flow and bedform dynamics in an alluvial channel with downward seepage abstract in this paper we report the findings from an experimental study on a parabolic cross sectional sand bed channel with uniform fine sand under no seepage and downward seepage conditions through experiments we observed that an alluvial channel which remained at threshold condition of sediment movement during the no seepage experiment started transporting sediments with the application of seepage in the downward direction shields stress of the threshold channel increased significantly from its critical value after the application of downward seepage which led to the deformation of the cross sectional shape and consequent development of the bedforms the role of turbulence in the development of bedforms has also been analyzed measures of turbulent statistics show that the time mean velocities and reynolds stresses were increased significantly with the application of downward seepage under the action of seepage conditions increase in the flux of streamwise turbulent kinetic energy in the streamwise direction was observed in the region close to the channel boundary also quadrant analysis exhibited an increase in the contributions from all the bursting events and the thickness of the sweep dominated zone in near bed region after the application of downward seepage a bedform tracking tool has been used to evaluate the variability in the geometry of bedforms we have classified these developing bedforms as current ripples and linguoid ripples according to their evolution with time under the downward seepage condition it has been further observed that the variation in shields stress and corresponding bedform geometry reached an equilibrium state in the presence of downward seepage when the experiments were run over a longer period of time 24 31 h

effective shear stress of graded sediments 1 a meta analysis of fractional mobilization data from 14 sets of experiments totaling 103 different mixed sand and gravel beds and flow conditions has been carried out in order to identify an expression for effective shear stress here defined as the component of bed shear stress that is directly involved in transporting each grain size fraction in graded sediment in doing so we test the assumption that excess stress should be defined solely in terms of a critical stress rather than effective stress which exhibits sensitivity to the flow stage in contrast to the approach which evaluates the size distribution effects on motion threshold by comparing inferred transport rates an alternative approach is utilized which is based on the skill of reproducing the measured mobilized particle size distribution a simple equation is developed for mobilization of sediment mixtures based on a well established transport law and employing a classical hiding function approach to the problem of mitigating the bias toward mobilizing fine material in the mixture we use inverse methods to find the optimal form of the hiding function which provides the best fit with the data we find that the hiding function is indeed sensitive to the flow and bed composition on this basis a simple deterministic equation is proposed for fraction specific effective stress which outperforms the next best existing formula based on critical stress by 34 on aggregate

polydisperse suspensions erosion deposition and flow capacity deposition from particle laden flows is often described in terms of the capacity and competence of the flow but robust definitions of these terms have proved elusive in this paper we provide a mathematical modelling framework within which erosion and deposition of polydisperse sediment and thus flow capacity and competence can be rigorously defined this framework explicitly captures the coupling between the suspension and an active layer of sediment at the top of the bed and is capable of describing both depositional and erosional flows over both erodible and non erodible beds crucially the capacity of a flow is shown to depend on the erosional and depositional history because these processes determine the composition of the active layer this dependence is explored within models of bidisperse and polydisperse suspensions it is further demonstrated that monodisperse representations of suspended sediment transport may severely underpredict actual flow capacity the polydisperse model is validated against recent experimental studies of the evolution of suspended material in waning turbulent flows and is used to demonstrate that loss of capacity is the principal driver of sediment deposition

simulation of preferential flow in three dimensional heterogeneous conductivity fields with realistic internal architecture subsurface flow is primarily controlled by the distribution of hydrogeological properties spatially correlated random fields currently the primary means of describing heterogeneity in these properties underutilizes the existing knowledge of geological systems a new computer code the braided channel simulator bcs 3d is used to geometrically simulate the spatial heterogeneity of hydrogeological properties using representations of surface topography to estimate the three dimensional arrangement of subsurface units four methods of assigning conductivity were used to generate conductivity fields as a basis for saturated flow simulation variograms measured for each of the conductivity fields give no indication of underlying discrete structure however particle tracking simulations showed that flow occurred along paths of preferentially high hydraulic conductivity results indicate that in systems where the contrast in conductivity is sufficiently great the location and magnitude of flow is constrained by discrete internal structure additionally geometrical simulation techniques such as bcs 3d can be used to produce property fields that embody these discrete geological structures

shear stress and hydrodynamic recovery over bedforms of different lengths in a straight channel abstractpools and riffles are common morphological features in rivers that are frequently used but poorly specified analogs in restoration design here straight two dimensional 2d bedforms are conceptualized as perturbations and flow recovery is measured in a laboratory flume with an array of ultrasonic doppler velocity profilers udvps the objectives are to 1 assess the variation of skin friction turbulent stresses and total stress 2 assess the role of topographical feedback on flow recovery and 3 compare flow recovery in isolated and bedforms in series the results show that the total shear stress and near bed turbulence greatly exceed the skin friction in decelerating flow and the pool and that hydrodynamic recovery tends to occur at length scales similar to geophysical scales despite potential negative feedback from the bed repeating short bedforms can push the flow to a more turbulent and laterally concentrated equilibrium condition implications for sediment entrainment thresholds e

hydrodynamics of a forced riffle pool in a gravel bed river 1 mean velocity and turbulence intensity 1 riffle pools are fundamental units of many gravel bed rivers considerable debate exists as to an appropriate hydrodynamic model for this bed form type sampling designs in previous studies have not always anticipated the degree of spatial variability of flow parameters in riffle pools nor considered the effect of the nonuniform boundary on hydrodynamics the objective of this paper is to detail the distribution of mean velocities and turbulence intensities in a forced riffle pool while limited by the lack of lateral velocity measurements the data set is of high quality and includes measurements during a bankfull flood key observations include the perturbation of velocity profiles from what is observed in uniform flow lateral convergence and divergence of flow and the generation of turbulence away from the channel boundary in the thalweg of the pool head velocities are high near the water surface and low near the bed turbulence intensities are relatively high near the bed and may be significant for sediment entrainment higher mean velocities occur over the side bar and could indicate that sediment is routed around the thalweg the midpool is characterized by the lateral constriction of flow and a shear zone downstream of the forcing element the pool tail has very high velocities and turbulence intensities near the bed a velocity reversal occurs in the pool tail at bankfull flow but does not occur in the pool head a consideration of deceleration and acceleration as a result of vertical expansion and contraction is shown to explain many of the key observations

preservation potential for late quaternary river alluvium valley sequences of late quaternary alluvial units reflect alluvial preservation as well as alluvial production factors effects of lateral channel migration incision aggradation and channel stability on preservation potential are explored and then considered in the light of 14 available data sets cartographically dated and model data based on lateral channel migration well mapped and dated late quaternary valley unit surveys and composite age frequency plots for dated alluvial units and flood sediments despite much expectable variation between sites and the complex effects of river activity combinations a common characteristic of the data sets examined is the significance of preservation factors lateral migration tends to eliminate older units as it creates new alluvial deposits whereas incision may lead to the preferential preservation of older units beyond the incision slot aggradational environments are likely to preserve more complete records although simultaneous lateral migration may eliminate possibly repeatedly the upper parts of alluvial units the common pattern of inset and incised streams within pleistocene and early holocene fills or bedrock gives finite extent to later units within narrowing valleys so that development of new valley floor units is necessarily at the expense of reprocessing earlier ones floods associated with both slack water deposits and berms are also responsible for the removal of accessible earlier materials thus limiting the preserved record of earlier events in light of these censoring effects of river activities the sequence of preserved late quaternary units within uk sequences is reconsidered it is concluded that preservation potential factors have led to spatial and temporal bias in the alluvial record and that both here and elsewhere preservation potential needs to be considered systematically alongside variable sedimentation resulting from allogenic environmental factors when interpreting the alluvial archive copyright 2003 john wiley sons ltd journal of quaternary science

relationship between fluvial bounding surfaces and the permeability correlation structure results of three meter scale outcrop studies suggest a quantifiable relationship between fluvial bounding surfaces and the permeability correlation structure mapping of bounding surfaces and in situ measurements of permeability were obtained in three types of deposits a low energy channel deposit a paleosol and a high energy channel deposit for the low energy channel deposit only second order surfaces separating lithofacies were mapped the variogram exhibits anisotropic exponential behavior and an analysis of variance anova suggests that the within facies variation dominates over between facies variation the paleosol contained no internal bounding surfaces and exhibited a bellshaped variogram consistent with a smoothly varying style of heterogeneity both firstand second order bounding surfaces were mapped in the high energy channel deposit results of the anova suggest that the between facies variation dominates over the within facies variation a model of spatial correlation using superposition of independent processes acting over different scales provides a good fit to the data these three studies suggest that fluvial bounding surfaces provide a geological basis for conceptualizing and modeling heterogeneity in alluvial deposits

clear water scour and flow field alteration around an inclined pile abstract the present experimental study investigates the scour pattern and the near wake flow field alteration around an emergent rigid cylinder which is inclined towards the downstream direction three different inclination angles were tested separately namely 14 30 and 42 with respect to the wall normal axis the induced flow and scour patterns were assessed and compared with the well known case of the emergent upright cylinder inclination angle 0 the experiments were conducted for steady flow conditions in a 26 m long recirculating flume and the flow velocity measurements were conducted with an acoustic doppler velocimeter for the clear water scour experiment a false bed with a sand pit was installed within the flume and a laser scanner was utilized to render a detailed representation of the scoured bed the results show how the scouring gets mitigated with increasing inclination angle spatial distribution of time averaged and fluctuation velocity patterns are presented which exhibit that the vertical mixing gets significantly enhanced behind the inclined cylinder with increasing inclination angle while the lateral mixing gets weakened at the upper flow region an upward flow is seen at the immediate downstream of the inclined pile close to the bed which becomes stronger with the inclination angle energy spectra as well as joint frequency distributions of velocity components were analyzed together with the time series revealing that the inclination of the pile alters the wake significantly the results further indicate that with increasing inclination angle the pile becomes more streamlined and the vortex shedding gets suppressed

influence of aquifer heterogeneity and return flow on pumping test data interpretation abstract analytical solutions of drawdown in unconfined aquifers are widely applied for determining the specific yield s y and the horizontal and the vertical hydraulic conductivity k r and k z respectively in many previous studies estimates of s y and k z were observed to be highly variable and physically unrealistic this has been attributed to the conceptualization of flow above the declining water table and aquifer heterogeneity in the applied models we present the analysis of time drawdown data from a pumping test instrumented with depth differentiated observation piezometers arranged in clusters applying homogeneous anisotropic aquifer models in combination with nonlinear least squares parameter identification techniques the data were analyzed in different groups analysis of data from individual piezometer clusters and simultaneous analysis of the entire data set from all piezometer clusters global analysis from the cluster analyses estimates of s y and k z exhibit large variances and depart from a priori estimates inferred from the hydrostratigraphy parameter estimates from the global analysis do not fall within the parameter bounds minimum and maximum values defined by the cluster analyses while heterogeneity appears to be the important reason for large parameter variances we discuss the influence of rarely considered aquifer return flow on drawdown and the inconsistent results from the cluster and global analyses we corroborate our findings with data on hydraulic gradients slug test data and results from the application of a more realistic numerical flow model

paleoclimatic signature in terrestrial flood deposits large scale process simulation was used to reconstruct the geologic evolution during the past 600 000 years of an alluvial fan in northern california in order to reproduce the sedimentary record the simulation accounted for the dynamics of river flooding sedimentation subsidence land movement that resulted from faulting and sea level changes paleoclimatic trends induced fluctuations in stream flows and dominated the development of the sedimentary deposits the process simulation approach serves as a quantitative means to explore the genesis of sedimentary architecture and its link to past climatic conditions and fault motion

application of an alluvial architecture model to better understand seepage risk in floodplains abstract the amount and distribution of coarse grained sediment e g sands and gravels relative to fine grained sediment e g clays and silts within a floodplain influences many of the floodplain geotechnical properties including the potential for groundwater seepage seepage is a primary driver of levee and dam failure and understanding its potential is of paramount concern to engineers and resource managers this paper reports the results of a computational modeling study that simulated alluvial floodplain construction using a suite of simple geomorphic process imitating rules a model aggrades a floodplain cross section within an alluvial basin creating floodplain architecture by differentiating between sediment deposited by channel processes sand and sediment deposited by overbank flood processes clay the evolution of two floodplain cross sections of the trinity river near dallas texas is simulated using five different experimental scenarios the study area is the site of large levee rehabilitation projects in which accurate characterization of the geologic environment has significant engineering importance study results predict that scenario components including the alluvial basin width the initial topography of the floodplain base level and the channel aggradation rate significantly affect the fraction of the floodplain width that contains channel deposits by influencing the avulsion frequency of the river during floodplain construction increased avulsion frequency equated to more numerous yet smaller channel deposits the dimensions of the channel deposits predicted by this study are similar to those typically observed in large fully meandering river systems the model devised for this study is relatively simple and can be run in multiple iterations to produce probabilistic outputs such as the likely range of channel deposit widths within a floodplain cross section this type of information is useful to engineers for a host of applications including predicting the data collection density necessary to characterize the geotechnical properties of a project site

near bed hydrodynamics and turbulence below a large scale plunging breaking wave over a mobile barred bed profile detailed measurements are presented of velocities and turbulence under a large scale regular plunging breaking wave in a wave flume measurements were obtained at 12 cross shore locations around a mobile medium sand breaker bar they focused particularly on the dynamics of the wave bottom boundary layer wbl and near bed turbulent kinetic energy tke measured with an acoustic concentration and velocity profiler acvp the breaking process and outer flow hydrodynamics are in agreement with previous laboratory and field observations of plunging waves including a strong undertow in the bar trough region the wbl thickness matches with previous studies at locations offshore from the bar crest but it increases near the breaking wave plunge point this relates possibly to breaking induced tke or to the diverging flow at the shoreward slope of the bar outer flow tke is dominated by wave breaking and exhibits strong spatial variation with largest tke above the breaker bar crest below the plunge point breaking induced turbulence invades the wbl during both crest and trough half cycle this results in an increase in the time averaged tke in the wbl with a factor 3 and an increase in peak onshore and offshore near bed reynolds stresses with a factor 2 from shoaling to breaking region a fraction of locally produced tke is advected offshore over a distance of a few meters to shoaling locations during the wave trough phase and travels back onshore during the crest half cycle the results imply that breaking induced turbulence for large scale conditions may significantly affect near bed sediment transport processes

real and apparent changes in sediment deposition rates through time 1 field measurements show that estimated sediment deposition rate decreases as a power law function of the measurement interval this apparent decrease in sediment deposition has been attributed to completeness of the sedimentary record the effect arises because of incorporation of longer hiatuses in deposition as averaging time is increased we demonstrate that a heavy tailed distribution of periods of nondeposition hiatuses produces this phenomenon and that observed accumulation rate decreases as t 1 over multiple orders of magnitude where 0 1 is the parameter describing the tail of the distribution of quiescent period length by using continuous time random walks and limit theory we can estimate the actual average deposition rate from observations of the surface location over time if geologic and geometric constraints place an upper limit on the length of hiatuses then average accumulation rates approach a constant value at very long times our model suggests an alternative explanation for the apparent increase in global sediment accumulation rates over the last 5 million years

chute channel dynamics in large sand bed meandering rivers meander bends of many large sand bed meandering rivers are partitioned by chute channels that convey permanent flow and co exist with the mainstem for decades as a first step toward understanding the dynamics and morphodynamic implications of these bifurcate meander bends this study applied binary logistic regression analysis to determine whether it is possible to predict chute initiation based on attributes of meander bend character and dynamics regression models developed for the strickland river papua new guinea the lower paraguay river paraguay argentina and the beni river bolivia revealed that the probability of chute initiation at a meander bend is a function of the bend extension rate the rate at which a bend elongates in a direction perpendicular to the valley axis trend image analyses of all rivers and field observations from the strickland suggest that the majority of chute channels form during scroll slough development rapid extension is shown to favour chute initiation by breaking the continuity of point bar deposition and vegetation encroachment at the inner bank resulting in widely spaced scrolls with intervening sloughs that are positively aligned with primary over bar flow the rivers plot in order of increasing chute activity on an empirical meandering braided pattern continuum defined by potential specific stream power pv and bedload calibre d50 increasing stream power is considered to result in higher bend extension rates with implications for chute initiation in addition chute stability is shown to depend on river sediment load relative to flow discharge qs q such that while the beni may plot in the region of highly braided rivers by virtue of a high potential specific stream power the formation of stable chute channels is suppressed by the high sediment load this tendency is consistent with previous experimental studies and results in a planform that is transitional between single thread meandering and braided copyright 2011 john wiley sons ltd

role of near bed turbulence structure in bed load transport and bed form mechanics the interactions between turbulence events and sediment motions during bed load transport were studied by means of laser doppler velocimetry and high speed cinematography sweeps u 0 w 0 w 0 which contribute negatively to the bed shear stress and are relatively rare individually move as much sediment as sweeps of comparable magnitude and duration however and much more than bursts u 0 and inward interactions u 0 w 0 when the magnitude of the outward interactions increases relative to the other events therefore the sediment flux increases even though the bed shear stress decreases thus although bed shear stress can be used to estimate bed load transport by flows with well developed boundary layers in which the flow is steady and uniform and the turbulence statistics all scale with the shear velocity it is not accurate for flows with developing boundary layers such as those over sufficiently nonuniform topography or roughness in which significant spatial variations in the magnitudes and durations of the sweeps bursts outward interactions and inward interactions occur these variations produce significant peaks in bed load transport downstream of separation points thus supporting the hypothesis that flow separation plays a significant role in the development of bed forms

a unified model for subaqueous bed form dynamics 1 bed form evolution remains dynamic even in the special case of steady uniform flow data from the sandy braided north loup river nebraska show that roughness features on the channel bottom display a statistical steady state and robust scaling that are maintained through the collective interactions of transient short lived bed forms motivated by such field data and laboratory observations of bed form growth we develop a nonlinear stochastic surface evolution model for the topography of bed load dominated sandy rivers in which instantaneous sediment flux explicitly depends on local elevation and slope this model quantitatively reproduces laboratory observations of initial growth and saturation of bed forms from a flat surface and also generates long term dynamical behavior characteristic of natural systems we argue that the variability in geometry and kinematics of bed forms in steady flow and the existence of roughness at all wavelengths up to the largest dunes are a consequence of the nonlinear relationship between sediment flux and topography subject to noise

modeling framework for sediment deposition storage and evacuation in the floodplain of a meandering river theory 1 a theory for the movement of suspendible sediment through the floodplain of a simple actively migrating river is developed the floodplain is represented as a series of sediment storage reservoirs each incorporating multiple bends of a river independent models for floodplain sediment deposition and for subsequent removal of sediment by lateral channel migration allow the volume of sediment stored in the floodplain and the associated average floodplain elevation to change over time and down the valley at a given quasi steady discharge deposition depends on a simple one dimensional partition between channel and floodplain discharge and on suspended sediment concentration one size class which varies along the reach depending on lateral supply and floodplain history sediment supply is specified at the upstream end of the reach using a suspended sediment rating curve long term average overbank deposition rates are approximated by weighting multiple steady state solutions using a flow duration curve the channel bed elevation of the system is assumed to be fixed and tributaries are handled using simple lateral source terms the interaction between the submodels is such that under constant boundary conditions the channel evolves toward a state of geomorphic equilibrium where the volume of sediment added to the floodplain by overbank deposition just balances the volume removed by channel migration the model is easily adapted to track conservative suspended sediment tracer material concentration as such material moves through the channel floodplain system

effects of turbulence on the transport of individual particles as bedload in a gravel bed river this study investigates the association between mean and turbulent flow variables and the movement of individual particles in a gravel bed river the experimental design implemented in the eaton north river quebec canada is based on the simultaneous observations at a high temporal resolution of both particle movements as bedload using an underwater video camera and of the streamwise and vertical flow velocity components using a vertical array of three electromagnetic current meters ecms the frequency and distance of displacement of particles larger than 20 mm that were sliding or rolling on the bed were measured from a 10 minutes long film mean and turbulent flow properties obtained for periods without sediment transport are compared to those when particles were sliding and rolling when particles are sliding weak differences are present for the mean streamwise velocity and normal vertical stresses instantaneous reynolds shear stresses are significantly lower for sliding events which was not expected but could be explained by the important dominance of quadrant 3 events inward interactions when particles are rolling only the vertical normal stresses show a weak difference from those observed in the absence of transport but they tend to occur when quadrant 2 ejections dominate the flow field for both sliding and rolling particles vertical and or streamwise fluid accelerations show high magnitude values when compared to periods without transport for sliding particles streamwise acceleration is mostly negative and combines most of the time with a positive vertical acceleration for rolling particles streamwise and vertical acceleration are predominantly of opposite sign these results suggest that fluid acceleration or deceleration in the streamwise and vertical directions is affecting the pressure field around particles in this study fluid acceleration seems to play a more important role than reynolds shear stress or normal stresses for bedload movements copyright 2010 john wiley sons ltd

hydro morphometric parameters controlling travel distance of pebbles and cobbles in three gravel bed streams abstract this study investigates the parameters controlling bedload distances in several gravel bed rivers of a medium mountain morvan france using pit tags introduced into pebbles and cobbles an examination of the relationship between several hydro morphometric variables and travel distance was first undertaken with bivariate analysis bedload distances of our 6 study sites show important differences and this discrepancy cannot fully be understood considering only the stream power for the peak discharge especially in multi peak surveys such as ours stream impulse a variable combining flow intensity and flow competence duration has a stronger correlation with bedload distances the analysis also indicates a varying influence of relative grain size relative flow depth bed slope and width depth ratio among all these parameters in order of importance the relative grain size the slope and the stream impulse emerge as the most significant explanatory variables from a multivariate analysis the role of the relative grain size on bedload transport underlines the importance of grain size sorting and microtopography in plane bed rivers the influence of the slope is ambivalent favoring bedload distances under certain circumstances and lowering them under others the direction of the influence of the slope seems to depend on its combination with other morpho sedimentary or hydraulical parameters finally we propose a single equation for bedload distance prediction that predicts travel distance rather well

modelling river history and evolution over the last few decades a suite of numerical models has been developed for studying river history and evolution that is almost as diverse as the subject of river history itself a distinction can be made between landscape evolution models lems alluvial architecture models meander models cellular models and computational fluid dynamics models although these models share some similarities there also are notable differences between them which make them more or less suitable for simulating particular aspects of river history and evolution lems embrace entire drainage basins at the price of detail alluvial architecture models simulate sedimentary facies but oversimplify flow characteristics and computational fluid dynamics models have to assume a fixed channel form while all these models have helped us to predict erosion and depositional processes as well as fluvial landscape evolution some areas of prediction are likely to remain limited and short term owing to the often nonlinear response of fluvial systems nevertheless progress in model algorithms computing and field data capture will lead to greater integration between these approaches and thus the ability to interpret river history more comprehensively

numerical computation of sand dune migration with free surface flow 1 this paper presents a morphodynamic model for free surface flows over bed forms the model reproduces bed form evolution and migration in a physically based manner the flow model component of the coupled morphodynamic model which is two dimensional in the streamwise and vertical directions explicitly treats unsteadiness and nonhydrostatic effects comparison with measurements shows that the flow model accurately simulates both mean flow and turbulence structure induced by bed forms under free surface flow the flow model performance is enhanced by the use of a high order godunov scheme known as the cubic interpolated pseudoparticle cip technique to compute the advection phase of the navier stokes equation in addition an enhanced k turbulence closure with nonlinear terms is incorporated in the present model in order to allow better predictions of reynolds stress anisotropy in regions with flow separation performance of the nonlinear k model is compared with standard k closure in the context of the flow as well as morphodynamic simulation nonequilibrium bed load sediment transport is treated using a eulerian stochastic formulation of the sediment exchange process in terms of pickup and deposition functions the proposed approach for sediment transport explicitly considers the local flow variability during morphodynamic computation model results show that the vertical grid distribution pattern affects the simulation result particularly for bed form morphodymics the model successfully simulates some important physical features of bed form evolution such as amalgamation and asymmetric geometry the simulation results are in agreement with laboratory experiments as well as some commonly used prediction methods for geometric characteristics of bed forms

statistical description on the role of turbulence and grain interference on particle entrainment from gravel beds abstracta complete understanding of the role of grain scale particle flow interaction in sediment entrainment and transport has still not been achieved in spite of recent technological advancement in measurement capabilities in this study the initial motion of natural sediment particles in a gravel deposit was detected and combined with simultaneous local measurements of the velocities on a horizontal plane located above the bed surface using a three component stereoscopic piv a series of experimental tests with increasing low values of boundary shear stress were conducted the acquisition system allowed coupling between streamwise and vertical near bed velocity and the entrainment of more than 900 individual grains initial analysis agreed with previous observations on the predominance of sweeps quadrant iv and to a lesser extent of outward interactions quadrant i in entraining gravel particles however the latter were found to move sediments just as efficiently as sweeps impacting on particles

effect of seepage flow on incipient motion of sand particles in a bed subjected to surface flow abstract understanding the interaction of the groundwater seepage flow and sediment transport along permeable boundaries is essential for managing soil beds and bank erosion a significant bank failure may occur due to sediment transport under the boiling condition in the present study an experiment is conducted to investigate the effects of injection or upward seepage on the critical shear stress of a cohesionless soil bed subjected to surface flow the upward seepage force acting on the soil bed particles may reduce the virtual weight of the particles in turn it may also reduce the critical shear stress acting on the particles a theoretical analysis examines how the upward seepage force acts to modify the critical shear stress for the sediment entrainment due to the increase in the hydraulic gradient of the seepage flow a force analysis reveals that the ratio of the critical shear stress with seepage to that without seepage is dependent on the ratio of the hydraulic gradient of seepage to its value at the quicksand condition a test apparatus was built and the effects of injection on the critical shear stress of cohesionless soil bed particles were measured an acrylic channel with a rectangular cross section was prepared and a section of a cohesionless soil bed subjected to an upward seepage flow was installed at the bottom of the channel the experiment demonstrates that the induced seepage affects the dynamics of the channel flow even though the magnitude of the seepage flow velocity is significantly smaller than that of the free surface water flow the test results show that the dimensionless critical shear stress of the cohesionless soil bed particles decreases slightly as the hydraulic gradient of the seepage flow is increased when critical shear stress is determined at the upstream edge of the seepage zone furthermore the dimensionless critical shear stress decreases sharply with the increment of the hydraulic gradient of the seepage flow when critical shear stress is determined in the seepage zone however it does not decrease in either case as was theoretically assumed even when the hydraulic gradient approaches to the critical hydraulic gradient or the quicksand condition

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

conditioning a process based model of sedimentary architecture to well data abstract prediction of sedimentary architecture for modeling of fluid flow in hydrocarbon reservoirs and aquifers is accomplished mainly using stochastic structure imitating models because these can be conditioned to data from wells seismic profiles and outcrop analogs conditioning implies that modeled architecture fits all available observations however the sedimentary architecture simulated by such models is commonly unrealistic process based forward models potentially provide more realistic prediction and understanding of sedimentary architecture but these models are not widely used because conditioning to well seismic or outcrop data is considered to be very difficult we show here that conditioning of process based models to well data is possible in principle using a 3d alluvial architecture model as an example this model considers the formation of alluvial deposits as a predominantly deterministic process with a single channel belt moving by avulsion over an aggrading floodplain however the initial floodplain topography is simulated by a random field thus yielding different model output for each run monte carlo simulation was used to produce model realizations that fit five hypothetical vertical wells within predetermined tolerance bands such simulation allows calculation of the probability of occurrence of channel belt deposits for each 3d cell in the 3d block of sediments generated by the model as well as the probability distributions of volumes of channel belt deposits and connectedness ratios adding more conditioning wells increases the precision of model predictions application of this approach in practice will require a major effort particularly in overcoming the anticipated large amounts of computing time

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

comparison of sediment pickup rates over plane bed and dunes abstractsediment pickup rate is useful for deriving bedload function and specifying boundary conditions for numerical modeling of sediment transport previous pickup functions were developed based only on data measured under the plane bed condition and they may not be applicable for dune covered beds the present study compares pickup rates for three bed conditions i e plane bed fixed dunes and mobile dunes all pickup functions are formulated by involving the densimetric froude number instead of the shields number the results show that the sediment pickup rates measured over fixed dunes can be described using the pickup function developed for the plane bed however the presence of mobile dunes causes a considerable reduction in the pickup rate when the densimetric froude number is greater than 5 which is largely due to flow particle and particle particle interaction this study also shows that under mobile dune conditions the particle step length for dune bed conditions scales with the dune len

a two dimensional discrete particle model of gravel bed river systems 1 the formation of bed forms in gravel bed rivers acts as a control on stream ecology and the response of rivers to floods available models do not reproduce the range of observed bed forms and do not consider interactions between the bed and flow hydraulics the model presented here considers a gravel bed river as a complex system in which sediment clasts are represented as discrete elements simple and local rules describe the sediment and flow dynamics using a trimodal sediment distribution irregular forms that scale with particle diameter develop without explicit feedback mechanisms because of the tendency of large particles to roll along the bed surface and collect into chains feedback mechanisms such as imbrication increase the effective entrainment threshold of groups of large particles and increase the stability of these imbricate forms a second type of bed form is associated with saltating grains and emerges where particles are transported at a preferred distance the development and maintenance of larger scale bed forms require feedback between the bed and flow properties by allowing mean velocity to adjust to bed morphology and considering the effect of acceleration on turbulence generation and mean velocity profiles we demonstrate the emergence of forms similar in morphology to gravel sheets dunes and riffle pools the model is best used to complement field based studies and is suitable for testing hypotheses of streambed behavior

spatial autoregressive structure in meander evolution the migration of a river bend depends in part on the high flow velocities that characteristically impinge on its outside bank recent models have treated this in terms of a spatial convolution whereby local bend migration is mathematically a weighted aggregate of up stream curvature and bed topography the convolution model can be tested using river migration data after it is discretized and recast into a finite autoregressive form published isochrones marking former positions of bends on the beatton river canada support the hypothesis that rates of bend migration follow a convolutional relation in addition a comparison of the underlying flow model with published flume experiments involving constant curvature bends illustrates how it predicts the near bank depth averaged velocity associated with a forced bar topography in absence of free bars the autoregressive form of the model is equivalent to a stochastic linear difference equation this allows bend curvature to be treated as a random process cast in the frequency domain the convolution model predicts that big bends tend to grow at the expense of little bends and curvature irregularities in complex trains there exists no tendency for preferential growth of an intermediate bend size the model also predicts the well known shift of maximum migration rates to positions down stream of curvature apexes and implies that the magnitude of this shift increases with decreasing bend size predicted shifts compare well with published measured shifts on the nishnabotna river iowa the sensitivity of the meandering process to initial bend geometries and entrance flow conditions ensures that diverse bend shapes arise along freely migrating rivers independently of factors such as unsteady flow and nonuniform erodibility no single geometrical form serves as an asymptotic evolutionary state for individual bends

numerical simulation of turbulence and sediment transport of medium sand a model of sand transport in water is produced by combining a turbulence resolving large eddy simulation les with a discrete element model dem prescribing the motion of individual grains of medium sand the momentum effect of each particle on the fluid is calculated at the les cell containing the particle and the fluid velocity and pressure interpolated to each particle center is used to derive fluid force on each particle in the dem eleven numerical experiments are conducted of an initially flat bed of particles the experiments span a range of motion from essentially no motion to vigorous suspension hydraulic roughness is found to increase abruptly at the transition from bed load to suspended load transport suspended sediment extracts momentum from the flow and decreases the rate of shear whereas slightly higher in the flow vertical drag by suspended grains damps turbulence and increases the rate of shear vertical sediment diffusivity and effective particle settling velocity are much smaller than is commonly assumed in suspended sediment models the bed load experiments suggest that saltation by itself is a poor model of bed load sand transport in contrast to expectations from saltation models the peak bed load flux occurs at essentially the same level as the bed and grains move slowly in frequent contact with other grains higher and faster moving bed load grains that can be considered to be in saltation represent a smaller portion of the total flux entrainment of bed load grains occurs in response to fluid penetration of the bed by high vorticity turbulence structures embedded within broader high speed fluid regions referred to as a sweeps or high speed wedges

fluvial architecture and reservoir compartmentalization in the oligocene middle frio formation south texas abstract seeligson stratton and agua dulce fields south texas are being studied as part of a gas research institute department of energy state of texas cosponsored program designed to develop and test methodologies and technologies for gas reserve growth in conventional reservoirs in mature gas fields over the last five decades each field has produced approximately 2 tcf of gas from middle frio reservoirs alone recent drilling old well workover results and reservoir pressure data however point to the possibility of additional reserves within these fields the middle frio oligocene is composed of sand rich channel fill and splay deposits interstratified with floodplain mudstones all forming part of the gueydan fluvial system channel fill deposits are 30 ft 9 m thick and 2 500 ft 76 m wide splay deposits are as much as 20 ft 6 m thick proximal to channels and extend as much as 2 mi 3 km from channels channel fill and associated splay sandstones are reservoir facies porosity 20 percent permeability 10 s to 100 s md floodplain mudstones and levee sandy mudstones impede or obstruct flow and separate individual reservoirs and compartments both vertically and laterally deposition on an aggrading coastal plain resulted in a continuum of fluvial architectural styles that has important implications for reservoir compartmentalization relatively slow aggradation resulted in laterally stacked channel systems whereas more rapid aggradation resulted in vertically stacked channel systems in seeligson field laterally stacked architecture alternates with vertically stacked architecture through the 2 000 ft 610 m thick middle frio section in stratton and agua dulce fields the same general alternation in architectural modes exists through the 2 500 ft 763 m thick middle frio section in stratton and agua dulce however the reservoir zones composed of laterally stacked architecture are not laterally continuous instead the laterally stacked architecture locally changes into a vertically stacked architecture because laterally stacked sandstone bodies lead to separate but potentially leaky reservoir compartments and vertically stacked sandstone bodies favor more isolated reservoir compartments a high potential for reserve growth through the identification of untapped poorly drained and bypassed gas reservoir compartments exists in each of these fields differences in reservoir architecture also must be taken into account as part of exploitation strategies

reservoir heterogeneity in the middle frio formation case studies in stratton and agua dulce fields nueces county texas abstract selected middle frio oligocene reservoirs of stratton field and the contiguous agua dulce field are being studied as part of a gas research institute department of energy state of texas cosponsored program designed to improve reserve growth in mature gas fields during the past four decades stratton has produced 1 8 tcf of gas from 110 middle frio reservoirs and agua dulce has produced 1 6 tcf from 120 reservoirs recent drilling and workover activities however suggest the presence of additional untapped or bypassed middle frio reservoirs the middle frio is composed of sand rich channel fill and splay deposits interstratified with floodplain mudstones all forming part of the gueydan fluvial system channel fill deposits are 30 ft 9 m thick and 2 500 ft 76 m wide splay deposits are as much as 20 ft 6 m thick proximal to channels and extend as much as 2 mi 3 km from channels channel fill and associated splay sandstones are reservoir facies porosity 20 percent permeability tens to hundreds of millidarcys floodplain mudstones and levee sandy mudstones impede or obstruct flow and separate individual reservoirs and compartments both vertically and laterally the e31 6100 and e25 6050 reservoirs are examples of vertically stacked channel systems reflecting higher rates of coastal plain aggradation pressure tests strongly suggest that bypassed compartments have only recently been contacted or are still present for exploitation vertically stacked architectures are considered to be more favorable for isolated compartments and therefore are better candidates for infield reserve growth

coupled dynamics of the co evolution of gravel bed topography flow turbulence and sediment transport in an experimental channel a series of flume experiments were conducted in a large experimental channel at the st anthony falls laboratory to understand the coupled dynamics of flow and bed forms above the sediment water interface simultaneous high resolution measurements of velocity fluctuations bed elevations and sediment flux at the downstream end of the channel were made for a range of discharges the probability density functions pdfs of bed elevation increments and instantaneous reynolds stress reveal a power law tail behavior and a wavelet cross correlation analysis depicts a strong dependence of these series across a range of scales indicating a feedback between bed form dynamics and near bed turbulence these results complement our previous findings in which the signature of bed form evolution on the near bed velocity fluctuations was confirmed via the presence of a spectral gap and two distinct power law scaling regimes in the spectral density of velocity fluctuations we report herein a strong asymmetry in the probability distribution of bed elevation increments and instantaneous reynolds stresses the latter being further analyzed and interpreted via a quadrant analysis of velocity fluctuations in the longitudinal and vertical directions we also report the presence of intermittency multifractality in bed elevation increments and interpret it in view of the asymmetric nature of the pdfs as the result of scale coupling in other words the geometric asymmetry at the bed form scale gets transferred down to a probabilistic asymmetry at all smaller scales indicating a local anisotropy in the energy transfer finally we propose a predictive relationship between bed form averaged sediment transport rates and bed form averaged instantaneous reynolds stress and validate it using our experimental data

sand dunes in steady flow at low froude numbers dune height evolution and flow resistance the development of sand dunes in an erodible bed exposed to flowing water is considered using a numerical flow model the bed is initially given a small perturbation which is followed in the time domain examples are given where a sinusoidal perturbation reaches the fully developed steady equilibrium shape the flow modeling is based on a k turbulence closure the sediment transport is assumed to be bed load only with an avalanche like movement on the steep dune front the model is also found capable of predicting the growth in wavelength if the initially prescribed wavelength is sufficiently short results of the dune development are presented for different initial wavelengths it is demonstrated that an equilibrium shape is developed for a range of wavelength depth ratios as long as this ratio is sufficiently small

numerical evaluation of the effects of planform geometry and inflow conditions on flow turbulence structure and bed shear velocity at a stream confluence with a concordant bed this study numerically investigates the effects of variations in inflow conditions and planform geometry on large scale coherent flow structures and bed friction velocities at a stream confluence with natural bathymetry and concordant bed morphology several numerical experiments are conducted in which either the kelvin helmholtz mode or the wake mode dominates within the mixing interface mi between the two confluent streams as the junction angle and alignments of the tributaries are altered in the kelvin helmholtz mode the mi contains mostly corotating vortices driven by the mean transverse shear across the mi while in the wake mode the mi contains counterrotating vortices forming by the interaction of the separated shear layers on the two sides of a zone of stagnant fluid near the junction corner a large angle between the two incoming streams is not necessary for the development of strongly coherent streamwise oriented vortical sov cells in the immediate vicinity of the mi results show that such sov cells can develop and produce high bed friction velocities even for cases with a low angle between the two tributaries and for cases where the downstream channel is approximately aligned with the axes of the two tributaries low curvature cases sov cells tend not to develop only when the incoming streams are parallel and aligned with the downstream channel junction angle of zero and the incoming flows produce a strong kelvin helmholtz mode under such conditions quasi 2 d mi vortices play the primary role in mixing and the production of high bed shear velocities simulations with and without natural bed morphology local bank line irregularities indicate that planform geometry and inflow conditions primarily govern the development of coherent flow structures but that bathymetric and bank line effects can locally modify details of these structures

a note on the krone deposition equation and significance of floc aggregation for modeling the rate of deposition of cohesive flocs in estuaries the krone equation is extensively used it was derived from flume experiments on muddy sediment from the san francisco bay and is applicable to low suspended sediment concentration environments in which shear induced aggregation the growth and break up of flocs has a limited role it is shown that the use of this equation can lead to erroneous estimates of the mass deposition flux at typically higher estuarine concentrations krone s own experimental data permit the development of a more general equation accounting for the effects of concentration and turbulent shear rate on aggregation these effects are dramatically observed in a deposition test in which a wire mesh was inserted in the flow to change the turbulent shearing rate and increase deposition even with the inclusion of aggregation effect in the general equation field based observations from san francisco bay suggest that typical flumes generally may not meet the space and time scaling requirements for field application of laboratory data thus although the krone equation should be eschewed in favor of the general equation interpretations of model predicted deposition rate must not be accepted without robust field based verification

universal bank erosion coefficient for meandering rivers an equation for bank erosion and thus channel migration rate is derived theoretically from the equation of sediment continuity the relation so derived lends credence to the hypothesis that bank

evaluation of a linear bank erosion equation field surveys and aerial photographs were used to measure the rate of migration of a bend of the brandywine creek near chadds ford pennsylvania velocities near the bank were measured in the field during high flows and also estimated by solving a form of the st venant equations engineering properties of the bank soils and the spatial density of trees growing along the bank were also measured the data indicate that rates of bank migration are linearly related to the magnitude of the near bank velocity if the st venant equations are used to estimate the near bank velocity the data also suggest that erosion rates are proportional to ub u where ub is the near bank velocity and u is the reach averaged velocity in addition rates of bank migration are reduced where the density of silver maples acer saccharinum is high boxelder acer negundo and white ash fraxinus americana are also found along the bend but these species do not noticeably influence rates of bank migration

a parameterization of flow separation over subaqueous dunes flow separation plays a key role in the development of dunes and modeling the complicated flow behavior inside the flow separation zone requires much computational effort to make a first step toward modeling dune development at reasonable temporal and spatial scales a parameterization of the shape of the flow separation zone over two dimensional dunes is proposed herein in order to avoid modeling the complex flow inside the flow separation zone flow separation behind dunes with an angle of repose slip face is characterized by a large circulating leeside eddy where a separation streamline forms the upper boundary of the recirculating eddy experimental data of turbulent flow over two dimensional subaqueous bed forms are used to parameterize this separation streamline the bed forms have various heights and height to length ratios and a wide range of flow conditions is analyzed this paper shows that the shape of the flow separation zone can be approximated by a third order polynomial as a function of the distance away from the flow separation point the coefficients of the polynomial can be estimated independent of flow conditions on the basis of bed form shape at the flow separation point and a constant angle of the separation streamline at the flow reattachment point

rans based simulation of wave induced sheet flow transport of graded sediments abstract a one dimensional vertical 1dv turbulence closure flow model coupled with sediment transport capabilities is extended to incorporate graded sediment mixtures the hydrodynamic model solves the horizontal component of the incompressible reynolds averaged navier stokes rans equations coupled with k turbulence closure the sediment transport description includes both bed and suspended load descriptions so called high concentration effects turbulence damping and hindered settling velocities are likewise included the sediment transport model treats the bed and suspended load individually for each grain fraction including effects associated with increased exposure of larger particles within a mixture the suspended sediment transport model also makes use of modified reference concentration approach wherein reference concentrations computed individually for each fraction are translated to a common level conveniently enabling use of a single computational grid for the simulation of suspended sediments parametric study shows that these two effects combine to help alleviate an otherwise systematic tendency towards over under predicted transport rates for fine coarse sand fractions the sediment transport model is validated against sheet flow experimental oscillatory tunnel measurements beneath velocity skewed wave signals and demonstrates similar accuracy transport rates generally within a factor of two for both graded and uniform sands the model is likewise validated against an extensive data set involving sheet flow transport beneath acceleration skewed wave signals limited to uniform sands it is then utilized to study potential effects of gradation on the net transport beneath such flows the simulations suggest that gradation effects can both increase as well as decrease the total transport rate depending largely on the behavior of the fine sand fraction the model is implemented within the matlab environment and is freely available upon request to the corresponding author

modeling river dune evolution using a parameterization of flow separation this paper presents an idealized morphodynamic model to predict river dune evolution the flow field is solved in a vertical plane assuming hydrostatic pressure conditions the sediment transport is computed using a meyer peter muller type of equation including gravitational bed slope effects and a critical bed shear stress to avoid the necessity of modeling the complex flow inside the flow separation zone we follow an approach similar to one used earlier to simulate the dynamics of wind blown desert dunes in case of flow separation the separation streamline acts as an artificial bed and sediment avalanches down the leeside distributing evenly on the leeside at the angle of repose model results show that bed slope effects play a crucial role in the determination of the fastest growing wavelength from a linear analysis flow separation is shown to be crucial to take into account if the dune lee exceeds a certain threshold slope if flow separation is not included dune shapes are incorrectly predicted and the dune height saturates at an early stage of bed form evolution yielding an underprediction of dune height and time to equilibrium the local bed slope at the dune crest plays a critical role for obtaining an equilibrium dune height the simulation model is able to predict the main characteristics of dune evolution such as dune asymmetry dune growth and saturation at a certain dune height dune dimensions migration rates and times to equilibrium compare reasonably well to various data sets

coupling channel evolution monitoring and rfid tracking in a large wandering gravel bed river insights into sediment routing on geomorphic continuity through a riffle pool sequence bedload transport and bedform mobility in large gravel bed rivers are not easily monitored especially during floods large reaches present difficulties in bed access during flows for flow measurements because of these logistical issues the current knowledge about bedload transport processes and bedform mobility lacks field based information while this missing information would precisely match river management needs the lack of information linking channel evolution and particle displacements is even more striking in wandering reaches the durance river is a large wandering gravel bed river catchment area 14 280 km2 mean width 240 m located in the southern french alps and highly impacted by flow diversion and gravel mining in order to improve current understanding of the link between sediment transport processes and river bed morphodynamics we set up a sediment particle survey in the channel using radio frequency identification rfid tracking and topographic surveys gps rtk and scour chains for a 4 year recurrence interval flood by combining topographic changes before and after a flood intraflood erosion deposition patterns from scour chains differential routing of tracer particles and spatial distribution of bed shear stress through a complex reach this paper aims to define the critical shear stress for significant sediment mobility in this setting gravel tracking highlights displacement patterns in agreement with bar downstream migration and transport of particles across the riffle within this single flood event because no velocity measurements were possible during flood a telemac three dimensional model helped interpret particle displacements by estimating spatial distribution of shear stresses and flow directions at peak flow although rfid tracking in a large wandering gravel bed river does have some technical limitations burial recovery process time consuming it provides useful information on sediment routing through a riffle pool sequence

flow and turbulence redistribution in a straight artificial pool 1 multiple hypotheses have been advanced to explain the occurrence of pools in gravel bed rivers these hypotheses were developed without a hydrodynamic model of how open channel flow is affected by pools and it is not clear why and when the flow phenomena they describe might occur laboratory experiments are warranted to improve our understanding of how a gradual convective deceleration and acceleration of the flow without flow separation redistributes flow and turbulence in an open channel experiments are conducted in a 1 5 m wide flume with a 0 25 m deep 7 29 m long straight pool entry and exit slopes of 5 vertical side walls and gravel sediment d50 9 9 mm three dimensional velocity components are recorded at 50 hz using nortek vectrinos velocity and reynolds stress profiles in the channel centerline agree with previous results in nonuniform flow and include increased reynolds stress during deceleration and high velocity near the bed during acceleration lateral flow convergence occurs where depth is increasing which demonstrates that convergence is induced during flow deceleration and does not require a lateral flow constriction turbulence during deceleration is characterized by sweeps angled toward the sidewall of the channel an effect that could lead to the formation of a nonuniform pool depth through lateral gradients in the deposition of mobile sediment a conceptual model of pool hydrodynamics is proposed that includes increased turbulence near bed acceleration and lateral flow convergence as linked aspects of convective deceleration and acceleration due to depth changes in the pool

the trouble with shear stress abstract predicted bedload fluxes often have large errors partly because calculations usually do not include spatial and temporal flow variability sediment motion is driven by a temporal distribution of applied fluid forces which are often simplified into time averaged flow velocities or shear stresses in sediment transport equations spatial variations in these flow parameters are also often neglected given the nonlinearities in the relation between flow and sediment flux the reach averaged sediment flux calculated with an average velocity or shear stress will not necessarily equal the measured spatially averaged bedload flux such spatial and temporal flow variations are ignored with the commonly used reach averaged shear stress ds that is a function of the flow depth and channel slope to demonstrate the uncertainties with using reach averaged shear stresses and even local shear stresses to predict bedload transport rates we have three goals first we outline the derivations and assumptions involved with commonly used estimates of shear stress second we summarize the literature on the uncertainties involved with using shear stress and other space and time averaged flow parameters to predict sediment flux third we use a new data set from experiments to add further support to a growing body of literature that suggests ds may not be linked to the mechanics of bedload transport we show considerable uncertainties exist in estimating a reach averaged shear stress by comparing ds and near bed shear stresses calculated from velocity profiles reynolds stresses and local turbulence for example ds was systematically greater than these near bed stresses even for experiments without large bed roughness we also find that correlations between local time averaged sediment fluxes and local reynolds stresses or turbulence intensities are relatively poor the near bed time averaged local flow velocity has the strongest relation with the time averaged local bedload flux because it is closely related to the forces that actually drive sediment transport however sediment transport rates in individual experiments could still vary by orders of magnitude for a given value of this flow velocity suggesting that additional work is needed to identity a parameter or distributions of parameters that will best predict sediment fluxes

three dimensional model of alluvial stratigraphy theory and applications abstract a three dimensional model of alluvial stratigraphy has been developed to simulate the spatial distribution proportion and connectedness of coarse grained channel belt deposits in alluvial strata as a function of channel belt width floodplain width bankfull channel depth channel belt and overbank sedimentation rates avulsion location and period compaction and tectonism tilting and faulting in this model a floodplain surface of variable width and length is occupied by a single channel belt changes in floodplain topography are produced by spatial and temporal variation of channel belt and floodplain deposition rates and by compaction and local or regional tectonism the location and timing of avulsions are determined by local changes in floodplain slope relative to channel b lt slope and by flood magnitude and frequency the diverted channel belt follows the locus of maximum floodplain slope at the end of each simulation architectural parameters are calculated including channel deposit proportion and connectedness and the dimensions of channel belt sandstone bodies three dimensional perspective diagrams mesh surfaces and two dimensional stratigraphic sections can be plotted to illustrate depositional surfaces time planes and the location and geometry of coarse grained channel belt deposits within finer grained overbank deposits the model predicts that channel belt proportion and connectedness and dimensions of sandstone bodies vary as a function of distance from avulsion points and cross section orientation upstream from avulsion points sandstone bodies have low width thickness ratios because of aggradation in a fixed channel belt immediately downstream from avulsion points channel belts tend to be connected resulting in sandstone bodies with high width thickness ratios avulsion sequences develop where points of avulsion shift up valley with a progressive decrease in avulsion period such sequences may produce successions in which channel belt proportion and connectedness vary vertically with a cyclic period of 103 to 105 years down valley increases in aggradation rate or down valley decreases in floodplain slope for example associated with a rise in base level may result in an increase in channel belt proportion and connectedness because of high avulsion frequencies in down valley regions of the floodplain down valley decreases in aggradation rate as in alluvial fans foreland basins and during base level fall may result in high avulsion frequencies in up valley parts of the floodplain tectonic tilting and faulting locally increase avulsion probabilities and channel belts generally shift toward areas of maximum subsidence under certain conditions however depositional topography may cause channels to shift away from areas of maximum subsidence channel deposit proportion and connectedness are gen rally high near downthrown areas of the floodplain but distribution clustering of channel belts may not be a reliable indicator of fault geometry or displacement models of alluvial architecture that consider only sediment accumulation rate as the main controlling factor are oversimplified the three dimensional model presented here predicts many of the features of channel behavior observed in modern rivers but there is a pressing need for better models and adequate natural data to test them

bedload and suspended load contributions to breaker bar morphodynamics abstract this study presents measurements of sheet flow processes grain sorting and bedload plus suspended load transport rates around a medium sand breaker bar in a large scale wave flume the results offer insights in effects of wave breaking on bedload and grain sorting processes and in the quantitative contributions by bedload and suspended transport to breaker bar morphodynamics sheet flow layer dynamics are highly similar to observations under non breaking waves revealing clear effects by velocity asymmetry but no evident effects by breaking generated turbulence bed slope or the cross shore non uniform flow the sheet flow layer thickness can be predicted using existing empirical formulations based on local hydrodynamic forcing at locations covering the shoaling region up to the bar crest the cross shore variation in bedload transport rates is explained by variations in wave shape i e velocity skewness and asymmetry at locations between bar crest and bar trough bedload transport rate magnitudes correlate positively with bed slope and turbulent kinetic energy bedload and suspended load transport rates are of similar magnitude but of opposite sign bedload transport is onshore directed and dominates in the shoaling zone but after wave breaking the offshore directed suspended sediment transport increases in magnitude and exceeds bedload transport rates in the breaking and inner surf zones bedload and suspended load transport contribute notably differently to bed profile evolution bedload transfers sand grains from the offshore slope to the bar crest and additionally leads to erosion of the shoreward bar slope and deposition at the bar trough while suspended load transport induces an opposite pattern of erosion at the bar trough and accretion at the bar crest grain size analysis of suspended sediment samples reveals size selective entrainment and vertical size segregation in the inner surf zone but suggest size indifferent entrainment and vertical mixing by energetic vortices in the breaking region size selective transport by bedload and suspended load leads to a cross shore coarsening of the bed from shoaling to inner surf zone with local additional sorting mechanisms around the breaker bar due to bed slope effects

multiscale flow vegetation sediment feedbacks in low gradient landscapes abstract low gradient fluvial landscapes 1 50 cm km 1 occupy diverse settings inland tidal and deltaic wetlands large river floodplains lowland streams but share many commonalities because of low flow energies these landscapes have abundant vegetation that is submersed or frequently inundated their sediment loads are predominantly fine with large loads transported in suspension the complexities of fluvial vegetation interactions and fine sediment transport have made these landscapes relatively poorly studied in the field of geomorphology yet the importance of understanding their dynamics is paramount these landscapes will be among the first inundated by rising seas and or are presently the focus of the world s largest restoration projects in this synthesis interactions between flow vegetation and sediment documented in inland and tidal marshes chalk and coastal plain streams large river floodplains and deltas are reviewed and classified into feedback processes occurring over a range of five spatiotemporal scales despite different morphologic appearances the feedback processes governing the coevolution of landscapes and vegetation are broadly consistent across settings though modified in their effects by life history traits of vegetation characteristics of the sediment supply external boundary forcing and initial conditions longitudinally elongated patches are common in many settings arising from stress divergence feedbacks however their ultimate morphology is strongly dependent upon the activation of patch or multipatch scale feedbacks which depends on initial densities at the time of colonization generally flow vegetation sediment feedbacks play a dominant role in landscape morphology when the setting is depositional and little initial topographic differentiation is present in that case these feedbacks can explain the apparently paradoxical emergence of high sinuosities or parallel drainage in very low gradients importantly for management flow vegetation sediment interactions may activate a chain of positive feedbacks that engages progressively larger scales resulting in massive destruction of marsh vegetation or topographic homogenization interrupting these feedbacks requires intervention over all scales activated

use of sedimentological information for geometric simulation of natural porous media structure a geometric simulation method was used to develop a three dimensional highly detailed synthetic representation of point bar sediments in the wabash river system geometric simulation methods in comparison to well known second order stochastic methods offer the advantage of being more closely related to depositional processes which are often similarly conceptualized i e described in terms of shapes of discrete bed forms trends in grain size and spatial relationships of defined geologic facies multiple scales of geometric variation were defined within a sedimentologically prescribed framework and shapes of discrete geometric elements were established at each scale the selected shapes were based on published field studies including sedimentological bed form studies and trench studies in active point bar sediments the parameterization of the shapes allowed for random variability of the shape descriptors discrete shapes were then generated and assimilated by computer hydraulic conductivity values were assigned to the discrete elements based on reports of observed variations in grain size and field measurements of hydraulic conductivity the synthetic model referred to as a numerical aquifer is being used as the basis for extensive numerical experimentation to study the relationship between natural spatial structure and subsurface flow and transport

laboratory observations of flow and sediment transport induced by plunging regular waves 1 two parallel experiments involving the evolution and runup induced by plunging regular waves near the shoreline of a sloping bed are considered 1 a rigid bed experiment allowing direct hot film measurements of bed shear stresses and 2 a sediment bed experiment allowing for the measurement of pore water pressures as well as observation of sediment suspension and bed morphological changes both experiments utilize the same initial bed profile and wave forcing the experiments show that the mean bed shear stresses experienced onshore of incipient breaking are amplified by nearly a factor of 2 relative to prebreaking conditions whereas their corresponding turbulent fluctuations are amplified even more strongly by a factor of 5 6 the plunging processes lead to a series of vortices whose formation may be explained as the result of shear layer instability measurements show that these vortices can significantly enhance peaks in the offshore directed bed shear stresses moreover near bed pore pressure measurements indicate that these vortices cause large upward directed pressure gradients which in turn produce a corresponding series of suspended sediment plumes shoreward of the initial breaking event these findings are related to the induced morphological changes over both short and long time scales the present results are also compared and contrasted with previous experiments utilizing a similar methodology but involving plunging solitary waves

the importance of splat events to the spatiotemporal structure of near bed fluid velocity and bed load motion over bed forms laboratory experiments downstream of a backward facing step flow separation reattachment on the lee side of alluvial bedforms is known to produce a complex turbulence field but the spatiotemporal details of the associated patterns of bedload sediment transported remain largely unknown here we report turbulence resolving simultaneous measurements of bedload motion and near bed fluid velocity downstream of a backward facing step in a laboratory flume two synchronized high speed video cameras simultaneously observed bedload motion and the motion of neutrally buoyant particles in a laser light sheet 6 mm above the bed at 250 frames s downstream of a 3 8 cm backward facing step particle imaging velocimetry piv and acoustic doppler velocimetry adv were used to characterize fluid turbulent patterns while manual particle tracking techniques were used to characterize bedload transport octant analysis conducted using adv data coupled with markovian sequence probability analysis highlights differences in the flow near reattachment versus farther downstream near reattachment three distinct flow patterns are apparent farther downstream we see the development of a dominant flow sequence localized intermittent high magnitude transport events are more apparent near flow reattachment these events are composed of streamwise and cross stream fluxes of comparable magnitudes transport pattern and fluid velocity data are consistent with the existence of permeable splat events wherein a volume of fluid moves toward and impinges on the bed sweep causing a radial movement of fluid in all directions around the point of impingement outward interaction this is congruent with flow patterns identified with octant analysis proximal to flow reattachment

entrainment and motion of coarse particles in a shallow water stream down a steep slope we investigate the entrainment deposition and motion of coarse spherical particles within a turbulent shallow water stream down a steep slope this is an idealization of bed load transport in mountain streams earlier investigations have described this kind of sediment transport using empirical correlations or concepts borrowed from continuum mechanics the intermittent character of particle transport at low water discharges led us to consider it as a random process sediment transport in this regime results from the imbalance between entrainment and deposition of particles rather than from momentum balance between water and particles we develop a birth death immigration emigration markov process to describe the particle exchanges between the bed and the water stream a key feature of the model is its long autocorrelation times and wide frequent fluctuations in the solid discharge a phenomenon never previously explained despite its ubiquity in both nature and laboratory experiments we present experimental data obtained using a nearly two dimensional channel and glass beads as a substitute for sediment entrainment trajectories and deposition were monitored using a high speed digital camera the empirical probability distributions of the solid discharge and deposition frequency were properly described by the theoretical model experiments confirmed the existence of wide and frequent fluctuations of the solid discharge and revealed the existence of long autocorrelation time but theory overestimates the autocorrelation times by a factor of around three particle velocity was weakly dependent on the fluid velocity contrary to the predictions of the theoretical model which performs well when a single particle is moving for our experiments the dependence of the solid discharge on the fluid velocity is entirely controlled by the number of moving particles rather than by their velocity we also noted significant changes in the behaviour of particle transport when the bed slope or the water discharge was increased the more vigorous the stream was the more continuous the solid discharge became moreover although 90 of the energy supplied by gravity to the stream is dissipated by turbulence for slopes lower than 10 particles dissipate more and more energy when the bed slope is increased but surprisingly the dissipation rate is nearly independent of fluid velocity a movie is available with the online version of the paper

suction removal of sediment from between armor blocks this paper presents the results of an experimental investigation on suction removal of sediment from between armor blocks stones placed on a loose bed the process of suction has been investigated it was found that the vortices that form in the holes between the armor blocks are key to the process the sediment swept into these vortices is entrained into the main body of the flow by these same vortices the suction removal of sediment from between the armor blocks the critical condition for the onset of suction was determined it was found that the onset of suction is governed by two parameters 1 the shields parameter based on the sediment size and 2 the ratio of sediment size to stone size d d the variation of the critical shields parameter for suction as a function of d d was determined for a broad range of the parameter d d namely 0 001 d d 1 the timescale of the suction process and the downward displacement of stones the general lowering of the armor layer have also been investigated

a stochastic approach to the characterization of lithofacies from surface seismic and well data heterogeneity of natural geologic formations strongly influences groundwater flow and contaminant migration this study presents a formal stochastic approach for the integration of surface seismic data and well data into the identification of the spatial arrangement location geometry and interconnectedness of lithofacies and incorporating this information in the estimation of the log permeability probability density function pdf to achieve this goal normal move out nmo corrections are applied to the seismic reflection data to estimate interval seismic velocities calibration curves constructed from the well logs transform these velocity estimates into a lithology indicator prior probability field from the well data and the indicator prior probability field the indicator covariance function and its associated confidence limits are computed neighboring lithology logs and the indicator covariance function are then combined to update the indicator probability field the conditional log permeability pdf is finally computed by weighting the log permeability distribution of each lithology with respect to its indicator probability field the effectiveness of the proposed procedure is shown to depend on the quality of the seismic data and the degree of correlation between seismic and hydrogeologic soil properties a synthetic case study is performed which shows that the surface seismic and well data complement each other with optimal results achieved when both types of data are incorporated into a joint identification procedure

rans based simulation of turbulent wave boundary layer and sheet flow sediment transport processes abstract a numerical model coupling the horizontal component of the incompressible reynolds averaged navier stokes rans equations with two equation k turbulence closure is presented and used to simulate a variety of turbulent wave boundary layer processes the hydrodynamic model is additionally coupled with bed and suspended load descriptions the latter based on an unsteady turbulent diffusion equation for simulation of sheet flow sediment transport processes in addition to standard features common within such rans based approaches the present model includes 1 hindered settling velocities at high suspended sediment concentrations 2 turbulence suppression due to density gradients in the water sand mixture 3 boundary layer streaming due to convective terms and 4 converging diverging effects due to a sloping bed the present model therefore provides a framework for simultaneous inclusion of a number of local factors important within cross shore wave boundary layer and sediment transport dynamics the hydrodynamic model is validated for both hydraulically smooth and rough conditions based on wave friction factor diagrams and boundary layer streaming profiles with the results in excellent agreement with experimental and or previous numerical work the sediment transport model is likewise validated against oscillatory tunnel experiments involving both velocity skewed and acceleration skewed flows as well as against measurements beneath real progressive waves model capabilities are exploited to investigate the importance of boundary layer streaming effects on sediment transport in selected velocity skewed conditions for the medium sand grain conditions considered the model results suggest that streaming effects can enhance onshore sediment transport rates by as much as a factor of two moreover for fine sand conditions streaming and related convective effects are demonstrated to potentially reverse the direction of net transport i e from offshore to onshore relative that predicted in oscillatory tunnel conditions the developed model is implemented within the popular matlab environment and hence may be attractive for both research and educational purposes

hydrostratigraphic interpretation using indicator geostatistics in this paper we describe an approach that uses indicator geostatistics to interpret qualitative borehole logs and compute experimental variograms for complex alluvial sediments borehole descriptions are first transformed into binary indicator values based on inferred relative permeability from the borehole descriptions the resulting indicator data can then be used to compute variograms and construct three dimensional variogram models the ranges of computed indicator variograms for a groundwater contamination site in santa clara valley california are very sensitive to the orientation of the search plane these variograms are consistent with known stratigraphie features and describe the spatial structure of deposits from different depositional environments indicator kriging weighs all the available data on the basis of a three dimensional anisotropic variogram model and provides an estimate of uncertainty in the hydrostratigraphic correlation kriged indicator values represent probabilities that sediments at a specific location fall into one of two indicator categories the location of the 0 5 indicator contour is approximately the boundary between high and low permeability sediments that might be constructed in a geologic cross section

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

anatomy and dynamics of a floodplain powder river montana u s a abstract centimeter scale measurements on several powder river floodplains provide insights into the nature of overbank depositional processes that created the floodplains during a 20 year period after a major flood in 1978 rising stages initially entered across a sill at the downriver end of the floodplains later as stages continued to rise water entered the floodplains through distinct low saddles along natural levees the annual maximum depth of water over the levee crest averaged 0 19 m from 1983 through 1996 and the estimated flow velocities were approximately 0 15 m s 1 water ponded in the floodplain trough a topographic low between the natural levee and the pre flood riverbank and mud settled as thin layers of nearly constant thickness mud layers alternated with sand layers which were relatively thick near the channel together these beds created a distinctive natural levee in some locations individual flood deposits began as a thin mud layer that gradually coarsened upwards to medium grained sand coarsening upwards sequences form initially as mud because only the uppermost layers of water in the channel supply the first overbank flows which are rich in mud but starved of sand at successively higher stages fine sands and then medium sands increase in concentration in the floodwater and are deposited as fine and medium sand layers overlying the initial mud layer theoretical predictions from mathematical models of sediment transport by advection and diffusion indicate that these processes acting alone are unlikely to create the observed sand layers of nearly uniform thickness that extend across much of the floodplain we infer that other transport processes notably bedload transport must be important along powder river even with the centimeter scale measurements of floodplain deposits daily hydraulic data and precise annual surface topographic surveys we were unable to determine any clear correspondence between the gauged flow record of overbank floods and the depositional layers mapped in the floodplain these results provide a detailed example of floodplain deposits and depositional processes that should prove useful for interpreting natural levee deposits in a variety of geologic settings

flow field complexity and design estimation of pier scour depth sixty years since laursen and toch abstractthis paper written to celebrate the 60th anniversary of the journal of hydraulic engineering presents a structured contemporary approach to scour depth estimation that matches design met

numerical and experimental investigation of flow and scour around a half buried sphere abstract the paper describes the results of a numerical and experimental investigation of flow and scour around a half buried sphere exposed to a steady current hot film bed shear stress and laser doppler anemometer measurements were made with a half sphere mounted on the smooth bed in an open channel the hydrodynamic model is a 3 d general purpose n s flow solver the k omega sst turbulence model was used for closure the flow model was used to study the horseshoe vortex and lee wake vortex flow processes around the sphere the flow model was coupled with a morphologic model to calculate scour around the half buried sphere in currents the morphologic model includes a sediment transport description and a description of surface layer sand slides for bed slopes exceeding the angle of repose the sediment transport description includes for the first time the effect of externally generated turbulence induced by the horseshoe vortex flow and the lee wake flow processes on sediment transport the results show that the scour depth increases and time scale decreases when the effect of externally generated turbulence is incorporated in the calculations empirical expressions representing the numerically obtained data on the equilibrium scour depth and the time scale are presented the results show that the equilibrium maximum scour depth in the live bed regime can be approximated by 0 5 d in which d is the sphere diameter

influence of turbulence on bed load sediment transport this paper summarizes the results of an experimental study on the influence of an external turbulence field on the bed load sediment transport in an open channel the external turbulence was generated by 1 a horizontal pipe placed halfway through the depth ih 2 a series of grids with a clearance of about one third of the depth from the bed and extending over a finite length of the flume and 3 a series of grids with a clearance in the range 0 1 1 0 ih from the bed but extending over the entire length of the flume two kinds of experiments were conducted plane bed experiments and ripple covered bed experiments in the former case the flow in the presence of the turbulence generator was adjusted so that the mean bed shear stress was the same as in the case without the turbulence generator in order to single out the effect of the external turbulence on the sediment transport in the ripple covered bed case the mean and turbulence quantities of the streamwise component of the velocity were measured and the shields parameter due to skin friction was determined the shields parameter together with the rms value of the streamwise velocity fluctuations was correlated with the sediment transport rate the sediment transport increases markedly with increasing turbulence level

the impact of coarse grain protrusion on near bed hydrodynamics in steep rivers sediment is often transported over immobile cobbles and boulders previous studies of such conditions have observed that the entrainment rate of the mobile sediment strongly depends on the level of protrusion of the immobile grains here experiments are conducted in a laboratory flume in order to quantify how different levels of protrusion of large aggregates above a fixed fine sediment bed modeled as a patch of hemispheres modify the local hydrodynamics near the fine sediment bed five protrusion levels defined by p k r 0 20 40 60 80 were investigated where k is the protrusion height and r the radius for small protrusion p 20 enhanced shear stress and turbulence intensity on the fine sediment bed is observed as the mixing layer generated at the hemisphere top impacts the fine sediment bed moreover sweep events generated near the top of the hemispheres reach the fine sediment bed for large protrusions p 60 the mixing layer generated near the top of the hemispheres does not reach the fine grains with the consequence that the shear stress drops the remaining turbulence near the fine sediment bed although enhanced by the wakes generated by the hemispherical caps is quasi isotropic the transition between these two distinct near bed flow regimes is found to be around p 40 corresponding to the protrusion levels observed by grams and wilcock 2014 https doi org 10 1002 2013jf002925 above which the erosion of fine sediment ceases

calculation of dune morphology 1 the shape and dimensions of dunes formed in an erodible bed and exposed to flowing water are investigated by using a numerical model the flow is calculated using a curvilinear flow model where we combine a k turbulence closure scheme with a sediment transport description and the equation of continuity for the sand bed the complete flow description allows for a discussion about what determines the length of dunes from the equation of continuity for sediment it turns out that the sediment transport over dunes is proportional to the local height of the dune this means that the maximum height of the sand wave occurs at the location of maximum sediment transport we relate the dune length to the location of maximum sediment transport it is demonstrated that the effect of streamline curvature is essential for determining the location of maximum sediment transport at low bed shear stresses due to an overshoot in bed shear stress for large dimensionless bed shear stresses the downstream decay of turbulence from the former dune is demonstrated to play a major role

coherent structure dynamics and sediment erosion mechanisms around an in stream rectangular cylinder at low and moderate angles of attack 1 local scour around elongated in stream structures e g high aspect ratio rectangular bridge piers is mainly driven by the interactions between the erodible bed and the large scale coherent structures generated by the presence of the flow obstruction the present investigation uses eddy resolving numerical simulations to study the mean flow and turbulence structure around a high aspect ratio rectangular cylinder placed in a flat bed channel simulations are conducted for three angles of attack 0 15 and 30 at a channel reynolds number of 2 4 105 this paper focuses on the dynamics of the large scale coherent structures forming around the rectangular cylinder and their role in controlling sediment entrainment at conditions corresponding to the start of the scour process simulation results show that most of the sediment is entrained from the bed by the eddies shed inside the separated shear layers ssls by the legs of the necklace vortices and by the strongly accelerated flow on the outer side of the ssls for 0 and 15 the horseshoe vortex hv system plays a relatively minor role in the entrainment of sediment in front of the cylinder and the passage of the wake vortices rollers results in a small amplification of the bed friction velocity in contrast for 30 the unsteady dynamics of the main necklace vortices part of the hv system and of the roller vortices results in a significant amplification of the instantaneous bed friction velocity the mean flux of sediment entrained from the bed calculated on the basis of the mean flow field is found to underestimate by 2 3 times the same quantity when estimated more correctly on the basis of the instantaneous flow fields the primary reason for this underestimation is sediment entrainment in regions where the mean flow bed friction velocity is smaller than the critical value for entrainment quantitative information on the extent of the regions of high values of the bed friction velocity and its standard deviation and on the sediment entrainment flux as a function of the angle of attack is essential to guide scour protection measures around the in stream noncircular obstructions

a geomorphological approach to determining the neogene to recent tectonic deformation in the coastal cordillera of northern chile atacama the large 10000 km2 and local scale 300 m sedimentary succession was deposited east of the afs the succession fills previously deep paleovalleys and it consists of gravel so called atacama gravels which passes laterally into fine grained playa related deposits near the afs we interpret the deposition of this succession as a result of a blocking closure of the valley flowing from the precordillera due to the activity on afs a pedimentation episode followed sediment deposition and is locally strongly re incised by the main modern day river valleys draining the precordillera incision may result from either regional uplift of the forearc and or from more localized activity on the afs furthermore recent quaternary tectonic activity on the afs has been observed which is consistent with a localized relative uplift of the crustal block west of the afs

suspended sediment transport around a large scale laboratory breaker bar this paper presents novel insights into suspended sediment concentrations and fluxes under a large scale laboratory plunging wave measurements of sediment concentrations and velocities were taken at 12 locations around an evolving breaker bar covering the complete breaking region from shoaling to inner surf zone with particular high resolution near the bed using an acoustic concentration and velocity profiler wave breaking evidently affects sediment pick up rates which increase by an order of magnitude from shoaling to breaking zone time averaged reference concentrations correlate poorly with periodic and time averaged near bed velocities but correlate significantly with near bed time averaged turbulent kinetic energy the net depth integrated suspended transport is offshore directed and primarily attributed to current related fluxes undertow at outer flow elevations i e above the wave bottom boundary layer the wave related suspended transport is onshore directed and is generally confined to the wave bottom boundary layer cross shore gradients of sediment fluxes are quantified to explain spatial patterns of sediment pick up and deposition and of cross shore sediment advection suspended particles travel back and forth between the breaking and shoaling zones following the orbital motion leading to local intra wave concentration changes at locations between the breaker bar crest and bar trough intra wave concentration changes are due to a combination of horizontal advection and of vertical exchange with the bedload layer sediment is entrained in the bar trough during the wave trough phase almost instantly advected offshore and deposited near the bar crest during the wave crest phase finally these results are used to suggest improvements for suspended sediment transport models

river and floodplain process simulation for subsurface characterization subsurface heterogeneity is characterized with a method based on facies delineation and process modeling a geologic process model is formulated to simulate the development of four facies channel fill levee splay and floodplain which commonly form in a meandering river and its floodplain the model accounts for meandering cutoff flooding and crevasse splay processes and links these formational processes to the statistical properties of the resulting facies the model is utilized in a case study to simulate the horizontal pattern of deposition and facies distributions of the stratton field part of the middle frio formation of southeast texas using known or estimated relationships and historical information for the stratton field region the simulated distributions of longitudinal and transverse facies dimensions and corresponding transition probabilities among facies are compared to those determined from sampling an observed section of the field yielding similar results though some differences similarities and differences are related to the model processes and sampling procedures model sensitivity is investigated by changing selected model variables and analyzing the change in the facies distributions the application of the geologic process model to the stratton field demonstrates the viability of linking process understanding and modeling of complex meandering stream processes to characterization of subsurface heterogeneity

evaluation of bed load transport subject to high shear stress fluctuations 1 many formulas available in the literature for computing sediment transport rates are often expressed in terms of time mean variables such as time mean bed shear stress or flow velocity while effects of turbulence intensity e g bed shear stress fluctuation on sediment transport were seldom considered this may be due to the fact that turbulence fluctuation is relatively limited in laboratory open channel flows which are often used for conducting sediment transport experiments however turbulence intensity could be markedly enhanced in practice this note presents an analytical method to compute bed load transport by including effects of fluctuations in the bed shear stress the analytical results obtained show that the transport rate enhanced by turbulence can be expressed as a simple function of the relative fluctuation of the bed shear stress the results are also verified using data that were collected recently from specifically designed laboratory experiments the present analysis is applicable largely for the condition of a flat bed that is comprised of uniform sand particles subject to unidirectional flows

sediment mobility in a forced riffle pool forced riffle pools occur in gravel bed rivers where a large nonalluvial element leads to local scour and deposition to manage rivers where this type of morphology is found and to specify restoration measures that mimic this process more field data on sediment mobility in forced riffle pools is needed the objectives of this study are to describe the spatial variability of sediment mobility and deposition in a developing forced riffle pool and to use high resolution flow velocity measurements to explain the observed dynamics the field site is a forced riffle pool in moras creek a 6 m wide gravel bed stream with a 1 2 bed slope in quebec canada topography and the movement of sediment particles equipped with passive integrated transponder pit tags are surveyed through a series of competent floods bed shear stress is estimated from near bed measurements of time averaged velocity and turbulent kinetic energy the sediment transport regime of the creek is characterized by partial mobility exponential distributions of path lengths and a negative relation between particle size and path length full mobility occurs in the center of the pool and over the exit slope where flow is accelerated from the constriction of flow during two events above the bankfull discharge partial mobility occurs during the same events over the entrance slope to the pool lateral gradients of deposition and mobility suggest that the majority of sediment in motion is routed over the side bar at the entrance to the pool high levels of turbulence intensity that occur as a result of flow deceleration may explain the removal of finer sediments from the head of the pool

variation in the reference shields stress for bed load transport in gravel bed streams and rivers 1 the present study examines variations in the reference shear stress for bed load transport r using coupled measurements of flow and bed load transport in 45 gravel bed streams and rivers the study streams encompass a wide range in bank full discharge 1 2600 m3 s average channel gradient 0 0003 0 05 and median surface grain size 0 027 0 21 m a bed load transport relation was formed for each site by plotting individual values of the dimensionless transport rate w versus the reach average dimensionless shear stress the reference dimensionless shear stress r was then estimated by selecting the value of corresponding to a reference transport rate of w 0 002 the results indicate that the discharge corresponding to r averages 67 of the bank full discharge with the variation independent of reach scale morphologic and sediment properties however values of r increase systematically with average channel gradient ranging from 0 025 0 035 at sites with slopes of 0 001 0 006 to values greater than 0 10 at sites with slopes greater than 0 02 a corresponding relation for the bank full dimensionless shear stress bf formulated with data from 159 sites in north america and england mirrors the relation between r and channel gradient suggesting that the bank full channel geometry of gravel and cobble bedded streams is adjusted to a relatively constant excess shear stress bf r across a wide range of slopes

flow and bed shear stresses in scour protections around a pile in a current abstract transport of bed sediment inside and beneath the scour protection may cause deformation and sinking of the scour protection for pile foundations this may reduce the stability of the mono pile and change the natural frequency of the dynamic response of an offshore wind turbine installed on it in an unfavourable manner using physical models and 3d computational fluid dynamic cfd numerical simulations the velocity and bed shear stresses are investigated in complex scour protections around mono piles in steady current in the physical model the scour protections consisted of an upper cover layer with uniformly distributed coarse stones and a lower filter layer with finer stones for the numerical simulations the flow 3d software was used the scour protection layers were simulated with different numerical approaches namely regularly arranged spheres porous media or their combinations hybrid models numerical simulations with one or four layers of cover stones without filter layer were first computed three additional simulations were then made for a scour protection with a cover layer and a single filter layer finally a simulation of a full scale foundation and scour protection was made with porous media approach based on the physical and numerical results a method to determine the critical stones size to prevent motion of the base sediment is established and compared to a full scale case with sinking of scour protection horns rev i offshore wind farm denmark it is also found that the cfd simulations are capable of calculating the flow velocities when the scour protection is represented by regular arranged spheres while the turbulence in general is underestimated the velocity can also be calculated using porous media flow approach but the accuracy is not as good as for spheres the deviation is more severe for more complex scour protections in general computational models provide valuable information for the prediction and design of scour protections for offshore wind farms

flow and sediment transport induced by a plunging solitary wave 1 two parallel experiments involving the evolution and runup of plunging solitary waves on a sloping bed were conducted 1 a rigid bed experiment allowing direct hot film measurements of bed shear stresses and 2 a sediment bed experiment allowing for the measurement of pore water pressures and for observation of the morphological changes the two experimental conditions were kept as similar as possible the experiments showed that the complete sequence of the plunging solitary wave involves the following processes shoaling and wave breaking runup rundown and hydraulic jump and trailing wave the bed shear stress measurements showed that the mean bed shear stress increases tremendously with respect to that in the approaching wave boundary layer by as much as a factor of 8 in the runup and rundown stages and that the rms value of the fluctuating component of the bed shear stress is also affected by as much as a factor of 2 in the runup and hydraulic jump stages the pore water pressure measurements showed that the sediment at or near the surface of the bed experiences upward directed pressure gradient forces during the down rush phase the magnitude of this force can reach values as much as approximately 30 of the submerged weight of the sediment the experiments further showed that the sediment transport occurs in the sheet flow regime for a substantial portion of the beach covering the area where the entire sequence of the wave breaking takes place the bed morphology is explained qualitatively in terms of the measured bed shear stress and the pressure gradient forces