hydraulic and sedimentary processes causing anastomosing morphology of the upper columbia river british columbia canada abstract the upper columbia river british columbia canada shows typical anastomosing morphology multiple interconnected channels that enclose floodbasins and lateral channel stability we analysed field data on hydraulic and sedimentary processes and show that the anastomosing morphology of the upper columbia river is caused by sediment bedload transport inefficiency in combination with very limited potential for lateral bank erosion because of very low specific stream power 2 3 w m 2 and cohesive silty banks in a diagram of channel type in relation to flow energy and median grain size of the bed material data points for the straight upper columbia river channels cluster separately from the data points for braided and meandering channels measurements and calculations indicate that bedload transport in the anastomosing reach of the upper columbia river decreases downstream because of lateral channel stability no lateral storage capacity for bedload is created therefore the surplus of bedload leads to channel bed aggradation which outpaces levee accretion and causes avulsions because of loss of channel flow capacity this avulsion mechanism applies only to the main channel of the system which transports 87 of the water and 90 of the sediment in the cross valley transect studied because of very low sediment transport capacity the morphological evolution of most secondary channels is slow measurements and calculations indicate that much more bedload is sequestered in the relatively steep upper anastomosing reach of the upper columbia river than in the relatively gentle lower anastomosing reach with anastomosing morphology and related processes e g crevassing being best developed in the upper reach this confirms the notion of upstream rather than downstream control of upper columbia river anastomosis

alluvial channel hydraulics abstract the development and utilisation of water resources for irrigation hydropower and public supply can be severely affected by sediment where there is a mature and well vegetated landscape sediment problems may be relatively minor but where slopes are steep and vegetation sparse the yield of sediment from the catchment gives high concentrations in the rivers in utilising these resources for whatever purpose an understanding of the hydraulics of alluvial channels is vital the regime of any conveyance channel in alluvium depends on the interrelationships of sediment transport channel resistance and bank stability the regime concept was originally based on empirical relations obtained from observations from canal systems in the indian subcontinent and for many years was surrounded by a certain degree of mystique and much scepticism from academics in more recent years the unabashed empiricism of the original method has been replaced by process based methods which have also served as broad confirmation of the classic regime formulae including their extension to natural channels and meandering channels the empirical approach to the hydraulics of alluvial channels has thus been updated by physically based formulae for sediment transport and resistance though there remains some uncertainty about the third function to complete the definition of slope and geometry latest thoughts in this respect are that the channel seeks a natural optimum state physical modelling using scaled down representations of rivers and estuaries has been used for almost a century but it requires the correct simulation of the relevant processes the coming of a better understanding of the physics of sediment transport and the complexity of alluvial channel roughness leads to the conclusion that only in very restricted circumstances can scale models simulate closely the full size condition however the quantification of these processes has been instrumental in the development of computational models which avoid such scale effects mathematical modelling is nonetheless dependent on the correct application of appropriate process equations within the program as well as reliable boundary conditions and other inputs and sensitive interpretation

development of bed features the concept of unification the opposite of branching theories used in biological sciences is introduced as a new avenue to investigate the behavior of bed features in alluvial channels under unidirectional flow the approach starts with the theoretical concepts initiated by exner according to which the features propagate at speeds inversely proportional to their heights this leads to coalescence and rearrangement of the general pattern of bed features numerical experiments show that an initial large number of arbitrary bed disturbances rapidly reduces to a small number if one feature reaches the maximum height for given flow conditions smaller features pass through it an initial uniform distribution of heights of disturbances slowly changes into a broad distribution of heights with some at the maximum height similar to what is observed in nature

using multi radiotracer techniques to better understand sedimentary dynamics of reworked muds in the changjiang river estuary and inner shelf of east china sea abstract reworked muds including mobile muds resuspended sediments and bio mixed muds are ephemeral layers in the benthic boundary of large river delta front estuaries ldes in this study multiple radiotracers 210pb 137cs 234th 7be 235u 228th 228ra 226ra and 40k were combined to evaluate the sedimentary dynamics of the mud belt on the inner shelf of the east china sea ecs adjacent to the changjiang river estuary we first categorized eight types of typical 210pb profiles in marine sediments and specified which ones could be used as possible evidence of reworked muds the types of 210pb profiles observed in previous studies and this study were then used to examine the depth distribution of reworked mud layers of the benthic boundary of ecs we found that reworked mud depth in the along shore mud belt of the inner shelf of ecs was deeper than those in the outer shelf and slope area reaching up to 150 cm deep in the changjiang river lde and up to 50 cm deep in the zhejiang fujian coast mud area sediment core tracer profiles also showed that the reworked mud layer could be further divided into several sub layers with distinct redox conditions and microbe sulfate reducing bacterial abundance srb abundance intensively fluctuated with changing redox environment and larger abundance values were usually observed in anoxic conditions based on 7be and 234th the top layer ca 2 4 cm thick was the most modern and active zone showing evidence of reworking on seasonal timescales the deeper sections of the reworked mud layer were generally modified over longer timescale years which were examined using the more long lived tracers e g 137cs 228thex and 228ra 226ra ratio we found for the first time in this region that age of the reworked layers was usually much younger than underlying accumulating burial layers we posit that this multi radionuclide approach is critical for evaluating the complex biogeochemical sediment record on delta front estuaries of large rivers subject to changing climate conditions and human impacts over the last several centuries

3d numerical simulation of turbulence and sediment transport within a tidal inlet abstract turbulence and sediment transport models are incorporated into a three dimensional hydrodynamics model to investigate the mechanisms of morphologic evolution of scour holes within the indian river inlet delaware usa the inlet bed had eroded slightly since stabilizing the channel walls in late 1930s through 1976 the mean rate of bed erosion roughly doubled as a response to anthropogenic activities within the inlet such as the removal of 80 piles remaining from an old bridge severe erosion near the in water bridge supports and cofferdams for the replacement bridge necessitated channel bed stabilization that along with the remained debris from the removal of old bridge piles enhanced the growth of two deep scour holes on the bayside and oceanside of the bridge cofferdams scour hole and channel bed evolution has decreased drastically since 1994 the present investigation suggests that initially flow concentration through the cofferdams of the replacement bridge was the main reason for scour hole development bed shear stress over the forward facing slope of the scour hole entrains sediment from the bed and extends the scour hole along the inlet and in the vertical direction flow separation within the developed scour holes after channel bed stabilization enhances turbulence and appears to be the dominant mechanism for further scour hole development

equivalent roughness of alluvial bed the eguivalent roughness of a movable bed is considered relationships are given which can be used to determine the equivalent bed roughness from the bed material size and the bed form dimensions in the case of a plane bed the equivalent roughness is related to the d 9 0 of the bed material based on flume and field data the equivalent roughness may vary from 1 10 d 9 0 similar values were reported by other research workers in the case of bed forms the equivalent roughness is related to the average height and length of the bed forms both flume and field data were used to determine a functional relationship the proposed relationship yields values which are considerably smaller than other existing relationships

morphodynamic modelling for a tidal inlet in the wadden sea abstract a dynamic model for morphological development in a tidal inlet het friesche zeegat in the wadden sea along the northern coast of the netherlands is set up to obtain a better understanding of the behaviour of the morphological system around tidal inlets the model is based on delmor a program package for morphological changes developed at delft hydraulics computations of the flow the sediment transport the initial bed level change rate as well as long term morphological development have been carried out the model has proven to be a useful research tool even though it does not yet reproduce reality in detail

investigations of continuous bed load saltating process particle saltating motions during bed load transport are dominated by the forces acting upon particles and the random process of the particles impacting on and rebounding from the channel bed a real time flow visualization technique is developed in this study to measure particle saltating trajectories corresponding velocities and impacting and rebounding angles based on the experimental data regression equations for the dimensionless saltating length height and velocity were obtained a numerical model that is able to simulate the continuous saltating process of a single particle was developed the model was calibrated and verified with the experimental data and the results were satisfactory the model was also used to generate a series of synthetic data based on these data and the flume data collected by previous investigators a bed load equation was derived

evaluating competing hypotheses for the origin and dynamics of river anastomosis anastomosing rivers have multiple interconnected channels that enclose flood basins various theories potentially explain this pattern including an increased discharge conveyance and sediment transport capacity of multiple channels deltaic branching avulsion forced by base level rise or a tendency to avulse due to upstream sediment overloading the former two imply a stable anabranching channel pattern whereas the latter two imply disequilibrium and evolution towards a single channel pattern in the absence of avulsion our objective is to test these hypotheses on morphodynamic scenario modelling and data of a well documented case study the upper columbia river proportions of channel and floodplain sediments along the river valley were derived from surface mapping initial and boundary conditions for the modelling were derived from field data a 1d network model was built based on gradually varied flow equations sediment transport prediction mass conservation transverse slope and spiral meander flow effects at the bifurcations the number of channels and crevasse splays decreases in a downstream direction also measured sediment transport is higher at the upstream boundary than downstream these observations concur with bed sediment overloading from upstream which can have caused channel aggradation above the surrounding floodplain and subsequent avulsion the modelling also indicates that avulsion was likely caused by upstream overloading in the model multi channel systems inevitably evolve towards single channel systems within centuries the reasons are that symmetric channel bifurcations are inherently unstable while confluenced channels have relatively less friction than two parallel channels so that more discharge is conveyed through the path with more confluences and less friction furthermore the present longitudinal profile curvature of the valley could only be reproduced in the model by temporary overfeeding

numerical modelling of storm and surge events on offshore sandbanks abstract this contribution uses a 3 dimensional coastal area numerical model dhi s mike3 to simulate the impact of storm and surge events on offshore sandbanks three offshore sandbanks in the bristol channel are considered due to the region s sensitivity to anthropogenic pressures and the gradients in wave and tidal forcing in the area two extreme storm and surge events are simulated one co incident with spring tide and the other with neap tide reference simulations of astronomical tidal forcing only are also presented it is shown that for the two sandbanks with greater wave exposure storm conditions can provide a mechanism for the maintenance of crest position for these cases bed level changes over the crest are in the opposite direction compared to astronomically forced change for the least wave exposed bank both wave and tide only cases exhibit similar patterns of bed level change volumetric changes under astronomical forcing are shown to vary with changing maximum tidal current accretion occurs over a neap tidal cycle for all three sandbanks and as maximum tidal current increases the amount of accretion increases however over a spring tidal cycle accretion is observed for the less tidally dominated site but increasing maximum tidal current leads to reduced accretion and then erosion for the most tidally dominated bank volumetric changes under storm conditions are related to sandbank morphology and setting rather than relative wave exposure the two single banks closely tied to headlands show similar magnitude of percentage volumetric change despite being at the two extremes of wave exposure and greater erosion occurs over the neap tide event the sandbank that has associated secondary banks shows lesser percentage change and greater erosion over the spring tide event

quantification of tsunami induced flows on a mediterranean carbonate ramp reveals catastrophic evolution cool water carbonates are the dominant limestones in the mediterranean basin since the early pliocene their deposition typically resulted in ramp morphologies due to high rates of resedimentation several such fossil carbonate ramps are characterised by a bimodal facies stacking pattern where background deposition of subaqueous dune and or tempestite deposits is repeatedly interrupted by anomalously thick sedimentary units dominated by backset stratification formed by supercritical flows a multitude of exceptional triggers e g storms floods tsunamis have been invoked to explain the origin of these supercritical flows which in the absence of a quantitative analysis remains speculative as yet here for the first time the catastrophic evolution of one such mediterranean carbonate ramp on favignana island italy is quantified by combining 87sr 86sr dating outcrop based palaeoflow reconstructions and hydraulic calculations we demonstrate that rare tsunami induced flows occurring on average once every 14 to 35 kyr lasting a few hours only deposited the anomalously thick backset bedded units that form half of the sedimentary record in between such events cumulative two years of storm induced flows deposited the remaining half of the succession by the stacking of subaqueous dunes the two to four orders of magnitude difference in average recurrence period between the two flow types and their associated sedimentation rates emphasises the genetic differences between the two styles of deposition in terms of sediment transport the studied carbonate ramp was inactive for at least 99 of the time with gradual progradation during decennial to centennial storm activity carbonate ramp evolution attained a catastrophic signature by the contribution of rare tsunamis producing short lived high energy sediment gravity flows

mechanism of the progressive failure of non cohesive natural dam slopes abstract progressive failure which begins in the downstream slopes of dams is one of the main failure modes for natural dams in the field however this failure mode lacks attention in the scientific literature especially regarding its formation mechanism in this paper flume tests were conducted to simulate the progressive failure of a natural dam the results show that the progressive failure process is induced by seepage water discharging on the downstream slope including the erosion of individual soil particles repeated minor slip failures upward head cutting erosion of the dam crest and finally the collapse of the dam when the processes have evolved sufficiently this study focuses on analyzing the initiation mechanism of soil particle migration the influence of seepage and interflow stresses on the incipient erosion of soil particles is analyzed in addition the buoyancy of soil particles on the downstream slope surface is not considered in the vertical direction in this paper but in the direction perpendicular to the downstream slope surface the paper also discusses how to estimate the occurrence of the progressive failure of a natural dam in the estimation method the stress of the interfacial flow the seepage flow stress and the friction stress of the soil particles are considered when the phreatic line reaches the downstream slope surface

variations in sediment wave dimensions across the tidally dominated irish sea nw europe abstract new high resolution multibeam echosounder data have been collected in the irish sea in the last decade sediment waves oriented transverse to tidal flow dominate many parts of the irish sea and exhibit an almost continuous spectrum of heights and spacings sediment wave growth remains poorly quantified and from the irish sea swath bathymetry data many bedform dimensions have been measured and examined statistically a strong positive power correlation between sediment wave height and spacing was observed s 0 0692 0 8020 n 935 r 0 853 while height and spacing only weakly vary with water depth to assess the main factors influencing sediment wave height and spacing deviations from the typical hydrodynamically analogue sediment wave geometry in equilibrium are qualitatively and semi quantitatively investigated in the irish sea in conjunction with seabed characteristics coarser sediment generally forms larger sediment waves while suppressed sediment growth is found likely due to the limitations in mobile sediment supply and inefficiency of very coarse bedload transport

sediment response to tsunami loading mechanisms and estimates tsunami effects on soil stability are evaluated by imposing hypothetical but typical tsunami loads on an idealised beach condition of a plane beach with homogeneous sediments under this model tsunami condition the extent of sediment motion in the form of bed load and suspended load on the beach is demonstrated sediment motions are particularly significant in the nearshore area between the initial shoreline and the maximum tsunami drawdown during the drawdown phase pore pressure gradients develop by rapid reduction in water pressure on the bed creating soil instability and triggering momentary liquefaction in some locations such effects of pore pressure gradients are quantitatively evaluated with a proposed modified shields parameter the analysis used for the model tsunami case is further applied to laboratory data and real field data collected in kesen numa japan during the 2011 east japan tsunami

the role of floodplain width and alluvial bar growth as a precursor for the formation of anabranching rivers abstract anabranching rivers are defined as a system of multiple channels separated by stable alluvial islands while substantial progress has been made in developing a physics based understanding of what drives the differences between meandering and braided river channels anabranching rivers have not been well integrated into these models here we propose that alluvial bar growth on the floodplain may be a precursor for the formation of anabranching rivers alluvial bar growth strongly depends on the aspect ratio of the flow width divided by depth and rivers with wide floodplains have flows with a large aspect ratio consistent with this idea remotely sensed measurements of floodplain width of four rivers from different climatic and tectonic settings show that anabranching river patterns are often associated with relatively wide floodplains to explore the physics behind that empirical relationship we carried out two sets of morphodynamic numerical simulations using boundary conditions from field scale modern anabranching rivers spanning different climatic and geologic settings as well as hypothetical floodplain widths results from the simulations show that for a given flood discharge widening the floodplain changes the river pattern from single channel to multi threaded with mobile bars to multi channeled with immobile islands multi channeled patterns arise because the emergence of bars causes flow bifurcation subsequent bifurcation instability leads to the emergence of multiple stable channels as the channels increase their cross sectional area shields stresses on intervening bars are reduced until the bars stabilize into islands we suggest that the presence of stable islands allows vegetation to grow or cohesive sediment to accumulate leading to enhanced channel bank strength and a stable anabranching pattern our results suggest that alluvial bar growth can be a precursor to formation of anabranching rivers compared with field measurements our simulations accurately predict the number of active channels to within 20 which seems to support the idea that some anabranching rivers may originate from alluvial bar growth

critical conditions of incipient motion of cohesive sediments the critical condition of incipient motion of cohesive sediments was investigated in a laboratory study one hundred experimental runs were performed with sediment samples by varying the yield stress to determine the relationship between the critical condition of incipient motion and the rheological properties of the cohesive sediments the results indicate that yield stress is a factor that has a major influence on the incipient motion of cohesive sediments in addition the critical shields parameter is found to be exponentially proportional to the yield stress and inversely proportional to the median grain size the effect of yield stress on the critical shields parameter is significant for the cohesive sediments and becomes progressively weaker with increasing median grain size furthermore an empirical formula for calculating the critical shields parameter of cohesive sediments that includes a rheological term and a gravity term is proposed by introducing the yield stress according to this formula a modified shields diagram is obtained in which the values of the critical shields parameter for cohesive sediments vary within a band that contains countless curves instead of on a single line to reflect the influence of the yield stress this modification of the traditional shields curve is effective for fine sediments but the effects tend to vanish for coarse sediments as the behavior of sediments changes from cohesive to non cohesive finally potential further investigations are discussed

measuring bedload sediment transport with an acoustic doppler velocity profiler abstractacoustic doppler velocity profilers advp measure the velocity simultaneously in a linear array of bins they have been successfully used in the past to measure three dimensional turbulent

active interactions between turbulence and bed load conceptual picture and experimental evidence 1 this paper reports results from experiments with simultaneous measurement of areal bed load sediment concentration and water velocity horizontal and vertical components made at 1 5 particle diameters above the mean bed the same spatial and temporal scales were employed to measure the kinematic properties of flowing water and sediments the obtained data covering a range of low sediment discharges were analyzed in terms of bulk statistics autocorrelation and cross correlation functions and quadrant decomposition of fluctuations at the lowest transport rates the motion of sediment particles was found to be mostly associated with sweep events however with increasing flow rate and bed load discharge the process mechanics changed and the transport of sediments was also found to be significantly correlated with ejections the obtained results are integrated into a conceptual picture attempting to bridge previous depictions of the bed load transport mechanics

transport rate of calcareous sand in unidirectional flow this paper examines the transport of calcareous sand in unidirectional flow and its prediction through existing sediment transport models a flume experiment of four sand samples collected on oahu hawaii provides 29 sets of sediment transport data in the bed form and suspended transport stages the measured transport data are compared with direct predictions from four energy based transport models developed for siliceous particles corrections for the grain size fall velocity and critical velocity of calcareous sand based on recent research are applied to the models and the results are compared with the direct calculations and measured data the comparison illustrates the important role particle shape plays in the transport of calcareous sand all four sediment transport models give consistent predictions and good agreement with the majority of the measured data two of the models respond positively to the corrections in both the bed form and suspended transport stages indicating that such an approach may provide an interim solution for the transport of calcareous sand

a description of water and sediment flow in the presence of obstacles with a two dimensional lattice bgk cellular automata model 1 the spatial distribution of water and sediment flow in the presence of obstacles on the soil surface is described with a coupled two dimensional lattice bgk the bhatnagar groos and krook version of the lattice boltzmann equation cellular automata model the model reproduces the main water flow characteristics of the bunte and poesen 1993 experiment well as well as the mean runoff velocity the model also approximates the main features of local scouring and sediment yield of the experiment although the results obtained in two dimensions are encouraging the consideration of the erosive action of the vortexes on a plane perpendicular to the bed would improve the characterization of the scouring patterns in the stagnation points developed upstream from the obstacles index terms 1815 hydrology erosion and sedimentation 1860 hydrology runoff and streamflow 1869 hydrology stochastic processes keywords flow erosion obstacles lattice bgk model cellular automata model

coarse sediment particle motion under highly asymmetrical waves with implications for swash zone sediment transport abstract hydrodynamics and sediment transport in the swash zone are unique and very complex phenomena acquiring a robust model for predicting sediment motion in the swash zone requires in depth insight about the behavior of sediment particles in highly asymmetric and turbulent waves that continuingly uprush the beach face and retrieve in backwashes in order to consider a physical system of the coarse particle motion in the swash zone with a reduced number of external parameters and capture some of the realism of the situation the experiments are conducted in rather simple conditions to provide some information about the particle responses in terms of jump length against asymmetric waves to be implicated for the swash zone the results show that despite reduction of many external parameters jump length is still a highly skewed stochastic parameter the probability distribution of jump length is quite wide large variance and skewed different from that of saltation length in steady unidirectional flow in which the distribution is close to normal considering integral of excess energy of an arbitrary single wave over its duration as a rational and meaningful representative of flow condition the average jump length j l incremental trends reduces in the higher energy condition resulting in a linear trend in logarithmic scale the j l s due to higher turbulent kinetic energy follow similar trend of less turbulent flow conditions

subaqueous barchans and plane beds from deposition of quartz silt abstractthe suspension flow of quartz silt geometric mean grain size of 4 15 m in unfavorable conditions for deposition is the motivation for the development of different bed morphologies particles deposit over a plane nonerodible surface and develop well defined barchan ripples barchanoids and plane beds in flume experiments bedload transport of quartz silt by bedform migration is several orders of magnitude smaller than the suspended transport the final bed morphology is controlled by the suspended sediment concentration and running time of the experiment the average dimensions of the bedforms after 1 day experiments are 4 93 cm wide 10 33 cm long and 0 45 cm high cohesive plane beds appear after 2 day and 3 day experiments with very high sediment concentrations 22 5 kg m3 viscous effects are deemed relevant for the formation of the beds

effect of sediment transport boundary conditions on the numerical modeling of bed morphodynamics abstractexperimental sediment transport and river morphologic studies in laboratory flumes can use two sediment supply methods an imposed feed at the upstream end or a recirculation of sediment f

fully coupled unsteady mobile boundary flow model a fully coupled one dimensional river model capable of predicting sediment transport and bed level changes under unsteady flow conditions is described the governing equations for mass and momentum balance of sediment water mixture under unsteady flow conditions in natural rivers with irregular geometries are solved simultaneously using the preissmann four point linear implicit scheme with weighting factors for space and time coordinates the resulting system of algebraic equations is solved using a solution procedure that bridges upstream and downstream boundary nodal values by successive substitutions the friction slope is expressed in a consistent form that allows the consideration of the changing alluvial roughness effect the system of governing equations is explicitly coupled by introducing the term representing the rate of change of bed level the fully coupled unsteady mobile boundary flow model fcm is applied to the classical problem of sediment deposition upstream of a dam with an arbitrar

supplementary data confirming the relationship between critical shields stress grain size and bed slope this article presents new experimental data on threshold conditions for motion of coarse uniform sediments the experiments were conducted with 2 8 mm gravel in a 7 5 m long by 0 3 m wide flume and included measurements of hydraulic characteristics and rate of bed particle movement for a range of flows at different bed slopes a reference transport method was used to define the beginning of sediment motion results from experiments with glass balls diameters 6 and 9 mm and coarse uniform gravels 17 5 and 38 6 mm conducted by other researchers were used as an additional independent data set the experimental data confirm the recent finding that the critical shields stress for motion of coarse uniform sediment varies with both grain size and bed slope copyright 2007 john wiley sons ltd

mathematical modeling of suspended sediment in nonuniform flows a two dimensional vertical mathematical model for suspended sediment is presented the model is based on the width integrated convection diffusion equation for the sediment particles including settling effects the local fluid velocities and mixing coefficients are described by a new so called profile model which is based on the application of flexible profiles to represent the vertical distribution of the basic variables measured and computed velocities of strongly nonuniform flows were used for calibration of the profile model a stochastic approach is introduced to represent the sediment input at the bed a bed concentration or an upward sediment flux can be specified optional the convection diffusion equation is solved by a finite element method which proved to be better than a finite difference method an extensive sensitivity analysis is presented to show the influence of the main controlling parameters of the model finally a verification analysis is presented using flume and field data of dredged trenches

analysis of environmental controls on tsunami deposit texture abstract tsunamis transport large amounts of sediment and can leave recognisable signatures in the landscape the form and composition of onshore tsunami deposits are a function of wave dynamics sediment availability and characteristics of the local environment the latter of which also partially controls preservation of the deposit this research reviews these relationships in a global context and assesses the connection between tsunami deposit particle size and four controlling parameters climate temperature and rainfall density of tsunami sediments degree of coastal protection and distance between tsunami source and sediment deposition an international dataset of tsunami deposit locations and texture was compiled from published literature and existing databases values for environmental variables were calculated for each location from global datasets of temperature rainfall coastline shape and tsunami source locations spearman s rank order correlation principal component analysis pca and hierarchical cluster analysis ca were used to analyse relationships between these variables pca results show an inverse relationship between particle size and sediment density climate variables and distance from source ca results support this suggesting a cluster structure controlled primarily by particle size and secondly by climate and sediment density these relationships can be explained by the influence of the environment on antecedent morphology and the composition of sediments available for tsunami transport

morphodynamics of intermittent coastal lagoons in southern spain zahara de los atunes abstract coastal lagoons are valuable water bodies since they are of great ecological and economic interest throughout the world their existence is controlled by variations in sea level and the geological substrate of their location their morphology is linked to local topography alternation of high and low pressure the presence of a river as well as tidal regime all these factors influence lagoons along the coastline in the south of spain the main morphological characteristics of such lagoons are the following intermittence one dimensional morphology small size shallow waters high area depth ratio no flood or ebb tide deltas overwash of their low barriers during storms high evaporation rates and feeding by rivers effective management of these systems requires the evaluation not only of their hydrodynamics and opening and closure rate but also the prediction of possible future scenarios as a response to meteorological events this paper describes the behavior of a coastal lagoon in zahara de los atunes cadiz by means of a numerical model implemented with the objective of serving as a tool for optimizing the coastal zone management although the coastal lagoon at zahara de los atunes is closed most of the year it is artificially opened at the beginning of the summer the results of our study showed that during this period the lagoon is flood dominated with a pumping mode response it naturally tends to close since it is a trap for littoral drift sediments the precise date of closure depends on the events that take place during the autumn which determine whether the sediments deposited in the inlet by the littoral drift are flushed out by the river flow or flushed in by the waves

sediment transport of fine sands at high velocities the predictive capability of the sediment transport formulas of ackers white engelund hansen and van rijn at high flow velocities is investigated total load transport at high velocities over a fine sand bed 100 400 m is studied by analyzing data from the literature and data from new flume and field measurements flume experiments were performed to measure flow velocity and sand concentration profiles in a self eroding flow initially free of sediment the flow velocities were up to 2 7 m s a two dimensional vertical mathematical model for suspended sediment was applied to compute the equilibrium transport rates finally predicted transport rates are compared with measured transport rates under flume and field conditions the formulas of engelund hansen and van rijn predict transport rates that are in reasonable agreement with the measurements

analysis of the time averaged properties of sediment motion in a local scour process 1 we examined the kinematics of sediment particles in the proximity of a vertical plate attached to the side wall of a pressurized duct the laboratory phenomenon investigated was archetypal of local scour near bridge abutments in covered rivers we conducted a clear water scour experiment where we measured the temporal evolution of the local erosion depth the latter was found to follow a logarithmic trend the concentration and velocity of the moving particles were measured on the basis of digital movies taken at various evolution stages of the process the spatial pattern of the sediment motion showed that the action of the principal vortex system becomes progressively more evident with the general lowering of the sediment transport intensity detected as the scour hole increases in time furthermore the phenomenology of local sediment transport was analyzed key findings of the research include 1 the time averaged values of the sediment transport rate are linked with those of concentration and velocity through relationships which are almost invariant regardless of the experimental time and of the location within the scour hole 2 intermittency and irregularity of the sediment fluxes increase as their mean intensity decreases 3 the relative weight of the temporal fluctuations of concentration and velocity in the time mean sediment transport activity is significant throughout the entire process potential implications of the present results for the modeling of local scour processes in pressurized flow conditions are discussed the considerations made are likely to have analogous applicability to local scour with a free surface since the large scale evolutions of the erosion depth in the two conditions may not be greatly different given the qualitative analogy of the present findings with earlier ones obtained for one dimensional bed load it is suggested that similar considerations may hold also for the small scale modeling of a wider class of sediment transport processes

punctuated sand transport in the lowermost mississippi river 1 measurements of sand flux and water flow in the mississippi river are presented for a portion of the system 35 50 km upstream from the head of its subaerial delta these data are used to provide insight into how nonuniform flow conditions present in the lower reaches of large alluvial rivers affect the timing and magnitude of sand transport near the river outlet field surveys during both low and high water discharge include 1 sequential digital bathymetric maps defining mobile river bottom topography which were used to estimate bed material flux 2 multiple water velocity profiles and 3 multiple suspended sediment profiles collected using a point integrated sampler these data show that total sand transport increases by two orders of magnitude over the measured range in water discharge 11 300 to 38 400 m3 s 1 during low water discharge no sand is measured in suspension and sand discharge via bed form migration is minimal during high water discharge 54 of the sand discharge is measured in suspension while 46 of the sand discharge is part of bed form migration the component of boundary shear stress associated with moving this sediment is estimated using a set of established sediment transport algorithms and values for the total boundary shear stress are predicted by fitting logarithmic velocity functions to the measured profiles the estimates of boundary shear stress using measurements of suspended sand transport bed form transport and downstream oriented velocity profiles are internally consistent moreover the analyses show that boundary shear stress increases by nearly 10 fold over the measured water discharge range we show how this increase in shear stress is consistent with backwater flow arising where the river approaches its outlet the hydrodynamic properties of backwater flow affect the timing and magnitude of sand flux and produce punctuated sand transport through the lowermost mississippi river our field data are used to evaluate the influence of this sand transport style on development of the mixed bedrock alluvial channel for the lowermost mississippi river

gravel saltation 2 modeling a lagrangian model for the motion of a sediment particle in a water flow is proposed the particle motion equation is averaged over flow turbulence specialized to the case of coarse sediment particles saltating in water and coupled with a stochastic model for particle collision with the bed model predictions of statistics of gravel saltation generally agree well with experimental observations as an application of the saltation model bed load transport rates are estimated from modeled mean saltation streamwise velocity and a dynamic friction coefficient the results obtained compare favorably with typical bed load equations but they overestimate experimental measurements of gravel transport which would suggest that a bagnoldean formulation for bed load transport of coarse material by saltating particles may not be valid

near bed sediment concentration distribution and basic probability of sediment movement sediment concentration distribution and the basic probability of sediment movement near the channel bed are two of the most important and fundamental issues in the study of sediments based on statistical analysis and considering the transport mechanisms the rules of sediment concentration distribution near a channel bed are studied analytical expressions for the near bed sediment concentration distribution and mean sediment concentration are derived and the expression for the mean sediment concentration near the bed is verified by measured data which were obtained from previous experiments with the help of statistical theory the expressions of basic probabilities i e rolling saltating and suspending probabilities for sediment movement near the bed are also derived the expression for starting probability is verified by the measured data the verification shows that the results from the proposed expression agree well with the measured data this research has both theoretical and practical significance for further investigation concerning rules of bed load and suspended sediment transport

initial stages of erosion and bed form development in a turbulent flow around a cylindrical pier 1 bed load transport and erosion in fine sediment beds are mainly driven by the dynamics of the near bed turbulent flow in situations when the shear stress is not sufficiently high to produce significant transport the presence of an obstacle can initiate erosion and trigger the development of bed forms which are produced by the emergence of the turbulent horseshoe vortex thv system we develop a numerical model to investigate the initial stages of erosion and the development of ripples produced by the thv system in the vicinity of a surface mounted cylindrical pier the flow is simulated using the detached eddy simulation approach which has been shown to accurately resolve most of the turbulent stresses produced by the thv to compute the erosion the exner equation is coupled to a new bed load transport model that directly incorporates the effect of the instantaneous flow field on sediment transport the morphodynamic model is integrated simultaneously with the flow equations using an arbitrary lagrangian eulerian method for moving boundaries even though the time rate of scour is slower compared to the observations the computed results exhibit essentially all the dynamics of erosion including the emergence of ripples reported in the experiments of dargahi 1990 the bed forms show similar velocities as reported in the experiments and are shown to be statistically similar to ripples measured in laboratory experiments and in nature to our knowledge this is the first three dimensional simulation to capture the ripple dynamics that evolve naturally from the nonlinear interactions between the flow and the bed

sediment transport on arbitrary slopes simplified model the paper presents a study on the influence of gravity on the incipient motion and the bed load transport of sediment the computation of critical bed shear stress is revisited considering the balance of forces hydrodynamic forces and submerged self weight acting on a solitary sediment particle lying on an arbitrary sloping bed modified effective bed shear stress and the corresponding critical bed shear stress which are defined to assess the incipient motion of sediment in the direction of resultant force are applied for the estimation of bed load transport rate in the direction of resultant force the sediment transport induced by the gravitational force which is oblique to the direction of the drag force induced by flow is incorporated into the bed load transport equation this modified model provides a reasonable prediction of the critical bed shear stress and the bed load transport rate the model is validated by experimental data it can be applied to steep slopes and can also avoid the problem of singularity that arises in numerically calculation of sediment transport rate additionally the vectorial transport rate obtained in the model calculation can be implemented in a numerical simulation of channel bed evolution

sand grain threshold in relation to bed stress history an experimental study besides particle size density and shape the erodibility of a sediment bed depends also upon the exposure to prethreshold velocities in the overlying flow such flow effectively rearranges the grains at and below the bed surface causing them to become more resistant to subsequent erosion the effects of the stress history leading up to the critical condition for sediment movement are investigated for unidirectional flows generated in a recirculating laboratory flume the sediment beds investigated consisted of cohesionless quartz sand grains with mean grain diameters of 0 194 mm fine sand 0 387 mm medium sand and 0 774 mm coarse sand with narrow particle size distributions the critical threshold shear velocity target value for the three beds was established within 2 5 min of increasing the flow from zero velocity the subsequent experiments were performed under prethreshold velocities at 70 for 5 10 20 40 and 80 min exposure duration 80 for 5 10 20 40 and 80 min exposure duration 90 and 95 for 5 10 20 40 80 and 120 min exposure duration of the target value following exposure to these different prethreshold conditions the flow was increased then to reach actual critical conditions within a period of 2 5 min the critical condition for the initiation of sediment movement was established using visual observation supplemented by video recordings according to the yalin criterion the results show that if the exposure duration to prethreshold velocities remains constant then the critical shear velocity increases with increasing prethreshold velocity likewise if the prethreshold velocity remains constant then the critical shear velocity increases with increasing exposure duration in some circumstances the critical shear velocity was found to increase by as much as 27 an empirical formula is proposed to account for the exposure correction to be applied to the critical shear velocities of sand sized sediment beds this is prior to their inclusion into bedload transport formulae for an improved prediction of the magnitude and nature of transport

variability of shallow overland flow velocity and soil aggregate transport observed with digital videography field experiments at tiramoana station 30 km north of christchurch new zealand using an erosion plot 16 5 m long 0 6 m wide and with a slope of 14 14 5 on rendzina soil aimed to measure the variability of flow velocity and of soil aggregates transport rate in shallow overland flow discharge cross section area ratio was used to estimate mean velocity and high speed digital video camera and image analysis provided information about flow and sediment transport variability six flow runs with 0 5 3 0 l s 1 discharges were supercritical with froude numbers close to or more than 1 mean flow velocity followed poiseuille law float numbers were more than 1 5 and hydraulic resistance was an inverse proportional function of the reynolds number which is typical for laminar flows hence actual velocity varied through time significantly and the power spectrum was of red noise which is typical for turbulent flow sediment transport rates had even higher variability and soil aggregates transport was a compound poisson process copyright 2008 john wiley sons ltd

breaching in a wave dominated barrier spit the trabucador bar north eastern spanish coast the trabucador bar is a barrier coast linking the main lobe of the ebro delta with its southern spit this coastal stretch which may be considered as a microtidal transgressive barrier is the most vulnerable area of the deltaic coast to storm induced geomorphologic changes during the second week of october 1990 a severe storm affected the ebro delta causing serious erosion in which the trabucador bar was one of the most damaged zones a breach 800 m long and with a maximum depth of 0 4 m below the mean water level was created during the breaching process approximately 70 000 m3 of sand were removed from the subaerial barrier in a few hours three factors are normally responsible for the loss of sediment longshore transport gradient offshore transport and overwash processes most of the eroded sediment 60 000 m3 was transported towards the inner bay due to overwash processes the post storm recovery of the zone was slow and far from complete as the breach remained a conduit for onshore sediment transport under a regime of breaking and reforming waves an artificial dune was subsequently constructed to close the breach and thus allow beachface recovery

application of 3d mobile bed hydrodynamic model the prediction of sediment erosion and deposition magnitudes has challenged many investigators one and two dimensional sediment transport models are commonly used for predicting sediment scour and deposition they are adequate for many engineering applications however for some problems only a three dimensional model should be used a three dimensional model is necessary for predicting sediment erosion and deposition whenever significant secondary currents exist such as in river bends crossings distributaries or diversions in diversions for example the sediment load may not split in the same proportions as the flow a three dimensional model can be used to estimate the sediment split this paper presents a description of the three dimensional numerical model ch3d sed and the governing equations for the model the validation of the model and its application to the deep draft navigation project on the lower mississippi river also are presented

measuring bed load transport rates by grain size fraction using the swiss plate geophone signal at the erlenbach abstractthe swiss plate geophone system is a bed load surrogate monitoring technique that is used to quantify bed load transport in steep streams the amplitude of the signal recorded by the swiss plate geophone contains information about the grain size distribution of the transported bed load to extract this information the authors computed the number of impulses and packets representing a single particle impact registered for different amplitude ranges the so called amplitude histograms for 46 samples when bed load was measured independently with automatic basket samplers at the erlenbach amplitude histograms can be interpreted as a statistical distribution of the signal s amplitude over a given time interval using the number of bed load particles per unit mass absolute bed load masses for each grain size class can be calculated the results show that the grain size distribution of the transported bed load for particles larger than 9 5 mm can be continuously monitored at the erlenbach with the

detailed simulation of morphodynamics 2 sediment pickup transport and deposition the paper describes a numerical model for simulating sediment transport with eddy resolving 3 d models this sediment model consists of four submodels pickup transport over the bed transport in the water column and deposition all based on a turbulent flow model using large eddy simulation the sediment is considered as uniform rigid spherical particles this is usually a valid assumption for sand bed rivers where underwater dune formation is most prominent under certain shear stress conditions these particles are picked up from the bed due to an imbalance of gravity and flow forces they either roll and slide on the bed in a sheet of sediment or separate from the bed and get suspended in the flow sooner or later the suspended particles settle on the bed again each of these steps is modeled separately yielding a physics based process model for sediment transport suitable for the simulation of bed morphodynamics the sediment model is validated with theoretical findings such as the rouse profile as well as with empirical relations of sediment bed load and suspended load transport the current model shows good agreement with these theoretical and empirical relations moreover the saltation mechanism is simulated and the average saltation length height and velocity are found to be in good agreement with experimental results

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

experimental study on coarse grain saltation dynamics in bedrock channels saltation of bed load particles on bedrock surfaces is important for landscape evolution and bedrock incision in steep landscapes however few studies have investigated saltation in bedrock channels where unlike alluvial channels the bed roughness height and the sediment size may be independent to address this data gap we measured the saltation hop height hop length and velocity of gravel saltating over a planar bed using 80 160 readings from high speed photography and direct measurements two separate dimensional analyses are used one leading to a bed shear stress scaling and another leading to a froude number fr scaling our new saltation data coupled with numerous data from previous studies suggest that both shear stress and fr scaling analyses are valid in characterizing bed load saltation dynamics with bed roughness ranging from smooth to alluvial beds however the fr approach has the advantages that 1 there is no need to estimate a critical shields stress c which alone can vary up to 2 orders of magnitude e g 0 001 0 1 due to changes in relative bed roughness and slope and 2 the fr based scaling fits the saltation data set better in a least squares sense results show that the saltation velocity of bed load is independent of grain density and grain size and is linearly proportional to flow velocity saltation height has a nonlinear dependence on grain size saltation length increases primarily with flow velocity and it is inversely proportional to submerged specific density our results suggest that either c or bed roughness coefficient must be properly estimated to yield accurate results in saltation abrasion models

acoustic bed velocity and bed load dynamics in a large sand bed river 1 development of a practical technology for rapid quantification of bed load transport in large rivers would represent a revolutionary advance for sediment monitoring and the investigation of fluvial dynamics measurement of bed load motion with acoustic doppler current profilers adcps has emerged as a promising approach for evaluating bed load transport however a better understanding of how adcp data relate to conditions near the stream bed is necessary to make the method practical for quantitative applications in this paper we discuss the response of adcp bed velocity measurements defined as the near bed sediment velocity detected by the instrument s bottom tracking feature to changing sediment transporting conditions in the lower missouri river bed velocity represents a weighted average of backscatter from moving bed load particles and spectral reflections from the immobile bed the ratio of bed velocity to mean bed load particle velocity depends on the concentration of the particles moving in the bed load layer the bed load layer thickness and the backscatter strength from a unit area of moving particles relative to the echo strength from a unit area of unobstructed bed a model based on existing bed load transport theory predicted measured bed velocities from hydraulic and grain size measurements with reasonable success bed velocities become more variable and increase more rapidly with shear stress when the transport stage defined as the ratio of skin friction to the critical shear stress for particle entrainment exceeds a threshold of about 17 this transition in bed velocity response appears to be associated with the appearance of longer flatter bed forms at high transport stages

sediment transport part i bed load transport a method is presented which enables the computation of the bed load transport as the product of the saltation height the particle velocity and the bed load concentration the equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity experiments with gravel particles transported as bed load are selected to calibrate the mathematical model using the lift coefficient as a free parameter the model is used to compute the saltation heights and lengths for a range of flow conditions the computational results are used to determine simple relationships for the saltation characteristics measured transport rates of the bed load are used to compute the sediment concentration in the bed load layer a simple expression specifying the bed load concentration as a function of the flow and sediment conditions is proposed a verification analysis using about 600 alternative data shows that about 77 of the predicted bed load transport rates are within 0 5 and 2 times the observed values

unified view of sediment transport by currents and waves i initiation of motion bed roughness and bed load transport attention is given to the properties of sediment beds over the full range of conditions silts to gravel in particular the effect of fine silt on the bed composition and on initiation of motion critical conditions is discussed high quality bed load transport data sets are identified and analyzed showing that the bed load transport in the sand range is related to velocity to power 2 5 the bed load transport is not much affected by particle size the prediction of bed roughness is addressed and the prediction of bed load transport in steady river flow is extended to coastal flow applying an intrawave approach simplified bed load transport formulas are presented which can be used to obtain a quick estimate of bed load transport in river and coastal flows it is shown that the sediment transport of fine silts to coarse sand can be described in a unified model framework using fairly simple expressions the proposed model is fully predictive in the sense that only the basic hydrodynamic parameters dep

identifying dynamic equilibrium of an undeveloped alluvial stream by extremal hypotheses abstract the indeterminate channel problem arises from uncertainty in finding a closure relation for alluvial channels created by self organizing erosional and depositional processes extremal hypotheses have been proposed as one potential approach to closing the system of governing equations for alluvial channels many different extremal hypotheses have been presented but no substantive evidence has been developed to select which hypothesis may be most appropriate for natural alluvial river systems this paper evaluates the ability of ten extremal hypotheses to identify dynamic equilibrium across a geomorphic gradient in the remote and undeveloped mid latitude watershed of rio murta chile this study a introduces extremal hypotheses b describes the field site and geomorphic conditions and c examines which extremal hypotheses are supported by the field data in identifying the evolutionary trend toward dynamic equilibrium the extremal hypotheses that identified dynamic equilibrium within the geomorphic gradient in the field are 1 minimum kinetic energy 2 minimum specific stream power 3 maximum friction factor and 4 maximum total friction factor which collectively support minimizing kinetic energy of the system

tail structure and bed friction velocity distribution of gravity currents propagating over an array of obstacles the bed friction velocity distribution and sediment entrainment potential of boussinesq compositional gravity currents propagating over a series of obstacles and over a smooth surface respectively are analysed based on high resolution three dimensional large eddy simulations the investigation focuses on the parameter regime for which currents with a high volume of release go through an extended slumping phase with approximately constant front velocity tokyay constantinescu meiburg j fluid mech vol 672 2011 570 605 under these conditions a quasi steady regime is reached between consecutive obstacles that is similar to the steady regime observed for constant density channel flows over bottom obstacles at a given location this quasi steady regime is reached in the tail of the current after the passage of the front and the associated hydraulic jumps reflected from the first few downstream obstacles a double averaging procedure is employed to characterize the global changes in the structure of the tail region between currents with a high volume of release propagating over smooth surfaces and over obstacles reynolds number induced scale effects on the flow and turbulence structure within the tail region are discussed in some detail the presence of this quasi steady regime is significant since the simulations with obstacles show that most of the sediment is entrained by the tail of the current rather than by its front a detailed analysis of the effects of the obstacle shape on the quasi steady mean flow and turbulence structure is presented which provides insight into why gravity currents over dunes can entrain more sediment than gravity currents over ribs of comparable size finally the bed friction velocity distributions and the potential to entrain sediment are compared for a compositional current with a high volume of release during the slumping phase and a current with a low volume of release for which transition to the buoyancy inertia phase occurs a short time after the release of the lock gate

wave actions and topography determine the small scale spatial distribution of newly settled asari clams ruditapes philippinarum on a tidal flat there are many studies on spatial distributions of asari clam ruditapes philippinarum adults on tidal flats but few have dealt with spatial distributions of newly settled asari clam 0 3 mm shell length indicative of settlement patterns in relation to physical topographical conditions on tidal flats we examined small scale spatial distributions of newly settled individuals on the matsunase tidal flat central japan during the low spring tides on two days 29th 30th june 2007 together with the shear stress from waves and currents on the flat the characteristics of spatial distribution of newly settled asari clam markedly varied depending on both of hydrodynamic and topographical conditions on the tidal flat using generalized linear models glms factors responsible for affecting newly settled asari clam density and its spatial distribution were distinguished between sampling days with crest sites always having a negative influence each on the density and the distribution on both sampling days the continuously recorded data for the wave current flows at the crest site on the tidal flat showed that newly settled asari clam as well as bottom sediment particles at the crest site to be easily displaced small scale spatial distributions of newly settled asari clam changed with more advanced benthic stages in relation to the wave shear stress

development of subaqueous barchanoid shaped dunes due to lateral grain size variability in a tidal inlet channel of the danish wadden sea development of barchanoid shaped dunes

stochastic prediction of sediment transport in sand gravel bed rivers classical deterministic bedload transport predictors are applied to sand gravel bed rivers the turbulent bed shear stress is modeled according to a probability distribution to obtain realistic bedload transport rates at incipient motion in extending the predictors to stochastic predictors for nonuniform sediment many parameters that represent near bed turbulence and the particle size distribution must be chosen the parameters that give realistic results are chosen by analyzing the results of a new experimental flume dataset with relatively large water depths choosing other combinations of parameters may give equal total bedload transport rates but at the cost of large errors in fractional transport rates attention is given to the hiding exposure phenomenon and a hindrance effect related to nonuni form sediment validation based on two independent field datasets shows that successful predictions of particle sizes near the threshold for motion are feasible using the stochastic approach while the deterministic approach gives successful predictions well above incipient motion

bed load coefficients a methodology is developed for evaluation of bed load transport based on the analytical solution presented in a previous publication the present day knowledge of this subject is such that it required empirical determined coefficients to evaluate bed load transport the equation proposed here does not have a coefficient therefore it has been used to calculate meyer peter and muller s coefficient as well as smart s shields and bagnold s bed load coefficients the application of the proposed equation is investigated under different kinds of conditions and it has been tested satisfactorily the close agreement between predicted and measured values allow for several different transport equations to be compared to each other by defining coefficients these comparisons suggest why some transport relations work better in some instances than in others

deterministic coastal morphological and sediment transport modeling a review and discussion 1 modern coastal ocean modeling systems are now capable of numerically simulating a variety of coastal and estuarine problems and can thus provide useful information for managing coastal zones here we review state of the art eulerian implementations of bottom up sediment transport and morphological change in coastal ocean hydrodynamic models in order to investigate the fate of suspended sediment in coastal and estuarine waters as well as the evolution of sea or river beds sediment dynamics need to be represented at a scale relevant to the numerical discretized solution and significant effort is devoted to parameterize sediment processes we discuss boundary layer hydrodynamics and the computation of the bed shear stress we also focus on approaches used to represent near bed processes such as bed load transport and sediment erosion and deposition sediment diffusivities settling velocities and cohesive processes such as flocculation all have an impact on suspended sediment throughout the water column we then describe the implementation of process parameterizations in coastal hydrodynamic models explicitly reviewing five widely used systems the approaches implemented in these coastal models may present distinct strengths and shortcomings with regard to some important issues for coastal zones both numerical and physical while these detailed limitations need to be considered as part of model assessment more general issues also hinder present state of the art models in particular sediment transport is inherently highly empirical which is further compounded by issues arising from turbulence closure schemes we conclude by suggesting some possible directions toward improving sediment dynamics understanding and coastal scale predictive ability

alluvial fans formed by channelized fluvial and sheet flow i theory alluvial fans and fan deltas are of three basic types those built up primarily by the action of constantly avulsing river and stream channels those constructed by sheet flows and those resulting from the successive deposition of debris flows the present analysis is directed toward the first two types a mechanistic formulation of flow and sediment transport through river channels is combined with a simple quantification of the overall effect of frequent avulsion to derive relations describing the temporal and spatial evolution of mean i e averaged over many avulsions bed slope and elevation in an axially symmetric fan an example of a fan formed predominantly by the deposition of sand is compared to a similar one formed predominantly by the deposition of gravel in each example the case of channelized flow is compared to the case of sheet flow the model is applied to the tailings basin of a mine in the companion paper

linking bed morphology changes of two sediment mixtures to sediment transport predictions in unsteady flows flume experiments were conducted to measure bed morphology adjustments in sand gravel and sand silt sediment mixtures during repeated hydrographs and to link these changes to sediment transport patterns over multiple time scales sediment composition and hydrograph flow magnitude greatly influenced channel morphology which impacted sediment yield hysteresis and transport predictions bed load yields were larger and more variable for the sand silt mixture as gravel in the sand gravel sediment inhibited grain entrainment limited bed form growth and acted to stabilize the bed hysteresis patterns varied due to bed form and surface structure adjustments as well as the stabilizing effect of antecedent low flows using half the data set a dimensionless fractional transport equation was derived based on excess shear stress dimensionless reference shear stresses were estimated in two ways as bulk values from all transport measurements and by applying a separate limb approach in which values were estimated for each limb of each hydrograph for the other half of the data set transport predictions with the separate limb approach were more accurate than those from six existing transport equations and the fractional relationship applied with bulk reference shear stresses thus hydrograph limb dependent dimensionless reference shear stress links changing bed morphology and sediment transport providing a parameter to improve transport predictions during individual flood events and in unsteady flow regimes this approach represents a framework with which to develop site specific transport relationships for varying flow regimes particularly in cases where detailed bed morphology measurements are not feasible and heterogeneous sediment complicates bed structure over time

szabolcs harangi vulkanok a karpat pannon terseg tűzhanyoi volcanoes the volcanoes of the carpathian pannonian region hardcover pp 440 in hungarian

bed load transport i mechanical characteristics this paper deals with the mechanical characteristics of saltation of bed load transport in flowing water experiments have been carried out by means of high speed photography and advanced data processing techniques taking saltation as the mode of bed load transport systematic analysis has been made with regard to the forces acting on grains and the variation of their magnitudes along the saltation trajectories to obtain the kinematic and dynamic properties of these grains moveover the relations between magnitudes of saltation parameters and flow intensity are attained from the measured data some parameters in bagnold s theory of bed load transport are also discussed

data analysis of bed concentration of suspended sediment an empirical relation for the bed concentration of suspended sediment cb defined at a few grain diameters above the bed is developed its derivation is based on the experimental data sets of guy et al in 1966 the values of the near bed concentration were obtained by first isolating the suspended load transport from the observed rates of total load transport by use of a bed load formula the suspended load was then equated to einstein s formulation which allowed the determination of cb the influence of large concentrations of suspended sediment and of the reference level for cb on the calculated values of bed concentration has been analyzed the proposed relation compares satisfactorily to values of near bed concentration obtained from independent data sets the procedure used to derive cb provides a simple method for the calculation of the total transport rate of noncohesive sediment

periodic saltation over hydrodynamically rough beds aeolian to aquatic we determine approximate analytical solutions for average periodic trajectories of particles that are accelerated by the turbulent shearing of a fluid between collisions with a hydrodynamically rough bed we indicate how the viscosity of the fluid may influence the collisions with the bed the approximate solutions compare well with periodic solutions for average periodic trajectories over rigid bumpy and erodible beds that are generated numerically the analytic solutions permit the determination of the relations between the particle flux and the strength of the shearing flow over a range of particle and fluid properties that vary between those for sand in air and sand in water

medium term coastal response at the ebro delta spain abstract measurements of shoreline displacements along the ebro delta coast have been used to estimate the medium term evolution of the coastline aerial photographs and beach profile surveys covering the last 35 years have been used shoreline data obtained from beach surveys have been analysed using a linear regression technique in order to filter out short term components the medium term scale has been derived from the asymptotic trend with this filtered analysis results have been compared with trends observed in the past and a similar qualitative behaviour has been found rates of change have decreased because the shoreline has slowly evolved towards a more stable configuration a profile closure depth of 7 m has been estimated based on morphological changes in the submerged profiles and then used to convert shoreline displacements into yolume changes from these a medium term sediment budget has been calculated based on the available evidence it has been assumed that these changes are mainly due to wave induced longshore transport gradients assuming proper boundary conditions the net longshore transport scheme has been estimated for each hemidelta the results obtained using this method are in good agreement with the longshore transport rates predicted by well known transport formulae