisera and cimoliana torrents northeast italy terrestrial laser scanning was used to produce point clouds and high resolution digital elevation models of the braid cells wet braid cells in humid temperate environments were surveyed by a total station roughness and the upper tail of grain size distributions were derived from the scanned point clouds or from wolman sampling we found that anabranches are commonly finer grained than the bars in dryland systems and in semi arid sandy braided systems contrary to the humid temperate braided systems in both climates chutes are similar or coarser grained than the bars which they dissect in accordance with their steeper gradients due to the considerable bar anabranch relief the saisera s morpho texture is similar to that of the dryland braided channels despite the very humid temperate environment in which it is located due to its short lived ephemeral type hydrograph hydrograph shape specifically the duration of flow recession typical of a climate but not confined to it determines the morpho texture of braided streams and the textural differentiation between a depositional bar and the adjacent anabranches the morpho texture of chutes and bars results also from local erosional processes affected by local topography i e ungraded longitudinal profiles and is not solely determined by flow recession this new morpho textural model enables identifying primary depositional and erosional braiding processes copyright 2015 john wiley sons ltd

geomorphic mapping and taxonomy of fluvial landforms abstract fluvial geomorphologists use close to a 100 different terms to describe the landforms that make up riverscapes we identified 68 of these existing terms that describe truly distinctive landforms in which form is maintained under characteristic conditions and fluvial processes clear topographic definitions for these landforms to consistently identify and map them are lacking with the explosion of continuous high resolution topography and digital elevation models we have plenty of new basemaps in which these landforms are clearly visible but very few examples of manual or automated classification of fluvial landforms fluvial landforms are the building blocks of a river and are variously referred to as geomorphic units morphological units habitat units and channel units we present a tiered framework for describing geomorphic units with tier 1 differentiating units on the basis of their stage tier 2 separating shape e g concave convex or planar tier 3 using particular key attributes to narrow in on the likely specific geomorphic unit type and tier 4 differentiating those types on the basis of vegetative or roughness modifiers information on the assemblage and configuration of geomorphic units can be used to inform process based interpretations of the range of river behavior the accuracy and transferability of such analyses is fundamentally tied to the taxonomy we assign to these discrete building blocks in this paper we clarify the terminology and definitions relating to the identification and delineation of geomorphic units margins and structural elements we establish a set of procedures that can be used to manually map and identify these features the proposed framework provides a rigorous and repeatable approach to identification of topographically defined features of riverscapes we demonstrate the application of these systematic yet flexible procedures with a series of maps from rivers in differing valley settings

conditions for branching in depositional rivers it is often taken for granted that rivers organize transport into a single active channel in some net depositional environments however flow of water and sediment is distributed in several stable channels such branching rivers may be confined in valleys anabranching or anastomosed or unconfined on deltas distributaries and their existence confronts us with the very basic question of what governs the spatial organization of channel patterns in sedimentary landscapes current models for equilibrium channel morphology cannot predict the occurrence of branching rivers because they do not consider dynamical processes such as avulsion i e the rapid abandonment of a channel in favor of a new path at lower elevation the requisite conditions for avulsion have been the subject of ongoing debate here we resolve the conditions leading to channel avulsion and show that branching rivers occur when avulsion is the dominant mechanism of lateral channel motion a compilation of field and laboratory data demonstrates that avulsion frequency scales with the time required for sedimentation on channel beds to produce a deposit equal to one channel depth from the relative rates of bank erosion and channel sedimentation we derive a dimensionless mobility number that accurately predicts the conditions under which anabranching and distributary channels occur results may be directly applied to modeling landscape evolution over human and geologic time scales and for inverting formative environmental conditions from channel deposits on earth and other planetary surfaces

uas based remote sensing of fluvial change following an extreme flood event the effects of large floods on river morphology are variable and poorly understood in this study we apply multi temporal datasets collected with small unmanned aircraft systems uass to analyze three dimensional morphodynamic changes associated with an extreme flood event that occurred from 19 to 23 june 2013 on the elbow river alberta we documented reach scale spatial patterns of erosion and deposition using high resolution 4 5 cm pixel orthoimagery and digital elevation models dems produced from photogrammetry significant bank erosion and channel widening occurred with an average elevation change of 0 24 m the channel pattern was reorganized and overall elevation variation increased as the channel adjusted to full mobilization of most of the bed surface sediments to test the extent to which geomorphic changes can be predicted from initial conditions we compared shear stresses from a two dimensional hydrodynamic model of peak discharge to critical shear stresses for bed surface sediment sizes we found no relation between modeled normalized shear stresses and patterns of scour and fill confirming the complex nature of sediment mobilization and flux in high magnitude events however comparing modeled peak flows through the pre and post flood topography showed that the flood resulted in an adjustment that contributes to overall stability with lower percentages of bed area below thresholds for full mobility in the post flood geomorphic configuration overall this work highlights the potential of uas based remote sensing for measuring three dimensional changes in fluvial settings and provides a detailed analysis of potential relationships between flood forces and geomorphic change copyright 2015 john wiley sons ltd

the relationship between particle travel distance and channel morphology results from physical models of braided rivers channel form and sediment transport are closely linked in alluvial rivers and as such the development of a conceptual framework for the downstream controls on particle mobility and likely deposition sites has immense value in terms of the way we understand and predictively model rivers despite the development of conceptual models which frame flood scale particle transport distance termed path length as a function of channel bar locations an understanding of the controls on such path lengths in braided rivers remains especially elusive in large part due to the difficulty in explicitly linking morphology and particle transport distances in the field here we utilize a series of laboratory flume experiments to link path length distances with channel morphology our morphologic characterization is based on ultrahigh resolution digital elevation models and bar classifications derived from structure from motion topography while we simultaneously capture particle path lengths using fluorescent tracer particles over the course of five physical model simulations our findings underscore the importance of channel bars in acting as deposition sites for particles in transport 81 of recovered tracers were found in association with compound point lateral or diagonal bars bar heads 29 and bar margins 41 were the most common bar related deposition surfaces for recovered tracers peaks in particle deposition frequency corresponding to channel bars were often noted on path length distributions from tracer data most tracers were deposited in areas that had experienced shallow z 0 002 m deposition average path length distance 2 5 m was closely related to average confluence diffluence spacing 2 3 m across all runs the transferability of this understanding to braided streams has important implications for the development of simplified morphodynamic models which seek to predict braided channel evolution across multiflood timescales

geomorphic process from topographic form automating the interpretation of repeat survey data in river valleys the ability to quantify the processes driving geomorphic change in river valley margins is vital to geomorphologists seeking to understand the relative role of transport mechanisms e g fluvial aeolian and hillslope processes in landscape dynamics high resolution repeat topographic data are becoming readily available to geomorphologists by contrasting digital elevation models derived from repeat surveys the transport processes driving topographic changes can be inferred a method termed mechanistic segregation unfortunately mechanistic segregation largely relies on subjective and time consuming manual classification which has implications both for its reproducibility and the practical scale of its application here we present a novel computational workflow for the mechanistic segregation of geomorphic transport processes in geospatial datasets we apply the workflow to seven sites along the colorado river in the grand canyon where geomorphic transport is driven by a diverse suite of mechanisms the workflow performs well when compared to field observations with an overall predictive accuracy of 84 across 113 validation points the approach most accurately predicts changes due to fluvial processes 100 accuracy and aeolian processes 96 with reduced accuracy in predictions of alluvial and colluvial processes 64 and 73 respectively our workflow is designed to be applicable to a diversity of river systems and will likely provide a rapid and objective understanding of the processes driving geomorphic change at the reach and network scales we anticipate that such an understanding will allow insight into the response of geomorphic transport processes to external forcings such as shifts in climate land use or river regulation with implications for process based river management and restoration copyright 2017 john wiley sons ltd

quantifying geomorphic change at ephemeral stream restoration sites using a coupled model approach abstract rock detention structures are used as restoration treatments to engineer ephemeral stream channels of southeast arizona usa to reduce streamflow velocity limit erosion retain sediment and promote surface water infiltration structures are intended to aggrade incised stream channels yet little quantified evidence of efficacy is available the goal of this 3 year study was to characterize the geomorphic impacts of rock detention structures used as a restoration strategy and develop a methodology to predict the associated changes we studied reaches of two ephemeral streams with different watershed management histories one where thousands of loose rock check dams were installed 30 years prior to our study and one with structures constructed at the beginning of our study the methods used included runoff sediment transport and geomorphic modelling and repeat terrestrial laser scanner tls surveys to map landscape change where discharge data were not available event based runoff was estimated using kineros2 a one dimensional kinematic wave runoff and erosion model discharge measurements and estimates were used as input to a two dimensional unsteady flow and sedimentation model nays2dh that combined a gridded flow transport and bed and bank simulation with geomorphic change through comparison of consecutive dems the potential to substitute uncalibrated models to analyze stream restoration is introduced we demonstrate a new approach to assess hydraulics and associated patterns of aggradation and degradation resulting from the construction of check dams and other transverse structures notably we find that stream restoration using rock detention structures is effective across vastly different timescales

early cretaceous calcareous nannofossils from high latitudes implications for palaeobiogeography and palaeoclimate abstract in order to better understand the palaeoceanography and palaeoclimate of the early cretaceous nannofossil data have been obtained from high latitudinal sites from offshore mid norway and from the barents sea no consistent nannofossil data are yet available for early cretaceous high latitudes which should more clearly reflect possible palaeoclimatic changes as recorded in fluctuations of diversity and abundance existing data from france italy romania poland and nw europe germany north sea england have been complemented by material from higher latitudes in order to record the arctic boreal nannofossil assemblages 400 samples from the norwegian shelf and the barents sea have been analysed sixty samples covering the berriasian barremian interval yielded calcareous nannofossils these are derived from cores between 63 and 73 n of present day latitudes the nannofossil assemblages recorded are generally of a low diversity and characterized by abundant watznaueria barnesae and crucibiscutum salebrosum whereas biscutum constans is less common c salebrosum rare or absent at low latitudes is extremely common in the norwegian samples it shows a bipolar distribution especially during valanginian hauterivian times in the early valanginian a distinctive latitudinal gradient in the abundance of c salebrosum impoverished in low latitudes and abundant in high latitudes possibly reflects latitudinal differences in temperature restricted palaeoceanographic settings caused by a sea level lowstand may have amplified these thermal gradients palaeoclimatically this implies the existence of climatic belts throughout parts of the early cretaceous early valanginian hauterivian resulting from considerable temperature gradients from north to south the palaeobiogeographic patterns discussed resulted in the formation of distinctive latitudinally bound nannofossil zones which to a certain extent are similar to those of modern oceans the palaeobiogeographic patterns described support the idea of an ice house phase for the early valanginian and disagree with the suggestion of a globally warm equable climate during that time

morphodynamic signatures of braiding mechanisms as expressed through change in sediment storage in a gravel bed river previous flume based research on braided channels has revealed four classic mechanisms that produce braiding central bar development chute cutoff lobe dissection and transverse bar conversion the importance of these braiding mechanisms relative to other morphodynamic mechanisms in shaping braided rivers has not yet been investigated in the field here we exploit repeat topographic surveys of the braided river feshie uk to explore the morphodynamic signatures of different mechanisms of change in sediment storage our results indicate that when combined the four classic braiding mechanisms do indeed account for the majority of volumetric change in storage in the study reach 61 total chute cutoff traditionally thought of as an erosional braiding mechanism appears to be the most common braiding mechanism in the study river but was more the result of deposition during the construction of diagonal bars than it was the erosion of the chute three of the four classic mechanisms appeared to be largely net aggradational in nature whereas secondary mechanisms including bank erosion channel incision and bar sculpting were primarily net erosional although the role of readily erodible banks in facilitating braiding is often conceptualized we show that bank erosion is as or more important a mechanism in changes in sediment storage than most of the braiding mechanisms and is the most important secondary mechanism 17 of total change the results of this study provide one of the first field tests of the relative importance of braiding mechanisms observed in flume settings

how do gravel bed rivers braid sedimentary processes and bed forms leading to the onset of braiding were observed in small scale hydraulic models of gravel bed streams the laboratory streams had a variety of combinations of constant discharge and slope but identical bed material particle size distributions from initially straight channels braiding occurred by four different processes deposition and accumulation of a central bar chute cutoff of point bars conversion of single transverse unit bars to mid channel braid bars and dissection of multiple bars in these experiments the chute cutoff mechanism was the most common but the predominant braiding mechanism depends upon sediment mobility excess bed shear stress and the bed form regime at very low excess bed shear stress the central bar process dominates but at higher excess bed shear stress slip face unit bars are more common bed scour at confluences is more pronounced and propogation of alternate convergence scour and divergence deposition is more likely thus chu

effects of riparian vegetation on topographic change during a large flood event rio puerco new mexico usa 1 the spatial distribution of riparian vegetation can strongly influence the geomorphic evolution of dryland rivers during large floods we present the results of an airborne lidar differencing study that quantifies the topographic change that occurred along a 12 km reach of the lower rio puerco new mexico during an extreme event in 2006 extensive erosion of the channel banks took place immediately upstream of the study area where tamarisk and sandbar willow had been removed within the densely vegetated study reach we measure a net volumetric change of 578 050 490 000 m3 with 88 3 of the total aggradation occurring along the floodplain and channel and 76 7 of the erosion focusing on the vertical valley walls the sediment derived from the devegetated reach deposited within the first 3 6 km of the study area with depth decaying exponentially with distance downstream elsewhere floodplain sediments were primarily sourced from the erosion of valley walls superimposed on this pattern are the effects of vegetation and valley morphology on sediment transport sediment thickness is seen to be uniform among sandbar willows and highly variable within tamarisk groves these reach scale patterns of sedimentation observed in the lidar differencing likely reflect complex interactions of vegetation flow and sediment at the scale of patches to individual plants

mechanisms of anabranch avulsion within gravel bed braided rivers observations from a scaled physical model the physical modelling of gravel bed braided rivers using a 1 20 froude scale model permits analysis of the types and relative occurrence of different avulsion mechanisms anabranch avulsion within braided rivers involves three main mechanisms choking avulsion caused by blockage of one channel by a sediment lobe constriction avulsion produced by deflection confinement and subsequent diversion of the flow by a barform and apex avulsion following erosion at the outside of sinuous thalwegs and confined meander bends each avulsion mechanism is described and analysis of the abundance of each type illustrates choking avulsion to be predominant without braided rivers three factors are found to control anabranch avulsions namely flow discharge sediment flux and floodplain topography these are briefly discussed together with the implications of avulsion type for the alluvial architecture of gravelly braided alluvium

geomorphological effectiveness of floods to rework gravel bars insight from hyperscale topography and hydraulic modelling bars are key morphological units in river systems fashioning the sediment regime and bedload transport processes within a reach reworking of these features underpins channel adjustment at larger scales thereby acting as a key determinant of channel stability despite their importance to channel evolution few investigations have acquired spatially continuous data on bar morphology and sediment size to investigate bar reworking to this end four bars along a 10 km reach of a wandering gravel bed river were surveyed with terrestrial laser scanning tls capturing downstream changes in slope bed material size and channel planform detrended standard deviations z were extracted from tls point clouds and correlated to underlying physically measured median grain size d50 across a greater range of z values than have hitherto been reported the resulting linear regression model was used to create a 1 m resolution median grain size map a fusion of airborne lidar and optical empirical bathymetric mapping was used to develop reach scale digital elevation models dems for rapid two dimensional hydraulic modelling using jflow software the ratio of dimensionless shear stress over critical shear stress was calculated for each raster cell to calculate the effectiveness of a range of flood events 2 33 100 year recurrence intervals to entrain sediment and rework bar units results show that multiple bar forming discharges exist whereby frequent flood flows rework tail and back channel areas whilst much larger less frequent floods are required to mobilise the coarser sediment fraction on bar heads valley confinement is shown to exert a primary influence on patterns of bar reworking historical aerial photography hyperscale dems and hydraulic modelling are used to explain channel adjustment at the reach scale the proportion of the bar comprised of more frequently entrained units tail back channel supra platform relative to more static units bar head exerts a direct influence upon geomorphic sensitivity

the relation between particle path length distributions and channel morphology in gravel bed streams a synthesis abstract the path length downstream displacement over a given time period of individual bed particles in gravel bed rivers is central to morphological methods for measuring bed load transport rate and is also fundamental to understanding the bed load transport process and the development of channel morphology previous studies of particle movement using tracers report predominantly strongly positively skewed frequency distributions of path length with modes close to the point of entrainment however gravel bed rivers often have regularly spaced erosion scour pools and deposition channel bars sites that are several channel widths apart and it is reasonable to expect that particle path length would reflect this morphological scale at least during flows large enough to create and modify the morphology here we synthesize and re analyze results from published bed load tracing experiments in gravel bed rivers to identify the variety of possible path length distributions for differing channel morphology channel dimensions bed particle size and particle mobility i e flow magnitude and to look for occurrences of path length coinciding with the length scale of the morphology the results show that path length distributions may be positively skewed symmetrical and uni bi or multi modal and may include modes that coincide with known or expected pool bar spacing primary path length modes equivalent to possible pool bar spacing are more probable at higher non dimensional bed shear stress from which it is inferred that both particle mobility and channel morphology exert an influence on particle path lengths and that particle movement is unlikely to be stochastic except at relatively low particle mobility existing data are inadequate for more than a preliminary analysis of this problem consequently there is a need for new data collected explicitly and systematically to confirm these preliminary results isolate the effect of the several variables that influence the characteristics of path length frequency distributions and identify the conditions under which path length coincides with the length scale of the dominant morphology

terrestrial structure from motion spatial error analysis of roughness and morphology structure from motion sfm photogrammetry is rapidly becoming a key tool for morphological characterisation and change detection of the earth surface this paper demonstrates the use of terrestrial structure from motion tsfm photogrammetry to acquire morphology and roughness data at the reach scale in an upland gravel bed river we quantify 1 spatially distributed error in tsfm derived digital elevation models dems and 2 identify differences in roughness populations acquired from tsfm photogrammetry versus tls we identify an association between local topographic variation and error in the tsfm dem on flatter surfaces e g bar and terrace surfaces the difference between the tsfm and tls dems are generally less than 0 1 m however in areas of high topographic variability 0 4 m such as berm or terrace edges differences between the tsfm and tls dems can be up to 1 m our results suggest that grain roughness estimates from the tsfm point cloud generate values twice those derived from the tls point cloud on coarse berm areas and up to four fold those derived from the tls point cloud over finer gravel bar surfaces this finding has implications when using sfm data to derive roughness metrics for hydrodynamic modelling despite the use of standard filtering procedures noise pertains in the sfm dem and the time required for its reduction might partially outweigh the survey efficiency using sfm therefore caution is needed when sfm surveys are employed for the assessment of surface roughness at a reach scale

changes in braided river morphology resulting from aggradation and degradation forty three experiments were completed in a large flume 1 8 x 18 3 m to examine the effects of sediment load sediment size and channel gradient on braided river morphology the laboratory results were supported by field research and analogs from the published literature subaerially exposed braid bars were formed by the dissection and further accretion of stalled linguoid dunes which are actively migrating bedforms bar forming processes and channel dynamics were the same in both sand and gravel bed channels however linguoid dunes stalled and were transformed into braid bars more frequently in gravel bed channels and therefore gravel bed channels were more intensely braided aggradation resulted in the development of more bars rather than in an increase in the size of preexisting braid bars the number of actively migrating linguoid dunes also increased with sediment load in the highly mobile sand bed channels conversely in degrading channels the number of braid bars decreased and average bar

channel adjustment and a test of rational regime theory in a proglacial braided stream the upstream reach of the sunwapta river alberta provides a useful quasi experimental field case of channel adjustment in a proglacial stream historically the formation of a proglacial lake deprived the river of its coarse sediment supply for several decades and lead to a dramatic decrease in braiding intensity close to the lake while braiding intensity increased further downstream this response to the reduction of gravel input is consistent with previous experimental results subsequent construction activity and channelization close to the lake have contributed to the continuation of these temporal and spatial trends in channel pattern the current state of adjustment of the river morphology can be explained in the context of these historical changes using rational regime equations the study reach has no tributaries and bed material size decreases twofold along the reach while width and braiding intensity increase yet channel slope decreases by only 10 the absence of any significant change in discharge downstream along the reach allows testing of regime equations under conditions in which discharge is held constant the current downstream trends in slope and fluctuations in width are predicted reliably from rational regime equations but not by the existing empirical hydraulic geometry relations the rational equations incorporate the effect of grain size and slope on channel width and the effect of width and grain size on channel slope the regime equations are successful even though they were devised for single channel gravel streams the small 10 decrease in slope along the reach despite a halving of median grain size is attributed to the counteracting positive effect on slope of the downstream increase in braiding intensity and width the downstream increase in braiding intensity must be largely the result of decreasing grain size this confirms the influence of grain size on channel pattern thresholds and demonstrates using spatial transitions in channel pattern that channel pattern predictions based on stream power alone are inadequate

supergene enrichment of precious metals by natural amalgamation in the las cruces weathering profile iberian pyrite belt sw spain abstract natural au ag hg alloys occur in the las cruces ore deposit in the eastern part of the iberian pyrite belt they are mainly concentrated in the lower part of the gossan profile including a sheared black shale level where the gossan makes contact with a barren pyrite zone within the supergene cu rich mineralization drill core analyses show a heterogeneous distribution of au ag and hg within the weathering profile with mean values of 5 1 ppm 155 ppm and 52 ppm respectively in general the absolute tenures increase towards the bottom of the weathered profile mineralogical studies conducted on samples from the active mine workings indicate that hg and precious metals occur mainly as au ag hg alloys these associations constitute the best potential resource for precious metals at the las cruces deposit this paper describes how this unusual precious metal enrichment is produced along the weathering profile by supergene processes combining paragenetic information mineral chemistry and the data pertaining to the solubilities of au ag and hg in a weathering profile we suggest a two stage genetic model for the formation of the las cruces au ag hg mineralization 1 release of au ag and hg from the massive sulfide deposit by weathering processes during the gossan formation at ph 0 9 v conditions au ag and hg are mobilized downward through the weathering profile as chloride complexes and fixed as elemental au halides oxides and sulfates and 2 remobilization of hg ag and au in the gossan after the deposit was buried beneath the neogene carbonate rich sedimentary cover the buffering capacity of the percolating fluids due to their interaction with the carbonate rich sedimentary pile leads to significant mineralogical and geochemical changes at near neutral conditions ph 6 7 eh 0 v hg ag and au are newly remobilized as thiosulfate sulfate and hydroxide complexes and newly fixed by sorption during ferric hydroxide formation and as sulfates several cycles of dissolution precipitation of au ag and hg near the redox front occur by oscillations in the water table and changes in the ph eh conditions the interaction of downward migrating fluids with high reductant lithologies black shales and massive sulfides seems to be responsible for the reduction of different complexes and for the precipitation of cinnabar ag sulfides and sulfosalts as well as the precipitation of au ag hg amalgams

splitting rivers at their seams bifurcations and avulsion river bifurcations are critical but poorly understood elements of many geomorphological systems they are integralelements of alluvial fans braided rivers fluvial lowland plains and deltas and control the partitioning of water and sediment throughthese systems bifurcations are commonly unstable but their lifespan varies greatly in braided rivers bars and channels migrate splitand merge at annual or shorter timescales thereby creating and abandoning bifurcations this behaviour has been studied mainly bygeomorphologists and fluid dynamicists bifurcations also exist during avulsion the process of a river changing course on afloodplain or in a delta which may take 102 103years and has been studied mainly by sedimentologists this review synthesizesour current understanding of bifurcations and brings together insights from different research communities and different environmen tal settings we consider the causes and initiation of bifurcations and avulsion the physical mechanisms controlling bifurcation andavulsion evolution mathematical and numerical modelling of these processes and the possibility of stable bifurcations we end thereview with some open questions copyright 2012 john wiley sons ltd

evaluating short term morphological changes in a gravel bed braided river using terrestrial laser scanner abstract braided rivers are dynamic and complex environments shaped by the balance of the flow and sediment regimes and by the influence of the riparian vegetation and disturbances such as floods in particular the balance between sediment supply and transport capacity can determine the morphological evolution of a river for instance aggrading and widening trends are distinctive of reaches where sediment supply is higher than transport capacity in contrast incising and narrowing tendencies are dominant the aim of the present study is to analyze the short term morphological dynamics and the processes of erosion and sediment deposition along a small reach of a relatively unimpacted gravel bed braided river tagliamento river northeast italy using a terrestrial laser scanner tls the study area is around 23 ha and has been surveyed before after two periods with relevant flood events two of which were higher than the bankfull level and occurred between september 2010 and september 2011 the very high point clouds density allowed us to derive three high resolution digital elevation models dems with 0 125 0 125 m pixel size scan data cloud merging was achieved with an overall high degree of accuracy and resolution subcentimeter topographic data were more accurate for exposed surfaces than those collected in wet areas a detailed net of dgps control points allowed us to verify the high quality of the dems derived from the surveys rmse of about 5 cm two dems of difference dod were computed revealing different and consistent episodes of erosion and deposition within the analyzed area and changes in morphology of channel and bars could also be detected such as bar edge accretion and bank erosion demonstrating a strong dynamicity of the tagliamento river moreover a very detailed estimation of the surface roughness in the study area has been carried out permitting a large scale analysis of the roughness values distribution the results of the analysis on the tls collected data show that along a river with a high natural character i e tagliamento river the dynamic processes are also common during low magnitude events

methodological sensitivity of morphometric estimates of coarse fluvial sediment transport abstract the estimation of fluvial sediment transport rate from measurements of morphological change has received growing recent interest the revival of the morphological method reflects continuing concern over traditional methods of rate determination but also the availability of new survey methods capable of high precision high resolution topographic monitoring remote sensing of river channels through aerial digital photogrammetry is a potentially attractive alternative to labour intensive ground surveys however while photogrammetry presents the opportunity to acquire survey data over large areas data precision and accuracy particularly in the vertical dimension are lower than in traditional ground survey methods this paper presents results of recent research in which digital elevation models dems have been developed for a reach of a large braided gravel bed river in scotland using both digital photogrammetry and high resolution rtk gps ground surveys a statistical level of change detection is assessed by comparing surfaces with independent check points the methodological sensitivity of the annual channel sediment budget 1999 2000 to the threshold is presented results suggest that while the remote survey methods employed here can be used to develop qualitatively convincing moderate precision dems of channel topography rmse 0 21 m the remaining errors imply significant limits on reliable change detection which lead to important information losses tests at a 95 confidence interval for change detection show that over 60 of channel deposition and 40 of erosion may be obscured by the lower level of precision associated with photogrammetric monitoring when compared to ground survey measurements this bias reflects the difficulty of detecting the topographic signature of widespread but shallow deposition on bar tops

braided channel pattern and palaeohydrology using an index of total sinuosity abstract channel patterns are commonly represented as discrete types e g straight meandering braided separated by threshold values of slope and discharge however for gravel bed river patterns an index of total sinuosity p can be defined which varies continuously with both stream power per unit channel belt length represented as the product of mean annual flood and valley gradient and median bed material diameter an empirical relationship between p and these controlling variables can be used to provide palaeo hydrological reconstructions for braided stream traces on terrace fragments as an alternative to methods based on bed material sizes and criteria for the threshold of grain motion

morphological response of an alpine braided reach to sediment laden flow events braided gravel bed rivers show characteristic temporal and spatial variability in morphological change and bedload transport under steady flow and sediment supply rates their morphodynamic behavior and long term evolution in response to nonstationary external forcing is less well known we studied daily morphological changes in a well constrained reach of an alpine braided river that is subject to regulated sediment laden flows associated with hydroelectric power exploitation as well as occasional floods we found that net reach erosion and deposition were forced by upstream sediment supply albeit in a nonlinear fashion the spatial distribution of morphological change and inferred spatially distributed sediment transport rates varied strongly along the braided reach and between successive sequences of flushing local morphological change was driven by two factors 1 local relief leading to the preferential filling of topographic lows and erosion of highs particularly during longer duration floods which allow braided dynamics to be maintained and 2 system memory leading to a negative autocorrelation in bed level changes where erosion was followed by deposition of similar magnitude and vice versa this effect was associated with the temporary storage of high sediment loads from flushing due to the abrupt on off nature of these flows and reveals the relatively efficient transport of sediment in a river that is heavily impacted upon by flow abstraction in general the internal morphodynamics of the braided river condition their own response to external forcing events and thus sediment transfer

revealing the natural complexity of topographic change processes through repeat surveys and decision tree classification title revealing the natural complexity of topographic change processes through repeat surveys and decision tree classification short title decision tree classification of topographic change processes authors joshua r wyrick a gregory b pasternack b a lafayette college 740 high street easton pa 18042 b university of california davis one shields drive davis ca 95616 corresponding author tel 1 610 330 5735 e mail wyrickj lafayette edu fax 1 keywords topographic change dem differencing river morphology regulated rivers geomorphic change abstract topographic change processes tcps are the mechanisms by which a landscape is interpreted to be experiencing landform deformation and are defined by the specific actions occurring within a contiguous localized region that cause sediment to be either deposited or eroded past topographic change studies have mostly been focused at the site scale the goal of this study was to identify and delineate spatially explicit tcp

temporal and spatial patterns of sedimentation within the batture lands of the middle mississippi river usa abstract sediment deposition and storage are important functions of batture lands the land between the channel s low water elevation and the flood mitigation levee however sedimentation processes within these areas are not fully understood in this paper we explore the spatiotemporal patterns rates and volume of sedimentation within the batture lands along the middle mississippi river mmr between the confluence of the missouri and ohio rivers using three approaches 1 comparison of historical to modern elevation data in order to estimate long term 100 yr sedimentation rates 2 estimation of medium to short term 70 attributed largely to sediment trapping by dams during the second half of the twentieth century the increase in mmr batture land sedimentation rates are attributed to at least two potential mechanisms 1 the above average frequency and duration of low magnitude floods 2 yr and 5 yr flood during the short term assessment periods which allowed for more suspended sediment to be deposited within the batture lands and 2 the construction of levees that substantially reduced the floodplain area 75 available for storage of overbank deposits increasing the vertical accumulation and consequently the detectability of a given volume of sediment the gcd estimated batture land sediment volumes were 9 0 of the suspended load at st louis this substantial storage of sediment 8 5 mt yr 1 along the mmr suggests batture lands are an important sink for suspended sediments

an evaluation of the effectiveness of low cost uavs and structure from motion for geomorphic change detection abstract the measurement of topography and of topographic change is essential for the study of many geomorphic processes in recent years structure from motion sfm techniques applied to photographs taken by camera equipped unmanned aerial vehicles uavs has become a powerful new tool for the generation of high resolution topography the variety of available uav systems continues to increase rapidly but it is not clear whether increased uav sophistication translates into improved quality of the calculated topography to evaluate the lower end of the uav spectrum a simple low cost uav was deployed to calculate high resolution topography in the daan river gorge in western taiwan a site with a complicated 3d morphology and a wide range of surface types making it a challenging site for topographic measurement terrestrial lidar surveys were conducted in parallel with uav surveys in both june and november 2014 enabling an assessment of the reliability of the uav survey to detect geomorphic changes in the range of 30 cm to several meters a further uav survey was conducted in june 2015 in order to quantify changes resulting from the 2015 spring monsoon to evaluate the accuracy of the uav derived topography it was compared to terrestrial lidar data collected during the same survey period using the cloud to cloud comparison algorithm m3c2 the uav generated point clouds match the lidar point clouds well with rms errors of 30 40 cm however the accuracy of the sfm point clouds depends strongly on the characteristics of the surface being considered with vegetation water and small scale texture causing inaccuracies the lidar and sfm data yield similar maps of change from june to november 2014 with the same areas of geomorphic change detected by both methods the sfm generated change map for november 2014 to june 2015 indicates that the 2015 spring monsoon caused erosion throughout the gorge and highlights the importance of event driven erosion in the daan river the results suggest that even very basic uavs can yield data suitable for measuring geomorphic change on the scale of a channel reach

semi determinate hydraulic geometry of river channels south island new zealand data to describe the morphologic hydrologic and sedimentologic characteristics of 72 south island new zealand rivers were collected and analysed nearly 70 per cent of variation in channel morphology is accounted for by differences in cross sectional area slope and cross section shape only 53 per cent of the morphologic variability could be statistically explained by the hydrologic and sediment variables used the level of explanation varied for different morphologic variables nearly 90 per cent of the variability in cross sectional area could be explained but aspect ratio maximum depth divided by hydraulic radius was completely independent apart from the inadequacy of the measured variables as indices of the true underlying controlling factors and the imperfect measurement and sampling procedures the low level of explanation is probably due to the influence of factors such as floodplain vegetation high quasi random variability in bark sediment character boundary effects imposed by bedrock bluffs and the precise sequence of flood events none of which are easily quantified in addition observations indicate that there is a large random variation in channel form which cannot be related to any factor an attempt to relate channel morphology to flow variability using simple indices of the latter was unsuccessful

contaminated sediment flux from eroding abandoned historical metal mines spatial and temporal variability in geomorphological drivers abstract abandoned historical metal mines represent significant long term sediment source locations contributing highly contaminated anthropogenic legacy sediments to river systems despite this our understanding of spatial and temporal variability in the rates and geomorphological drivers of specific contaminated sediment source locations across abandoned mines remains poorly constrained in this study sediment flux from two abandoned historical lead mines in the north pennines uk was monitored over an 18 month period using repeat terrestrial laser scanning enabling the spatial and temporal significance of several common geomorphological processes to be quantified for the first time a novel contaminated sediment budget approach is used to integrate topographical change data with a pxrf survey of surface sediment metal concentrations approximately 434 t 289 t a 1 of eroded sediment entered the stream from a source area of 0 023 km2 the majority of the erosion was driven by two dominant processes with gullying accounting for 60 and bank erosion contributing 30 redeposition of eroded material within the survey area was minimal 3 indicating very high levels of coupling between source locations and the stream network and the export of the vast majority of eroded sediments 97 from the mined area rates for all erosive processes were highly episodic and primarily driven by high magnitude low frequency storm events metal concentrations in surface sediments exhibited considerable spatial variability with notable hotspots around the former ore processing areas and on the tailings heaps however 84 of all sediments sampled were in excess of available soil guideline values for pb and 65 in excess of equivalent guideline values for zn indicating that abandoned mine sites still have the potential to be significant sources of contaminant metals and pose a risk to the wider environment in total an estimated 4 59 t of pb and 2 14 t of zn entered the stream network in a sediment associated form during the 18 month monitoring period although these overall contaminated sediment inputs are high they are restricted to particular geomorphological processes are spatially variable in terms of the magnitude of specific source locations and are delivered in fairly discrete events this provides invaluable information for the future management of other abandoned mines and targeted mitigation of their potential legacy effects

sediment supply and channel morphology in mountain river systems 2 single thread to braided transitions differences in sediment supply between single thread and braided channel types provide a long recognized though difficult to quantify pattern discrimination building on the results from our preceding paper we present a multiscale assessment of the sediment supply geomorphology and sediment transport characteristics of braided gravel bedded reaches in the northern rocky mountains usa first we present a quantitative theoretically based discriminant function that stratifies single thread and braided reaches on the basis of variations in bankfull sediment concentration and dimensionless discharge following the work of millar 2005 and eaton et al 2010 this function correctly classifies 50 of the 53 channel types where bed load concentrations are known second while channel pattern transitions are often linked to changes in slope field studies along sunlight creek wyoming show that downstream transitions between single thread and braided reaches are instead caused by valley constrictions and changes in the grain size of sediment from tributaries finally we demonstrate that the two dimensional variability in flow properties in braided reaches produces locally high values of shear stress and bed load transport yet bed load measurements and sediment transport calculations also show that sediment transport rates between adjoining braided and single thread reaches may be approximately equal where channels are near the pattern threshold and downstream variations in bank fortitude and channel constriction force pattern transitions taken together these results indicate that high bed load concentrations are fundamental to the braided channel planform and that braided channels likely reflect a quasi equilibrium state within watersheds with persistent high sediment supply

empirical relationship between river slope and the elongation of bars in braided rivers a potential tool for paleoslope analysis from subsurface data abstract paleoslope of ancient river systems is a fundamental parameter needed to reconstruct paleohydrology and paleoclimate from the fluvial sedimentary record the shape of braid bars in 22 modern rivers yields a relationship between average bar elongation length width and river slope steep rivers display more elongated bars than gently dipping reaches this relationship has potential application to ancient braided systems preserved in the subsurface and imaged by 3d seismic data the average elongation of bars identified on a stratal slice through the dagang river deposits in north east china yields a slope prediction which combined with empirical data on grain size and slope of alluvial rivers predicts a median grain size of between 0 1 and 1 mm for the considered river sediment in agreement with grain size data in an adjacent isochronous belt this study provides an additional approach for paleohydraulics in sedimentary basins and grain size prediction in exploration

the effects of topographic surveying technique and data resolution on the detection and interpretation of geomorphic change abstract change detection of high resolution topographic data is commonly used in river valleys to quantify reach and site scale sediment budgets by estimating the erosion deposition volume and to interpret the geomorphic processes driving erosion and deposition field survey data are typically collected as point clouds that are often converted to gridded raster datasets and the ultimate choice of grid resolution is left to the user this choice may have important implications for both the quantification and interpretation of geomorphic change here we used concurrent topographic data collected by terrestrial laser scanning tls and structure from motion sfm photogrammetry to quantify the influence of grid resolution and sampling technique on a the sediment budget and b the presence and role of geomorphic processes i e alluvial colluvial aeolian and fluvial transport driving topographic change at four sites along the colorado river in grand canyon arizona usa we found that while both techniques produced similar estimates for site scale sediment budgets the magnitude of detected topographic change was dampened at coarser pixel resolutions an overall decrease in the areal extent of erosion and deposition were observed respectively when coarsening pixel size from 5 cm to 1 m among all sites coarser resolution data tended to affect interpretation of landscape change along the margins of river valleys for example when changing from 5 cm to 1 m pixel resolution the inferred contribution of aeolian changes to total site scale geomorphic change increased in area by 7 9 whereas the inferred contribution of alluvial and colluvial processes decreased in area by 97 9 and 88 2 respectively more generally we found that coarsening pixel sizes disproportionately attributed geomorphic change to one or more of the most common processes operating at a site we also found that coarsening pixel resolution amplified the net sediment imbalance at the site scale driving the imbalance at erosional sites further into erosion and vice versa for depositional sites our results have implications both for point cloud data collection and for raster dataset processing we argue that selecting the finest obtainable resolution is not always warranted to accurately quantify and interpret geomorphic change because remote sensing technique topographic data resolution and analysis procedure can be optimized to capture the spatial scale of those processes driving landscape change however in landscapes at or near sediment equilibrium i e equal amounts of erosion and deposition the finest obtainable topographic data resolution is warranted to avoid amplifying sediment imbalance and erroneously inferring that sites are trending toward erosion or deposition

morphology and evolution of bars in a wandering gravel bed river lower fraser river british columbia canada a hierarchical typology for the channels and bars within aggradational wandering gravel bed rivers is developed from an examination of a 50 km reach of lower fraser river british columbia canada unit bars built by stacking of gravelly bedload sheets are the key dynamic element of the sediment transfer system linking sediment transport during individual freshets to the creation development and remoulding of compound bar platforms that have either a lateral or medial style primary and secondary unit bars are identified respectively as those that deliver sediment to compound bars from the principal channel and those that redistribute sediment across the compound bar via seasonal anabranches and smaller channels the record of bar accretion evident in ground penetrating radar sequences is consistent with the long term development of bar complexes derived from historical aerial photographs for two compound bars inter annual changes associated with individual sediment transport episodes are measured using detailed topographic surveys and longer term changes are quantified using sediment budgets derived for individual bars from periodic channel surveys annual sediment turnover on the bars is comparable with the bed material transfer rate along the channel indicating that relatively little bed material bypasses the bars bar construction and change are mainly accomplished by lateral accretion since the river has limited capacity to raise bed load onto higher surfaces styles of accretion and erosion and therefore the major bar form morphologies on fraser river are familiar and consistent with those in gravelly braided channels but the wandering style does exhibit some distinctive features for example 65 year histories reveal the potential for long sequences of uninterrupted accretion in relatively stable wandering rivers that are unlikely in braided rivers

expanding the active layer discussion of church and haschenburger 2017 what is the active layer water resources research 53 5 10 doi 10 1002 2016wr019675 church and haschenburger 2017 https doi org 10 1002 2016wr019675 make helpful distinctions around the issue of defining the active layer with which we agree we propose expanding discussion and definition of the active layer in fluvial bedload transport to include the concept of the morphological active layer this is particularly applicable to laterally unstable rivers such as braided rivers in which progressive morphological change over short time periods is the process by which much of the bedload transport occurs the morphological active layer is also distinguished by variable lateral and longitudinal extent continuity over a range of flows and transport intensity we suggest that the issue of forms of active layer raised by church and haschenburger opens up an important discussion on the nature of bedload transport in relation to river morpho dynamics over the range of river types

assessment of morphological changes induced by flow and flood pulses in a gravel bed braided river the tagliamento river italy large gravel bed braided rivers show a highly dynamic evolution where even moderate flow pulses can produce significant morphological adjustment an estimation of network variations is needed by river authorities as well as by ecologists for better managing river ecosystems however few field investigations have been performed to measure the effect of unsteady discharges in braided rivers in this paper we report on the morphological changes induced by six different floods in a 1 km long reach of the tagliamento river italy topographic surveys were performed after each significant flood and an automatic digital camera continuously monitored the planimetric configuration repeated measurements of cross section profiles allowed the quantification of the transported sediments volume and in particular provided a basis to estimate the percentage of the floodplain subject to morphological evolution data analysis showed a good relationship between peak flow level active width and mean bed level changes similarly lateral channel shifting is likely to increase for larger floods monitoring of a range of discharges up to bankfull conditions revealed a fundamental difference between flow pulses events on the average occurring one or more times per year and flood pulses with a return period larger than two years the morphological evolution in the former case is mainly limited to a few active branches and is locally driven by bank erosion at the bend apex on the other hand larger floods induce a complete reworking of the network configuration where bifurcations and confluences play a crucial role single morphological units like branches nodes bars are no longer recognizable after this type of event braided rivers are therefore characterized by the occurrence of two different spatial and temporal scales that force the ecosystem dynamics

filtering spatial error from dems implications for morphological change estimation abstract scour and fill estimation from digital elevation model dem subtraction or differencing is an increasingly common technique in morphological and sediment transport investigations the technique is commonly used to estimate scour and fill volumes and to produce scour and fill maps that provide process based information to geomorphologists accounting for sources of uncertainty within the dem is of critical importance dem error is spatially variable and has a tendency to be greater at breaks of slope such as bar and bank edges in the past however this has been achieved using a uniform error metric across the dem resulting in over conservative estimates of error in turn this has led to over conservative scour and fill volumes and incorrect process interpretation this paper applies a new approach that permits assessment of spatially distributed error across a dem the method is tested on a sequence of field surveys of the gravel bed river nent cumbria uk the results demonstrate some dramatic differences application of conventional techniques that account for mean error across a dem led to a 15 and 31 underestimation in scour and fill volumes respectively between july and october 1998 whilst for the october 1998 june 1999 subtraction 31 and 13 of scour and fill were underestimated respectively use of a uniform error across a surface captures less change in comparison to a spatially distributed approach furthermore the changes captured using a uniform error are biased toward areas of the channel that have more local topographic variability such as bar and bank edges in contrast the use of a spatially distributed approach provides information on change from flatter surfaces such as bar tops that would otherwise be missed this study also demonstrates that estimates of morphological change can be misleading in the absence of an error filter where the raw survey data is available it is recommended that sediment budgeting studies take account of the spatial variability of error in each dem involved in the subtraction

a quantitative soil stratigraphic approach to the correlation and dating of post glacial river terraces in glen feshie western cairngorms little is known about holocene river terrace development in upland scottish valleys interpretation of many of the terrace sequences previously suggested to have been formed by meltwaters either from the last scottish ice sheet or the loch lomond advance has generally been based on morphological data in this paper an alternative approach to the traditional height based method of terrace correlation and dating is presented using data from glen feshie western cairngorms terrace fragments are numerically classified and objectively grouped using quantitative soil stratigraphic data principal components analysis is used to both quantify pedological data and separate temporal trends in the data from variance due to local site factors the scores on the temporal component are used to derive soil stratigraphic units developed on the surficial sediments of the glen feshie terraces by grouping soil sites using a hierarchical clustering technique this provides evidence for at least five soil stratigraphic units developed on the fluvial surfaces various methods of absolute dating control permits association of these surfaces with five phases of terrace development these are placed tentatively at 13 000 10 000 3600 1000 and 80 radiocarbon years b p suggesting at least three phases of valley floor incision in glen feshie during the late holocene

from experimental plots to experimental landscapes topography erosion and deposition in sub humid badlands from structure from motion photogrammetry in the last decade advances in surveying technology have opened up the possibility of representing topography and monitoring surface changes over experimental plots 10 m2 in high resolution 103 points m 1 yet the representativeness of these small plots is limited with structure from motion sfm and multi view stereo mvs techniques now becoming part of the geomorphologist s toolkit there is potential to expand further the scale at which we characterise topography and monitor geomorphic change morphometrically moving beyond previous plot scale work using terrestrial laser scanning tls surveys this paper validates robustly a number of sfm mvs surveys against total station and extensive tls data at three nested scales plots 30 m2 within a small catchment 4710 m2 within an eroding marl badland landscape 1 km2 sfm surveys from a number of platforms are evaluated based on i topography ii sub grid roughness and iii change detection capabilities at an annual scale oblique ground based images can provide a high quality surface equivalent to tls at the plot scale but become unreliable over larger areas of complex terrain degradation of surface quality with range is observed clearly for sfm models derived from aerial imagery recently modelled doming effects from the use of vertical imagery are proven empirically as a piloted gyrocopter survey at 50m altitude with convergent off nadir imagery provided higher quality data than an unmanned aerial vehicle uav flying at the same height and collecting vertical imagery for soil erosion monitoring sfm can provide data comparable with tls only from small survey ranges 5 m and is best limited to survey ranges 10 20 m synthesis of these results with existing validation studies shows a clear degradation of root mean squared error rmse with survey range with a median ratio between rmse and survey range of 1 639 and highlights the effect of the validation method e g point cloud or raster based on the estimated quality

computing spatially distributed sediment delivery ratios inferring functional sediment connectivity from repeat high resolution digital elevation models high resolution digital elevation models dems from repeat lidar or sfm surveys have become an important tool in process geomorphology the spatial pattern of negative and positive changes of surface elevation on raster dems of difference dod can be interpreted in terms of geomorphic processes and has been used for morphological budgeting we show how the application of flow routing algorithms and flow accumulation opens new opportunities for the analysis of dod by accumulating the values of the dod along downslope flowpaths delineated on a dem these algorithms lend themselves to computing the net balance i e sediment yield sy for the contributing area of each cell doing the same for the negative subset of the dod yields a minimum estimate of erosion e within the contributing area the division of sy by e yields a maximum estimate of the sediment delivery ratio sdr that is the proportion of material eroded within the contributing area of each cell that has been exported from that area the resulting sdr is a spatially distributed measure of functional sediment connectivity in this letter we develop the computationally simple approach by means of an example dod from a lateral moraine section in the upper kaunertal valley austrian central alps we also discuss advantages assumptions and limitations and outline potential applications to connectivity research using field laboratory and model based dod

coupled simulations of fluvial erosion and mass wasting for cohesive river banks the erosion of sediment from riverbanks affects a range of physical and ecological issues bank retreat often involves combinations of fluvial erosion and mass wasting and in recent years bank retreat models have been developed that combine hydraulic erosion and limit equilibrium stability models in related work finite element seepage analyses have also been used to account for the influence of pore water pressure in controlling the onset of masswasting this paper builds on these previous studies by developing a simulation modeling approach in which the hydraulic erosion finite element seepage and limit equilibrium stability models are for the first time fully coupled application of the model is demonstrated by undertaking simulations of a single flow event at a single study site for scenarios where i there is no fluvial erosion and the bank geometry profile remains constant throughout ii there is no fluvial erosion but the bank profile is deformed by simulated mass wasting and iii the bank profile is allowed to freely deform in response to both simulated fluvial erosion and mass wasting the results are limited in scope to the specific conditions encountered at the study site but they nevertheless demonstrate the significant role that fluvial erosion plays in steepening the bank profile or creating overhangs thereby triggering mass wasting however feedbacks between the various processes also lead to unexpected outcomes specifically fluvial erosion also affects bank stability indirectly as deformation of the bank profile alters the hydraulic gradients driving infiltration into the bank thereby modulating the evolution of the pore water pressure field consequently the frequency magnitude and mode of bank erosion events in the fully coupled scenario differ from the two scenarios in which not all the relevant bank process interactions are included

short term geomorphic analysis in a disturbed fluvial environment by fusion of lidar colour bathymetry and dgps surveys abstract objective estimating river s underwater bed elevations is a necessary but challenging task the objective of this study is to develop a revised approach to generate accurate and detailed digital terrain models dtms of a river reach by merging lidar data for the dry area with water depth indirectly derived from aerial imagery for wet areas methods this approach was applied along three sub reaches of the brenta river italy before and after two major flood events a regression model relating water depth and intensity of the three colour bands derived from aerial photos was implemented more than 2400 in channel depth calibration points were taken using a differential global positioning system dgps along a wide range of underwater bed forms results the resulting dtms closely matched the field surveyed bed surface and allowed to assess that a 10 year recurrence interval flood generated a predominance of erosion processes erosion dominated in the upper part of the study segment 104 082 m3 whereas a near equilibrium is featured on the lower reach 45 232 m3 the dtms allowed the detection of processes such as riffle pool downstream migration and the progressive scour of a pool located near a rip rap conclusion the presented approach provides an adequate topographical description of the river bed to explore channel adjustments due to flood events practice combining colour bathymetry and dgps surveys proved to represent a useful tool for many fluvial engineering ecology and management purposes implications the proposed approach represents a valuable tool for river topography description river management ecology and restoration purposes when bathymetric data are not available

a cellular model of braided rivers a broad sheet of water flowing over non cohesive sediment typically breaks up into a network of interconnected channels called a braided stream fig 1 the dynamics of such networks are complex channels migrate laterally split rejoin and develop bars with the flow shifting unpredictably from one part of the network to another many processes are known to operate in a braided river1 3 but it is unclear which of these are essential to explain the observed dynamics we describe here a simple deterministic numerical model of water flow over a cohesionless bed that captures the main spatial and temporal features of real braided rivers the patterns arise from local scour and deposition caused by a nonlinear dependence of bedload sediment flux on water discharge although the morphology of the resulting network depends in detail on the sediment transport rule used in the model our results suggest that the only factors essential for braiding are bedload sediment transport and laterally unconstrained free surface flow

linking the spatial distribution of bed load transport to morphological change during high flow events in a shallow braided river this paper provides novel observations linking the connections between spatially distributed bed load transport pathways hydraulic patterns and morphological change in a shallow gravel bed braided river these observations shed light on the mechanics of braiding processes and illustrate the potential to quantify coupled material fluxes using remotely sensed methods the paper focuses upon a 300 m long segment of the rees river new zealand and utilizes spatially dense observations from a mobile acoustic doppler current profiler adcp to map depth velocity and channel topography through a sequence of high flow events apparent bed load velocity is estimated from the bias in adcp bottom tracking and mapped to indicate bed load transport pathways terrestrial laser scanning tls of exposed bar surfaces is fused with the adcp surveys to generate spatially continuous digital elevation models which quantify morphological change through the sequence of events results map spatially distributed bed load pathways that were likely to link zones of erosion and deposition the coherence between the channel thalweg zone of maximum hydraulic forcing and maximum apparent bed load pathways varied this suggests that in places local sediment supply sources exerted a strong control on the distribution of bed load distinct from hydraulic forcing the principal braiding mechanisms observed were channel choking leading to subsequent bifurcation results show the connection between sediment sources pathways and sinks and their influence on channel morphology and flow path directions the methodology of coupling spatially dense adcp surveys with tls has considerable potential to understand connections between processes and morphological change in dynamic fluvial settings

reconceptualising coarse sediment delivery problems in rivers as catchment scale and diffuse this paper assesses river channel management activities in the context of the interaction between coarse sediment delivery climate change river channel response and flood risk it uses two main sources of evidence 1 an intensive instrumentation of an upland river catchment using both traditional hydrometric and novel sediment sensing methods and 2 a sediment delivery model that combines a treatment of sediment generation from mass failure with a treatment of the connectivity of this failed material to the drainage network the field instrumentation suggests that the precipitation events that deliver sediment from hillslopes to the drainage network are different to those that transfer sediment within the network itself extreme events that could occur at any time in the year i e they are not dependent on wet antecedent conditions were crucial for sediment delivery however sustained high river flows were responsible for the majority of transfer within the river itself application of three downscaling methods to climate model predictions for the 2050s and 2080s suggested a significant increase in the number and potential volume of delivery events by the 2050s regardless of the climate downscaling scenario used first approximations suggested that this would translate into annual bed level aggradation rates of between 0 10 and 0 20 m per year in the downstream main channel reaches second the importance of this delivery for flood risk studies was confirmed by simulating the effects of 16 months of measured in channel simulation with river flows scaled for climate change to the 2050s and 2080s short term sedimentation could result in similar magnitude increases in inundated area for 1 in 0 5 and 1 in 2 year floods to those predicted for the 2050s in relation to increases in flow magnitude finally we were able to develop an alternative approach to river management in relation to coarse sediment delivery based upon reducing the rates of coarse sediment delivery through highly localised woodland planting under the assumption that reducing delivery rates should reduce the rate of channel migration and hence the magnitude of the bank erosion problem thus the paper demonstrates the need to conceptualise local river management problems in upland river environments as point scale manifestations of a diffuse sediment delivery process with a much more explicit focus on the catchment scale if our river systems are to become more insulated from the impacts of future climate changes

dynamic single thread channels maintained by the interaction of flow and vegetation most rivers on earth today flow as a single channel in some cases with occasional islands and follow a more or less sinuous course however single thread channels have proven difficult to reproduce and study experimentally experimental self formed channels tend to widen and subdivide leading to a braided pattern cohesive sediment has been the main mechanism studied for stabilizing banks and producing a single thread channel we show how laboratory experiments using vegetation to stabilize banks can organize the flow and convert the planform morphology from braided to single thread our experimental strategy a repeated cycle of short periods of high water discharge alternating with longer periods of low discharge accompanied by plant seeding and growth leads to the evolution of a dynamic self maintaining single thread channel with well defined banks and floodplain by eliminating weak flow paths the vegetation corrals the water into a single dominant channel until the reduction in total wetted width leads to a new self organized state in which the flow removes vegetated area as fast as it is produced the new channel is deeper and has a broader distribution of depths than the braided one with channel size adjusted to carry almost all the flood flow the resulting system maintains a dynamic steady state via similar mechanisms to those that operate in meandering channels in the field specifically erosion at the outside of bends bend growth and bar development our methodology provides a basis for experimental development of self sustaining high amplitude meanders and has applications for river management and basic research purposes

characterizing braided rivers in two nested watersheds in the source region of the yangtze river on the qinghai tibet plateau abstract large and complex braided channels 1 km wide in the source region of the yangtze river sryr on the qinghai tibet plateau china are characterized by a unique alpine environment with very high elevations and glacier sources yet little is known about the morphological complexity and changes of large braided channels owing to the scarcity of hydrological and topographical data in this study we provided the first insight into these issues using compiled long term several decades climatic and suspended sediment data and landsat images of braided channels in two nested headwater watersheds i e tuotuo and tongtian river watersheds in the sryr analysis of annual and monthly mean temperature precipitation and water discharges illustrated the nature of the hydrological regime and their response to glacier melting in the two watersheds examination of annual mean suspended sediment loads and concentrations c led to two sediment rating curves and generally similar c values between the two watersheds among a suite of morphological indices for braided rivers braiding intensity may be quantified using four different ones after comparing the indices we showed that they had similar ability of characterizing braiding patterns and adopted branch count index bit3 for further analysis we found that bit3 was linearly correlated with active valley width wr during both flood and dry seasons for the 17 selected braided reaches distributed within the two nested watersheds in addition braiding density defined as the ratio of bit3 to wr remained approximately unchanged irrespective of elevations and locations of these reaches indicating clearly that morphological structures of braided channels are spatially uniform in the sryr along the main channels of the two nested watersheds over the entire study period bit3 always reached the maximum as rw defined as the ratio of water body to exposed active riverbed area was around 0 43 furthermore rw was always positively correlated with the associated water discharge q variable degrees of braiding adjustment in response to changes of hydrological regime were represented by hysteresis loops between bit3 and q these results revealed relatively homogeneous morphologic properties of braided channels across the two nested watersheds and provided an important benchmark for future morphodynamic research on braided rivers in the sryr

modeling the topography of shallow braided rivers using structure from motion photogrammetry abstract recent advances in computer vision and image analysis have led to the development of a novel fully automated photogrammetric method to generate dense 3d point cloud data this approach termed structure from motion or sfm requires only limited ground control and is ideally suited to imagery obtained from low cost non metric cameras acquired either at close range or using aerial platforms terrain models generated using sfm have begun to emerge recently and with a growing spectrum of software now available there is an urgent need to provide a robust quality assessment of the data products generated using standard field and computational workflows to address this demand we present a detailed error analysis of sub meter resolution terrain models of two contiguous reaches 1 6 and 1 7 km long of the braided ahuriri river new zealand generated using sfm a six stage methodology is described involving i hand held image acquisition from an aerial platform ii 3d point cloud extraction modeling using agisoft photoscan iii georeferencing on a redundant network of gps surveyed ground control points iv point cloud filtering to reduce computational demand as well as reduce vegetation noise v optical bathymetric modeling of inundated areas and vi data fusion and surface modeling to generate sub meter raster terrain models bootstrapped geo registration as well as extensive distributed gps and sonar based bathymetric check data were used to quantify the quality of the models generated after each processing step the results obtained provide the first quantified analysis of sfm applied to model the complex terrain of a braided river results indicate that geo registration errors of 0 04 m planar and 0 10 m elevation and vertical surface errors of 0 10 m in non vegetation areas can be achieved from a dataset of photographs taken at 600 m and 800 m above the ground level these encouraging results suggest that this low cost logistically simple method can deliver high quality terrain datasets competitive with those obtained with significantly more expensive laser scanning and suitable for geomorphic change detection and hydrodynamic modeling