an experimental investigation of mechanisms involved in bed load sheet production and migration 1 field measurements indicate that in gravel bed rivers bed load may not be a one to one response to shear stress but may instead fluctuate a great deal over time for a given flow condition both in flume and field experiments these fluctuations were often associated with migration of low relief bed forms called bed load sheets whereas several studies have described bed load sheets as a consequence of grain sorting little is known about the mechanisms responsible for their production and migration these were investigated in flume experiments a set of 20 experiments was conducted under constant feeding rate conditions with mixtures of different uniform sediments and for slopes varying from 0 8 to 9 except for runs performed in high flow conditions we observed periodic bed load sheet production and migration associated with fluctuations of bed slope bed state bed fining and paving and bed load observations allowed us to conclude that bed load sheets resulted from very efficient vertical and longitudinal grain sorting that produced periodic local bed aggradation and erosion clearly observed in the upstream section of the flume fractional transport rates were measured in one run combined with the results of experiments previously conducted by authors with uniform sediments this experiment showed that the highest peak solid discharges were essentially caused by the much greater mobility of the coarser gravels when transported within bed load sheets a scenario is proposed for the mechanisms involved in bed load sheet production and migration

differential bedload transport rates in a gravel bed stream a grain size distribution approach the grain size distributions of bedload gravels in oak creek oregon follow the ideal rosin distribution at flow stages which exceed that necessary to initiate breakup of the pavement in the bed material the distributions systematically vary with flow discharge and bed stress such that at higher flow stages the grain sizes are coarser while the spread of the distribution decreases a differential bedload transport function for individual grain size fractions is formulated utilizing the dependence of the two parameters in the rosin distribution on the flow stress the total transport rate which is also a function of the flow stress is apportioned within the rosin grain size distribution to yield the fractional transport rates the derived bedload function has the advantage of yielding smooth continuous frequency distributions of transport rates for the grain size fractions in contrast to the discrete transport functions which predict rates for specified sieve fractions successful reproduction of the measured fractional transport rates and bedload grain size distributions in oak creek by this approach demonstrates its potential for evaluations of transport rates of size fractions in gravel bed streams the approach will be useful in investigations of downstream changes in bed material grain size distributions

an integrated approach to modelling hydrology and water quality in glacierized catchments the results are summarized of an integrated investigation of glacier geometry ablation patterns water balance meltwater routing hydrochemistry and suspended sediment yield the ultimate objective is to evaluate the assumptions of lumped two component mixing models as descriptors of glacier hydrology and to develop a semi distributed physically based model as an alternative the results of the study demonstrate that a reconstruction of probable subglacial drainage alignments can be achieved through a combination of terrain modelling based on estimated potential surface and dye tracing experiments recession curve analysis evidence of the seasonal instability of the englacial and subglacial electrical conductivities assumed in a mixing model evidence of the non conservative behaviour of water chemistry in the presence of suspended sediment and evidence of the seasonal evolution of the subglacial drainage system based on dye tracing all indicate that an alternative to a lumped static model of the hydrology is necessary the alternative presented in this paper is based on the combination of an energy balance model for surface melt which operates on an hourly time step and accounts for the changing spatial distribution of melt through the day as shading patterns change and routing procedures that transfer surface melt to moulins on the basis of glacier surface gradients then route water through reconstructed conduit systems using a hydraulic sewer flow routing procedure

convergence improvement and noise attenuation considerations for beyond alias projection onto convex sets reconstruction a reconstruction method known as projection onto convex sets pocs is an effective uncomplicated and robust method for the recovery of irregularly missing seismic traces however slow convergence of the pocs reconstruction method could jeopardize its computational appeal for this reason we investigate the performance of the pocs reconstruction method in terms of different threshold schedules and present a new data driven threshold that leads to an efficient implementation of the pocs method in particular we show that high quality solutions can be obtained in a few iterations in addition we address an important issue with the classical implementations of pocs reconstruction in that they cannot interpolate regularly missing data to solve this problem we introduce a masking operator that is based on a dominant dip scanning method into the pocs iteration at the end we present a variant of the pocs method that permits de noising seismic volumes during the reconstruction stage this is achieved by defining a weighted trace re insertion strategy that alleviates the influence of noisy traces in the final reconstruction of the seismic volume we show the effectiveness of the proposed method using synthetic and field data

marginal bed load transport in a gravel bed stream sagehen creek california marginal bed load transport describes the condition when relatively few bed particles are moving at any time bed particles resting in the shallowest bed pockets will move when the dimensionless shear stress exceeds a value of about 0 020 as increases the number of bed particles moving increases significant motion of bed particles i e when a substantial fraction of the bed particles are moving occurs when exceeds a value of about 0 060 thus marginal bed load transport occurs over the domain 0 020 0 060 marginal bed load transport rates and associated hydraulic characteristics of sagehen creek a small mountain gravel bed stream were measured on 55 days at discharges ranging from slightly less than one half of the bank full discharge to more than 4 times the bank full discharge dimensionless shear stress varied from 0 032 to 0 042 and bed particles as large as the 80th percentile of the bed surface were transported the relation between reference dimensionless shear stress and relative particle protrusion for sagehen creek was determined by varying ri to obtain the best fit of the parker bed load function to the measured transport rates during the period of record water years 1954 1991 the mean annual quantity of bed load transported past the sagehen creek gage was 24 7 tons forty seven percent of all bed load transported during the 38 years of record occurred in just 6 years during 10 of the 38 years of record essentially no bed load was transported the median diameter of bed load was 26 mm compared to 58 mm in the surface bed material

routing of heterogeneous sediments over movable bed model development a one dimensional numerical model of sediment routing is derived to simulate erosion transport and deposition of individual size density fractions in the bed material within a relatively straight nonbifurcating alluvial channel the reach of interest is subdivided into a number of longitudinal elements of varying width averaged properties during each time step flow depths and velocities in each element are determined from the gradually varied flow equation using the standard step method for backwater calculations the bedload transport rate of each size fraction is calculated from a modified bagnold equation implementing a novel approach that takes into consideration the effects of turbulent fluctuations in the bed shear stress critical shear stresses for entrainment of particles from the mixed bed are determined using relationships that treat grain protrusion and hiding the transport of particles in suspension is modeled using a convection diffusion sediment continuity equation either explicitly

joint sensing of bedload flux and water depth by seismic data inversion rivers are the fluvial conveyor belts routing sediment across the landscape while there are proper techniques for continuous estimates of the flux of suspended solids constraining bedload flux is much more challenging typically involving extensive measurement infrastructure or labour intensive manual measurements seismometers are potentially valuable alternatives to in stream devices delivering continuous data with high temporal resolution on the average behaviour of a reach two models exist to predict the seismic spectra generated by river turbulence and bedload flux however these models require estimating a large number of parameters and the spectra usually overlap significantly which hinders straightforward inversion we provide three functions contained in the r package eseis that allow generic modelling of hydraulic and bedload transport dynamics from seismic data using these models the underlying monte carlo approach creates lookup tables of potential spectra which are compared against the empirical spectra to identify the best fitting solutions the method is validated against synthetic data sets and independently measured metrics from the nahal eshtemoa israel a flash flood dominated ephemeral gravel bed river our approach reproduces the synthetic time series with average absolute deviations of 0 01 0 04 m water depth ranging between 0 1 m and 0 00 0 04 kg sm bedload flux ranging between 0 4 kg sm the example flash flood water depths and bedload fluxes are reproduced with respective average deviations of 0 10 m and 0 02 kg sm our approach thus provides generic testable and reproducible routines for a quantitative description of key metrics hard to collect by other techniques in a continuous and representative manner

numerical simulation of downstream fining by selective transport in gravel bed rivers model development and illustration a numerical model has been developed for the routing of gravel sized sediment along a river channel which is free to adjust both its long profile and surface texture hydraulic calculations use a step backwater approach and sediment transport is predicted with the method of parker 1990a which uses a low degree of size selectivity exchange of sediment between the surface and subsurface is described using the modified exner equation of parker and sutherland 1990 the model is applied to an idealized channel based on the highly concave allt dubhaig scotland in which fining by particle wear is minor the rapid downstream fining observed in this river is closely matched by model predictions after a time equivalent to 102 years under the present flow regime of the river the evolution of the fining pattern during the model run and associated changes in sediment transport and bed aggradation are described it is concluded that strong profile concavity can force rapid downstream fining even though bed load transport is only slightly size selective this run of the model serves as a basis for testing of the sensitivity of downstream fining to alternative choices of parameter values and boundary conditions which are summarized here and will be described in a subsequent paper

stabilizing self organized structures in gravel bed stream channels field and experimental observations stable reticulate structures which we call stone cells have been observed in cobble gravel channel beds with low bed material transport rates experiments show that such structures develop simultaneously with the armor layer during an extended period when flows do not exceed the shields threshold by more than 2 times so that bed material transport is low they are constructed by particles moving from less stable positions into more stable configurations against each other intermediate developments include clusters and stone lines they reduce sediment transport by orders of magnitude and are evidently a major stability promoting mechanism in gravel channels the timescale for their development suggests that the boundaries of many gravel bed channels are not in equilibrium with recent competent flows but reflect the history of recent dominant flows

variability of bedload transport and channel morphology in a braided river hydraulic model this paper investigates variability in bedload transport and channel morphology for 11 replicate experimental runs in an approximately 1 50 braided river model the experiments each of 90 h duration were carried out in a 20 3m tilting flume all the experiments started with the same initial conditions bedload transport was measured at 5 min intervals in a collection drum at the exit from the flume the model showed reasonable hydraulic similarity when compared to prototype rivers results show that mean bedload transport rates for the 11 runs vary in the range 0 98 to 1 49gs 1 mean 1 21 coefficient of variation 11 per cent within run transport rates commonly vary from close to zero to two and occasionally three or four times the mean rate within the bedload series several irregular phases of transport intensity can be observed but time series analysis of the data show little underlying serial structure an ar 2 autoregressive model is appropriate channel patterns are narrow braided are established quickly and remain relatively stable throughout the runs although channel widths increase between 20 and 103 per cent over the 11 runs channel behaviour varies from aggradational to transitional between aggradation and degradation time averaged bedload transport rate is weakly correlated with braiding intensity in general these results demonstrate that for a given set of controlling variables bedload transport and channel morphology can be approximately replicated

dune migration in a steep coarse bedded stream during 1986 and 1987 migrating bed forms composed of coarse sand and fine gravel d50 1 8 to 9 1 mm were documented in the north fork toutle river at kid valley washington at flow velocities ranging from 1 6 to 3 4 m s 1 and depths of 0 8 to 2 2 m the bed forms predominantly lower regime dunes were studied with a sonic depth sounder transducer suspended in the river at a stationary point twelve temporal depth sounding records were collected during storm runoff and nearly steady average streamflow with record durations ranging from 37 to 261 min waveform height was defined by dune front heights which ranged from 12 to 70 cm a weak correlation between flow depth and the standard deviation of bed elevation was noted dune front counts and spectral analyses of the temporal records showed that dune crests passed the observation point every 2 to 5 min dunes were often superposed on larger bed forms with wave periods between 10 and 30 min gradual changes in waveform height and periodicity occurred over several hours during storm runoff the processes of dune growth and decay were both time dependent and affected by changes in streamflow rates of migration for typical dunes were estimated to be 3 cm s 1 and dune wavelengths were estimated to be 6 to 7 m

quantifying fluvial non linearity and finding self organized criticality insights from simulations of river basin evolution abstract a numerical study was undertaken to investigate non linearity and the potential for self organized criticality soc in the evolution of river basins twenty three simulations were carried out using the authors caesar landscape evolution model in which the magnitude of storm events variability of storm events sediment heterogeneity sources of sediment supply and catchment morphology are systematically varied to evaluate their importance as possible drivers for non linear behavior and soc temporal fluctuations in simulated sediment yield show notable non linear behavior storm magnitude and occurrence of landslides appear to have little impact on variability of the sediment yield when compared to the impacts of sediment heterogeneity rainfall variability and catchment morphology particularly it appears that the non linearity of sediment yields results from the manner in which the catchment processes the variable rainfall rather than just the rainfall variability itself the variations in sediment yield show a power law magnitude frequency distribution which is a possible but inconclusive indicator of soc however several other more qualitative arguments can be made to support the case for soc in these simulations specifically we identify the nature of the critical state and suggest two cascade mechanisms by which the system can organize itself around this critical state combined these arguments indicate that simulated evolution of river basins indeed exhibits soc at least with respect to sediment yield the critical state appears to be an indicator of the connectivity of the drainage network thus the simulations indicate that unlike traditional soc systems the critical state of the system can vary in time as sudden changes in drainage network connectivity may result in sudden changes in the soc behavior of the system

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

coarse sediment transport in a bedrock channel with complex bed topography 1 independent lithologic and structural controls in fluvial bedrock systems interact with coarse sediment transport processes to play a key role in bedrock incision processes such as abrasion during a 3 year study on the ocoee river in the blue ridge province of the southern appalachians usa we used painted tracer clasts to measure coarse sediment transport dynamics and address whether different scales of morphologic variability in bedrock channels lead to coarse sediment transport processes that differ from alluvial channels at the reach scale folded metasedimentary units are exposed in the channel bed and appear as linear bedrock ribs that vary in amplitude and orientation to flow under similar flow conditions for which size dependent transport has been observed in alluvial channels dimensionless shields stress within 1 5 2 0 times the dimensionless critical shear stress transport distance was a significant function of grain size where bedrock ribs were longitudinal to flow reach 1 and reach 2 however transport distance was not size dependent where bedrock ribs were oblique to flow reach 3 at different intrareach scales the variables characterizing the local bedrock topography and sediment architecture were the best predictors of transport distance in all three reaches therefore bed load transport processes may be influenced by bed forms in bedrock streams bedrock ribs but at potentially smaller scales than bed forms in alluvial channels the strong influence of bedrock ribs on coarse sediment transport suggested that coarse sediment transport processes are controlled by different factors in bedrock channels only when bedrock ribs cross the channel at a high angle to the flow

unequal mobility of gravel and sand in weakly bimodal river sediments bed load was trapped during flood events over a 20 month period at the lower end of the allt dubhaig a small river in scotland with rapid downstream fining of gravel bed material on a slowly aggrading concave long profile the channel bed near the trap is predominantly gravel with a secondary sand mode total transport in each event depended mainly on peak shear stress rather than duration over a threshold bed load was mainly sand in smaller events bimodal in intermediate events and mainly gravel in the biggest floods mean and maximum grain diameter both increased with peak shear stress but in different ways analysis of fractional transport rates and maximum grain size in relation to peak shear stress suggests that gravel transport is slightly size selective but sand transport is close to equal mobility the slight selectivity in gravel transport is consistent with previous field studies of near equilibrium unimodal beds and supports assumptions made in the numerical model of hoey and ferguson 1994 which successfully simulates the observed amount of downstream fining over the 2 5 km upstream of the bed load trap

controls of strength and rate of downstream fining above a river base level we report sensitivity tests on a numerical model of the development of downstream fining by size selective transport and deposition above a base level in a gravelbed river with no lateral inputs of water or sediment strong fining requires deposition mainly to the surface otherwise its amount and streamwise distribution are not highly sensitive to any single factor but vary somewhat with hiding factor excess shear stress and bed sorting low initial concavity inhibits fining but different higher concavities generate fairly similar fining profiles lower sediment supply leads to a coarser bed with less fining but there is no simple relationship between fining and aggradation rate the rate of development of fining is sensitive to all these factors but is always rapid initially followed by a far slower approach towards final equilibrium surface grain size adjustment is potentially an important degree of freedom in river response to any environmental change or human impact which causes overloading

sedimentological characterization of antarctic moraines using uavs and structure from motion photogrammetry in glacial environments particle size analysis of moraines provides insights into clast origin transport history depositional mechanism and processes of reworking traditional methods for grain size classification are labour intensive physically intrusive and are limited to patch scale 1m2 observation we develop emerging high resolution ground and unmanned aerial vehicle based structure from motion uav sfm photogrammetry to recover grain size information across an moraine surface in the heritage range antarctica sfm data products were benchmarked against equivalent datasets acquired using terrestrial laser scanning and were found to be accurate to within 1 7 and 50mm for patch and site scale modelling respectively grain size distributions were obtained through digital grain classification or photo sieving of patch scale sfm orthoimagery photo sieved distributions were accurate to 2mm compared to control distributions derived from dry sieving a relationship between patch scale median grain size and the standard deviation of local surface elevations was applied to a site scale uav sfm model to facilitate upscaling and the production of a spatially continuous map of the median grain size across a 0 3 km2 area of moraine this highly automated workflow for site scale sedimentological characterization eliminates much of the subjectivity associated with traditional methods and forms a sound basis for subsequent glaciological process interpretation and analysis

coupled numerical analytical approach to landscape evolution modeling the earth s topography is shaped by surface processes that operate on various scales in particular river processes control landscape dynamics over large length scales whereas hillslope processes control the dynamics over smaller length scales this scale separation challenges numerical treatments of landscape evolution that use space discretization large grid spacing cannot account for the dynamics of water divides that control drainage area competition and erosion rate and slope distribution small grid spacing that properly accounts for divide dynamics is computationally inefficient when studying large domains here we propose a new approach for landscape evolution modeling that couples irregular grid based numerical solutions for the large scale fluvial dynamics and continuum based analytical solutions for the small scale fluvial and hillslope dynamics the new approach is implemented in the landscape evolution model dac divide and capture the geometrical and topological characteristics of dac s landscapes show compatibility with those of natural landscapes a comparative study shows that even with large grid spacing dac predictions fit well an analytical solution for divide migration in the presence of horizontal advection of topography in addition dac is used to study some outstanding problems in landscape evolution i the time to steady state is investigated and simulations show that steady state requires much more time to achieve than predicted by fixed area calculations due to divides migration and persistent reorganization of low order streams ii large scale stream captures in a strike slip environment are studied and show a distinct pattern of erosion rates that can be used to identify recent capture events iii three tectono climatic mechanisms that can lead to asymmetric mountains are studied each of the mechanisms produces a distinct morphology and erosion rate distribution application to the southern alps of new zealand suggests that tectonic advection precipitation gradients and non uniform tectonic uplift act together to shape the first order topography of this mountain range copyright 2014 john wiley sons ltd

channel morphology and bedload pulses in braided rivers a laboratory study bedload pulses in gravel bed rivers have been widely reported in recent years and attempts have been made to relate them to channel morphology bedload transport and channel morphology were measured in a small scale generic model of braided gravel bed streams two experiments are described in which braided channels developed in a 14 m 3 m sand tray total bedload output from the tray was weighed every 15 minutes stream bed geometry was surveyed every four hours pulses were observed in the bedload output time series and were qualitatively related to the channel morphology immediately upstream of the measuring section the bagnold 1980 bedload equation generally overpredicts measured bedload transport rates when applied to channels that were in equilibrium or aggrading underprediction occurred when applied to degrading channels aggradation was associated with channel multiplication and bar deposition channel pattern simplification occurred when degradation took place and bars emerged from the water flow development of phases of aggradation and degradation is dependent upon the three dimensional geometry of the stream beds spatial and temporal feedback loops can be identified enabling links between channel morphology and bedload transport rate to be directly identified

continuous monitoring of bedload discharge in a small steep sandy channel this paper reports on bedload flux and texture monitored in a natural steep sandy ephemeral channel draining a small gullied sandy watershed the barranca de los pinos 1 32 ha spain bedload flux was continuously monitored with two independent reid type slot samplers bedload texture was determined from the sediment collected in the samplers channel morphology was surveyed with a high spatial resolution with a terrestrial laser scanner the monitored instantaneous bedload fluxes are among the highest measured in natural rivers characterized by high temporal and spatial variability related to the presence of bedforms shallow bars and sand sheets and to the reworking of the dry bed between and at the end of individual flow events the grain size distribution of the bedload indicates equal mobility but bedload texture fluctuates depicting the transport of coarser bar surfaces and of finer grained anabranch surfaces as well as of the overall bed subsurface

sorting and bed waves in unidirectional shallow water flows the stability of a uniform flow above an erodible bed composed of a bimodal mixture of sediments is investigated by means of linear analysis results show that for any given set of the flow and sediment parameters two distinct modes of instability arise each one characterized by its own wave speed growth rate and longitudinal wavelength each one involving spatial variations of both grain size density and bed elevation although at a linear level no information on the amplitude of the perturbations is gathered the analysis of the eigenvectors associated with the two modes of instability allows for an easy classification in terms of the relative amplitudes of the perturbations of bed elevation and size density one eigenvalue is shown to be associated with the modifications of bed forms induced by the presence of the heterogeneous mixture such as the local accumulation of finer and coarser material along the unit wavelength the other with the formation of the low amplitude sorting waves known as bedload sheets in the present unidirectional shallow water framework only the sorting wave is found to be unstable since dunes and antidunes the relevant bed forms for this case require a more refined rotational flow model in order to become unstable on the other hand the simple flow model adopted allows for the formulation of an algebraic eigenvalue problem that can be solved analytically allowing for a deep insight into the mechanisms that drive both instabilities

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

a modified morphodynamic model for investigating the response of rivers to short term climate change near future climate change will affect the discharge and base level of rivers and thus cause channel changes the nature and pace of such changes can be simulated using morphodynamic models as part of an investigation of how the changing hydrology of the st lawrence river quebec canada will affect its tributaries we have made additions and modifications to a one dimensional morphodynamic model developed for gravel bed rivers sedrout the changes allow simulation of sand bed rivers variable discharge downstream water level fluctuations and flow and sediment routing in channels with islands a revised formulation for calculating the grain size distributions of the surface and subsurface material is presented to allow for alternating sedimentation and erosion we test the enhanced model using small scale simulations and present day conditions in four tributaries of the st lawrence river the model is calibrated and validated for the tributaries and the capability to simulate river morphology over a 100 year period is tested good validation agreement on water level cross sectional mean velocity and sediment transport rate is obtained for the four tributaries of the st lawrence river with these modifications modelling a very wide range of river morphodynamic problems is now possible

partial transport of a sand gravel sediment grains of a single size within a mixed size bed are entrained over a range of flows within this range some grains exposed on the bed surface are active entrained at least once over the duration of a transport event while the remaining surface grains are immobile a condition we define as partial transport we demonstrate the existence and domain of partial transport using observations of grain entrainment on time series of bed photographs of flume experiments with a widely sorted sand gravel mixture the active proportion of the bed surface increases with bed shear stress 0 at a given 0 90 of the active grains are entrained when the cumulative mass transported exceeds approximately 4 times the active mass on the bed mobilization of grains in a size fraction increases from 10 to 90 over a range of 0 of a factor of 2 the bounds of this range increase with grain size di so that at a given 0 sizes over a range of a factor of 4 are in a state of partial transport fractional transport rates are independent of di for fully mobilized fractions and decrease rapidly with di for partially mobile fractions partial transport is associated with substantial transport rates of finer fully mobile sizes limits both the rate and size distribution of grain exchange with the bed subsurface and may be the dominant transport condition in many gravel bed rivers

river adjustment to changes in sediment load the effects of tin mining on the ringarooma river tasmania 1875 1984 the mining of alluvial tin in the ringarooma basin began in 1875 reached a peak in 1900 20 and had virtually ceased by 1982 during that time 40 million m3 of mining waste were supplied to the main river quickly replacing the natural bed material and requiring major adjustments to the channel based on estimates of sediment supply from more than 50 widely scattered mines and the frequency of flows capable of transporting the introduced load the river s transport history is reconstructed using a mass conservation model because of the lengthy time period 110 years and river distance 75 km involved the model cannot predict detailed change but it does reproduce the main pattern of sediment movement in which successive phases of aggradation and degradation progress downstream peak storage is predicted in that part of the river where braiding and anastomosis are best developed aggradation was most rapid in the upper reaches close to major supply points becoming slower and later with distance downstream channel width increased by up to 300 per cent where the valley floor was broad and braiding became relatively common bridges had frequently to be replaced while bed levels were still rising in lower reaches degradation began in upper ones notably after 1950 and by 1984 had progressed downriver over 30 km rates of incision reached 0 5 m yr 1 especially in the early 1970s when record high flows occurred as a result of degradation the bed material became gravelly through either reexposure of the original bed or lag concentration of coarser fractions also a narrower unbraided channel has developed the river is beginning to heal itself and upper reaches now have reasonably stable beds but at least another 50 years will be required for the river to cleanse its channel of mining debris

experiments on the effect of hydrograph characteristics on vertical grain sorting in gravel bed rivers 1 desert ephemeral gravel bed streams typically have bed surfaces that are relatively unarmored compared to the substrate below while gravel bed streams in humid and snowmelt areas typically have well armored surfaces the degree of armoring can be characterized in terms of an armor ratio defined as the ratio of the surface median size to the substrate median size a set of field data shows desert ephemeral gravel bed streams with armor ratios ranging from 0 5 to 2 4 and with an average value of 1 2 the armor ratio of snowmelt fed gravel bed streams in the same set ranges from 2 to 7 with an average value of 3 4 the reason for this difference is sought in terms of differing hydrological characteristics and sediment supply regimes thirteen experiments were conducted to study the formation of armoring under a range of hydrological conditions the experiments have two limiting cases a relatively flat hydrograph that represents conditions produced by continuous snowmelt and a sharply peaked hydrograph that represents conditions associated with flash floods all constant hydrograph experiments developed a well armored structured surface while short asymmetrical hydrographs did not result in substantial vertical sorting all symmetrical hydrographs show some degree of sorting and the sorting tended to become more pronounced with longer duration sediment supply appears to be a first order control on bed surface armoring while the shape of the hydrograph plays a secondary role

temporal variations in bedload transport rates associated with the migration of bedforms temporal variations in bedload transport rates that occur at a variety of timescales even under steady flow conditions are accepted as an inherent component of the bedload transport process rarely however has the cause of such variations been explained clearly we consider three data sets obtained from laboratory experiments that refer to measurements of bedload transport made with continuously recording bedload traps each data set is characterized by a predominant low frequency oscillation on which additional higher frequency oscillations generally are superimposed the period of these oscillations as isolated through the use of spectral analysts ranged between 0 47 and 168 minutes and was associated unequivocally with the migration of bedforms such as ripples dunes and bars the extent to which such oscillatory behaviour may be recognized in a data set depends on the duration of sampling and the length of the sampling time with respect to the period of a given bedform several theoretical probability distribution functions have been developed to describe the frequency distributions of relative bedload transport rates that are associated with the migration of bedforms einstein 1937b hamamori 1962 carey and hubbell 1986 these distribution functions were derived without reference to a sampling interval we present a modification of hamamori s 1962 probability distribution function generated by monte carlo simulation which permits one to specify the sampling interval in relation to the length of a bedform comparisons between the simulated and observed frequency distributions that were undertaken on the basis of the data described herein are good significant at the 90 per cent confidence level finally the implications that temporal variability which is associated with the migration of bedforms have for the accurate determination of bedload transport rates are considered

surface based fractional transport rates mobilization thresholds and partial transport of a sand gravel sediment twenty eight coupled observations of flow transport and bed surface grain size distribution were made in a laboratory flume using a wide range of flows and a sediment with a very poorly sorted bimodal grain size distribution these observations permit the transport rates of individual size fractions to be scaled by the proportion of each size immediately available for transport on the bed surface the key to our observations is the use of a sediment in which each size fraction has been painted a different color which permits reliable repeatable and nondestructive measurement of the bed surface grain size distribution from photographs of the bed surface at a given flow the fractional transport rates may be divided into two parts a finer grained portion within which fractional transport rates are a function only of their proportion on the bed surface and total transport rate and a coarser grained portion for which fractional transport rates also depend on the proportion of individual grains within a fraction that remain essentially immobile throughout the experimental run we define the latter condition as one of partial transport and observe that the grain size separating partial and fully mobilized transport consistently increases with flow strength complete mobilization of a size fraction occurs at roughly twice the shear stress necessary for incipient motion of that fraction zones of partial and full mobility are quite distinct when fractional transport rates are scaled by the bed surface grain size distribution although a region of partial transport is evident when these data and other experimental and field observations are scaled by the bulk grain size distribution of the sediment bed critical shear stresses for the incipient motion of individual fractions in our experimental sediment vary over an order of magnitude a result strongly in contrast to many earlier observations but consistent with our observations of incipient motion in sediments with bimodal grain size distributions

a model of two phase bedload transport in an oregon coast range stream a descriptive model for bed material routing in small sand and gravel bedded channels with sequences of pools and armoured riffles was developed aspects of the model are demonstrated at flynn creek a 202 ha third order drainage in the oregon coast range assuming that channel geometry sediment transport competence and the availability of sediments for transport are all non uniform in the downstream direction the model described bedload transport as occurring in two phases phase i involves the transport of fine predominantly sand sized bed materials over stable gravel armoured riffles phase ii occurs at higher flows that can entrain riffle armour and transport riffle sediments in addition to phase i sediments phase i bedload transport was sampled during three moderate flow events a power function related phase i bedload transport to water discharge the relationship was consistent between storms and between two successive years phase ii bedload transport sampled during a 1 8 yr return period streamflow event in february 1979 proved non uniform in a downstream direction and unsteady over time at a given stream discharge transport rates closely correlated with the rapid scour and redeposition of the riffle at the bedload sampling cross section transport peaks corresponded to scour and transport decreased greatly during deposition the transport of large 12 5 mm diam bed material increased up to 12 fold during riffle scour

stochastic modeling of the cover effect and bedrock erosion 1 several important fluvial bedrock erosion processes are driven by the impact of bed load particles bed load transport rates fluctuate strongly in both nature and experiment and stochastic models of the transport processes have been put forward to describe this behavior in this paper i adapt a model based on a markov chain formulation to derive probability distributions for bed load transport rate over a rock bed only partly covered by sediment i propose a way to calculate the probability distribution of bed cover for given sediment supply using a combinatoric model and combine the two curves to calculate probability distributions for bed cover and erosion rate at constant hydraulics in the proposed model mean bed cover is an exponentially declining function of the number of particles in the control volume the model describes recently published experimental data well but at the moment it is not possible to finally discriminate between the exponential and the previously proposed linear model formulation distributions of erosion rate are fairly broad functions slightly skewed toward high erosion rates

the causes of bedload pulses in a gravel channel the implications of bedload grain size distributions unsteady bedload transport was measured in two c 5 m wide anabranches of a gravel bed braided stream draining the haut glacier d arolla switzerland during the 1998 and 1999 melt seasons bedload was directly sampled using 152 mm square helley smith type samplers deployed from a portable measuring bridge and independent transport rate estimates for the coarser size fractions were obtained from the dispersion of magnetically tagged tracer pebbles bedload transport time series show pulsing behaviour under both marginal 1998 and partial 1999 transport regimes there are generally weak correlations between transport rates and shear stresses determined from velocity data recorded at the measuring bridge characteristic parameters of the bedload grain size distributions d50 d84 are weakly correlated with transport rates analysis of full bedload grain size distributions reveals greater structure with a tendency for transport to become less size selective at higher transport rates the bedload time series show autoregressive behaviour but are dif cult to distinguish by this method state space plots and associated measures of time series separation reveal the structure of the time series more clearly the measured pulses have distinctly different time series characteristics from those modelled using a one dimensional sediment routing model in which bed shear stress and grain size are varied randomly these results suggest a mechanism of pulse generation based on irregular low amplitude bedforms that may be generated in channel or may represent the advection of material supplied by bank erosion events copyright 2003 john wiley sons ltd

self organized criticality in river basins challenging sedimentary records of environmental change for many years researchers have linked increases in sediment and bedload from drainage basins to external factors such as increased rainfall however natural systems have always shown a high degree of scatter or nonlinearity in this response which has made prediction of sediment yields difficult we identify and describe a mechanism for self organized criticality in the bedload sediment output from a simple drainage basin evolution model this implies that identical floods will give considerably different sediment yields which effectively renders the system unpredictable therefore existing empirical methods for estimating sediment yields may need to be radically reevaluated furthermore sedimentary records used to infer past climate or environmental conditions could simply reflect the internal system dynamics instead of external drivers

the concept of transport capacity in geomorphology the notion of sediment transport capacity has been engrained in geomorphological and related literature for over 50 years although its earliest roots date back explicitly to gilbert in fluvial geomorphology in the 1870s and implicitly to eighteenth to nineteenth century developments in engineering despite cross fertilization between different process domains there seem to have been independent inventions of the idea in aeolian geomorphology by bagnold in the 1930s and in hillslope studies by ellison in the 1940s here we review the invention and development of the idea of transport capacity in the fluvial aeolian coastal hillslope debris flow and glacial process domains as these various developments have occurred different definitions have been used which makes it both a difficult concept to test and one that may lead to poor communications between those working in different domains of geomorphology we argue that the original relation between the power of a flow and its ability to transport sediment can be challenged for three reasons first as sediment becomes entrained in a flow the nature of the flow changes and so it is unreasonable to link the capacity of the water or wind only to the ability of the fluid to move sediment secondly environmental sediment transport is complicated and the range of processes involved in most movements means that simple relationships are unlikely to hold not least because the movement of sediment often changes the substrate which in turn affects the flow conditions thirdly the inherently stochastic nature of sediment transport means that any capacity relationships do not scale either in time or in space consequently new theories of sediment transport are needed to improve understanding and prediction and to guide measurement and management of all geomorphic systems

changes in bedload transport rate associated with episodic sediment supply in a japanese headwater channel abstract we conducted field monitoring of bedload transport rate associated with experimental sediment release in a natural channel to clarify behavior of the supplied sediment on mixed size bed observation of bedload rate at two sites along the 30 m channel reach revealed that downstream migration of finer particles delay compared with coarser particles ratio of the bedload sediment that deposited during the migration was higher for finer sediments these behaviors of the mixed size particles were clear during passage of the sediment wave without changes in water discharge flashing peak of discharge that caused artificially by opening of the dam gate did not destroy channel bed structure including steps and pools formed by coarser sediments and only small amount of bedload was mobilized both reach scale channel features including steps pools and riffles as well as fine scale features i e armour coat likely increased critical shear stress of particles and decreased bedload rate during our experiment extreme sediment supply induced two types of sediment deposition 1 filling the pools in reach sales and 2 the intrusion of fine particles into the coarser sediment that formed an armour layer the all grain size fractions can deposit as type 1 when shear stress of stream water is not enough to entrain bedload particles while deposition type 2 occurs when finer sediment pass over channel bed on which armour coat is well developed deposition of finer sediment into coarser sediment that forms armour coat is affected by grain size distribution of bed surface sediment thus impact of the sediment supply on downstream channel depends on both bedforms and grain size distribution of bed surface sediment over which the supplied sediment pass

simplicity and complexity of bed load response during flash floods in a gravel bed ephemeral river a 10 year field study 1 a decade of data for the nahal eshtemoa an unarmored gravel bed ephemeral river reveals that bed load flux during rain fed flash floods is a simple function of channel average boundary shear stress however the relation is inadequately described by a power function of the type commonly used in predictive bed load equations and a linear function gives a much better fit the success of a linear function is related to the unarmored nature of the bed material typical of ephemeral gravel bed rivers and the ready availability of sediment at all levels of transport stage bed load response to changing shear stress is largely undifferentiated as flash floods wax or wane however while most data conform to a simple relation between bed load and hydraulic stress some for individual floods or flood segments do not reflecting variability in sediment supply and texture three type behaviors are identified that assist in explaining both the general simple pattern and the limited scatter of the bed load shear stress plot type 1 provides the majority of the data giving the general linear relation between bed load flux and boundary shear stress type 2 is rare given the flashy nature of the hydrograph but represents comparatively steady flows well above the entrainment threshold during which bed load sheets or the breakup of grain clusters lead to spasmodic changes in bed load flux type 3 shows a weak relation between shear stress and bed load flux representing flow conditions just above the entrainment threshold

bedload sheets in heterogeneous sediment field observations in streams with beds of coarse sand and fine gravel have revealed that bedload moves primarily as thin migrating accumulations of sediment and coarse grains cluster at their leading edge these accumulations are one or two coarse grains high and are much longer 0 2 0 6 m long in sand 0 5 2 0 m in fine gravel than their height the authors propose the term bedload sheet for these features and the authors argue that they result from an instability inherent to bedload movement of moderately and poorly sorted sediment in essence coarse particles in the bedload slow or stop each other trap finer particles in their interstices and thus cause the coarse particles to become mobile again bedload sheets develop on the stoss side of dunes causing the dune to advance incrementally with the arrival of each sheet successive deposition of coarse sediment from the leading edge followed by fine sediment may generate the grain size sorting that distinguishes cross bedding available flume experiments and field observations indicate that bedload sheets are a common but generally unrecognized feature of heterogeneous sediment transport

nearly pure sorting waves and formation of bedload sheets bedload sheets are coherent migrating patterns of bed material recently observed both in flume studies and in field streams with beds of coarse sand and fine gravel this newly recognized feature is inherently associated with the heterogeneous character of the sediment and consists of sorting waves with distinct coarse fronts only one or two coarse grains high the question of the formation of bedload sheets poses an interesting and peculiar stability problem for the grain size distribution sorting waves are essentially two dimensional migrating perturbations associated with variations of this distribution we show that their growth is strictly associated with grain sorting in fact the latter gives rise to perturbations of bedload transport which drive small perturbations of bottom elevation the amplitude of which scales with grain size the sorting wave also induces spatial variations of bottom roughness and consequently alters the fluid motion which conversely exerts a spatially varying stress on the bed the feature of bedload sheets which allows them to be distinguished from dunes over beds with coarse sand or fine gravel is then the fact that sorting is the dominant effect controlling their growth rather than being a relatively small perturbation of the mechanism which gives rise to dunes in the case of uniform sediment the requirement that perturbations should not alter the sediment budget leads to an integral condition which gives rise to an integro differential mathematical problem with the help of recently developed bedload relationships suitable for mixtures as well as appropriate modelling of turbulent channel flow over a bed with spatially periodic perturbations of bottom elevation and roughness we are able to derive a general dispersion relation which can be readily solved in terms of undisturbed size densities in the form of sums of dirac distributions perturbations are found to be unstable within a range of wavenumbers depending on the relative roughness and froude number we show that when the effects of perturbations of bottom elevation are neglected the unstable region corresponds to the range of conditions where the bottom stress leads bottom roughness a range distinct from that which characterizes the formation of dunes this result is given a physical explanation which depends crucially on the deviation from equal mobility of different grain sizes in the surface layer the effect of perturbations of bottom elevation is however not negligible when the bottom roughness is fairly large compared to depth in the latter case perturbations of bottom elevation and of bottom roughness are equally important and gravel sheets are not easily distinguished from small amplitude dunes comparison with the field observations of whiting et al 1985 1988 is satisfactory insofar as the bedload sheet mode is unstable under the conditions of the experiments and the predicted wavelengths fall within the experimental range the laboratory observations of kuhnle southard 1988 on the other hand appear to fall within a range of bottom roughness where the observed bedforms do not exhibit features unambiguously distinct from those of small amplitude dunes

fluvial transport of sand and gravel mixtures with bimodal size distributions abstract initiation of motion and fractional transport rates of sediments with bimodal size distributions were measured in a laboratory channel and in a natural channel transport experiments were conducted with unimodal 100 sand and 100 gravel bed sediments and three bimodal mixtures of the two sediments 10 gravel 90 sand 25 gravel 75 sand and 45 gravel 55 sand in the bimodal sediment beds the critical shear stress for the initiation of motion showed very little change with grain size for the sand sizes but increased with grain size for the gravel sizes for low flow strengths only the sand sizes were in transport while for the highest flow strengths the bed load sediment size distribution approached that of the bed material

bedload transport in se asian streams uncertainties and implications for reservoir management article this paper reviews the current state of knowledge regarding bedload transport in se asian streams and presents the results from a case study on bedload transport in a mountain stream in northern thailand together the review and new data help contextualize the paucity of work done in the region in the face of a rapid increase in development and reservoir building throughout se asia data from both the reviewed studies and the case study indicate that bedload transport in many se asian streams e g catchment areas b 100 km 2 i s often much higherthan iscommonly assumed for tropicalstreams i e about 10 of the totalsediment load estimat ed annual bedload proportion was 18 of the total annual sediment load in the 74 km

restoration of missing offsets by parabolic radon transform1 restoration of missing offsets and trace interpolation is an interesting and important problem in seismic data processing based on the parabolic radon transform a method is presented for missing offset restoration resampling and regularization of prestack individual cmp gathers the method is also valid for resampling spatially aliased seismic data the method is based on the parabolic assumption of the seismic events which is generally verified after a partial nmo correction in the cmp organization of the data the essence of the method consists of a band limited forward parabolic radon transform of the data containing zero traces at the missing offset locations the curvature range is chosen to map properly the coherent energy while the zero traces map beyond that range after inverse transform the originally zero traces are partly filled with information several iterations of forward and inverse transform every time replacing the zero traces in the original gather with the partially reconstructed ones almost fully restore the zero traces efficient and fast algorithms can be built up to process data having a uniform geometry examples on synthetic as well as on field data demonstrate clearly the robustness of the method

meso scale catchment sediment budgets combining field surveys and modeling in the dragonja catchment southwest slovenia in this paper we present a methodology to construct a sediment budget for meso scale catchments we combine extensive field surveys and expert knowledge of the catchment with a sediment delivery model the meso scale mediterranean drainage basin of the dragonja 91 km2 southwest slovenia was chosen as case study area during the field surveys sheet wash was observed on sloping agricultural fields during numerous rainfall events which was found to be the main source of sediment with the sediment yield model watem sedem the estimated net erosion on the hillslopes 4 1 t ha 1 y 1 91 of inputs the second source bank erosion 4 2 0 25 t ha 1 y 1 was monitored during several years with erosion pins and photogrammetric techniques the last source channel incision was derived from geomorphological mapping and lichenomery and provided 3 8 0 17 t ha 1 y 1 of the sediment input the river transports its suspended sediment mainly during high flow events sampled with automated water samplers about 27 1 2 t ha 1 y 1 of the sediment delivered to the channel is deposited on floodplains and low terraces downstream estimated with geomorphological mapping coring and cesium 137 measurements the sediment transported as bedload disintegrates during transport to the outlet due to the softness of the bedrock material as a result the river carries no bedload when it reaches the sea the results imply a build up of sediment in the valleys catchment however extreme flood events may flush large amounts of sediment stored in the lower parts of the system geomorphological evidence exists in the catchment that such high magnitude low frequency events have happened in the past

cyclonic circulation of saturn s atmosphere due to tilted convection saturn displays cyclonic vortices at its poles and the general atmospheric circulation at other latitudes is dominated by embedded zonal jets that display cyclonic circulation the abundance of small scale convective storms suggests that convection plays a role in producing and maintaining saturn s atmospheric circulation however the dynamical influence of small scale convection on saturn s general circulation is not well understood here we present laboratory analogue experiments and propose that saturn s cyclonic circulation can be explained by tilted convection in which buoyancy forces do not align with the planet s rotation axis in our experiments conducted with a cylindrical water tank that is heated at the bottom cooled at the top and spun on a rotating table warm rising plumes and cold sinking water generate small anticyclonic and cyclonic vortices that are qualitatively similar to saturn s convective storms numerical simulations complement the experiments and show that this small scale convection leads to large scale cyclonic flow at the surface and anticyclonic circulation at the base of the fluid layer with a polar vortex forming from the merging of smaller cyclonic storms that are driven polewards saturn s cyclonic atmospheric circulation may be explained by the dynamics of small scale convection suggest laboratory analogue experiments

particle size variations between bed load and bed material in natural gravel bed channels particle sizes of bed load and bed material that represent materials transported and stored over a period of years are used to investigate selective transport in 13 previously sampled natural gravel bed channels the ratio d of median particle size of bed material to the transport and frequency weighted mean of median bed load size decreases to unity with increasing drainage area bank full discharge dimensionless stream power and bed material sorting in channels with high values of d significant volumes of fine bed load are transported during discharges that are less than bank full which is commonly associated with general entrainment of the coarse pavement in many gravel bed channels this indicates transport of fine bed load over a more stable substrate of coarser bed material the apparent breakdown in equal mobility of the bed as a whole may be caused by areal segregation of poorly sorted bed material into superiorly sorted patches of varying mean size likely sources of selectively transported fine bed load include fine patches that have low entrainment thresholds and high virtual particle velocities a simple sediment budget applied to measurements from three channels indicates that velocities of material from fine patches in pools relative to velocities of average bed material are high in low order channels and decrease distally as more bed material that represents the bed as a whole is accessed for bed load by deeper annual scour

the incidence and nature of bedload transport during flood flows in coarse grained alluvial channels a continuous record reveals that the incidence of bedload in a coarse grained river channel changes from flood to flood long periods of inactivity encourage the channel bed to consolidate sufficiently so that bedload is largely confined to the recession limb of the next flood wave but when floods follow each other closely the bed material is comparatively loose and offers less resistance to entrainment in this case substantial amounts of bedload are generated on the rising limb this is confirmed by values of bed shear stress or stream power at the threshold of initial motion which can be up to five times the overall mean in the case of isolated floods or those which are the first of the season this produces a complicated relationship between flow parameters and bedload and explains some of the difficulties in establishing bedload rating curves for coarse grained channels besides this the threshold of initial motion is shown to occur at levels of bed shear stress three times those at the thresholds of final motion this adds further confusion to attempts at developing predictive bedload equations and clearly indicates at least one reason why equations currently in use are unsatisfactory bedload is shown to be characterized by a series of pulses with a mean periodicity of 1 7 hours in the absence of migrating bedforms it is speculated that this well documented pattern reflects the passage of kinematic waves of particles in a slow moving traction carpet the general pattern of bedload including pulsations is shown to occur more or less synchronously at different points across the stream channel