sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

modelling of the evolution of ground waters in a granite system at low temperature the stripa ground waters sweden abstract from chemical data collected by nordstrom and his colleagues on stripa ground waterswe have tried to model the evolution of the chemical composition of a ground water in a granitic system at low temperature the existence of two end member ground water compositions made it possible first to test the conventional model of a geothermal system according to which an overall equilibrium between the waters and a given mineral assemblage can be defined and then to show that such a model could be extended to low temperatures 10 c conversely if we know the mineral assemblage the equilibration temperature and the charge of the mobile ions in this case cl the composition of the solution is entirely fixed in our model of the stripa ground waters the existence of two end member ground water compositions can be explained by an evolution from a kaolinite albite laumontite equilibrium to a prehnite albite laumontite equilibium the latter requiring less al than the former we have also emphasized the importance of the cl ion concentrions ofof the ground waters because they cab be considered as indicators of the degree of reaction progress between rock and water thus determining the degree of equilibration of the system

lead and zinc distribution in carbonate rocks abstract a polarographic technique was utilized to determine lead and zinc concentrations in the acid soluble portion of limestones and dolostones the detection limit of the described technique is 0 2 ppm the studied samples mostly from australia cover the time span of 110 to 2700 ma the geometric mean of pb concentrations in both limestones and dolostones was found to be 3 1 ppm and for zn it was 4 2 and 6 1 ppm respectively statistical evaluation r mode factor analysis of these data complemented by the previously published chemical and isotopic measurements on identical samples shows that pb and zn load on a unique factor perhaps reflecting their substitution for ca and mg in the carbonate lattice however a weak secondary control on zn distribution in dolostones appears to be excercized by the presence of illite muscovite and or k feldspar and pb may be concentrated in reef bank rather than lagoonal environments furthermore zn concentrations in limestones appear to decrease slightly with increasing age of the samples

on the genesis and evolution of barchan dunes morphodynamics barchan dunes are crescent shaped formations of sand that can dominate both desert and subaqueous landscapes when the supply of sand is scarce because of the complexity and scale of the underlying phenomena the mechanisms governing the entire process from the genesis to the long term evolution of barchan fields still remain to be better understood herein we attempt to present a description of this process in a subaqueous environment by employing a large eddy simulation approach that couples turbulent flow and sand bed morphodynamics we show that the seeds of the emergent structure in barchan fields are random turbulent flow motions near the initially flat bed we also provide high resolution insights into phenomena such as barchan migration and merging and show how transverse sand waves are formed and migrate over the barchan horns furthermore the transverse sand waves over the barchan horns are shown to be the seeds of the newly born barchans at the end points of the two horns of a barchan through the process known as calving to show this we examine the celerity wavelength and amplitude of the transverse sand waves over the barchan as they approach the end of its horn the celerity and wavelength of these transverse sand waves are shown to be the defining factors in determining the frequency of the calving process the amplitude of the newly born barchans through calving is also shown to be associated with the amplitude of the transverse waves near the end of the horn the simulation data also show that the wavelength of the newly born barchans the distance between individual dunes is closely related to that of the transverse sand waves over their maternal barchan finally we use the simulation results to discuss past conclusions derived from theory conventional models and field observations

sediment flushing at the nakdong river estuary barrage the nakdong river estuary barrage nreb prevents salt water intrusion but causes sedimentation problems in the lower nakdong river in south korea its mitigation requires mechanical dredging to maintain the flood conveyance capacity during typhoons this analysis focuses on the possibility of replacing mechanical dredging with sediment flushing through gate operations changes at nreb the new approach first defines sediment flushing curves as a function of river stage and discharge the feasibility of flushing is then assessed from the comparison of the flushing curves with the flow duration curves the detailed analysis of long term simulations using a quasi steady numerical model provides detailed simulation results the model applications from 1998 to 2003 incorporate tidal effects at 15 min intervals and also include major floods caused by typhoons rusa in 2002 and maemi in 2003 accordingly about 54 of the mean annual dredging volume could be eliminated by sediment flushing at nreb the model also

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

flow resistance in ice covered alluvial channels this paper describes the influences of floating level ice covers on flow and bed load transport in alluvial channels and proposes a semi empirical procedure for calculating flow resistance in such channels the procedure can be applied in conjunction with several existing methods for estimating flow resistance in alluvial channels under open water conditions previously cover influence was poorly understood with the consequence that flow resistance calculations for ice covered alluvial channels entailed an inordinate amount of guesswork the cover influences described herein were determined from the results of experiments conducted with a laboratory flume the main findings of the flume experiments are that ice covers increase flow depth decrease bulk flow velocity increase dune length and significantly decrease bed load transport rate additionally it was found that sediment transport relationships developed for open water flow are applicable to ice covered flow provided they are used in conjunctio

modeling river dune development and dune transition to upper stage plane bed large asymmetric bedforms known as dunes commonly dominate the bed of sand rivers due to the turbulence generation over their stoss and lee sides dunes are of central importance in predicting hydraulic roughness and water levels during floods in steep alluvial rivers dunes are observed to grow rapidly as flow strength increases undergoing an unstable transition regime after which they are washed out in what is called upper stage plane bed this transition of dunes to upper stage plane bed is associated with high transport of bed sediment in suspension and large decrease in bedform roughness in the present study we aim to improve the prediction of dune development and dune transition to upper stage plane bed by introducing the transport of suspended sediment in an existing dune evolution model in addition flume experiments are carried out to investigate dune development under bed load and suspended load dominated transport regimes and to get insight in the time scales related to the transition of dunes to upper stage plane bed simulations with the extended model including the transport of suspended sediment show significant improvement in the prediction of equilibrium dune parameters e g dune height dune length dune steepness dune migration rate dune lee side slope both under bed load dominant and suspended load dominant transport regimes the chosen modeling approach also allows us to model the transition of dunes to upper stage plane bed which was not possible with the original dune evolution model the extended model predicts change in the dune shapes as was observed in the flume experiments with decreasing dune heights and dune lee slopes furthermore the time scale of dune transition to upper stage plane bed was quite well predicted by the extended model

regional fluid characterisation and modelling of water rock equilibria in the boom clay formation and in the rupelian aquifer at mol belgium abstract interstitial water from the boom clay formation around the hades high activity disposal experimental site an underground research facility belonging to the nuclear research centre sck cen at mol dessel belgium underground research facility at mol belgium and waters sampled at different locations in the rupelian aquifer underlying the clay formation have been studied the boom clay is a tertiary mudrock containing about 55 clay and the rupelian aquifer is located in a silty layer special care was taken to adapt or improve measurement sampling conservation and analysis methods to get a reliable regional and local database for the purpose of testing a general model describing the regulation and acquisition of the composition of these fluids the isotopic and chemical composition of the waters allows them to be assigned to a common origin namely mixing between a marine endmember and the clay interstitial water followed by reequilibration with the host rock through dissolution precipitation reactions involving identified secondary minerals oxidation reduction state and trace element behavior are also discussed and the limits of the model are outlined

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

flow resistance and bed form geometry in a wide alluvial channel 1 this paper explores the underlying mechanism of flow resistance in a wide alluvial channel with bed forms on the basis of published data it is shown that the grain roughness can be taken as equal to 2 times the median diameter of the bed sediment an empirical equation for the bed form roughness has been proposed and it depends on the bed form height and bed form steepness the influence of the bed form length and height on the total bed shear stress and energy slope is deliberated and empirical expressions for the length of the separation zone behind the bed forms are also proposed the study proposed an equation to compute the total bed shear stress as a function of the grain and bed form roughness as well as the important role of the bed form geometry in the overall flow resistance in alluvial channels the model is tested and verified against 670 flume measurements and 1540 field observations the computed and measured energy slopes are in good agreement with close to 71 of all data sets within the 20 error band

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

closed conduit bed form initiation and development nonintrusive measurement of closed conduit erodible bed development was undertaken for 12 experiments of ranges of flow strengths and sediment solids sizes analogous to open channel flows wavelets on the sediment bed of a closed conduit are instigated by discontinuities in the bed with wavelet lengths for laminar and turbulent open channel and closed conduit flows given by 175d0 75 where and sediment size d are in millimeters for closed conduit flows ripples and dunes grow from these wavelets at rates increasing with increasing flow strength and utilizing the mechanisms of bed form coalescence and throughpassing to limiting lengths heights steepnesses and bed friction factors that are approximately maintained or possibly decrease thereafter limitation of free surface deformation results in increased rates of bed wave development for closed conduit flows in comparison to open channel flows measured results indicate that equilibrium closed conduit ripple and dune magnitudes can be pre

applying the squeezing technique to highly consolidated clayrocks for pore water characterisation lessons learned from experiments at the mont terri rock laboratory abstract knowledge of the pore water chemistry in clayrock formations plays an important role in determining radionuclide chemical speciation and migration in the context of nuclear waste disposal among the different in situ and ex situ techniques for pore water sampling in clay sediments and soils the squeezing technique dates back 115 years although different studies have been conducted on the reliability and representativeness of squeezed pore waters most of these involved high porosity high water content and unconsolidated clay sediments very few of them analysed squeezed pore water from low porosity low water content and highly consolidated clayrocks in this paper a specially designed and fabricated one dimensional compression two directional fluid flow cell was used to extract and analyse the pore water composition of opalinus clay core samples from mont terri switzerland with water contents between 6 2 and 7 8 wt a study of the influence of the squeezing pressure on the chemistry of the pore water was performed at pressures of up to 200 mpa to validate and demonstrate the validity of the squeezing technique for obtaining reliable pore water different tests were performed at various pressures and the squeezed waters were compared with those obtained by other methods such as in situ collected borehole waters the reproducibility and quality of the squeezing method was also checked as well as different artifacts which could affect the reliability of the pore water data the results show that the reproducibility of the technique is good and no membrane effect ionic ultrafiltration chemical fractionation anion exclusion was found in opalinus clay at mont terri in the range of pressures analysed 70 200 mpa pore waters extracted in this range of pressures do not decrease in concentration as a function of pressure which indicates that a dilution of water by mixing of the free pore water and the outer layers of diffuse layer water does not occur and a threshold safety squeezing pressure of 175 mpa could be established to avoid membrane effects furthermore a direct comparison against in situ collected borehole waters shows that the pore waters extracted at these pressures are representative of the opalinus clay formation at mont terri extraction artifacts such as temperature effect oxidation and degassing can be avoided or minimised by taking special precautions when preparing and handling the core sample and extracting the pore water finally we show that it is possible to obtain insightful information on anion accessible porosity by combining squeezing data with aqueous leaching data to characterise the pore water composition and solute distribution for different rock porosities

modelling hydrodynamics in the rio parana argentina an evaluation and inter comparison of reduced complexity and physics based models applied to a large sand bed river abstract depth averaged velocities and unit discharges within a 30 km reach of one of the world s largest rivers the rio parana argentina were simulated using three hydrodynamic models with different process representations a reduced complexity rc model that neglects most of the physics governing fluid flow a two dimensional model based on the shallow water equations and a three dimensional model based on the reynolds averaged navier stokes equations flow characteristics simulated using all three models were compared with data obtained by acoustic doppler current profiler surveys at four cross sections within the study reach this analysis demonstrates that surprisingly the performance of the rc model is generally equal to and in some instances better than that of the physics based models in terms of the statistical agreement between simulated and measured flow properties in addition in contrast to previous applications of rc models the present study demonstrates that the rc model can successfully predict measured flow velocities the strong performance of the rc model reflects in part the simplicity of the depth averaged mean flow patterns within the study reach and the dominant role of channel scale topographic features in controlling the flow dynamics moreover the very low water surface slopes that typify large sand bed rivers enable flow depths to be estimated reliably in the rc model using a simple fixed lid planar water surface approximation this approach overcomes a major problem encountered in the application of rc models in environments characterised by shallow flows and steep bed gradients the rc model is four orders of magnitude faster than the physics based models when performing steady state hydrodynamic calculations however the iterative nature of the rc model calculations implies a reduction in computational efficiency relative to some other rc models a further implication of this is that if used to simulate channel morphodynamics the present rc model may offer only a marginal advantage in terms of computational efficiency over approaches based on the shallow water equations these observations illustrate the trade off between model realism and efficiency that is a key consideration in rc modelling moreover this outcome highlights a need to rethink the use of rc morphodynamic models in fluvial geomorphology and to move away from existing grid based approaches such as the popular cellular automata ca models that remain essentially reductionist in nature in the case of the world s largest sand bed rivers this might be achieved by implementing the rc model outlined here as one element within a hierarchical modelling framework that would enable computationally efficient simulation of the morphodynamics of large rivers over millennial time scales

application of a roughness length representation to parameterize energy loss in 3 d numerical simulations of large rivers 1 recent technological advances in remote sensing have enabled investigation of the morphodynamics and hydrodynamics of large rivers however measuring topography and flow in these very large rivers is time consuming and thus often constrains the spatial resolution and reach length scales that can be monitored similar constraints exist for computational fluid dynamics cfd studies of large rivers requiring maximization of mesh or grid cell dimensions and implying a reduction in the representation of bedform roughness elements that are of the order of a model grid cell or less even if they are represented in available topographic data these subgrid elements must be parameterized and this paper applies and considers the impact of roughness length treatments that include the effect of bed roughness due to unmeasured topography cfd predictions were found to be sensitive to the roughness length specification model optimization was based on acoustic doppler current profiler measurements and estimates of the water surface slope for a variety of roughness lengths this proved difficult as the metrics used to assess optimal model performance diverged due to the effects of large bedforms that are not well parameterized in roughness length treatments however the general spatial flow patterns are effectively predicted by the model changes in roughness length were shown to have a major impact upon flow routing at the channel scale the results also indicate an absence of secondary flow circulation cells in the reached studied and suggest simpler two dimensional models may have great utility in the investigation of flow within large rivers

modelling free forming meander evolution in a laboratory channel using three dimensional computational fluid dynamics abstract the present study investigated the use of computational fluid dynamics cfd in predicting the formation development and migration of free forming meander bends the three dimensional cfd model computed water flow and sediment transport in alluvial channels and predicted vertical and horizontal bed changes different algorithms and parameters were tested to provide an insight into the application range of cfd when modelling free forming meander formation the computational domain was discretized by an unstructured grid a control volume method was used for the discretization of the navier stokes equations for the flow calculation and of the convection diffusion equation for the sediment transport calculation turbulence was modelled by the k e turbulence model the simulation was started from an initially straight grid with neither sediment feed nor any perturbation at the inflow boundary the model computed the river bed evolution over a real time period of 3 d results were compared with laboratory experiments and showed that the cfd model can predict many of the characteristics of the alluvial meander formation and migration however some limitations and uncertainties exist that have to be clarified in future investigations

saline groundwaters in the hercynian granites chardon mine france geochemical evidence for the salinity origin abstract in this study the chemical evolution of high cl chardon mine groundwaters is modelled as a mixing between an oxidising recharge and an old marine component on which the water rock interaction is superimposed chemical and isotopic similarities with saline carnmenellis mine groundwaters are emphasised and a general comparison with other brines is discussed the cation content of deep granitic groundwaters is indicative of the water rock interaction in the case of chardon and carnmenellis groundwaters the high na cl ratio can still be related to the contribution of a brine of sedimentary origin to the water salinity the differences in the hydrochemistry related to their geological context only appears at the trace metals level on the contrary brines in plutonic rocks which exhibit a low na cl ratio represent groundwaters having a residence time in the host rock long enough to equilibrate with secondary aluminosilicates in that case the brine origin is difficult to assess if only based on the water cation content

morphological changes of gumara river channel over 50 years upper blue nile basin ethiopia summary in response to anthropogenic disturbances alluvial rivers adjust their geometry the alluvial river channels in the upper blue nile basin have been disturbed by human induced factors since a longtime this paper examines channel adjustment along a 38 km stretch of the gumara river which drains towards lake tana and then to the blue nile over a 50 years period agriculture developed rapidly in the catchment and flooding of the alluvial plain has become more frequent in recent times the objectives of this study were to document the changes in channel planform and cross section of the gumara river and to investigate whether the changes could have contributed to the frequent flooding or vice versa two sets of aerial photographs 1957 and 1980 were scanned and then orthorectified recent channel planform information was extracted from spot images of 2006 and google earth channel planform and bed morphology vertical changes were determined for these nearly 50 years period the vertical changes were determined based on aggradation along a permanent structure historic information on river cross sections at a hydrological gauging station and field observations the results indicate that the lower reach of gumara near its mouth has undergone major planform changes a delta with approx 1 12 km 2 of emerged land was created between 1957 and 1980 and an additional 1 km 2 of land has been added between 1980 and 2006 the sinuosity of the river changed only slightly negatively 1 1 i e meandering decreased for the period from 1957 to 1980 and positively 3 0 for the period 1980 2006 comparison of cross sections at the hydrological gauging station showed that the deepest point in the river bed aggraded by 2 91 m for the period 1963 2009 the importance of sediment deposition in the stream and on its banks is related to land degradation in the upper catchment and to artificial rising of lake tana level that creates a backwater effect and sediment deposition in gumara river direct anthropogenic impacts irrigation activities and building of dykes along the river banks have contributed to the huge deposition in the river bed where the abstraction of water for irrigation is intensive seepage water through the banks has contributed to river bank failure in general this study showed that changes to the planform at the mouth of the river and to the riverbed level are substantial moreover the study indicated that the flood carrying capacity of the gumara river channel has diminished in recent times

variability in bedform morphology and kinematics with transport stage bedform geometry is widely recognized to be a function of transport stage bedform aspect ratio height length increases with transport stage reaches a maximum then decreases as bedforms washout to a plane bed bedform migration rates are also linked to bedform geometry in so far as smaller bedforms in coarser sediment tend to migrate faster than larger bedforms in finer sediment however how bedform morphology height length and shape and kinematics translation and deformation change with transport stage and suspension have not been examined a series of experiments is presented where initial flow depth and grain size were held constant and the transport stage was varied to produce bedload dominated mixed load dominated and suspended load dominated conditions the results show that the commonly observed pattern in bedform aspect ratio occurs because bedform height increases then decreases with transport stage against a continuously increasing bedform length bedform size variability increased with transport stage leading to less uniform bedform fields at higher transport stage total translation related and deformation related sediment fluxes all increased with transport stage however the relative contribution to the total flux changed at the bedload dominated stage translation related and deformation related flux contributed equally to the total flux as the transport stage increased the fraction of the total load contributed by translation increased and the fraction contributed by deformation declined because the bedforms got bigger and moved faster at the suspended load dominated transport stage the deformation flux increased and the translation flux decreased as a fraction of the total load approaching one and zero respectively as bedforms washed out to a plane bed

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

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

river width adjustment i processes and mechanisms in 1993 a task committee tc of the asce was established to study the hydraulics bank mechanics and modeling of width adjustment in alluvial channels the work of the tc in reviewing width adjustment processes and mechanisms is reported in this paper a companion paper presents the findings of the tc with regard to width adjustment modeling this paper first establishes the geomorphic context within which width adjustments occur and it demonstrates that width adjustment may take place over a wide range of scales in time and space in the past engineering analyses of channel width have tended to concentrate on prediction of the equilibrium width for stable channels most commonly the regime extremal hypothesis and rational mechanistic approaches are used and these are reviewed herein more recently attention has switched to channels that are adjusting their morphology either due to natural instability or in response to changes in watershed land use river regulation or channel engineering chara

large eddy simulation of three dimensional dunes in a steady unidirectional flow part 2 flow structures we performed large eddy simulations of the flow over a series of three dimensional 3d dunes at laboratory scale the bedform three dimensionality was imposed by shifting a standard two dimensional 2d dune shape in the streamwise direction according to a sine wave the turbulence statistics were discussed in part 1 of this article omidyeganeh piomelli j fluid mech vol 721 2013 pp 454 483 coherent flow structures and their statistics are discussed concentrating on two cases with the same crestline amplitudes and wavelengths but different crestline alignments in phase and staggered the present paper shows that the induced large scale mean streamwise vortices are the primary factor that alters the features of the instantaneous flow structures wall turbulence is insensitive to the crestline alignment alternating high and low speed streaks appear in the internal boundary layer developing on the stoss side whereas over the node plane the plane normal to the spanwise direction at the node of the crestline they are inclined towards the lobe plane the plane normal to the spanwise direction at the most downstream point of the crestline due to the mean spanwise pressure gradient spanwise vortices rollers generated by kelvin helmholtz instability in the separated shear layer appear regularly over the lobe with much larger length scale than those over the saddle the plane normal to the spanwise direction at the most upstream point of the crestline rollers over the lobe may extend to the saddle plane and affect the reattachment features their shedding is more frequent than in 2d geometries vortices shed from the separated shear layer in the lobe plane undergo a three dimensional instability while being advected downstream and rise toward the free surface they develop into a horseshoe shape similar to the 2d case and affect the whole channel depth whereas those generated near the saddle are advected downstream and toward the bed when the tip of such a horseshoe reaches the free surface the ejection of flow at the surface causes boils upwelling events on the surface strong boil events are observed on the surface of the lobe planes of 3d dunes more frequently than in the saddle planes they also appear more frequently than in the corresponding 2d geometry the crestline alignment of the dune alters the dynamics of the flow structures in that they appear in the lobe plane and are advected towards the saddle plane of the next dune where they are dissipated boil events occur at a higher frequency in the staggered alignment but with less intensity than in the in phase alignment

on the relationship between flow and suspended sediment transport over the crest of a sand dune rio parana argentina the links between large scale turbulence and the suspension of sediment over alluvial bedforms have generated considerable interest in the last few decades with past studies illustrating the origin of such turbulence and its influence on flow resistance sediment transport and bedform morphology in this study of turbulence and sediment suspension over large sand dunes in the rio parana argentina time series of three dimensional velocity and at a point suspended sediment concentration and particle size were measured with an acoustic doppler current profiler and laser in situ scattering transmissometer respectively these time series were decomposed using wavelet analysis to investigate the scales of covariation of flow velocity and suspended sediment the analysis reveals an inverse relationship between streamwise and vertical velocities over the dune crest where streamwise flow deceleration is linked to the vertical flux of fluid towards the water surface in the form of large turbulent fluid ejections regions of high suspended sediment concentration are found to correlate well with such events the frequencies of these turbulent events have been assessed from wavelet analysis and found to concentrate in two zones that closely match predictions from empirical equations such a finding suggests that a combination and interaction of vortex shedding and wake flapping changing length of the lee side separation zone are the principal contributors to the turbulent flow field associated with such large alluvial sand dunes wavelet analysis provides insight upon the temporal and spatial evolution of these coherent flow structures including information on the topology of dune related turbulent flow structures at the flow stage investigated the turbulent flow events and their associated high suspended sediment concentrations are seen to grow with height above the bed until a threshold height ca 0 45 flow depth is reached above which they begin to decay and dissipate

influence of mixtures of grain size populations on the parametric and modal characteristics of coastal sands herault mediterranean sea france abstract grain size distributions in lower beach and nearshore sands of a segment of the coast of the golfe du lion france were analyzed by a parametric method and by modal analysis the results have been considered both in a spatial framework delineating geographically distinct sedimentary compartments and cells and in a morphodynamic framework separating the dynamic components of the shoreline berm collision zone inner bar outer bar lower shoreface modal statistics indicate that a mixture of three dominant components end members contributes to the grain size distribution gsd of the sediments fine sand sedimentary type i modal value 0 195 mm i 0 35 medium and coarse sand st ii modal value 0 680 mm i 0 8 and very coarse sand and gravel st iii i modal value 2 3 mm i 1 5 quasi log normal one component gsds form a minority group and mixtures produce various apparently unimodal sands and bimodal sediments a large variation of grain size indices results from mixing a simulation of mixing of log normal populations close to the end members shows the great sensitivity of parameters sorting skewness and kurtosis to small changes in the compositional formula of the mixture the procedure followed supplies a good preliminary tool enabling rapid identification and localization of the main sand sources on a regional scale these components derive from potential sources available in the region well known from previous studies st i originates from the river rhone and provides the textural base for most of the sediments st ii and iii form a local component originating either from fluvial input aude orb and herault rivers or from the nearshore reworking of ancient quaternary sediments and late holocene beachrocks each st takes on local aspects in relation to the morphological environment but the regional scale of the study was too large to precisely reflect the local morphodynamic regime a significant change in the st i sorting of bar sands is however observed probably due to the net offshore migration reported for the bar system

a simplified 2d model for meander migration with physically based bank evolution abstract the rate of migration calculated by numerical models of river meandering is commonly based on a method that relates the rate of migration to near bank excess velocity multiplied by a dimensionless coefficient notwithstanding its simplicity since the early 1980s this method has provided important insight into the long term evolution of meander planforms through theoretical exercises its use in practice has not been as successful because the complexity of the physical processes responsible for bank retreat the heterogeneity in floodplain soils and the presence of vegetation make the calibration of the dimensionless coefficient rather challenging this paper presents a new approach that calculates rates of meander migration using physically based streambank erosion formulations the university of illinois rvr meander model which simulates meandering river flow and bed morphodynamics is integrated with algorithms for streambank erosion of the us department of agriculture channel evolution computer model concepts the performance of the proposed approach is compared to that of the more simple classic method through the application to several test cases for idealized and natural planform geometry the advantages and limitations of the approach are discussed focusing on simulated planform pattern the impact of soil spatial heterogeneity the relative importance of the different processes controlling bank erosion hydraulic erosion cantilever and planar failure the requirements for obtaining stable migration patterns centerline filtering and interpolation of bank physical properties and the capability of predicting the planform evolution of natural rivers over engineering time scales i e 50 to 100 years the applications show that the improved physically based method of bank retreat is required to capture the complex long term migration patterns of natural channels which cannot be merely predicted from hydrodynamics only

correlation of carbon dioxide abundance with temperature in clastic hydrocarbon reservoirs relationship to inorganic chemical equilibrium the mol co2 of gas reservoired in sandstones tends to increase with increasing temperature along both the us gulf coast and the norwegian continental shelf each of these provinces displays identical linear correlations between temperature and the log of the partial pressure of co2 i e pco2 in the reservoir fluid that is the product of the mol co2 the reservoir pressure this correlation is the same both in gulf coast reservoirs younger than 17 ma and in norwegian reservoirs of jurassic to triassic age 144 245 ma indicating that it is not dependent on reaction kinetics norwegian shelf data indicate that the same correlation also applies for gas condensate and oil reservoirs we suggest that the log pco2versus temperature correlation is the result of inorganic chemical equilibria between feldspar clay and carbonate minerals a trend of decreasing ph with increasing temperature is fixed by equilibria between aluminosilicate minerals feldspar kaolinite at lower temperatures followed by various reactions between kaolinite illite chlorite and feldspar as temperatures exceed 110 140 c responding to the ph set by the aluminosilicate system co2 activity in the formation water and thereby co2 partial pressure in any gas phase present is controlled by equilibrium with carbonate minerals this model predicts that co2 released by organic maturation will in general result in precipitation of carbonate minerals below 100 120 c and that there should be widespread carbonate dissolution at higher temperatures

riffle pool morphometry and stage dependant morphodynamics of a large floodplain river vereinigte mulde sachsen anhalt germany riffle pool sequences are a common feature of gravel bed rivers however mechanisms of their generation and maintenance are still not fully understood in this study a monitoring approach is employed that focuses on analysing cross sectional and longitudinal channel geometry of a large floodplain river vereinigte mulde sachsen anhalt germany with a high temporal and spatial resolution in order to conclude from stage dependant morphometric changes to riffle and pool maintaining processes in accordance with previous authors pool cross sections of the mulde river are narrow and riffle cross sections are wide suggesting that they should rather be addressed as two general types of channel cross sections than solely as bedforms at high flows riffles and pools in the study reaches changed in length and height but not in position pools were scoured and riffles aggraded a development which was reversed during receding flows below the threshold of 0 4qbf 40 bankfull discharge an index for the longitudinal amplitude of riffle pool sequences the bed undulation intensity or bedform amplitude is introduced and proved to be highly significant as a form parameter its first derivative as a process parameter the process of pool scour and riffle fill is addressed as bedform maintenance or bedform accentuation it is indicated by increasing longitudinal bed amplitudes according to the observed dynamics of bed amplitudes maintenance of riffle pool sequences lags behind discharge peaks maximum bed amplitudes may be reached with a delay of several days after peak discharges increasing bed undulation intensity is interpreted to indicate bed mobility post flood decrease of the bed undulation intensity indicates a retrograde phase when transport from pools to riffles has ceased and bed mobility is restricted to riffle tails and heads of pools this type of transport behaviour is referred to as disconnected mobility the comparison of two river reaches one with undisturbed sediment supply the other with sediment deficit suggests that high bed undulation intensity values at low flows indicate sediment deficit and potentially channel degrading conditions it is more generally hypothesized that channel bed undulations constitute a major component of form roughness and that increased bed amplitudes are an important feature of channel bed adjustment to sediment deficit be it temporally during late floods or permanently due to a supply limitation of bedload copyright 2011 john wiley sons ltd

influence of lateral water withdrawal on bed form geometry in a channel in flood protection engineering side weirs or overflow dams are used to divert water in a controlled way into flood plains as soon as the discharge capacity of the main channel is reached because of the lateral loss of water the sediment transport capacity is reduced resulting in local sediment deposition near the side overflow moreover bed form characteristics such as length height steepness and stoss and lee slope angle are affected by the lateral water withdrawal both phenomena are responsible for an increased side overflow intensity compared with plane bed conditions the results from a systematic flume study show that the shape of observed bed forms is highly threedimensional and that three distinct regions along the channel axis can be identified the first one extends from the channel entrance to the upstream weir corner the second one comprises the reach of the weir and the third one represents the reach downstream of the weir the description of bed form shape by approaches from literature shows reasonable agreement with measured bed form geometry

evolution of coarse gravel bed forms field measurements at flood stage field measurements to investigate the origin and growth of mesoscale gravel bed forms in deep flows were made in the north fork toutle river washington sonar observations of the gravel streambed at a stationary point were recorded during two storm flows in december 1989 and january 1990 with concurrent bed load sampling and continuous velocity measurements mean diameter of bed load was about 3 cm flow depths were 1 4 2 4 m and bed shear stresses were 2 5 times the critical stress of mean bed load diameter as computed from the depth slope product these records document the hydrodynamic conditions under which dunelike coarse gravel bed forms were observed coarse gravel dunes height 20 cm length 6 15 m evolved more than 24 hours after peak stage primarily by accretion as inferred from bed form changes revealed in dual sonar records dune heights increased to 40 cm as mean trough elevation rose about 50 cm over several hours smaller dunes wavelength 1 3 m transitional from bed load sheets migrated on the backs of the large dunes the superposed dunes finally became indistinguishable from the large dunes which diminished in height by increasing the mean level of troughs gravel deposition occurred at the observation point in conjunction with migration of gravel dunes the direct comparison of known bed form regimes and gravel bar facies provides alternative interpretations of gravelly deposits

geochemical characterization and modelling of the toarcian domerian porewater at the tournemire underground research laboratory abstract for safety evaluation of hazardous waste repositories in clay rocks a thorough assessment of porewater chemistry and water rock interactions is required however this objective is a challenging task due to the low hydraulic conductivity and water content of such rocks which subsequently renders porewater sampling difficult without inducing perturbations for this reason an indirect approach was developed to determine porewater composition of clay rocks by a geochemical model of water rock interaction using some properties of the rock and the solution the goal of this paper is to obtain the porewater composition of the toarcian domerian argillaceous formation at tournemire south of france for which a reliable model is still lacking the following work presents a comprehensive characterization of the geochemical system of the tournemire clay rock including mineralogy petrology mobile anions cation exchange properties accessible porosity and co 2 partial pressure perturbation corrections from fracture water sampling were also computed these water were found in sealed fractures beaucaire et al 2008 and their radiocarbon apparent age is estimated at 20 ka their age together with their equilibrium situation allow considering these fracture waters as representative of the formation porewater the model developed to calculate the tournemire porewater composition is essentially based on cation exchange by a multi site approach but equilibrium with some mineral phases calcite quartz and pyrite is also considered different exchange sites of different affinities towards cations are used which proportions are given by the mineralogy exchange on illite is performed with a three sites model while one site is considered for smectite phases multi site model results are compared with corrected fracture water data and two other models a model only based on mineral equilibrium and a model using cation exchange on one global site the best results were obtained with the models that take into account cation exchange and particularly with the multi site model the interest in considering a model with exchange sites of different affinities is particularly obvious for a satisfactory representation of the k content in solution a dependence of k content to the amount of high affinity sites was observed leading to an improvement of its simulation when uncertainty on mineralogical data is considered once validated the multi site model was applied at different levels of the tournemire argillaceous formation to obtain a profile of the porewater composition

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

neural network prediction of alluvial stream bedforms abstractsubstantial laboratory field and theoretical studies have been carried out by many to understand alluvial stream bedform origin their shapes equilibrium with the flow and their deposit

three dimensional modeling of turbid density currents in imha reservoir south korea abstractthe propagation dynamics of the turbid density currents of the imha reservoir is investigated using the flow 3d computational fluid dynamics code the renormalization group rng e turbulence scheme in a reynolds averaged navier stokes rans framework was applied for the field investigation a new particle dynamics algorithm was developed and coupled with the flow 3d model to simulate the settling of sediment particles and the model was tested with field measurements during typhoon ewiniar the coupled model correctly predicted the spatial and temporal evolution of intrusive density currents with plunging flows at a depth of 20 m and interflows propagating downstream at about 0 2 m s the simulation results with sediment settling demonstrated that the ratio of transported to initial sediment concentration c0 ci varies as a function of particle size ds and sediment concentration density currents can be classified into three regimes 1 a suspended regime ds 10 m where interflows will

shape and dimensions of stationary dunes in rivers the shape and dimensions length height of sand dunes in rivers are calculated by use of the measured bed shear stress distribution downstream a rearward facing step the transport of sediment is split up into bed load and suspended load which makes it possible to explain the transition to plane bed the model can predict flow resistance curves in alluvial streams

investigating the role of clasts on the movement of sand in gravel bed rivers the bed morphology of mountain rivers is characterized primarily by the presence of distinguishable isolated roughness elements such boulders or clasts the objective of this experimental study was to provide a unique insight into the role of an array of clasts in regulating sand movement over gravel beds for low relative submergence conditions h dc 1 and flow depth h to the diameter of the clast dc a process that has not been studied thoroughly to assess the role of clasts in controlling incoming sand movement detailed flume experiments were conducted by placing 40 equally spaced clasts atop a well packed glass bead bed for replicating the isolated roughness flow regime the experiments were performed for moderate 2 50 cr where cr is the critical dimensionless bed shear stress and high 5 50 cr applied bed shear stress conditions representative of gravel bed rivers for comparison purposes experiments were also repeated for nearly identical flow conditions but without the presence of

dynamic routing of flow resistance and alluvial bed form changes from the lower to the upper regime on the basis of a strouhal number and the definition of the control factor m a new routing to calculate the energy slope in the lower and upper alluvial regimes is proposed the control factor m representing the interactions in alluvial rivers is reckoned as a bed form index while the flow evolves through transition the control factor m decreases from m 2 associated with two dimensional fully developed dunes to m 1 associated primarily with in phase waves the way to predict the value of the control factor m is drawn from a previously published criterion for delineating the upper regime and is calibrated with experimental data on several data from flumes and rivers the routing is tested and compared with other methods from the literature it appears that the new routing is the most robust because it allows researchers to obtain low averages of the discrepancy ratio for a wide range of ratios between the water depth and the median sediment diameter on a selection of contrasted freshet events the new routing allows for the capture of the primary dynamic of the flow resistance decrease

in situ interaction of cement paste and shotcrete with claystones in a deep disposal context in situ sampling was performed in the andra meuse haute marne france underground research laboratory url allowing the study of two cement based materials claystone interfaces that have undergone 4 to 5 years of interaction the first interface concerned a shotcrete that was sprayed on the wall of an access drift at the laboratory level and the second one a class g cement paste that was injected in a borehole filled from the surface and was intercepted during the excavation of a new gallery in the first case the hydrodynamic conditions were controlled by the ventilation of the drift while in the second the cement paste and claystone materials were considered saturated and far from any mechanical perturbation a multi scale investigation was carried out to identify any evidence of alkaline perturbation in the cement based materials and the claystone chemical mineralogical and textural measurements were thus performed on the different materials in contact at the nanometer to a centimeter scale results showed that all the perturbations resulting from the geochemical contrast between the cement materials and the claystone were limited to a m scale on each side of the interfaces carbonation was observed in the cement materials leading to an opening or a clogging of the porosity according to the hydrodynamic conditions and the formulation of the cement material the distribution of the cation exchange population was also modified in the claystone in contact with the cement paste where a potassium saturation of the exchangeable fraction was identified the originality of the present work is that realistic field controlled samples from the andra url were studied hereby allowing the evaluation of the impact of natural heterogeneities of the in situ experimental conditions that is hydrodynamic conditions engineered damage zone mineralogical variations on the perturbations at the cement paste claystone interfaces an important result is that the clogging of porosity was not homogenous along the interfaces

fluvial dunes initiation characterization flow structure research into fluvial dunes spans disciplines studies at grain to reach scales and methodological approaches that include theoretical experimental numerical and field investigations despite significant research efforts to date it remains difficult to provide definitive answers to some fundamental questions regarding dunes this paper reviews three notable challenges that remain regarding fluvial dunes namely scale consistent linking of bed morphologies with turbulent flow fields the intriguing question of what causes trains of highly ordered sediment waves to form in beds of river sediments and how to define the important characteristics of a dune covered bed including lengths shapes and their statistical nature in each case the particular challenge is discussed and then recent research and ways forward are presented copyright 2010 john wiley sons ltd

on interfacial instability as a cause of transverse subcritical bed forms 1 recent experimental results suggest there are at least two distinct bed form initiation processes bed forms may be generated from local bed defects that are propagated down and across stream by flow separation processes when sediment transport is patchy and sporadic alternatively bed form development may occur over the whole bed at once when sediment transport is general and widespread herein we critically test a simple model for this latter bed form initiation mode that was originally presented by h k liu in 1957 but not tested because of the complex nature of the measurements required the theory is based on the idea that a moving sand bed might be likened to a dense fluid and that a hydrodynamic instability develops at the interface between the sediment transport layer and the near bed fluid leading to the organization of the transport system into laterally extended discrete bed forms our predicted initial bed form lengths are within 10 of the lengths observed in a series of flume experiments suggesting that transverse waveforms on sand beds sheared by unidirectional currents can be initiated as an interfacial hydrodynamic instability of kelvin helmholtz type when the current is sufficiently vigorous to produce general sediment movement that is to create a sediment transport layer that acts as a pseudofluid with density composed of solid and fluid components

groundwater characterisation and modelling of water rock interaction in an argillaceous formation tournemire france abstract chemical na k mg ca cl so 4 hco 3 si al fe mn toc and isotopic 18 o h 2 o 2 h h 2 o 3 h h 2 o 14 c dic 13 c dic 34 s so 4 18 o so 4 data were obtained on groundwater collected from fractures inside the consolidated argillaceous formation of tournemire aveyron and from the aquifers surrounding this formation because of the very low transmissivity of such fractures 10 10 m 2 s 1 specific devices were developed for limiting out gassing and air contamination of groundwater during the sampling two modelling approaches are proposed to account for the chemical evolution of fracture groundwater from na cl hco 3 to na so 4 type the first one is based on mineral equilibria only and the second one also takes into account the ion exchange reactions the two modelling approaches are able to reproduce k concentrations and they led to an almost constant p co 2 10 2 6 atm which only depends on equilibrium with the calcite dolomite kaolinite quartz assemblage the modelling of na ca 2 and hco 3 behaviours is improved by taking the ion exchange reactions into account in some boreholes the time evolution of the chemical composition of fluids was greatly influenced by so 4 reduction combined with oxidation of dissolved organic c the isotopic composition of aqueous so 4 in fracture groundwater confirms that so 4 reduction processes have occurred since the drilling of these boreholes but also previously during the natural evolution of groundwater these redox reactions constitute a source of aqueous inorganic c that has to be considered in the computation of groundwater ages with 14 c for the studied fracture groundwaters the maximum age estimates range from 17 to 29 ka this shows that fractures may induce relatively fast groundwater flow compared to the very long migration times that are calculated by only considering diffusive transport in the rock microporosity

algorithm for resistance to flow and transport in sand bed channels an algorithm is developed that relates depth to discharge and determines bed and suspended load transport for the entire range of bed forms found in sand bed channels equilibrium state geometry of lower flow regime bedforms is also predicted grain shear stress and form resistance are differentiated using a drag coefficient closure and a two segment logarithmic velocity profile a meyer peter type formulation is used to compute sand transport in the bed load layer and for computing suspended sand transport mclean s procedure of 1991 and 1992 is adopted a bed form classification scheme is developed that uses a particle size parameter and the transport strength to predict bed form type it correctly identifies 73 of the 1 192 mostly flume scale calibration data sets for 194 sets of dune transition bed form calibration data a modified version of van rijn s 1984 bed form geometry predictor yields a geometric average predicted to observed height ratio of 1 00 after calibration the algorithm produces overall geometric averages of predicted to observed depth and predicted to observed transport of 1 00 for a verification data set of 855 observations mostly from rivers and canals the overall geometric averages of predicted to observed depth and transport are 0 87 and 1 14

geologic significance of trace element abundances in the red scaglia limestones from gubbio central italy abstract contents of al cu fe mn pb tl and zn in 29 samples of pelagic limestones red scaglia have been determined by sequential chemical leaching cu mn pb and zn are mostly associated with the carbonate fraction while the bulk of fe is carried by the residual fraction and finally the bulk of al and the whole tl are contained in the residual mineral phases such as k bearing silicates the element distribution patterns in the limestones analyzed provide information about the materials sedimented and the redox conditions occurring during sedimentation and diagenesis in particular they suggest that most of the fe oxides carried by these rocks formed in the sea basin

bed form geometry in sand bed flows a new method is proposed for predicting relative bed form height h d in sand bed flows the proposed method is based on the concept of relating energy loss due to form drag to the head loss across a sudden expansion in open channel flows a unique feature of the proposed method is that it can be applied to various bed forms i e ripples dunes antidunes standing waves and transitional bed regimes that occur in alluvial flows the relation thus developed was applied to a large number 251 flows 14 different data sets of laboratory and river data and was found to give good agreement with the observed h d values in a comparison of prediction accuracies with seven existing relationships the proposed method was found to give significantly better agreements with the observed data future improvements in the prediction of h d will depend on improved formulations of the two parameters incorporated in the present relation i e energy loss coefficient k and the relative bed form length l d for various b

direct dating of phanerozoic sediments by the 238 u 206 pb method direct radiometric age determination of phanerozoic carbonates has been a long standing problem in geochronology rb sr and k ar dating schemes commonly used to constrain the chronology of phanerozoic sediments have so far proved to be unsuccessful in dating these rocks because of their poor enrichment in radiogenic 87sr and 40ar and also because of analytical difficulties recent studies1 2 have demonstrated that large amounts of radiogenic pb exist in some carbonates and that they could be dated by the pb pb method however the precision of this method is severely limited to samples having very high uranium to lead ratios because by the beginning of the phanerozoic 590 myr ago 98 of 235u originally present in the earth had decayed to 207pb here we report the first isochron age of carbonates using the 238u 206pb method on corals this method which gives good accuracy even for low u concentrations has great potential for the direct dating of sedimentary sequences and should be valuable for refining the phanerozoic timescale

upper regime plane bed the analysis of a laboratory and field data set for sand bed channels defines the characteristics of upper regime plane bed with sediment transport the occurrence of upper regime plane bed relates to the laminar sublayer thickness and depends on shear velocity u median grain size d50 and grain shear reynolds number r two different boundary conditions are recognized 1 transition to hydraulically smooth when r 11 6 in the first case upper regime plane bed is obtained when u 2 g where g is the gravitational acceleration in the second case upper regime plane bed is observed when d50 2 temperature effects are possible when r approaches 11 6 which explains the observations on the missouri river resistance to flow for plane bed with sediment transport increases with the shields parameter

numerical modeling of flow and scour below a pipeline in currents part ii scour simulation abstract a vertical two dimensional 2d numerical model for time dependent local scour below offshore pipelines subject to unidirectional steady flow is developed the governing equations for the flow and sediment transport are solved by using finite difference method in a general curvilinear coordinate system the performance of two turbulence models the standard k model and smagorinsky subgrid scale sgs model on modeling time dependent scour processes is examined both suspended load and bed load are considered in the scour model the suspended load model is verified against two channel sediment transport cases the change of bed level is calculated from the continuity equation of total sediment transport a new time marching scheme and a sand slide scheme are proposed for the scour calculation it is found that the proposed time marching scheme and sand slide model work well for both clear water and live bed scour situations and the standard k turbulence closure is more preferable than the sgs model in the 2d scour model developed in this study

sediment transport part iii bed forms and alluvial roughness a method is presented that makes the classification of bed forms the prediction of the bed form dimensions and the effective hydraulic roughness of the bed forms feasible the proposed relationships are based on the analysis of reliable flume and field data a verification analysis using about 1 500 alternative reliable flume and field data shows good results in predicting the hydraulic roughness friction factor for field conditions the proposed method yields considerably better results than previously proposed methods which are reviewed here the proposed method has also been used to predict the flow depth and the total bed material load

transport of sand and partly cohesive sediments in a circular pipe run partially full many sediment deposits contain not only a granular but also a mineral and or organic cohesive fraction which has the potential to change significantly the erosion response when compared to noncohesive sediment deposits sediment deposits containing a low proportion of cohesive sediment display a specific transitional behavior between cohesive and noncohesive sediments in the past several studies have examined partly cohesive sediment however the quantification of its erosion behavior is still unsatisfactory in an attempt to advance the understanding and qualitative description of erosion and transport of mixed sediments in pipes a comprehensive experimental investigation on the erosion behavior was designed tests were conducted in a flume with semicircular cross section with a diameter of 0 39 m using fine sand with a d50 0 19 mm and partly cohesive sediment deposits being a mixture of sand and clay with proportion of 3 10 by weight of clay tests covered a range of flow conditions with froude

aquitard characteristics of clay rich till deposits in east anglia eastern england summary an extensive area of quaternary glacial deposits lowestoft till of elsterian anglian age overlies the regionally important cretaceous chalk aquifer in east anglia in eastern england the glacial deposits act as an aquitard potentially affording protection from surface derived mainly agricultural contaminants however there has been little previous research on the physical and chemical characteristics of the glacial tills and contained pore waters in east anglia to demonstrate this benefit hence this study presents the results from the drilling of two boreholes in northern and southern east anglia at morley and cowlinge respectively and the construction of a high pressure squeezing rig to obtain pore water for major and minor ion stable isotope 18 o 2 h and dissolved organic carbon analysis special features of the mechanical squeezing rig included a high diameter to length ratio of the squeezer dual seepage faces and a unique pore water collection system designed to eliminate the risk of alteration of in situ pore water redox characteristics the hydrochemistry of the pore waters is found to be controlled by i incongruent carbonate dissolution given the high proportion of chalk clasts contained in the till ii cation exchange in the unweathered clay rich till and iii pyrite oxidation associated with the mineralogy of both the chalk and clay material content that comprises the till matrix the clay material is sourced from upper jurassic clays oxford and kimmeridge clay formations found to the west of the region these clays are also considered to be the source of organic material contributing relatively high concentrations of dissolved organic carbon above 2 mg l found in till pore waters below the soil zone concentrations of dissolved inorganic constituents increase with depth with a high total dissolved solids tds content in excess of 1500 mg l measured in the unweathered till below a depth of 5 m below ground level with the highest concentrations maximum of 3738 mg l associated with low permeability clay rich till the stable isotope composition of the pore waters with mean values for 18 o and 2 h of 7 01 and 51 7 at cowlinge and 6 44 and 49 9 at morley respectively are similar to local meteoric water and indicate that groundwater recharge of the tills has occurred during the holocene in the last 10 000 years overall the physical and chemical characteristics of the lowestoft till suggest only limited groundwater recharge of the order of 10 mm a or less in interfluve areas where the till deposits are greater than 15 m thick although higher rates are expected where the till becomes more sand rich for example at valley margins and also northwards in east anglia where the lowestoft till is influenced by the component of anglian ice that advanced from the north containing sand material derived from the floor of the north sea basin

continuous measurements of discharge from a horizontal acoustic doppler current profiler in a tidal river 1 acoustic doppler current profilers adcps can be mounted horizontally at a river bank yielding single depth horizontal array observations of velocity across the river this paper presents a semideterministic semistochastic method to obtain continuous measurements of discharge from horizontal adcp hadcp data in a tidal river in the deterministic part single depth velocity data are converted to specific discharge by applying the law of the wall which requires knowledge of local values of the bed roughness length z0 a new filtration technique was developed to infer cross river profiles of z0 from moving boat adcp measurements width averaged values of z0 were shown to be predominantly constant in time but differed between ebb and flood in the stochastic part of the method specific discharge was converted to total discharge on the basis of a model that accounts for the time lag between flow variation in the central part of the river and flow variation near the banks model coefficients were derived using moving boat adcp data the consistency of mutually independent discharge estimates from hadcp measurements was investigated to validate the method analyzing river discharge and tidal discharge separately inaccuracy of the method is attributed primarily to mechanisms controlling transverse exchange of momentum which produce temporal variation in the discharge distribution over the cross section specifically development of river dunes may influence the portion of the discharge concentrated within the range of the hadcp

wave current interactions in a wave dominated tidal inlet 1 wave current interactions play a major role in the dynamics of shallow tidal inlets this study investigates these interactions at a natural inlet with a strong focus on current induced changes on wave propagation the analysis of hydrodynamic data collected at the albufeira lagoon portugal revealed spatiotemporal variations of water levels and wave heights along the inlet attributed to wave current interaction processes we compared the simulations of a coupled wave circulation modeling system computed with and without waves and propagated with and without current feedback the wave induced setup inside the lagoon represented 7 15 of the offshore significant wave height the accuracy of the wave s predictions improved when current feedback was included during ebb the currents increased the wave height at the mouth of the inlet up to 20 and decreased the wave height in the inlet up to 40 due to current induced refraction steepness dissipation and partial blocking during flood the currents decreased the wave height in the inlet up to 10 and increased the wave height at the exterior parts of the ebb shoal up to 10 due to current induced refraction these effects significantly attenuate seaward sediment fluxes during ebb and contribute to the sediment accretion in the inlet

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

biogeochemical processes in a clay formation in situ experiment part e equilibrium controls on chemistry of pore water from the opalinus clay mont terri underground research laboratory switzerland the chemistry of pore water particularly ph and ionic strength is an important property of clay rocks being considered as host rocks for long term storage of radioactive waste pore waters in clay rich rocks generally cannot be sampled directly instead their chemistry must be found using laboratory measured properties of core samples and geochemical modelling many such measurements have been made on samples from the opalinus clay from the mont terri underground research laboratory url several boreholes in that url yielded water samples against which pore water models have been calibrated following a first synthesis report published in 2003 this paper presents the evolution of the modelling approaches developed within mont terri url scientific programs through the last decade 1997 2009 models are compared to the composition of waters sampled during dedicated borehole experiments reanalysis of the models parameters and database enabled the principal shortcomings of the previous modelling efforts to be overcome the inability to model the k concentrations correctly with the measured cation exchange properties was found to be due to the use of an inappropriate selectivity coefficient for na k exchange the inability to reproduce the measured carbonate chemistry and ph of the pore waters using mineral water reactions alone was corrected by considering clay mineral equilibria re examination of the measured ca mg activity ratios and consideration of the mineralogical composition of the opalinus clay suggested that ca mg cation exchange rather than dolomite saturation may control the ratio of these ions in solution this re examination also suggests that the ca mg ratio decreases with increasing pore water salinity several possible reasons for this are proposed moreover it is demonstrated that feldspar equilibria must not be included in opalinus clay modelling because feldspars are present only in very small quantities in the formation and because na k ratios measured in pore water samples are inconsistent with feldspar saturation the principal need to improve future modelling is additional or better data on rock properties in particular i a more detailed identification of phases in the opalinus clay that include redox sensitive elements together with evaluation of their thermodynamic properties ii an improved understanding of the distribution of celestite throughout the opalinus clay for sr so4 concentrations control iii improvements in analytic and thermodynamic data for ca mg rock cation exchange and mineral chemical properties and iv the measurement of composition and stability constants of clay minerals actually present in the formation

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

constraining porewater chemistry in a 250m thick argillaceous rock sequence the geochemistry of an argillaceous rock sequence from a deep borehole in ne switzerland was investigated the focus was to constrain the porewater chemistry in low permeability jurassic rocks comprising the liassic the opalinus clay formation the brown dogger unit and the effingen member malm a multi method approach including mineralogical analysis aqueous and ni ethylenediamine extraction squeezing tests and pco2 measurements as well as geochemical modelling was applied for this purpose a consistent dataset was obtained with regard to the main solutes in the porewaters a fairly constant anionaccessible porosity of 50 of the total porosity was deduced for all analysed samples which displayed variable clay mineral contents sulphate concentrations were shown to be constrained by a sulphate bearing phase presumably by celestite or a sr ba sulphate application of a simple equilibrium model including cation exchange reactions calcite and celestite equilibrium showed good agreement with squeezing data indicating the suitability of the modelling approach to simulate porewater chemistry in the studied argillaceous rocks the modelling highlighted the importance of correct determination of the exchangeable cation population the analysis corroborates that squeezing of the studied rocks is a viable and efficient way to sample porewater

reevaluating dune scaling relations abstract in sand bedded rivers dunes dominate sediment transport and flow resistance dunes are also commonly preserved in fluvial deposits as cross stratified units that record their size shape and migration rates prediction of dune dimensions is therefore important for forecasting modern river channel dynamics as well as reconstructing past fluvial environments on earth and other planets predictions are often made by assuming that the formative flow depth h sets dune dimensions with height scaling as 1 6h and length as 5h yet there is a suite of other scaling relations that link dune dimensions to other variables like grain size transport stage and froude number here we present a new compilation of flow and dune dimension data to evaluate scaling relations the data reveal approximately two orders of magnitude variation in dune height and length at any given flow depth dune heights in shallow flows 2 5 m are often more symmetric have lower lee angles are relatively shorter in height than 1 6h and have a wider range of observed heights for a given depth none of the scaling relations predict the observations exceptionally well likely because of natural variability in dune dimensions and because they do not explicitly account for the apparent scaling break that occurs at 2 5 m we propose new simple depth scaling relations with added statistical uncertainty for the prediction of dune height and length from flow depth as well as flow depth from dune height we conclude that shallow and deep flow dunes exhibit different scaling due to a change in the dominant process controls as dunes get larger

flow and grain size control of depth independent simple subaqueous dunes 1 in the gradyb tidal inlet danish wadden sea simple medium to large dunes which are superimposed on large to very large dunes increase in size with decreasing grain size under quasi constant ebb dominated mean flow conditions the mean height of the superimposed dunes increases from 0 1 m to 0 5 m and the mean dune length from 7 m to 12 m this happens over a distance of 1 5 km from the inner to the outer part where mean depth 12 m and the dominant ebb current 1 0 m s 1 remain constant over this reach the grain size changes from 0 6 mm in the inner part to 0 3 mm in the outer part as the water depth is constant and more than 1 order of magnitude larger than the height of the dunes these are regarded as being depth independent relationships between dune dimensions and grain size established in previous studies are transformed into more general statements bed form dimensions being directly related to the form corrected shields parameter in this way dune dimensions and flow strength grain size have for the first time been directly related to both bed load and free stream velocity in deeper flow systems the former relationship is based on a recalibrated form migration version of the meyer peter and muller bed load formula four diagrams describing flow conditions and dune migration rates as a function of grain size and dune length are presented

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

flow resistance over mobile bed in an open channel flow this paper deals with the underlying mechanism of flow resistance in an alluvial channel the effects of sidewall and bed form on flow resistance einstein s divided hydraulic radius approach and engelund s energy slope division approach are reexamined these two approaches assume that the shear stress on a mobile bed is the summation of shear stresses caused by skin friction and bed form using a different approach this paper presents a theoretical relationship between the total bed shear stress with grain and bed form shear stresses the contribution of sidewall on the total bed shear stress is also discussed the writers found that the size of bed form plays a significant role for the flow resistance and developed relevant expressions for the length of the separation zone behind the bed forms in addition a systematical approach has been developed to compute the flow velocity in an alluvial channel this approach is tested and verified against 5 989 flume and field measurements the computed and mea

morphodynamic river processes and techniques for assessment of channel evolution in alpine gravel bed rivers abstract over the past 10 years many restoration projects have been undertaken in austria and river engineering measures such as spur dykes and longitudinal bank protection which imposed fixed lateral boundaries on rivers have been removed the eu life project auenverbund obere drau has resulted in extensive restoration on the river drau aimed to improve the ecological integrity of the river ecosystem to arrest riverbed degradation and to ensure flood protection an essential part of the restoration design involved the consideration of self forming river processes which led to new demands being imposed on river management this paper illustrates how model complexity is adapted to the solution and evaluation of different aspects of river restoration problems in a specific case point scale monitoring data were up scaled to the whole investigation area by means of digital elevation models and a scaling approach to the choice of model complexity was applied simple regime analysis methods and 1 d models are applicable to the evaluation of long term and reach scale restoration aims and to the prediction of kilometre scale processes e g mean river bed aggradation or degradation flood protection 2 d models gave good results for the evaluation of hydraulic changes e g transverse flow velocities shear stresses discharges at diffluences for different morphological units at the local scale 100 m 10 m and imposed an intermediate demand on calibration data and topographic survey the study shows that complex 3 d numerical models combined with high resolution digital elevation models are necessary for detailed analysis of processes 1 m 0 01 m but not for the evaluation of the restoration aims on the river drau in conclusion model choice complexity will depend on both lower limits determined by the complexity of processes to be analysed and upper limits field data quality and process understanding for numerical models

turbulent flow over three dimensional dunes 2 fluid and bed stresses 1 dunes formed in response to fluid flow exert a total boundary stress on the fluid that is made up of form drag and skin friction the latter of which is generally considered important for predicting sediment transport and dune evolution previous research has used various methods to estimate the total stress and its subcomponents with recent work suggesting the application of a spatial average to the equations of motion a complete three dimensional 3 d form of this analysis is derived and applied to recent measurements of turbulent open channel flow over 3 d dunes spatial averages of reynolds shear stresses over 3 d dunes cannot be used to predict total boundary shear stress however estimations of total boundary shear stress from the spatially averaged equations of motion agree with not only the sum of form drag and skin friction but also the direct measurements of average free surface slope form induced stresses from secondary circulations augment the relatively low reynolds shear stresses over the 3 d dunes these low turbulence levels have ramifications for sediment transport predictions in that use of the total boundary shear stress in prediction of sediment transport over 3 d dunes must account for these low turbulence levels so as not to overpredict transport rates

introduction to special section on marine sand wave and river dune dynamics marine sand waves and river dunes are rhythmic patterns formed at the interface between a sandy bed and turbulent flows driven by tidal and river currents their origin development and dynamics are far from being fully understood to enhance the discussion on this topic we organized the international conference marine sand wave and river dune dynamics marid in april 2004 in enschede netherlands scientific papers that originated from the marid conference are presented in this special section this introduction places these papers in the context of recent progress

coupled thermo hydro bio geochemical reactive transport model of cerberus heating and radiation experiment in boom clay abstract final disposal of high level radioactive waste in deep repositories in clay formations is being considered by several countries repository safety assessment requires the use of numerical models of groundwater flow solute transport and chemical processes these models are being developed from data and knowledge gained from in situ experiments such as the cerberus experiment carried out at the hades facility excavated in the boom clay formation at mol belgium this long term experiment is aimed at evaluating the effect of heating and radiation in boom clay the test was performed in a cased well drilled at 223 m depth and lasted from 1989 to 1994 a 60 co source of 400 tbq and two heaters were emplaced inside the well dose rate temperature porewater pressure and ph eh were measured in situ during the experiment and gas and porewater samples were taken for chemical analyses here a coupled thermo hydro geochemical thc model of the cerberus experiment is presented which accounts simultaneously for heating radiation solute diffusion and a suite of geochemical reactions including aqueous complexation acid base redox mineral dissolution precipitation cation exchange and gas dissolution ex solution computed results indicate that heating and radiation causes a slight oxidation a decrease in ph slight changes in porewater chemistry and pyrite dissolution near the well thc model results follow the general evolution of chemical data but cannot fit so 4 data model discrepancies are partly overcome when microbially mediated fe and so 4 reduction are taken into account in a coupled thermo hydro bio geochemical thbc model this thbc model captures the trends of geochemical data improves the fit to dissolved so 4 and predicts pyrite precipitation a process observed near the cerberus well the ability of the thbc numerical model to reproduce the overall trends of geochemical data of the cerberus experiment provides confidence in such a model as a suitable tool for the long term prediction of geochemistry in the near field of a hlw repository in clay however the small number of available chemical data throughout the experiment and the lack of doc and microbial data allow only a partial validation of the thbc model

propagation of tides along a river with a sloping bed conceptually tidal rivers are seen as narrow channels along which the cross section geometry remains constant and the bed is horizontal as tidal waves propagate along such a channel they decrease exponentially in height the more rapid the decrease the stronger the river flow near the coast the tidally averaged width and depth change little throughout the year even if the river discharge varies strongly between the seasons however further upstream the water depth varies considerably with the river discharge recent observations from the kapuas river indonesia show that the water surface forms a backwater profile when the river flow is low in this case the depth converges i e it gradually decreases between the river mouth and the point where the bed reaches sea level this effect distinctly influences how tidal waves propagate up river so that their wave height does not decrease exponentially any more we present a theoretical analysis of this phenomenon which reveals several so far overlooked aspects of river tides these aspects are particularly relevant to low river flow along the downstream part of the tidal river depth convergence counteracts frictional damping so that the tidal range is higher than expected along the upstream parts of the tidal river the low depth increases the damping so that the tide more rapidly attenuates the point where the bed reaches sea level effectively limits the tidal intrusion which carries over to the overtide and the subtidal water level set up

predicting fine sediment dynamics along a pool riffle mountain channel abstract fine sediment dynamics in mountain rivers are of concern because of implications for aquatic habitat channel stability and downstream sediment yields many mountain river systems have episodic fine sediment transport because of infrequent point source sediment inputs from landslides basin instability triggered by land uses such as logging or infrequent mobilization of the coarse surface layer in channels dam removal which is now more likely along mountain rivers may also provide a substantial fine sediment input to downstream channel reaches fine sediment storage in the interstices of spawning gravels and within pools along mountain rivers is of particular interest because of impacts to aquatic organisms in this study we focus on sediment dynamics within pools of the north fork poudre river in colorado as an example of the processes controlling fine sediment deposition storage and transport within laterally constricted pools the 1996 release of 7000 m3 of silt to gravel sized sediment from a reservoir on the north fork provided an opportunity to develop a field data set of fine sediment dynamics and to test the predictions of three different one or two dimensional sediment transport and hydraulic models against the field observations the models were calibrated against quantitative measurements of pool scour and fill one dimensional hec 6 results indicate that robust simulations yield the greatest agreement between predicted and measured pool bed elevation change model calibration on two pools and validation on one pool indicate that at least 58 of observed bed changes after the sediment release were predicted by hec 6 modeling accuracy using quasi two dimensional gstars 2 0 was considerably more variable and no pool wide trends were obtained the two dimensional model rma2 substantially improved the representation of eddy pool hydraulics within a compound pool of the north fork results from the hydraulic modeling coupled with bed load and total load computations delineate areas of scour and deposition which are consistent with observations in the field a conceptual model of sediment delivery and storage for laterally confined pools suggests that persistent deposition of fine sediment within eddies distal from the sediment source may result from sediment releases the original loss of channel capacity facilitated additional deposition within eddies as sediment within upstream proximal pools became mobilized at high discharges the development of a strong shear zone prevents degradation of sediment deposits within the eddy central portions of these proximal pools may clear according to existing models whereas deposition within recirculating zones may be long term water managers could use these models to estimate minimum pool volume for overwinter habitat and residence time of pool sediment