large scale dam removal on the elwha river washington usa river channel and floodplain geomorphic change abstract a substantial increase in fluvial sediment supply relative to transport capacity causes complex large magnitude changes in river and floodplain morphology downstream although sedimentary and geomorphic responses to sediment pulses are a fundamental part of landscape evolution few opportunities exist to quantify those processes over field scales we investigated the downstream effects of sediment released during the largest dam removal in history on the elwha river washington usa by measuring changes in riverbed elevation and topography bed sediment grain size and channel planform as two dams were removed in stages over two years as 10 5 million t 7 1 million m3 of sediment was released from two former reservoirs downstream dispersion of a sediment wave caused widespread bed aggradation of 1 m greater where pools filled changed the river from pool riffle to braided morphology and decreased the slope of the lowermost river the newly deposited sediment which was finer than most of the pre dam removal bed formed new bars largely pebble granule and sand material prompting aggradational channel avulsion that increased the channel braiding index by almost 50 as a result of mainstem bed aggradation floodplain channels received flow and accumulated new sediment even during low to moderate flow conditions the river system showed a two to tenfold greater geomorphic response to dam removal in terms of bed elevation change magnitude than it had to a 40 year flood event four years before dam removal two years after dam removal began as the river had started to incise through deposits of the initial sediment wave 1 2 million t of new sediment 10 of the amount released from the two reservoirs was stored along 18 river km of the mainstem channel and 25 km of floodplain channels the elwha river thus was able to transport most of the released sediment to the river mouth the geomorphic alterations and changing bed sediment grain size along the elwha river have important ecological implications affecting aquatic habitat structure benthic fauna salmonid fish spawning and rearing potential and riparian vegetation the response of the river to dam removal represents a unique opportunity to observe and quantify fundamental geomorphic processes associated with a massive sediment influx and also provides important lessons for future river restoration endeavors

riverscape mapping and hyperscale analysis of the sediment links concept abstract longitudinal patterns in channel complexity play an important role in our understanding of fluvial systems the spatial scales over which external controls such as tributaries landslides and debris flows alter channel form and influence the broader basin wide trends in channel form channel complexity across a basin has important implications for how we conceptualize basin wide trends in channel form such as downstream hydraulic geometry and the sediment links concept this study takes a hyperscale approach to mapping channel morphology across 200 km of the rogue river in southwest oregon that is high resolution data over large spatial extents allowing analysis to be conducted simultaneously at and across multiple spatial scales using a suas and digital photosieving we measured gravels on exposed gravel bars for the study area we also measured thalweg depth in the field using a singlebeam echo sounder slope and channel width were derived using existing gis datasets we used these data to create a hyperscale view of the rogue river examining the impact of tributary and non tributary sediment links we used a statistical approach to determine if changes in channel form were truly unique in the context of larger scale channel variability our findings show inconsistent statistical significance of the identified lateral sediment sources lss between variables e g a statistically significant change in slope would not necessarily correlate with an increase in unit stream power there were many lss which triggered statistically significant changes to channel form we used hyperscale graphs to reveal the complexity and spatial trends associated with the relationships between a given sediment link and channel form the results of this study illustrate the complexity with which sediment links impact channel form and the distances below a given sediment link that a detectable signal exists if a detectable signal exists

migration of a coarse fluvial sediment pulse detected by hysteresis in bedload generated seismic waves a b s t r a c t seismic signals near rivers are partially composed of the elastic waves generated by bedload particles impacting the river bed in this study we explore the relationship between this seismic signal and river bedload transport by analyzing high frequency broadband seismic data from multiple stations along the chijiawan river in northern taiwan following the removal of a 13 m check dam this dam removal provides a natural experiment in which rapid and predictable changes in the river s profile occur which in turn enables independent constraints on spatial and temporal variation in bedload sediment transport we compare floods of similar magnitudes with and without bedload transport and find that the amplitude of seismic shaking produced at a given river stage changes over the course of a single storm when bedload transport is active hysteresis in the relationship between bedload transport and river stage is a well documented phenomenon with multiple known causes consequently previous studies have suggested that hysteresis observed in the seismic amplitude stage response is the signature of bedload transport field evidence and stream profile evolution in this study corroborate that interpretation we develop a metric for the normalized magnitude of seismic hysteresis during individual floods this metric appears to scale qualitatively with total bedload transport at each seismic station indicating a dominance of transport on the rising limbs of both storms we speculate that hysteresis at this site arises from time dependent evolution of the bed for example due to grain packing mobile armoring or the temporal lag between stage and bedform growth reveals along stream variations in hysteresis for each storm with a peak in hysteresis further downstream for the second event the pattern is consistent with a migrating sediment pulse that is a predicted consequence of the dam removal our results indicate that hysteresis in the relationship between seismic wave amplitude and river stage may track sediment transport

sediment budget for salmonid spawning habitat rehabilitation in a regulated river bed elevation feature adjustments and spawning use were monitored at three chinook salmon oncorhynchus tschawytscha spawning habitat rehabilitation sites to measure project longevity in a regulated river sites enhanced with 649 1323 m 3 of gravel lost from 3 20 of remaining gravel volume annually during controlled flows of 8 70 m 3 s and 2 6 4 6 of placed material during a short duration 19 days release of 57 m 3 s the oldest site lost 50 of enhancement volume over 4 years of the mechanisms monitored gravel deflation was the greatest contributor to volumetric reductions followed by hydraulic scour spawning local scour around placed features and oversteepened slopes contributed to volumetric changes as sites matured volumetric reductions decreased sites captured as much large woody debris as was lost while complexity is an extremely important aspect of ecological function artificial production of highly diverse and complex habitat features may lead to limited longevity without natural rejuvenation d 2005 elsevier b v all rights reserved

sediment pulses in mountain rivers 2 comparison between experiments and numerical predictions 1 mountain rivers in particular are prone to sediment input in the form of pulses rather than a more continuous supply these pulses often enter in the form of landslides from adjacent hillslopes or debris flows from steeper tributaries the activities of humans such as timber harvesting road building and urban development can increase the frequency of sediment pulses the question as to how mountain rivers accommodate pulses of sediment thus becomes of practical as well as academic significance in part 1 cui et al 2003 the results of three laboratory experiments on sediment pulses are reported it was found there that the pulses were eliminated from the flume predominantly by dispersion of the topographic high significant translation was observed only when the pulse material was substantially finer than the ambient load in the river here the laboratory data are used to test a numerical model originally devised for predicting the evolution of sediment pulses in field scale gravel bed streams the model successfully reproduces the predominantly dispersive deformation of the experimental pulses rates of dispersion are generally underestimated largely because bed load transport rates are underestimated by the transport equation used in the model the model reproduces the experimental data best when the pulse is significantly coarser than the ambient sediment in this case the model successfully predicts the formation and downstream progradation of a delta that formed in the backwater zone of the pulse in run 3 the performance of the model is less successful when the pulse is composed primarily of sand this is likely because the bed load equation used in the study is specifically designed for gravel when the model is adapted to conditions characteristic of large sand bed rivers with low froude numbers it predicts substantial translation of pulses as well as dispersion

patterns of sediment slug translation and dispersion following typhoon induced disturbance oyabu creek kyushu japan a six year monitoring programme characterized the migration dispersion patterns of sediment slugs generated following typhoon induced disturbances in 1993 and 1997 along a single thread gravel bed stream oyabu creek on kyushu island japan this laterally con ned creek comprises rif e pool sequences with intervening bedrock outcrops the passage of sediment pulses associated with sediment slug processes re ected and was controlled by the rif e pool structures which provided channel bed roughness the volume of sediment stored along valley oors and the distribution of bedrock outcrops changes to bed material size following major sediment inputs during the disturbance events also exerted an in uence on subsequent sediment slug processes the sequence of rainfall events together with changes to channel bed structure induced different phases in the sediment slug processes the capacity of a reach to store or trap sediment as recorded by the longitudinal structure of the channel varied during these differing phases copyright 2004 john wiley sons ltd

effects of sediment pulses on bed relief in bar pool channels to further develop prediction of the range of morphological adjustments associated with sediment pulses in bar pool channels we analyze channel bed topographic data collected prior to and following the removal of two dams in oregon marmot dam on the sandy river and brownsville dam on the calapooia river we hypothesize that in gravel bed bar pool channels the response of bed relief to sand and gravel sediment pulses is a function of initial relief and pulse magnitude modest increases in sediment supply to initially low relief sediment poor cross sections will increase bed relief and variance of bed relief via bar deposition modest increases in sediment supply to initially high relief cross sections characteristic of alternate bar morphology will result in decreased bed relief and variance of relief via deposition in bar adjacent pools these hypothesized adjustments are measured in terms of bed relief which we define as the difference in elevation between the pool bottom and bar top we evaluate how relief varies with sediment thickness where both relief and mean sediment thickness at a cross section are normalized by the 90th percentile of observed relief values within a reach prior to a sediment pulse field measurements generally supported the stated hypotheses demonstrating how introduction of a sediment pulse to low relief reaches can increase mean and variance of relief while introduction to high relief reaches can decrease the mean and variance of bed relief at least temporarily in general at both sites the degree of impact increased with the thickness of sediment delivered to the cross section results thus suggest that the analysis is a useful step for understanding the morphological effects of sediment pulses introduced to gravel bed bar pool channels copyright 2015 john wiley sons ltd

response of bed surface patchiness to reductions in sediment supply 1 river beds are often arranged into patches of similar grain size and sorting patches can be distinguished into free patches which are zones of sorted material that move freely such as bed load sheets forced patches which are areas of sorting forced by topographic controls and fixed patches of bed material rendered immobile through localized coarsening that remain fairly persistent through time two sets of flume experiments one using bimodal sand rich sediment and the other using unimodal sand free sediment are used to explore how fixed and free patches respond to stepwise reductions in sediment supply at high sediment supply migrating bed load sheets formed even in unimodal sand free sediment yet grain interactions visibly played a central role in their formation in both sets of experiments reductions in supply led to the development of fixed coarse patches which expanded at the expense of finer more mobile patches narrowing the zone of active bed load transport and leading to the eventual disappearance of migrating bed load sheets reductions in sediment supply decreased the migration rate of bed load sheets and increased the spacing between successive sheets one dimensional morphodynamic models of river channel beds generally are not designed to capture the observed variability but should be capable of capturing the time averaged character of the channel when applied to our experiments a 1 d morphodynamic model rte bookagdegnormgravmixpw xls predicted the bed load flux well but overpredicted slope changes and was unable to predict the substantial variability in bed load flux and load grain size because of the migration of mobile patches our results suggest that 1 the distribution of free and fixed patches is primarily a function of sediment supply 2 the dynamics of bed load sheets are primarily scaled by sediment supply 3 channels with reduced sediment supply may inherently be unable to transport sediment uniformly across their width and 4 cross stream variability in shear stress and grain size can produce potentially large errors in width averaged sediment flux calculations

fluvial evacuation of landslide material from bedrock confined channels under controlled experimental conditions abstract the supply of sediment from hillslopes to channels is rarely constant with discrete events e g landslides known to transfer large volumes of sediment in geologically short periods of time especially in tectonically active areas understanding the rates and patterns of subsequent sediment evacuation is important for understanding variability of landscape evolution as well as mitigating the risk of geohazards associated with bed aggradation and the loss of channel capacity to convey flood waters here we performed a series of controlled laboratory flume experiments to explore the controls on sediment transport after a single sediment input in scenarios with i different initial input volumes 4 25 kg under constant flow conditions 40 l s ii a constant initial input volume 12 kg under different flow magnitudes 5 60 l s and iii a repeat of the input sediment volumes in scenario i but with the same volume of water delivered using a ramped hydrograph 0 60 0 l s we find the presence of sediment piles impacts the flow hydraulics with a backwater effect developing upstream of the pile that causes a flow acceleration around the location of the pile for a given discharge larger sediment piles have a greater impact on the flow hydraulics which in turn induces higher rates of sediment transport and erosion of the pile in all cases sediment remains at the initial pile input location for the duration of the sediment evacuation acting to protect the bed from erosion we highlight the role of geomorphic hydraulic interactions in controlling the sediment evacuation and suggest there is an optimal combination of pile size and flow conditions flow magnitude and hydrograph shape for accelerated rates of sediment transport which are important for the short term and long term channel dynamics and the landscape evolution variability

behaviour of granites and limestones subjected to slow and homogeneous temperature changes abstract we have studied the evolution of the texture in two granites and two limestones subjected to slow and uniform temperature change each granite has a different grain size and each limestone a different texture carrare crystalline limestone and crepey oolitic limestone temperature was varied from 200 c to 700 c scanning electron microscope observations of different rock samples show that during thermal cycling intercrystalline boundaries in granites widen out progressively and porosity increases new microcracks appear in crystals between 500 c and 600 c in carrare crystalline limestone intercrystalline cracks appear at temperatures as low as 200 c due to its heterogeneous cracks appear at temperatures as low as 200 c due to its heterogeneous increasing temperature longitudinal wave velocity and intrinsic permeability show good correlation with the scanning electron microscope observations

taking the river inside fundamental advances from laboratory experiments in measuring and understanding bedload transport processes bedload transport in gravel bed rivers impacts channel stability the lifespan of hydraulic structures physical components of aquatic habitat and long term channel evolution field measurements of bedload transport are notoriously difficult which precludes understanding many of the processes and mechanics associated with grain motion such uncertainties are exacerbated when using bedload transport equations most of which were derived using data from a single river or set of laboratory flume experiments recently laboratory experiments have focused on better quantifying the processes that impact bedload fluxes which can then be used to improve sediment transport predictions we highlight recent advances in laboratory instrumentation that can be used in bedload transport studies in particular more accurate ways to measure bedload fluxes near bed turbulence bed grain sizes and topography hold great promise laboratory experiments have also fundamentally improved our understanding of the influence of sediment supply and armoring processes on bedload fluxes and channel conditions the importance of flow hydrographs in controlling total bedload transport rates and bedload hysteresis has also been demonstrated using flume experiments finally many details about the mechanics of grain motion including flow turbulence bed arrangement and particle transport statistics are only possible through laboratory investigations and we feature key knowledge gaps that can be improved with further study

characteristic time of sediment transport decrease in static armour formation abstract a substantial laboratory data set from the literature is gathered for studying sediment transport rates under steady flow without any upstream sediment feeding we analysed the decrease in sediment transport rate from bed armouring i e coarsening of the bed surface and structure development we quantified an equilibrium time which corresponds to the time after which sediment transport rate is reduced by a factor of twenty this choice is highly correlated to a characteristic time of the exponential decrease in the sediment transport rate this equilibrium time was found to be mainly controlled by a set of four parameters the ratio between bed shear stress and its critical value for sediment incipient motion the reynolds particle number the dimensionless median diameter and the width to depth ratio the influence of each parameter can be linked to either bed mobility armouring or bedform development a formula to quantify the equilibrium time as function of these four parameters is proposed this is of great value to scale unsteady sediment transport experiments for which stepped hydrographs are very convenient and often used a new dimensionless time is also proposed merging the decrease of sediment transport rate for hydraulically rough beds

characterization of alluvial formation by stochastic modelling of paleo fluvial processes the concept and method summary modelling fluvial processes is an effective way to reproduce basin evolution and to recreate riverbed morphology however due to the complexity of alluvial environments deterministic modelling of fluvial processes is often impossible to address the related uncertainties we derive a stochastic fluvial process model on the basis of the convective exner equation that uses the statistics mean and variance of river velocity as input parameters these statistics allow for quantifying the uncertainty in riverbed topography river discharge and position of the river channel in order to couple the velocity statistics and the fluvial process model the perturbation method is employed with a non stationary spectral approach to develop the exner equation as two separate equations the first one is the mean equation which yields the mean sediment thickness and the second one is the perturbation equation which yields the variance of sediment thickness the resulting solutions offer an effective tool to characterize alluvial aquifers resulting from fluvial processes which allows incorporating the stochasticity of the paleoflow velocity

development of channel organization and roughness following sediment pulses in single thread gravel bed rivers large episodic inputs of coarse sediment sediment pulses in forested mountain streams may result in changes in the size and arrangement of bed forms and in channel roughness a conceptual model of channel organization delineates trajectories of response to sediment pulses for many types of gravel bed channels channels exhibited self organizing behavior to various degrees based on channel gradient presence of large in channel wood or other forcing elements the size of the sediment pulse and the number of bed mobilizing flows since disturbance typical channel changes following a sediment pulse were initial decreases in water depth in variability of bed elevations and in the regularity of bed form spacing trajectories of change subsequently showed increased average water depth more variable and complex bed topography and increased uniformity of bed form spacing bed form spacing in streams with abundant forcing elements developed at a shorter spatial scale two to five channel widths than in streams without such forcing mechanisms five to 10 channel widths channel roughness increased as bed forms developed

translation and dispersion of sediment pulses in flume experiments simulating gravel augmentation below dams 1 the effectiveness of gravel augmentation as a river restoration strategy depends on the extent and duration of the topographic and bed texture changes created by the pulse of added sediment previous work has emphasized the strong tendency for natural sediment waves to propagate primarily by dispersion however pulse translation may occur for gravel additions to armored channels downstream of dams where added sediments are finer than the preexisting bed material here we report results of a laboratory investigation in which we created an immobile armored bed and documented the spatial and temporal evolution of the bed topography and bed texture in response to gravel pulses of various volumes and grain sizes the introduced sediment waves evolved by a combination of translation and dispersion with a significant translational component pulse translation and dispersion can be readily discerned on a graph of the time evolution of the downstream cumulative distribution of elevation differences from the preexisting bed topography translation was most evident for smaller volumes of added sediment pulses of finer grained gravel moved through the flume more rapidly resulting in a larger magnitude but shorter duration of bed fining more work is needed to understand the influence of bar pool topography and flow magnitude and duration before the grain size and volume of gravel additions can be selected to achieve optimal patterns of pulse propagation

use of slope creation for rehabilitating incised regulated gravel bed rivers 1 gravel bedded channels often become incised and degraded below dams gravel can be added to the channel to rehabilitate hydrogeomorphic conditions including those promoting salmon spawning when implemented without increasing bed slope gravel addition at downstream riffles back floods upstream riffles a 2 year gravel augmentation project was done to test the efficacy of a new method for slope creation riffle to riffle slope was raised from 0 002 to 0 008 by adding gravel to the most upstream riffle when gravel was added to the next downstream riffle a year later riffle to riffle slope decreased to the sought after 0 004 after the study the area of high quality chinook salmon spawning habitat increased 471 the number of redds observed went from 62 to 161 during the study despite a 50 decline of in river spawners this eliminates variations in migrant population size and hatchery take as alternative explanations slope creation can be a useful aid for rehabilitating regulated rivers

sediment replenishment influence of the geometrical configuration on the morphological evolution of channel bed dams trap sediment in the upstream reservoir which may lead to river bed armoring streambank erosion and failure channel incision and reduction of the morphological diversity in the downstream river reaches the replenishment of sediment is a mitigation measure for this problem to be applied in river reaches downstream of dams previously performed field experiments always used one single volume of sediment replenishment to explore different alternatives the replenished volume was here divided in four deposits with the motivation to influence also the morphological evolution downstream six different geometrical configurations together with three submergence conditions of sediment replenishment were tested for the first time in a laboratory experiment and are herein discussed the results of the sediment replenishment mitigation technique are described in terms of occupied surface of the flume bed and the temporal evolution of erosion and transport of the introduced sediments it is shown that under our experimental conditions complete submersion of the replenishment volume results in complete erosion of the placed sediment with a high persistence of the added material along the channel length the geometrical configuration of the replenishment volume plays a key role for the evolution of bed forms downstream parallel configurations lead to a wider spread of material across the channel alternated configurations are suitable to produce sediment clustering and high persistence of placed material in the channel observed periodic mounds considered as the initiating condition for alternate bars follow a wavelength related to the length of the replenishment when the replenishment volumes are alternating

experiment on temporal variation of bed load transport in response to changes in sediment supply in streams a flume experiment was conducted to study channel adjustment to episodic sediment supply in mountain streams the bulk sediment used for the bed and feed included grain sizes 0 5 64 mm with geometric mean dg bulk of 5 7 mm water discharge was held constant for 40 h and 300 kg of sediment was supplied through a range of scenarios bed slope sediment storage sediment transport and bed surface texture responded to sediment supply during the first of seven runs bed slope decreased from 0 022 m m flume slope to 0 018 m m due to sediment starvation bed slope increased beginning in the second run as the bed aggraded due to preferential storage of grains 8 mm transport rate and bed surface particle size were significantly affected by magnitude frequency of sediment feed under constant feed transport rate increased gradually and dg surface ranged between 12 15 mm instead sediment pulses caused a pronounced increase in sediment transport rate and surface fining trends that were inverted as sediment evacuated at the run scale sediment transport and storage behaved as with constant feed if pulse relaxation time exceeded time between pulses the increase in transport rate and surface fining were proportional to pulse size after the 300 kg pulse transport rate reached 100 g m 1 s 1 and dg surface was 12 mm textural differences on the initial bed surface influenced the patterns of sediment transport channel adjustment was controlled by magnitude frequency of sediment feed and not by total feed this article is protected by copyright all rights reserved

stochastic forcing of sediment routing and storage in channel networks the stochastic field of sediment supply to the channel network of a drainage basin depends on the large scale interactions among climatically driven processes such as forest fire and rainstorms topography channel network topology and basin scale during infrequent periods of intense erosion large volumes of colluvium are concentrated in parts of a channel network particularly near tributary junctions the rivers carry bed material and wash load downstream from these storage sites at different rates the bed material travels slowly creating transient patterns of sediment transport sediment storage and channel morphology along the channel network as the concentrations of bed material migrate along the network their waveforms can undergo changes by diffusion interference at tributary junctions and loss of mass through temporary sediment storage in fans and terraces and through particle abrasion which converts bed material to wash load we investigated how these processes might influence the sediment mass balance in channels of third and higher order in a 215 km 2 drainage basin within the oregon coast range over a simulated 3000 year period with a climate typical of the late holocene we used field measurements and a simulation model to illustrate interactions between the major controls on large scale processes functioning over long periods of time in complex drainage basins

the dominance of dispersion in the evolution of bed material waves in gravel bed rivers bed material waves are temporary zones of sediment accumulation created by large sediment inputs recent theoretical experimental and field studies examine factors influencing dispersion and translation of bed material waves in quasi uniform gravel bed channels exchanges of sediment between a channel and its floodplain are neglected within these constraints two factors influence relative rates of dispersion and translation 1 interactions between wave topography flow and bed load transport and 2 particle size differences between wave material and original bed material our results indicate that dispersion dominates the evolution of bed material waves in gravel bed channels significant translation requires a low froude number which is uncharacteristic of gravel bed channels and low wave amplitude which for a large wave can be achieved only after substantial dispersion wave material of small particle size can promote translation but it primarily increases bed load transport rate and thereby accelerates wave evolution copyright 2001 john wiley sons ltd

reconstructing a sediment pulse modeling the effect of placer mining on fraser river canada gold mining along 525 km of the fraser river between 1858 and 1909 added an estimated 1 1 108 t of tailings half gravel and the rest finer to the river s natural sediment load we simulate the response using a 1 d multigrain size morphodynamic model since premining conditions are unknown and modern data are insufficient for tuning the process representation we devised a novel modeling strategy which may be useful in other data poor applications we start the model from a smoothed version of the modern longitudinal profile with bed grain size distributions optimized to match alternative assumptions about natural sediment supply and compare runs that include mining with control runs that can be used to quantify the effects of deficiencies in process representation and initialization simulations with an appropriate choice of natural supply rate closely match the best available test data which consist of a detailed 1952 1999 gravel budget for the distal part of the model domain the simulations suggest that the main response to mining was rapid bed fining which allowed a major increase in bed load transport rate with only slight 0 1 m mean aggradation within the mining region and most of the excess sediment exported well beyond the mountain front within the mining period or soon afterward we compare this pattern of response by a large powerful river with previous case studies of river adjustment to sediment supply change

wave emplaced coarse debris and megaclasts in ireland and scotland boulder transport in a high energy littoral environment abstract many coastlines of the world particularly those at higher latitudes and those located in tropical cyclone belts are regularly battered by strong storm waves drowning of low lying areas by storm surges and storm floods has been thoroughly recorded however storm deposits at rocky shorelines or on cliffs have been underrepresented in the literature this article presents observations of extraordinary wave deposits along the high wave energy coastlines of western ireland and the northern scottish isles and discusses possible wave event types and time windows of the processes responsible we used archaeological geomorphological and geochronological disciplines to compare our findings with earlier results published for these areas and to contribute to the debate on whether large clasts found well above sea level and or a considerable distance inland were deposited by storms or by tsunamis

management responses to pulses of bedload sediment in rivers abstract rivers can experience sudden pulses of sediment from human and natural erosion processes that can accumulate in the bed abundant studies have examined the sources and dynamics of sediment pulses and problems caused by these pulses particularly flooding avulsions and habitat simplification much less has been written about what managers can do about sediment pulses and that is the purpose of this review the first option for managers is to do nothing and this decision can be informed by many case studies and by theory on the propagation and character of sediment pulses their diffusion translation and celerity doing nothing should be informed by the secondary effects of sediment pulses on channels including widening avulsions and tributary interactions if managers decide that something needs to be done about the sediment they have four options 1 reducing the sediment supply at source 2 trapping sediment in the channel 3 accelerating sediment transport through a reach and 4 directly extracting sediment the most common of these actions is undoubtedly to reduce the supply at source but there are few examples of the consequences of this for sediment pulses there are even fewer examples of trapping accelerating and extracting sediment all of these options have great potential for managing sediment pulses however they also have the potential to trigger incision of tributaries and of the channel behind the passing sediment wave overall the literature equips managers to understand the dynamics of sediment pulses but it does not yet equip them to confidently manage these geomorphic events

stochastic forcing of sediment supply to channel networks from landsliding and debris flow sediment influx to channel networks is stochastically driven by rainstorms and other perturbations which are discrete in time and space and which occur on a landscape with its own spatial variability in topography colluvium properties and state of recovery from previous disturbances the resulting stochastic field of sediment supply interacts with the topology of the channel network and with transport processes to generate spatial and temporal patterns of flux and storage that characterize the sedimentation regime of a drainage basin the regime varies systematically with basin area we describe how the stochastic sediment supply is generated by climatic topographic geotechnical and biotic controls that vary between regions the general principle is illustrated through application to a landscape where sediment is supplied by mass wasting and the forcing variables are deterministic thickening of colluvium random sequences of root destroying wildfires and random sequences of rainstorms that trigger failure in a population of landslide source areas with spatial variance in topography and colluvium strength landslides stop in channels or convert to scouring debris flows depending on the nature of the low order channel network sediment accumulates within these channels for centuries before being transferred downstream by debris flows time series of sediment supply transport and storage vary with basin scale for any combination of climatic topographic and geotechnical controls in a companion paper benda and dunne this issue we use simulations of timing volumes and locations of mass wasting to study the interaction between a stochastically forced sediment supply and systematic changes of storage and flux through channel networks

alternate bar response to sediment supply termination 1 sediment supply is widely held to be one of the primary controls on bar topography in alluvial channels yet quantitative linkages between sediment supply and bar topography are not well developed we explore the conditions under which alternate bars form and how they respond to the elimination of sediment supply in two linked laboratory experiments the first set of experiments was conducted in a 28 m long 0 86 m wide flume channel using a unimodal sand gravel mix the second set of experiments was conducted at field scale in a 55 m long 2 74 m wide channel using a unimodal gravel mixture in both experiments alternate bars and patchy surface grain size distributions developed under steady flow and sediment supply conditions the cessation of the sediment supply induced a reduction in the surface grain size heterogeneity and the bars were eliminated in both flumes mean boundary shear stress had declined but were capable of moving sediments after the bars disappeared albeit at relatively small rates compared to when the bars were present in the smaller flume the previously stationary bars migrated out of the flume and were not replaced with new bars a nearly featureless bed formed with limited surface grain size heterogeneity a slightly coarsened surface and a slightly reduced slope in the larger flume the formation of alternate bars was induced by an imposed upstream flow constriction and as such the bars did not migrate termination of sediment supply led to progressive erosion of bed topography and loss of the bars coarsening of the bed surface loss of bed texture patchiness and significant slope reduction the original alternate bar topography redeveloped when the sediment supply was restored once sufficient deposition had occurred to reconstruct the original channel slope this shows that the bar loss was reversible by establishing the previous conditions and highlights the importance of sediment supply for bar formation the role of sediment supply in bar formation and stability is not often recognized in stream restoration our results suggest that the loss of sediment supply can significantly affect alternate bar topography and that considerable volumes of sediment may be needed restore channel bars

evolution of a sediment wave in an experimental channel the routing of bed material through channels is poorly understood we approach the problem by observing and modeling the fate of a low amplitude sediment wave of poorly sorted sand that we introduced into an experimental channel transporting sediment identical to that of the introduced wave the wave essentially dispersed upstream and downstream without translation although there was inconclusive evidence of translation late in the experiment when the wave was only 10 20 grain diameters high alternate bars migrated through zones of differing bed load transport rate without varying systematically in volume celerity or transport rate sediment that overpassed migrating bars was apparently responsible for dispersion of the wave the evolution of the wave was well predicted by a one dimensional model that contains no adjusted empirical constants numerical experiments demonstrate however that the theory does not predict sediment waves that migrate long distances downstream such waves can only be explained by the following processes not represented by the theory selective bed load transport spatial variations in bar and other form roughness the mechanics of mobile armor and perhaps other mechanisms

numerical model of sediment pulses and sediment supply disturbances in mountain rivers sediment pulses in rivers can result from many mechanisms including landslides entering from side slopes and debris flows entering from tributaries artificial sediment pulses can be caused by the removal of a dam this paper presents a numerical model for the simulation of gravel bedload transport and sediment pulse evolution in mountain rivers a combination of the backwater and quasi normal flow formulations is used to calculate flow parameters gravel bedload transport is calculated with the surface based bedload equation of parker in 1990 the exner equation of sediment continuity is used to express the mass balance at different grain size groups and lithologies as well as the abrasion of gravel the river is assumed to have no geological controls such as bedrock outcrops and immobile boulder pavements the results of nine numerical experiments designed to study various key parameters relevant to the evolution of sediment pulses are reported here results of the numerical runs indicate that the evol

a network based framework for identifying potential synchronizations and amplifications of sediment delivery in river basins long term prediction of environmental response to natural and anthropogenic disturbances in a basin becomes highly uncertain using physically based distributed models particularly when transport time scales range from tens to thousands of years such as for sediment yet such predictions are needed as changes in one part of a basin now might adversely affect other parts of the basin in years to come in this paper we propose a simplified network based predictive framework of sedimentological response in a basin which incorporates network topology channel characteristics and transport process dynamics to perform a nonlinear process based scaling of the river network width function to a time response function we develop the process scaling formulation for transport of mud sand and gravel using simplifying assumptions including neglecting long term storage and apply the methodology to the minnesota river basin we identify a robust bimodal distribution of the sedimentological response for sand of the basin which we attribute to specific source areas and identify a resonant frequency of sediment supply where the disturbance of one area followed by the disturbance of another area after a certain period of time may result in amplification of the effects of sediment inputs which would be otherwise difficult to predict we perform a sensitivity analysis to test the robustness of the proposed formulation to model parameter uncertainty and use observations of suspended sediment at several stations in the basin to diagnose the model the proposed framework has identified an important vulnerability of the minnesota river basin to spatial and temporal structuring of sediment delivery

effects of sediment pulses on channel morphology in a gravel bed river sediment delivery to stream channels in mountainous basins is strongly episodic with large pulses of sediment typically delivered by infrequent landslides and debris flows identifying the role of large but rare sediment delivery events in the evolution of channel morphology and fluvial sediment transport is crucial to an understanding of the development of mountain basins in july 2001 intense rainfall triggered numerous debris flows in a severely burnt watershed in the sapphire mountains of montana ten large debris flow fans were deposited on the valley floor and investigations focused on the channel response to these sediment pulses the channel has aggraded immediately upstream of each fan and braided in reaches immediately downstream channel incision through the fans has created sets of coarse grained terraces the deposition upstream of the pulses consists almost exclusively of fine material resulting in a median bed material size d 50 1 2 orders of magnitude lower than the ambient channel material the volume of sand being transported is so great that these aggrading reaches can extend hundreds of meters upstream of the fans with 1 2 m of sand deposited across the entire valley floor along a 10 km study reach cross section surveys longitudinal profiles and pebble counts chronicle channel response to a punctuated increase in sediment supply and provide insight on the processes of sediment wave dispersal

bedload pulses in a hydropower affected alpine gravel bed river abstract this study investigated the sediment resupply and transport dynamics at the upper drau river upstream of lienz eastern tyrol austria due to a hydropower plant a 24 km long river reach of this alpine gravel bed river is under residual flow conditions although sediment is still resupplied into the reach through many active torrents and tributaries as a result sediment deposition in the residual flow reach intensified hence increasing maintenance efforts to stabilize this river section and ensure flood protection in combination with a new sediment management program a continuous bedload monitoring system was installed 2 km downstream of the residual reach in 2001 to support the development of adapted sediment management strategies the surrogate bedload monitoring system consists of 16 impact plate geophones installed over a 17 m wide cross section the unprecedented 15 year dataset of high resolution bedload intensity revealed a complex process of gravel storage and intermittent resupply from the residual reach allowing the authors a detailed analysis of frequently occurring bedload pulses these transport features are triggered by increased discharges during floods in the residual reach and created pronounced anticlockwise bedload hysteresis or with a temporal shift to the event peak caused distinct shifts in the bedload activity downstream bedload pulses produce very high bedload fluxes while in transit tend to increase bedload flux in the post event phase and can alter and reduce the upstream sediment storage leading to a lowering of bedload availability for future pulses the observed time lags between main discharge events and the arrival of the macro pulses are correlated with mean water discharge during pulse propagation thus enabling a prediction of the pulse arrival at the monitoring station solely based on the hydrograph in combination with the hydrological setup of the reach the observed bedload pulse time lags allowed an estimation of pulse velocities in the range 0 002 0 05 m s 1

morphodynamic response of a variable width channel to changes in sediment supply river channels commonly exhibit downstream variations in channel width which can lead to the development of alternating shallow and deep areas known as riffle pool sequences the response of these channels to variations in sediment supply remains largely unexplored here we investigate the morphodynamic response of a variable width channel to changes in sediment supply through laboratory experiments conducted in a straight flume in which we imposed sinusoidal variations in width we first developed equilibrium conditions under a constant sediment supply and then eliminated the sediment feed to create a degraded armored bed this sediment starved bed was subjected to two types of sediment supply increases a return to the initial constant supply and the introduction of a well sorted sediment pulse analogous to gravel augmentation riffles and pools formed in wide and narrow areas respectively and the location of and relief between riffles and pools remained the same throughout all experimental runs regardless of the sediment supply the primary channel response to changes in supply was adjustment of the overall slope the sediment pulse evolved primarily through dispersion rather than translation which contrasts with prior gravel augmentation experiments conducted in constant width channels and suggests that width variation and resulting riffle pool topography enhances pulse dispersion our results indicate that width variation is a primary control on the location and relief of riffles and pools in straight channels and sediment supply changes are unlikely to affect riffle pool morphology when bank geometry is fixed and water discharge is steady

movement of finite amplitude sediment accumulations the movement of finite amplitude sediment accumulations is studied using a simple advection diffusion relation derived from the sediment continuity equation and using some heuristic reasoning the movement of a finite amplitude sediment accumulation is found to be strongly diffusive with a small advection component due to the increase in transport rate of the sediment accumulation relative to the transport rate of the original bed material a semianalytical solution to the advection diffusion equation is found and the equation is applied to two laboratory experiments the equation is found to predict the general movement of finite amplitude sediment accumulations with a minimal number of parameters

classification of geomorphological effects downstream of dams abstract the effects of dams on downstream geomorphology are reviewed and a typology is devised consisting of nine cases the classification can be seen as a further development of lane s balance between water discharge sediment load grain size and river slope depending on changes in released water flow and changes in released sediment load relative to the transport capacity of the flow it is possible to estimate resulting cross sectional geomorphology the longitudinal extent of changes and their variability with time and the tributary response to altered mainstream cross section changes are also discussed

seismic cycles earthquakes landslides and sediment fluxes linking tectonics to surface processes using a reduced complexity model in tectonically active mountain ranges landslides triggered by earthquakes mobilise large volumes of sediment that affect river dynamics this sediment delivery can cause downstream changes in river geometry and transport capacity that affect the river efficiency to export this sediment out of the epicentre area the subsequent propagation of landslide deposits in the fluvial network has implications for the management of hazards downstream and for the long term evolution of topography over multiple seismic cycles a full understanding of the processes and time scales associated with the removal of landslide sediment by rivers following earthquakes however is still lacking here we propose a nested numerical approach to investigate the processes controlling the post seismic sediment evacuation at the mountain range scale informed by results from a reach scale model first we explore the river morphodynamic response to a landslide cascade at the reach scale using a 2d modelling approach the results are then used to describe empirically the evacuation of a landslide volume which avoids using a computationally extensive model in catchments which may have thousands of co seismic landslides second we propose a reduced complexity model to quantify evacuation times of earthquake triggered landslide clusters at the scale of a mountain range examining the hypothetical case of a mw 7 9 earthquake and its aftershocks occurring on the alpine fault new zealand our approach combines an empirical description of co seismic landslide clusters with the sediment export processes involved during the post seismic phase our results show that the inter seismic capacity of the mountain range to evacuate co seismic sediment is critical to assess the sediment budget of large earthquakes over one to several seismic cycles we show that sediment evacuation is controlled by two timescales 1 the transfer time of material from hillslopes to channels and 2 the evacuation time of the landslide deposits once it has reached the fluvial network in turn post seismic sediment evacuation can either be connectivity limited when sediment delivery along hillslopes is the main limiting process or transport limited when the transport by rivers is the limiting process despite high values of runoff we suggest that the southern alps of new zealand are likely to be in connectivity limited conditions for connection velocities 2 m yr 1 are sufficient to allow most of co seismic sediments to be mobilised and potentially exported out of the range within less than one seismic cycle because of the poorly constrained rate of sediment transfer along hillslopes our results potentially raise the issue of co seismic sediment accumulation within mountain ranges over several seismic cycles and of the imbalance between tectonic inputs and sediment export we therefore call for renewed observational efforts to better describe and quantify the physical processes responsible for the redistribution and mobilization of sediment from landslide scars and deposits

ten conceptual models of large scale legacy sedimentation a review abstract considerable interest has been directed toward the recognition and documentation of legacy sediment i e anthropogenic sediment in fluvial systems little has been written however to identify implicit or explicit theories about how these deposits form and evolve over decennial to centennial time scales this review attempts to redress this void by examining conceptual models of the physical behavior and characteristics of catchment scale anthropic fluvial sedimentation events these concepts which are not unique to anthropogenic sediment include cascades sediment delivery ratios waves aggradation degradation episodes residence times budgets connectivity stream power nonlinear dynamical systems and geohistorical geoarchaeological and chronostratigraphic principles a broad definition of legacy sediment as episodically produced anthropogenic sediment is adopted that includes early episodes of large scale human induced sedimentation throughout the world the models apply to a variety of environments so the examples from north america following the introduction of european settlement can be related to other post settlement sedimentation episodes elsewhere during aggradation episodes rates of erosion and sedimentation often increased an order of magnitude in response to land clearance for agriculture timbering or mining these sediments may remain as a lasting geomorphic legacy that provides evidence of anthropogenic change and governs modern rates of sediment production and nonpoint source pollution

effects of punctuated sediment supply on valley floor landforms and sediment transport large infrequent fluxes of sediment to streams by mass wasting are intrinsic to the erosion regime of mountain drainage basins to elucidate the role of mass wasting in the construction and evolution of steep land channel environments it is crucial that we identify the processes involved and recognize their legacy on the valley floor in the winter of 1996 nine storm triggered debris flows carried 18 000 m 3 of coarse debris into the upper reaches of the south fork of gate creek oregon cascade range during flood flow analysis of resulting channel morphologies and bed textures shows that the sediment moved downstream as a wave like pulse or pulses overwhelming the channel and causing it to braid with flooding and alluvial deposition over the valley floor downstream progression of the sediment wave resulted in vertical accretion of the valley floor with sediment carried as bedload the maximum depth of valley floor burial being set by the amplitude of the wave passage of the wave left a channel incised to bedrock inset between coarse grained alluvial terraces this study examines the genesis of these features at gate creek and points to such terraces as field indicators of massive episodic influxes of sediment and the associated formation of fluvially transported sediment waves

application of structure from motion photogrammetry in laboratory flumes abstract structure from motion sfm photogrammetry has become widely used for topographic data collection in field and laboratory studies however the relative performance of sfm against other methods of topographic measurement in a laboratory flume environment has not been systematically evaluated and there is a general lack of guidelines for sfm application in flume settings as the use of sfm in laboratory flume settings becomes more widespread it is increasingly critical to develop an understanding of how to acquire and process sfm data for a given flume size and sediment characteristics in this study we 1 compare the resolution and accuracy of sfm topographic measurements to terrestrial laser scanning tls measurements in laboratory flumes of varying physical dimensions containing sediments of varying grain sizes 2 explore the effects of different image acquisition protocols and data processing methods on the resolution and accuracy of topographic data derived from sfm techniques and 3 provide general guidance for image acquisition and processing for sfm applications in laboratory flumes to investigate the effects of flume size sediment size and photo overlap on the density and accuracy of sfm data we collected topographic data using both tls and sfm in five flumes with widths ranging from 0 22 to 6 71 m lengths ranging from 9 14 to 30 48 m and median sediment sizes ranging from 0 2 to 31 mm acquisition time image overlap point density elevation data and computed roughness parameters were compared to evaluate the performance of sfm against tls we also collected images of a pan of gravel where we varied the distance and angle between the camera and sediment in order to explore how photo acquisition affects the ability to capture grain scale microtopographic features in sfm derived point clouds a variety of image combinations and sfm software package settings were also investigated to determine optimal processing techniques results from this study suggest that sfm provides topographic data of similar accuracy to tls at higher resolution and lower cost we found that about 100pixels per grain are required to resolve grain scale topography we suggest protocols for image acquisition and sfm software settings to achieve best results when using sfm in laboratory settings in general convergent imagery taken from a higher angle with at least several overlapping images for each desired point in the flume will result in an acceptable point cloud

geomorphic response to gravel augmentation and high flow dam release in the trinity river california the geomorphic effect of introducing a gravel augmentation totaling 520 m3 into a gravel bed stream during a dam controlled flood in may of 2015 was monitored with bedload transport measurements an array of seismometers and repeated topographic surveys half of the augmented gravel was injected into the flow with front end loaders on the rising limb of the flood and the other half was injected on the first day of the peak virtually all of the gravel transported past the injection point was deposited within about 7 to 10 channel widths of the injection point most of the injected gravel deposited along the left bank of the river whereas the right half of the channel bed was dominated by scour the downstream third of the depositional area consisted of a small dune field that developed prior to the second gravel injection and subsequently migrated about one channel width downstream a second depositional front was observed upstream from the gravel injection point where a delta like wedge of bed material developed in the first hours of the flow release and changed little over the remainder of the release these two depositional areas represent small scale bed material storage reservoirs with the potential to accumulate and periodically release packets of bed material interactions with such storage reservoirs are hypothesized to cause large bed material pulses to disperse by fragmenting into multiple smaller pulses as a refinement to the conceptual model that views sediment pulse evolution in terms of dispersion and translation the concept of pulse fragmentation has practical implications for gravel management it implies that gravel augmentations can produce morphologic changes at locations that are separated from the augmentation point by arbitrarily long reaches and it highlights the dependence of pulse propagation rates on the nature and distribution of the bed material storage reservoirs in the channel system copyright 2017 john wiley sons ltd

sediment pulses in mountain rivers 1 experiments 1 sediment often enters rivers in discrete pulses associated with landslides and debris flows this is particularly so in the case of mountain streams the topographic disturbance created on the bed of a stream by a single pulse must be gradually eliminated if the river is to maintain its morphological integrity two mechanisms for elimination have been identified translation and dispersion according to the first of these the topographic high translates downstream according to the second of these it gradually diffuses away in any given river both mechanisms may operate this paper is devoted to a description of three controlled experiments on sediment pulses designed to model conditions in mountain streams each of the experiments began from the same mobile bed equilibrium with a set rate and grain size distribution of sediment feed in one experiment the median size of the pulse material was nearly identical to that of the feed sediment in the other two the pulse material differed in grain size distribution from the feed sediment being coarser in one case and finer in the other case in all cases the mode of pulse deformation was found to be predominantly dispersive a result that constitutes the main conclusion of this paper the pulses resulted in a notable but transient elevation of sediment transport rate immediately downstream when the pulse was coarser than the ambient sediment the bed downstream remained armored and a migrating delta formed in the backwater upstream when the pulse was finer than the ambient sediment translation was observed in addition to dispersion the presence of the finer material notably elevated the transport of ambient coarse material on the bed downstream in part 2 cui et al 2003 the experimental results are used to test a numerical model

re evaluation of the wave model as a tool for quantifying the geomorphic recovery potential of streams disturbed by sediment slugs abstract a central principle of stream rehabilitation is that managers should accelerate the natural recovery of degraded streams in this paper we explore the recovery of channel morphology behind translating sediment waves using an observed expected space for time substitution sfts model channel recovery is defined by the variability of the thalweg cross sections and bed sediments of the three streams investigated in se australia one followed the general response described by gilbert s classic wave model with the stream bed returning to its pre disturbance geomorphic variability as the sediment wave passed in this case the recovery did not necessarily decline gradually with the distance away from the peak of the slug instead the geomorphic variability remained low within the slug and then increased dramatically once the slug evacuated by contrast the other two streams continued on their pre slug trajectory of channel incision which has not allowed geomorphic variability to establish once the sediment slug has passed the three study streams showed different recovery responses to a relatively simple pulse of sediment

evolution of a landslide induced sediment wave in the navarro river california a streamside landslide delivered 60 000 m3 of mixed size sediment to the navarro river a sinuous gravel bed channel drainage area 535 km2 at the end of the annual high runoff period in spring 1995 the deposit formed a 9 m high dam that partially breached within several hours but recessional flows entrained little material until the following high runoff season the landslide afforded the opportunity to measure the evolution of a sediment wave from its inception to near obliteration and particularly to test relative tendencies for translation and dispersion of a sediment wave in a natural gravel bed channel this study represents a simple case the wave originated from a single input the preexisting channel was relatively uniform and resistant banks prevented adjustments in width we surveyed channel topography over a 1 5 4 5 km reach centered on the landslide dam each year from 1995 to 1999 and we sampled bed material downstream of the dam in 1995 and 1997 landslide material was coarser than ambient bed material but all sizes were mobilized by subsequent peak flows abrasion of weathered and fractured graywacke sandstone landslide material was roughly an order of magnitude greater than the ambient river gravel the sediment wave dispersed and mostly disappeared within a few years with no measurable translation sediment filled the reservoir created by the eroding landslide dam until throughput of bed load was restored in 1998 the stationary wave crest eroded until in 1999 it was 1 m higher e mail dsutherl fs fed us than the preslide elevation as the wave profile flattened its detectable leading edge extended downstream from 620 m in 1995 to 1600 m in 1997 downstream advance of the wave was associated with coarsening of bed material the sediment wave created a longitudinal disturbance in sediment transport by using the dam as a reference datum of zero bed load transport we computed longitudinal variations in annual bed load and suspended sediment transport rates in 100 m increments downstream of the dam these longitudinal variations were controlled by scour and fill of the bed and by abrasion of bed load particles bed load transport rates in the first and second years after the landslide increased in the landslide vicinity and then decreased downstream as sediment deposited behind the advancing leading edge of the wave the location of peak bed load transport rate advanced from the first year 400 m to the second 800 m we used a physically based one dimensional model cui et al 2002b to hindcast annual changes in transversely averaged bed elevation over the study reach agreement between measured and predicted bed elevations was very good this result supports our conclusion that once emplaced sediment waves in gravel bed rivers tend to disperse with little or no translation

coarser and rougher effects of fine gravel pulses on experimental step pool channel morphodynamics understanding how steep mountain rivers respond to natural and anthropogenic sediment supply perturbations is important for predicting effects of extreme events e g floods and landslides and for restoring rivers to more natural conditions using flume experiments we show that stabilized step pool like channel beds can respond to pulses of finer gravel by becoming even coarser and rougher than before adding finer gravel initially reduces bed roughness and also increases the mobility of previously stable bed grains small and intermediate diameter clasts are then preferentially winnowed from the bed surface leaving behind higher concentrations of even larger clasts ultimately this results in both a coarser and rougher bed our experiments demonstrate that steep river beds become stable through the coevolution of bed roughness and surface grain size distribution and that these morphological variables can be sensitive to the history of upstream sediment supply

mobilization of coarse surface layers in gravel bedded rivers by finer gravel bed load 1 additions of sand to gravel beds greatly increase the mobility and flux of gravel however it is not known how additions of finer gravel to coarser gravel beds will affect the mobility of bed material here we examine the effect of fine gravel pulses on gravel bed material transport and near bed flow dynamics in a series of flume experiments bed material refers exclusively to sediment in the channel prior to the pulse introduction the observations indicate that fine sediment pulses tend to migrate downstream in low amplitude waves as the waves pass over the gravel bed the interstitial pockets in the bed material surface fill and coarse gravel particles are entrained this increases bed material transport rates and causes a distinct shift from a selective mobility transport regime where particles coarser than the bed material median 8 mm make up 30 of the load to an equal mobility transport regime where bed materials coarser than 8 mm and finer than 8 mm are transported in equal proportions the only possible source for this coarser bed load material is the sediment bed suggesting that portions of the coarse surface layer are being mobilized observations of near bed velocity and turbulence suggest that fine gravel pulses cause fluid acceleration in the near bed region associated with a reduction in the level of turbulence produced at the sediment boundary this accelerated fluid at the bed increases drag exerted on coarse surface layer particles promoting their mobilization our findings suggest that in general finer bed sediment not just sand can mobilize coarser sediment and that expressions for the influence of sand on bed mobility need to be generalized on the basis of grain ratios

influence of the sediment supply texture on morphological adjustments in gravel bed rivers the role played by the texture of the sediment supply on channel bed adjustments in gravel bed rivers is poorly understood to address this issue an experimental campaign has been designed flume experiments lasting 96 h in a 9 m long 0 60 m wide have been performed with different sand gravel mixtures as feed textures the response of the surface texture has been found to be highly dependent on the grain size distribution of the feed when the feed texture included gravel the finest fractions of the sediment supply infiltrate beneath the surface conversely sand remains on the surface when the feed texture lacks gravel this different textural response becomes obscured when water discharge increases further the sediment transport rate approaches the feed rate differently depending on the content of gravel in the feed texture when a small proportion of gravel is part of the feed texture bed load transport rate asymptotically approaches the feed rate however when a significant fraction of gravel is part of the feed grain size distribution bed load transport rate approaches the feed rate by following an oscillatory path these findings have been verified in terms of a one dimensional numerical model this modeling reveals that the higher the differences in mobility among the grain sizes contained in the feed texture the more evident is the nonasymptotic transient trend toward equilibrium

modelling sediment transport as a moving wave the transfer and deposition of mining waste abstract the movement of slugs of bedload from a discrete input point down a river has proved difficult to model using conventional finite difference formulations of equations of motion a model is proposed which makes explicit allowance for the mean sediment velocity and through a dispersion coefficient the distribution of sediment velocity about the mean a second comparative model uses the normal mass conservation or sediment transport continuity approach the models have been tested over a 43 month period using data from seven monitored cross sections of the kawerong river on bougainville island papua new guinea a system which receives waste from a large copper mine the dispersion model performs considerably better than the mass conservation model

effect of sediment pulse grain size on sediment transport rates and bed mobility in gravel bed rivers 1 sediment supply to gravel bed river channels often takes the form of episodic sediment pulses and there is considerable interest in introducing sediment pulses in stream restorations to alter bed surface grain size distributions and bed mobility a series of laboratory experiments was conducted in order to examine how sediment pulse grain size and volume affects the mobility of bed material in gravel bed channels pulses used in the experiments were composed of either the fine tail or the median of the subsurface bed material grain size distribution bed material refers to sediment in the channel prior to the pulse introduction exclusively both types of pulse were finer than the bed material surface median two pulse sizes were used which were either equivalent to the volume of sediment required to cover the entire bed one median subsurface bed material grain diameter deep full unit or 1 4 of this volume 1 4 unit the latter was designed to produce a transitory pulse with the exception of the 1 4 unit coarse pulse introduction of the sediment pulses to the channel caused dramatic increases in the bed load flux the coarse sediment pulses fine the bed surface and coarsen the bed load finer pulses also fine the surface but the bed load fines while the bed material load that excludes pulse material coarsens the greatest effects on the fractional transport occurred during the full unit fine pulse where the pulse covered the greatest bed surface and effectively smoothed the bed increasing near bed velocity and mobilizing the coarse particles overall the coarse pulses were not very effective at mobilizing bed material the large fine pulse mobilized 35 of the bed material surface 35 of its input weight and was most effective at mobilizing the surface however the small fine pulse mobilized 50 of its input weight as it passed through the channel making it the most efficient at mobilizing the bed material

bedload hysteresis in a glacier fed mountain river sediment transport during flood events often reveals hysteretic patterns because flow discharge can peak before counterclockwise hysteresis or after clockwise hysteresis the peak of bedload hysteresis in sediment transport has been used in the literature to infer the degree of sediment availability counterclockwise and clockwise hysteresis have been in fact interpreted as limited and unlimited sediment supply conditions respectively hysteresis has been mainly explored for the case of suspended sediment transport but it was rarely reported for bedload transport in mountain streams this work focuses on the temporal variability of bedload transport in an alpine catchment saldur basin 18 6 km2 italian alps where bedload transport was monitored by means of an acoustic pipe sensor which detects the acoustic vibrations induced by particles hitting a 0 5m long steel pipe runoff dynamics are dominated by snowmelt in late spring early summer mostly by glacier melt in late summer early autumn and by a combination of the snow and glacier melt in mid summer the results indicate that hysteretic patterns during daily discharge fluctuations are predominantly clockwise during the snowmelt period likely due to the ready availability of unpacked sediments within the channel or through bank erosion in the lower part of the basin on the contrary counterclockwise hysteresis tend to be more frequent during late glacier melting period possibly due to the time lag needed for sediment provided by the glacial and peri glacial area to be transported to the monitoring section however intense rainfall events occurring during the glacier melt period generated predominantly clockwise hysteresis thus indicating the activation of different sediment sources these results indicate that runoff generation processes play a crucial role on sediment supply and temporal availability in mountain streams

experimental evidence for the effect of hydrographs on sediment pulse dynamics in gravel bedded rivers 1 gravel augmentation is a river restoration technique applied to channels downstream of dams where size selective transport and lack of gravel resupply have created armored relatively immobile channel beds augmentation sediment pulses rely on flow releases to move the material downstream and create conditions conducive to salmon spawning and rearing yet how sediment pulses respond to flow releases is often unknown here we explore how three types of dam releases constant flow small hydrograph and large hydrograph impact sediment transport and pulse behavior translation and dispersion in a channel with forced bar pool morphology we use the term sediment pulse generically to refer to the sediment introduced to the channel the zone of pronounced bed material transport that it causes and the sediment wave that may form in the channel from the additional sediment supply which can include input sediment and bed material in our experiments we held the volume of water released constant which is equivalent to holding the cost of purchasing a water volume constant in a stream restoration project the sediment pulses had the same grain size as the bed material in the channel we found that a constant flow 60 greater than the discharge required to initiate sediment motion caused a mixture of translation and dispersion of the sediment pulse a broad crested hydrograph with a peak flow 2 5 times the discharge required for entrainment caused pulse dispersion while a more peaked hydrograph 3 times the entrainment threshold discharge caused pulse dispersion with some translation the hydrographs produced a well defined clockwise hysteresis effecting sediment transport as is often observed for fine sediment transport and transportlimited gravel bed rivers the results imply a rational basis for design of water releases associated with gravel augmentation that is directly linked to the desired sediment behavior