hot water drilling and bore hole closure in cold ice drilling bore holes in deep cold ice masses by hot water methods and maintaining these holes with sufficient diameter to allow down hole experimentation poses a major obstacle to the investigation of conditions beneath ice sheets and ice streams closure of the water filled holes by refreezing is the dominant difficulty in this paper we describe calculations of heat transfer from the drilling system to the ice and the subsequent time dependent motion of the phase boundary defining the bore hole wall results are presented with the view of optimizing the bore hole radius at depth for a fixed drill performance and a variable rate of drilling calculation of melting refreezing rates at the bore hole wall requires the use of a one dimensional time dependent numerical heat flow model with a distorting mesh which follows the changing hole size the delay of hole closure is discussed with a view to keeping holes open long enough to allow instruments to be lowered to the glacier bed while realizing that drilling system performance may be marginal because of logisitical and or expenditure constraints the relative merits of drilling a large hole which is very time consuming with a small drill and the use of water soluble antifreezes which have a history of creating plugs of ice slush are discussed a method of creating a stable hole filled with antifreeze in which ice slush does not occur is described the recent application of these theoretical ideas to the planning and implementation of successful hot water drilling programs in antarctica and greenland is also presented

mineralogy and geochemistry of alluvium contaminated by metal mining in the rio tinto area southwest spain the rio tinto in sw spain drains cu and pyrite mines which have been in operation since at least the bronze age extensive metal mining especially from 1873 to 1954 has resulted in contamination of the rio tinto alluvium with as cu pb ag and zn x ray diffraction xrd wavelength dispersive x ray mapping scanning electron microscope petrography and x ray energy dispersive edx analysis has revealed that 4 major groups of contaminant metal and as bearing minerals including sulphides fe as oxides fe oxides hydroxides oxyhydroxides and fe oxyhydroxysulphates occur in the alluvium sulphide minerals including pyrite chalcopyrite arsenopyrite and sphalerite occur in alluvium near the mining areas iron hydroxides and oxyhydroxides such as goethite and possibly ferrihydrite occur in cements in both the mining areas and alluvium downstream and carry minor amounts of as cu and zn iron oxyhydroxysulphates including jarosite plumbojarosite and possibly schwertmannite are the most common minerals in alluvium downstream of the mining areas and are major hosts of cu pb zn and of as next to the fe as minerals this work and other field observations suggest that 1 the extreme acidity and elevated metal concentrations of the river water will probably be maintained for some time due to oxidation of pyrite and other sulphides in the alluvium and mine waste tips and from formation of secondary oxide and oxyhydroxysulphates 2 soluble fe oxyhydroxysulphates such as copiapite which form on the alluvium are a temporary store of contaminant metals but are dissolved during periods of high rainfall or flooding releasing contaminants to the aqueous system 3 relatively insoluble fe oxyhydroxysulphates and hydroxides such as jarosite and goethite may be the major long term store of alluvial contaminant metals and 4 raising river ph will probably cause precipitation of fe oxyhydroxides and oxides hydroxides oxyhydroxides and thus have a positive effect on water quality but this action may destabilise some of these contaminant metal bearing minerals releasing metals back to the aqueous system

fracture propagation to the base of the greenland ice sheet during supraglacial lake drainage surface meltwater that reaches the base of an ice sheet creates a mechanism for the rapid response of ice flow to climate change the process whereby such a pathway is created through thick cold ice has not however been previously observed we describe the rapid 2 hours drainage of a large supraglacial lake down 980 meters through to the bed of the greenland ice sheet initiated by water driven fracture propagation evolving into moulin flow drainage coincided with increased seismicity transient acceleration ice sheet uplift and horizontal displacement subsidence and deceleration occurred over the subsequent 24 hours the short lived dynamic response suggests that an efficient drainage system dispersed the meltwater subglacially the integrated effect of multiple lake drainages could explain the observed net regional summer ice speedup

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

sedfoam a multi dimensional eulerian two phase model for sediment transport and its application to momentary bed failure abstract a multi dimensional eulerian two phase model for sediment transport called sedfoam is presented the model was developed under the open source framework via the cfd toolbox openfoam with closures of particle stresses and fluid particle interactions the model is able to resolve processes in the concentrated region of sediment transport and hence does not require conventional bedload suspended load assumptions a modified k closure was adopted for the carrier flow turbulence the model was validated for reynolds averaged steady and oscillatory sheet flows and verified with empirical formulae for scour downstream of an apron the model was used to study momentary bed failure or plug flow under sheet flow conditions model results revealed the existence of instabilities of the near bed transport layer when momentary bed failure criteria was exceeded these instabilities evolved into 5 10 cm billows and were responsible for the large transport rate the instabilities were associated with a large erosion depth which was triggered by the combination of large bed shear stresses and large horizontal pressure gradients further numerical experiments confirmed the conjecture by previous studies that a criterion for onset of momentary bed failure in oscillatory sheet flow was a function of both the shields parameter and sleath parameter

sediment transport over ripples in oscillatory flow in this paper we present results of a large eddy simulation of flow and suspended sediment transport around prototypical ripples based on long wave ripples as measured at duck n c in waves of height 1 m and period of 10 s solving the volume filtered navier stokes equations for the momentum and an advection diffusion equation with a setting term for the suspended sediment we obtain time dependent three dimensional descriptions of the velocity pressure and sediment concentration fields although the main flow and sediment transport patterns are governed by a quasi two dimensional vortex formation ejection mechanism we illustrate the three dimensional structure of both and make qualitative comparisons with the results of other researchers we conclude with analysis of concentration time series measured at a point and interpret them within the larger framework of the flow the present simulations demonstrate that the flow over these larger scale ripples resembles that over vortex ripples quite s

englacial latent heat transfer has limited influence on seaward ice flux in western greenland surface meltwater can refreeze within firn layers and crevasses to warm ice through latent heat transfer on decadal to millennial timescales earlier work posited that the consequent softening of the ice might accelerate ice flow potentially increasing ice sheet mass loss here we calculate the effect of meltwater refreezing on ice temperature and softness in the p kitsoq near swiss camp and jakobshavn isbrae regions of western greenland using a numeric model and existing borehole measurements we show that in the jakobshavn catchment meltwater percolation within the firn warms the ice at depth by 3 5 c by contrast meltwater refreezing in crevasses cryo hydrologic warming at depths of 300 m warms the ice in p kitsoq by up to 10 c but this causes minimal increase in ice motion 10 m a 1 p kitsoq is representative of western greenland s land terminating ice where the slow movement of ice through a wide ablation zone provides ideal conditions for cryo hydrologic warming to occur we find that only 37 of the western greenland ice flux however travels through such areas overall our findings suggest that cryo hydrologic warming will likely have only a limited effect on the dynamic evolution of the greenland ice sheet

over winter persistence of supraglacial lakes on the greenland ice sheet results and insights from a new model we present a newly developed 1 d numerical energy balance and phase transition supraglacial lake model glacierlake glacierlake incorporates snowfall in situ snow and ice melt incoming water from the surrounding catchment ice lid formation basal freeze up and thermal stratification snow cover and temperature are varied to test lake development through winter and the maximum lid thickness is recorded average wintertime temperatures of 2 to 30 circ rm c and total snowfall of 0 to 3 45 m lead to a range of the maximum lid thickness from 1 2 to 2 8 m after sim 250 days with snow cover exerting the dominant control an initial ice temperature of 15 circ rm c with simulated advection of cold ice from upstream results in 0 6 m of basal freeze up this suggests that lakes with water depths above 1 3 to 3 4 m dependent on winter snowfall and temperature upon lid formation will persist through winter these buried lakes can provide a sizeable water store at the start of the melt season expedite future lake formation and warm underlying ice even in winter

vertical fluxes of sediment in oscillatory sheet flow time series of vertical sediment fluxes are derived from concentration time series in sheet flow under waves while the concentrations c z t vary very little with time for z 10d50 the measured vertical sediment fluxes qzs z t vary strongly with time in this vertical band and their time variation follows to some extent the variation of the grain roughness shields parameter 2 5 t thus sediment distribution models based on the pickup function boundary condition are in some qualitative agreement with the measurements however the pickup function models are only able to model the upward bursts of sediment during the accelerating phases of the flow they are so far unable to model the following strong downward sediment fluxes which are observed during the periods of flow deceleration classical pickup functions which essentially depend on the shields parameter are also incapable of modelling the secondary entrainment fluxes which sometimes occur at free stream velocity reversal the measured vertical fluxes indicate that the effective sediment settling velocity in the high 0 3 c z t 0 4 concentration area is typically only a few percent of the clear water settling velocity while the measurements of richardson and jeronimo chem eng sci 34 1979 1419 from a different physical setting lead to estimates of the order 20 the data does not support gradient diffusion as a model for sediment entrainment from the bed that is detailed modelling of the observed near bed fluxes would require diffusivities that go negative during periods of flow deceleration an observed general trend for concentration variability to increase with elevation close to the bed is also irreconcilable with diffusion models driven by a bottom boundary condition

mechanisms of fast flow in jakobshavn isbrae west greenland part iii measurements of ice deformation temperature and cross borehole conductivity in boreholes to the bedrock at a site on the ice sheet adjacent to the jakobshavn ice stream in west greenland ice deformation rates and temperatures have been measured in boreholes to the bedrock at 830 m depth enhanced deformation rates were recorded just below the holocene wisconsin transition at 680 m depth a 31 m layer of temperate ice and the temperature minimum of 22 c at 520 m depth were detected the good agreement of these data with results of a two dimensional thermomechanically coupled flow model implies that the model input is adequate discrepancies between modelled and measured temperature profiles on a flowline at the ice stream centre have been attributed to effects not accounted for by the model we have suggested that the convergent three dimensional flow leads to a vertical extension of the basal ice entering the stream a thick basal layer of temperate and wisconsin ice would explain the fast flow of this ice stream as a test of this hypothesis the new core borehole conductivity cbc method has been used to compare conductivity sequences from the ice stream to those of the adjacent ice sheet the correlation thus inferred suggests that the lowest 270 m of the ice sheet correspond to the lowermost 1700 m of the stream and consequently that the lower part of the ice stream has experienced a very large vertical extension

temperature distribution and thermal anomalies along a flowline of the greenland ice sheet englacial and basal temperature data for the greenland ice sheet gris are sparse and mostly limited to deep interior sites and ice streams providing an incomplete representation of the thermal state of ice within the ablation zone here we present 11 temperature profiles at five sites along a 34 km east west transect of west greenland these profiles depict ice temperatures along a flowline and local temperature variations between closely spaced boreholes a temperate basal layer is present in all profiles increasing in thickness in the flow direction where it expands from 3 of ice height furthest inland to 100 at the margin temperate thickness growth is inconsistent with modeled heat contributions from strain heating heat conduction and vertical extension of the temperate layer we suggest that basal crevassing facilitated by water pressures at or near ice overburden pressure is responsible for the large temperate ice thicknesses observed high temperature kinks at 51 85m depth are likely remnants from the thermal influence of partially water filled crevasses up ice sheet steep horizontal temperature gradients between closely grouped boreholes suggest the recent thermal influence of a moulin these profiles demonstrate the ability of meltwater to rapidly alter ice temperatures at all depths within the ablation zone

hyperconcentrated sand water mixture flows over erodible bed field surveys and experiments in a tilting flume on hyperconcentrated sand water mixture swm flows were conducted at slopes slightly smaller than the equilibrium slope a rapid development of sand bars propagating upstream was observed these bars consist of an almost horizontal terrace with subcritical flow a steep lee side slope with supercritical flow and a hydraulic jump between subsequent bars the erosion processes on the bar are limited by the high sand concentrations and flow velocities on the steep slopes as a result the erosion rate is more moderate than predicted by the pickup functions used in classical sediment transport theory a simple one dimensional model is presented to study the behavior of triangular schematized bars from an analysis of the equations it is concluded that an increase in erosion rate requires an increase in bed slope to maintain equilibrium flow conditions finally simulations with the model are compared with observations in the field and in the tilting flume t

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

permafrost active layer abstract this article discusses the properties and occurrence of an active layer al in the near surface of the lithosphere in glacial and periglacial environments this layer shows a seasonal variability in temperature as a result of the climate the al as classically understood seasonally thaws and freezes while in glacial environments it usually only reaches 0 c the definition of al is currently not consistent with the definition of permafrost even though both concepts usually appear linked for these terms to be comparable both should be defined based on temperature variability and not exclusively on phase change thus the al would be described not only as the upper section of perennially frozen ground presenting seasonal thaw freeze cycles 1 but as a layer presenting a seasonal variation in temperature 2 classical active layer can be thawed to a depth of approximately 2 8 cm the thickest al reaches over 20 m in the particularly favorable conditions al might be completely absent with the permafrost beginning at the ground surface in glacial and sub marine permafrost environments the al includes a layer of liquid water that seasonally accompanies the permafrost glaciers and ice sheets are usually devoid of the classical al in both cases the al is usually horizontal but in specific terrains such as sea shore cliffs or karst environments the al may have a vertical course and may even be reversed both al and permafrost are common in other frozen bodies in the solar system differing mainly in their thermal character

prediction of time dependent sediment suspension in the surf zone using artificial neural network abstract a predictive model of time dependent sediment suspension was developed with artificial neural network using velocity and integrated sediment concentration i e suspended load data observed from a large scale laboratory experiment under erosive and accretive beach conditions low frequency motion wave induced motion and turbulent kinetic energy per unit mass at lower 1 cm above the bed and upper 50 cm above the bed adv were used as inputs and suspended load near the bed was used as output to account for the history prior to sediment suspension five time steps corresponding to 2 s of data prior to sediment suspension were included in the inputs the artificial neural network model shows a predictive capability of the time dependent sediment suspension in the surf zone for both erosive and accretive conditions the correlation coefficient r between the measured and predicted suspended load reached up to r 0 79 at the bar crest in the accretive beach condition and typical average correlation coefficients over all subsets r were 0 53 over the bar crest the results from various input cases showed that turbulent kinetic energy near the bed is most important to predict the sediment suspension in the surf zone for both erosive and accretive conditions also the best predictive performance was shown at the bar crest supporting the hypothesis that turbulence induced by intense wave breaking at the bar crest is a dominant mechanism for sediment suspension outside the surf zone the wave induced motion was the highest contributing factor for the sediment suspension furthermore when the information from the upper adv was included as inputs the model improved the prediction capability by 40 at the bar trough in the erosive beach condition the increased prediction at this location may possibly be attributed to the effect of vertical shear motion in the low frequency range due to strong undertow from wave breaking

distribution of metals in soils and plants around mineralized zones at cartagena la union mining district se spain a geochemical and mineralogical characterization of three zones namely oxides zones hydrothermal alteration zone and mining wastes zone from a mineralized zone in the upper part of the cartagena la union range was carried out by analysing rocks soils and three plant species piptatherum miliaceum ditrichia viscosa and hirsfeldia incana the transference and bioavailability of some metals especially pb zn as and fe from soils to plants was also checked results show that rocks have a large content of fe and pb which are transferred to surrounding soils also highly enriched in these elements fe ranges from 9 to 35 and pb 1 to 2 9 regarding soil to plant transfer it was shown a differential behaviour for both the three plant species and the soil zones with a higher level of metal accumulation rates for piptatherum miliaceum in the hydrothermal alteration zone values of accumulation rates obtained for pb in piptatherum miliaceum allow considering it a good choice for phytoremediation purposes

sediment entrainment at high flow velocity in dredging practice sand is eroded at very high flow velocities using water jets breaching of dikes or dams is another process where sediments are eroded under the influence of high flow velocities the existing pick up functions were developed for relative low values of bed shear stress and hence overestimate erosion conventional pick up functions can be made suitable for dealing with high velocity erosion by taking the permeability of the sediment into account this can be achieved by modifying the critical shields parameter the procedure is demonstrated using the van rijn pick up function the theory is compared with experiment and agreement is found to be good

pickup probability for sediment entrainment the study presents a theoretical derivation for a new pickup probability formulation for sediment transport sand particles are assumed to be subjected to a hydraulically rough flow the derived equation compares well with the experimental data found in published literature using the proposed relation the shields criterion for the definition of the threshold condition for sediment transport is equivalent to 0 6 of the pickup probability

large eddy simulation of sediment transport currents over ripples a large eddy simulation has been performed to study the detailed sediment dynamics that occur in channel flow over ripples the code solves the navier stokes equations and an advection diffusion equation for the sediment and has been verified to produce quantitatively accurate hydrodynamic results for the flow domains used in this study the main features of interest in this flow are seen because of the high resolution of the grid especially near the ripple boundary this yields a detailed bottom shear stress distribution properly identified coherent structures and resolved sharp gradients in the sediment concentration globally the sediment is carried up into the flow from locations where the shear stress is high on the upslopes of ripple crests and is advected downstream by the current and upward by the vertical velocity component regions of positive vertical velocity are associated with gortler vortices which represent a significant sediment transport mechanism in this flow

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

sediment pick up functions experimental research has been performed to determine the sediment pick up by a uniform flow without initial sediment load a sediment lift was designed by which the sediment particles were moved upwards at a constant rate through a circular opening in the flume bottom five types of bed material sand have been used with d d5 d0 values in the range 130 1500 m the mean flow velocities were in the range 9 5 1 0 m s the experimental results have been used to derive an empirical pick up function the results have also been used to evaluate several existing pick up functions finally the proposed empirical pick up function has been applied to predict the bed load and suspended load transport in the latter application the proposed function has been used as a bed boundary condition in a mathematical model for suspended sediment transport

bed load sediment transport on steep longitudinal slopes the results of new experiments on bed load transport on steep longitudinal slopes are presented the experiments were carried out in a large tilting duct with a fine sand median grain diameter of 208 micro m covering the range of slope angles beta of angle of repose for the sand phi sub s of 32 deg 0 56 rad measurements included bed shear stress flow discharge and the sediment pickup rate on slopes the results suggest that existing theories for bed load transport on slopes are not adequate for all bed slopes and the new data are used to formulate a semiempirical relation that satisfactorily predicts the transport rate on horizontal as well as mild and steep slopes the following are two important findings correcting the threshold term for slope in the meyer peter and muller formula adequately describes the transport rate on positive slopes elevation increasing in direction of flow and on small negative slopes while on steeper negative slopes an extra correction term is required although the value of beta phi sub s at which this term becomes necessary is a function of shear stress and the influence of slope vanishes at high shear stresses

divergent behavior of the swash zone in response to different foreshore slopes and nearshore states abstract ultrasonic distance sensors were used to measure changes in bed elevation to a resolution of 0 1 mm following individual swash excursions in the high tide swash zone of an intermediate foreshore changes in bed elevation are related to depth averaged eularian swash velocities estimated by assuming mass balance of the swash discharge also measured using the ultrasonic distance sensors early in the study may 21 25 2008 the alongshore uniform foreshore had a cross shore slope of 0 18 and was fronted by a nearshore bar that forced wave breaking at low tide towards the end of the study june 5 9 2008 the foreshore had a slope of 0 12 and was fronted by a nearshore terrace that developed as the innermost bar migrated landward despite similar inshore wave heights and periods during these times the steeper foreshore eroded by 0 69 m 3 m 1 while the more gently sloped foreshore accreted by 0 21 m 3 m 1 the divergent behavior of the swash zone is attributed to the welding of the innermost bar to the foreshore creating a shallow nearshore terrace that saturated the inshore wave field this in turn led to a faster uprush velocity that promoted the landward advection of sediment picked up over the shallow terrace it is argued that accretion in the upper swash zone was the result of a larger supply of sediment at the base of the foreshore and a transformation of the wave field by the shallower depths of the welded feature in this respect swash hydrodynamics and morphological change can only be made if the swash zone is considered within the context of the broader nearshore state

radio tracking gravel particles in a large braided river in new zealand a field test of the stochastic theory of bed load transport proposed by einstein hans a einstein initiated a probabilistic approach to modelling sediment transport in rivers his formulae were based on theory and were stimulated by laboratory investigations the theory assumes that bed load movement occurs in individual steps of rolling sliding or saltation and rest periods so far very few attempts have been made to measure stochastic elements in nature for the first time this paper presents results of radio tracing the travel path of individual particles in a large braided gravel bed river the waimakariri river of new zealand as proposed by einstein it was found that rest periods can be modelled by an exponential distribution but particle step lengths are better represented by a gamma distribution einstein assumed an average travel distance of 100 grain diameters for any bed load particle between consecutive points of deposition but larger values of 6 7 m or 150 grain diameters and 6 1 m or 120 grain diameters were measured for two test particle sizes together with other available large scale field data a dependence of the mean step length on particle diameter relative to the d50 of the bed surface was found during small floods the time used for movement represents only 2 7 of the total time from erosion to deposition the increase in percentage of time being used for transport means that it then has to be regarded in stochastic transport models tracing the flow path of bed load particles between erosion and deposition sites is a step towards explaining the interactions between sediment transport and river morphology copyright 2001 john wiley sons ltd

dimensionless erosion laws for cohesive sediment abstracta method of achieving a dimensionless collapse of erosion rate data for cohesive sediments is proposed and shown to work well for data collected in flume erosion tests on mixtures of sand and mud silt plus clay sized particles for a wide range of mud fraction the data collapse corresponds to a dimensional erosion law of the form e c m where e is erosion rate is shear stress c is the threshold shear stress for erosion to occur and m 7 4 this result contrasts with the commonly assumed linear erosion law e kd c where kd is a measure of how easily sediment is eroded the data collapse prompts a re examination of the way that results of the hole erosion test het and jet erosion test jet are customarily analyzed and also calls into question the meaningfulness not only of proposed empirical relationships between kd and c but also of the erodibility parameter kd itself fuller comparison of flume erosion data with hole erosion and jet erosion data will require revised analyses o

flow structure of turbidity currents a two dimensional numerical model is used to describe the flow structure of turbidity currents in a vertical plane to test the accuracy of the model it is applied to historical flows in bute inlet and the grand banks flow the two dimensional spatial and temporal distributions of velocity and sediment concentration and non dimensionalized vertical profiles of velocity turbulent kinetic energy and sediment concentration are discussed for several simple computational currents the flows show a clear interaction between velocity turbulence and sediment distribution the results of the numerical tests show that flows with fine grained sediment have low vertical and high horizontal gradients of velocity and sediment concentration show little increase in flow thickness and decelerate slowly steadiness and uniformity in these flows are comparable for velocity and concentration in contrast flows with coarse grained sediment have high vertical and low horizontal velocity gradients and high horizontal concentration gradients these flows grow considerably in thickness and decelerate rapidly steadiness and uniformity in flows with coarse grained sediment are different for velocity and concentration the results show the influence of spatial and temporal flow structure on flow duration and sediment transport

a conceptual framework for shear flow induced erosion of soft cohesive sediment beds this paper proposes a conceptual framework for erosion of cohesive sediment beds we focus on cohesive beds distinguishing between floc erosion surface erosion and mass erosion by our definition surface erosion is a drained soil mechanical process whereas mass erosion occurs under undrained conditions the eroding shear stress is modeled through a probability density function this yields a continuous description of floc erosion and surface erosion as a function of mean bed shear stress furthermore we assume a distribution for the bed strength the mean values of the bed strength are derived from soil mechanical theory assuming that the surface erosion rate is limited by the swelling rate from the undrained shear strength in the bed to its drained value at its surface the rate of erosion then relates to the undrained shear strength of the soil and its consolidation swelling coefficient the critical shear stress for erosion is slightly larger than the true cohesion of the bed i e the drained strength and follows a power law relation with the plasticity index the conceptual framework proposed herein has been validated against a limited number of experimental data and has a series of advantages above other methods of direct measuring erodibility as it is inexpensive and can be used to attain space covering information on the sediment bed moreover the use of bulk soil mechanical parameters accounts implicitly for the effects of organic material though the role of e g macrophytobenthos mats and or bioturbation is difficult to capture a priori

turbulent bursting based sediment entrainment function one of the basic impediments to a clear understanding of a variety of fundamental problems in the context of sediment transport has been the lack of a well grounded formulation of bed sediment entrainment this is dealt with herein physically based on the mechanism that bed sediment particles are actually entrained by the bursting process inherent in wall turbulent flows a simple theoretical model for sediment entrainment from flat loose bed is established using the averaged bursting period scaled on inner variables and the spatial scales of turbulent bursts sediment entrainment is shown to depend strongly on bed shear velocity the theoretical entrainment flux is compared to available laboratory data sets covering both hydraulically smooth and transitional bed situations generally good agreement is obtained representing the best performance of the present model in relation to existing entrainment functions it appears to characterize a rather encouraging aspect for a new approach to sediment transport given the enhanced understanding of turbulent bursting

mobility and microbially mediated mobilization of gold and arsenic in soils from two gold mines in semi arid and tropical australia the mobility and microbially mediated solubilization of au and as in regolith materials from two au mines in australia i e the peak hill gold mine in semi arid new south wales and the hit or miss gold mine in tropical northern queensland was studied using a combination of geochemical and microbiological techniques gold is highly mobile in both environments the mobility of au increases with increasing degree of weathering of host materials and the resident microbiota are capable of mediating its solubilization the results of the microcosm experiments demonstrate that the activity of microorganisms needs to be taken into account when studying the mobility and solubilization of au in the australian regolith in primary unweathered mineralization material from the hit or miss mine 99 wt of au was extracted only in the strongest final step of the sequential extractions in concentrated aqua regia in alteration zone material from the peak hill gold mine 80 wt of au was associated with the operationally defined mn and fe oxides in contrast in auriferous soils overlying mineralization at both sites 90 95 wt of au was associated with the operationally defined exchangeable claybound and organic fractions microcosm experiments were incubated biologically active and inactive sterilized in 1 4 w v aqueous slurries at 25 c in the dark for up to 95 days in biologically active microcosms with soils from the peak hill and the hit or miss gold mines approximately 55 wt 907 ng g 1 d w soil and 20 wt 233 ng g 1 d w soil of the total au respectively was solubilized during the incubation in contrast no or significantly lower au concentrations were observed in biologically inactive microcosms the mobility and microbially mediated release of as was limited at both sites and appears to be mostly controlled by abiotic adsorption and desorption on mn and fe oxides arsenic has a low solubility in the more mobile fractions and is mostly associated with mn and fe oxides and the residual fraction the release of as was not elevated in biologically active compared to inactive microcosms from the peak hill gold mine in contrast in biologically active microcosms with samples from the hit or miss mine elevated concentrations of as were detected in solution compared to the biologically inactive experiments crown copyright 2006 published by elsevier inc all rights reserved

sensitivity of the frozen melted basal boundary to perturbations of basal traction and geothermal heat flux isunnguata sermia western greenland a full stress thermomechanically coupled numerical model is used to explore the interaction between basal thermal conditions and motion of a terrestrially terminating section of the west greenland ice sheet the model domain is a two dimensional flowline profile extending from the ice divide to the margin we use data assimilation techniques based on the adjoint model in order to optimize the basal traction field minimizing the difference between modeled and observed surface velocities we monitor the sensitivity of the frozen melted boundary fmb to changes in prescribed geothermal heat flux and sliding speed by applying perturbations to each of these parameters the fmb shows sensitivity to the prescribed geothermal heat flux below an upper threshold where a maximum portion of the bed is already melted the position of the fmb is insensitive to perturbations applied to the basal traction field this insensitivity is due to the short distances over which longitudinal stresses act in an ice sheet

measured horizontal temperature gradients constrain heat transfer mechanisms in greenland ice ice in the ablation zone of the greenland ice sheet is known to contain vertical temperature gradients that arise from conduction at the boundaries the addition of strain and latent heat and advective heat transport a three dimensional array of temperature measurements in a grid of boreholes reveals horizontal ice temperature gradients that challenge the present conceptualization of heat transfer we measure two distinct types of temperature variability in the horizontal direction one impacting a confined region where ice temperatures span a range of 5 c and another with temperatures consistently varying by approximately 2 c across the entire 3 d block we suggest the first demonstrates the localized and limited nature of latent heat input and the second demonstrates that vertical heat advection outpaces diffusion these findings imply that ice flow is highly variable over sub ice thickness length scales which in turn generates contrasts in ice temperature that may impact ice deformation and fracturing

spectral roughness and glacial erosion of a land terminating section of the greenland ice sheet spectral roughness offers a significant potential for understanding the evolution of glaciated landscapes here we present the first roughness study combining a high resolution 250 to 500 m dem

a stochastic formulation for erosion of cohesive sediments the linear formulation for erosion e m b c often applied in engineering applications has two properties which do not always comply with field and laboratory observations they are as follows 1 the erosion rate is zero below the critical bed shear stress c and increases linearly with bed shear stress b when exceeding the critical bed shear stress incipient motion b simeq c is poorly represented 2 the erosion rate is constant in time for constant values of m and c whereas observations often suggest time dependency in this paper we analyze the process of incipient motion and time dependency by using a stochastic forcing bed shear stress and a stochastic bed strength critical bed shear stress it is well known that the bed shear stress is not constant but varies due to turbulence this stochastic nature of the turbulent motion is accounted for by a probability density distribution for the bed shear stress which is based on the formulation of hofland and battjes 2006 this distribution is implemented in the linear erosion formulation an analytical solution for the erosion rate is obtained which only depends on the mean bed shear stress a parametrization is made for efficient application in numerical models the sediment in the bed is considered to be nonuniform therefore it is subdivided into several classes distinguished by the critical bed shear stress and not necessarily by the grain size the variability of the critical bed shear stress is treated in a discritized way sediment balance equations are solved for each class considering different classes the total erosion rate becomes time dependent as the erosion depends on the availability of sediment the model is applied to two annular flume data sets jacobs 2009 and amos et al 1992a the results show that with a proper choice of the required parameters the time dependence of the erosion rate and the concentration can be reproduced we conclude that the occurrence of incipient motion can be explained from a stochastic forcing time varying erosion rates can be explained from a stochastic bed strength distribution or from a vertical gradient in bed strength the latter is however not likely and not measurable in the top layers of dense consolidated cohesive sediment beds

a review of the source behaviour and distribution of arsenic in natural waters the range of as concentrations found in natural waters is large ranging from less than 0 5 g l 1 to more than 5000 g l 1 typical concentrations in freshwater are less than 10 g l 1 and frequently less than 1 g l 1 rarely much higher concentrations are found particularly in groundwater in such areas more than 10 of wells may be affected defined as those exceeding 50 g l 1 and in the worst cases this figure may exceed 90 well known high as groundwater areas have been found in argentina chile mexico china and hungary and more recently in west bengal india bangladesh and vietnam the scale of the problem in terms of population exposed to high as concentrations is greatest in the bengal basin with more than 40 million people drinking water containing excessive as these large scale natural as groundwater problem areas tend to be found in two types of environment firstly inland or closed basins in arid or semi arid areas and secondly strongly reducing aquifers often derived from alluvium both environments tend to contain geologically young sediments and to be in flat low lying areas where groundwater flow is sluggish historically these are poorly flushed aquifers and any as released from the sediments following burial has been able to accumulate in the groundwater arsenic rich groundwaters are also found in geothermal areas and on a more localised scale in areas of mining activity and where oxidation of sulphide minerals has occurred the as content of the aquifer materials in major problem aquifers does not appear to be exceptionally high being normally in the range 1 20 mg kg 1 there appear to be two distinct triggers that can lead to the release of as on a large scale the first is the development of high ph 8 5 conditions in semi arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates this ph change leads either to the desorption of adsorbed as especially as v species and a range of other anion forming elements v b f mo se and u from mineral oxides especially fe oxides or it prevents them from being adsorbed the second trigger is the development of strongly reducing conditions at near neutral ph values leading to the desorption of as from mineral oxides and to the reductive dissolution of fe and mn oxides also leading to as release iron ii and as iii are relatively abundant in these groundwaters and so4 concentrations are small typically 1 mg l 1 or less large concentrations of phosphate bicarbonate silicate and possibly organic matter can enhance the desorption of as because of competition for adsorption sites a characteristic feature of high groundwater as areas is the large degree of spatial variability in as concentrations in the groundwaters this means that it may be difficult or impossible to predict reliably the likely concentration of as in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well arsenic affected aquifers are restricted to certain environments and appear to be the exception rather than the rule in most aquifers the majority of wells are likely to be unaffected even when for example they contain high concentrations of dissolved fe

breaching in fine sands and the generation of sustained turbidity currents in submarine canyons natural moderately loosely packed sands can only erode from the surface of the bed after an increase in pore volume because of this shear dilatancy negative pore pressures are generated in the bed in cases of low permeability these negative pressures are released relatively slowly which retards the maximum rate of erosion this effect is incorporated in a new analytically derived pick up function that can explain the observation of gradual retrogressive failure of very steep subaqueous slopes sometimes more than 5 m high in fine non cohesive sands this process termed breaching in the field of sediment dredging may produce large failures in sand bars or river banks the analytical function that describes the breaching process in fine sand is incorporated in a one dimensional steady state numerical model of turbidity currents describing the spatial development of flow this model is applied to simulate a large flushing event in scripps submarine canyon pacific coast of california breach retrogradation and the successive evolution in time of the resulting turbidity current in the canyon are predicted in a sequence of discrete steps predicted velocities are compared with values measured during a flushing event implications for the interpretation of deep water massive sands are discussed

geochemistry of metals and metalloids in siliceous sinter deposits implications for elemental partitioning into silica phases abstract sinter deposits are formed by precipitation of silica from hydrothermal fluids that have reached the surface environment they are commonly found around hot springs and represent surface expressions of underlying geothermal systems and or low sulfidation epithermal gold silver hydrothermal deposits several studies have reported ppm to weight percent concentrations of metals e g au ag cu and metalloids e g as sb b in sinters capping geothermal systems and epithermal gold silver deposits however the relation between the maturity of the siliceous sinter and its metal enrichment remains unknown here we use geochemical and mineralogical data that link the silica crystallinity degree with trace metal and metalloid contents in sinter in this paper we provide in situ trace element data in metal rich silica sinter samples from the puchuldiza geothermal field in the altiplano of northern chile that record the complete diagenetic sequence from non crystalline opal a to microcrystalline quartz combined sem xrd and la icp ms data show that the concentration of metals and metalloids in sinters from puchuldiza display a strong correspondence with silica crystallinity while arsenic and boron are predominantly enriched in the more amorphous silica phases opal a ct gold and silver show higher concentrations in the more crystalline phases opal c quartz silica structural morphological and geochemical transformations from its initial precipitation to its final maturation after diagenesis are responsible for this differential enrichment during the initial stages gold and silver are incorporated into silica microspheres as cationic species and or metal nanoparticles or colloids while arsenic and boron incorporation is controlled by as bearing accessory minerals and fe oxyhydroxides as diagenesis progresses and the crystallinity of silica increases diffusion driven processes such as ostwald ripening may progressively enrich gold and silver in the sinter while metalloids are depleted owing to the low retention of arsenic by silica these findings indicate that the diagenetic transitions of silica defined by significant structural changes that involve generation of surface defects and the creation of reactive sites may play an important role in elemental uptake by silica in near surface environments

experiments on particle turbulence interactions in the near wall region of an open channel flow implications for sediment transport a high speed video system was used to study the interaction between sediment particles and turbulence in the wall region of an open channel flow with both smooth and transitionally rough beds in smooth flows particles immersed within the viscous sublayer were seen to accumulate along low speed wall streaks apparently due to the presence of quasi streamwise vortices in the wall region larger particles did not tend to group along streaks however their velocity was observed to respond to the streaky structure of the flow velocity in the wall region in transitionally rough flows particle sorting was not observed coherent flow structures in the form of shear layers typically observed in the near wall region interacted with sediment particles lying on the channel bottom resulting in the particles being entrained into suspension although there has been some speculation that this process would not be effective in entraining particles totally immersed in the viscous sublayer the results obtained demonstrate the opposite the entrainment mechanism appears to be the same independent of the roughness condition of the bottom wall smooth or transitionally rough in the latter case however hiding effects tend to preclude the entrainment of particles with sizes finer than that of the roughness elements the analysis of particle velocity during entrainment shows that the streamwise component tends to be much smaller than the local mean flow velocity while the vertical component tends to be much larger than the local standard deviation of the vertical flow velocity fluctuations which would indicate that such particles are responding to rather extreme flow ejection events

caterpillar like ice motion in the ablation zone of the greenland ice sheet current understanding of ice dynamics predicts that increasing availability and variability of meltwater will have an impact on basal motion and therefore on the evolution and future behavior of the greenland ice sheet we present measurements of ice deformation subglacial water pressure and surface velocity that show periodic and episodic variations on several time scales seasonal multiday and diurnal these variations observed with gps and sensors at different depths throughout the ice column are not synchronous but show delayed responses of ice deformation with increasing depth and basal water pressure in antiphase with surface velocity with the help of a full stokes ice flow model these observations are explained as ice motion in a caterpillar like fashion caused by patches of different basal slipperiness horizontal stress transfer through the stiff central part of the ice body leads to spatially varying surface velocities and ice deformation patterns variation of this basal slipperiness induces characteristic patterns of ice deformation variability that explain the observed behavior ice flow in the ablation zone of the greenland ice sheet is therefore controlled by activation of basal patches by varying slipperiness in the course of a melt season leading to caterpillar like ice motion superposed on the classical shear deformation

erosion velocity of large grains subjected to a high uniform flow velocity abstractthere is limited knowledge on the erosion rates of large grains the available erosion models of granular material at large flow velocities are only validated up to a median particle diamet

nearshore sandbar migration predicted by an eddy diffusive boundary layer model 1 we simulated the erosion and accretion of a natural beach using a wave resolving eddy diffusive model of water and suspended sediment motion in the bottom boundary layer nonlinear advection was included in this one dimensional vertical profile model by assuming that waves propagated almost without change of form flows were forced by fluctuating pressure gradients chosen to reproduce the velocity time series measured during the duck94 field experiment the cross shore flux of suspended sediment beneath each field deployed current meter was estimated and beach erosion accretion was calculated from the divergence convergence of this flux horizontal pressure forces on sediment particles were neglected the model successfully predicted two bar migration events one shoreward bar migration and one seaward but failed to predict a third seaward migration event simulated seaward sediment transport was due to seaward mean currents simulated shoreward sediment transport was due to covariance between wave frequency fluctuations in velocity and sediment concentration and was mostly confined to the wave boundary layer predicted seaward shoreward bar migration was driven by a maximum in the current generated wave generated flux over the sandbar a wave generated downward flux of shoreward momentum into the wave boundary layer contributed to shoreward sediment transport and often had a local maximum over the bar crest second order nonlinear advection of sediment mostly representing shoreward advection by the stokes drift also often had a local maximum over the bar crest together wave generated momentum fluxes and the stokes drift substantially increased shoreward transport and were essential to predictions of shoreward bar migration

a framework for attenuation method selection evaluated with ice penetrating radar data at south pole lake all radar power interpretations require a correction for attenuative losses moreover radar attenuation is a proxy for ice column properties such as temperature and chemistry prior studies use either paired thermodynamic and conductivity models or the radar data themselves to calculate attenuation but there is no standard method to do so and before now there has been no robust methodological comparison here we develop a framework meant to guide the implementation of empirical attenuation methods based on survey design and regional glaciological conditions we divide the methods into the three main groups 1 those that infer attenuation from a single reflector across many traces 2 those that infer attenuation from multiple reflectors within one trace and 3 those that infer attenuation by contrasting the measured power from primary and secondary reflections to assess our framework we introduce a new ground based radar survey from south pole lake comparing selected empirical methods to the expected attenuation from a temperature and chemistry dependent arrhenius model based on the small surveyed area lack of a sufficient calibration surface and low reflector relief the attenuation methods that use multiple reflectors are most suitable at south pole lake

large eddy simulation of sediment deformation in a turbulent flow by means of level set method sediment transport in a turbulent channel flow over the sediment bed with a ripple structure is numerically simulated by means of a large eddy simulation the filtered navier stokes equations for the channel flow and the filtered advection diffusion equation with a settling term for the suspended sediment are numerically solved in which the unresolved subgrid scale processes are modeled by the dynamic subgrid scale model of germano et al the migration and deformation of the interface between the sediment bed and the fluid flow is captured by the level set method the sediment erosion is approached by means of three different pickup relations postulated by van rijn einstein and yalin respectively partly modified by the authors generally the sediment is entrained into the flow from locations where the shear stress exceeds a critical value on the upstream slopes of ripple crests and is advected downstream in suspension by the flow until it settles again when the local flow condition cannot further t

length and time scales of response of sediment suspensions to changing flow conditions turbulent suspensions of sediment are investigated to establish the characteristic length and time scales on which they adjust from one state to another the suspensions are modeled by using a simple closure for the turbulent fluctuations in which the average flux of sediment is treated as a diffusion process a key dimensionless settling parameter which is closely related to the rouse number measures the magnitude of the settling to diffusive fluxes of particles it is shown how the length and time scales on which the suspension responds are a function of the settling parameter and the assumed form of the eddy diffusivity and that the predictions are broadly in accord with laboratory experiments it is further established analytically that in the regimes of the settling parameter much greater or much less than unity the timescale of response is independent of the form of the eddy diffusivity this motivates the use of simple eddy diffusivity laws to provide generic insight to the unsteady evolution of complex suspension and sedimentation problems doi 10 1061 asce hy 1943 7900 0000532 2012 american society of civil engineers ce database subject headings suspended sediment eddies turbulence author keywords suspended sediment concentration sedimentation timescale of response eddy diffusivity flow boundary conditions

bed sediment entrainment function based on kinetic theory bed sediment entrainment function is derived based on kinetic theory the entrainment rate is expressed as an upward flux by integrating the particle velocity over all possible upward motions the possibility of upward motion is determined by a sediment particle velocity distribution function which is obtained by solving the boltzmann equation instead of using a prior assumed distribution external forces and turbulence intensity of the flow are shown to exert significant influences on the velocity distribution function and in turn the entrainment rate comparisons between available laboratory data and the entrainment function show that the calculated entrainment rates agree well with the observations applications of the entrainment function to the specification of the bottom boundary condition for convection diffusion equation of suspended load are also presented which show that the calculated concentration profiles are in good agreement with observations the study also suggests that kinetic theory is a promising analytical approach for the study of sediment motion near a riverbed

the behavior of arsenic and antimony at pezinok mining site southwestern part of the slovak republic arsenic and antimony contamination is found at the pezinok mining site in the southwest of the slovak republic investigation of this site included sampling and analysis of water mineralogical analyses sequential extraction in addition to flow and geochemical modeling the highest dissolved arsenic concentrations correspond to mine tailings up to 90 000 g l and the arsenic is present predominately as as v the primary source of the arsenic is the dissolution of arsenopyrite concentration of antimony reaches 7 500 g l and its primary source is the dissolution of stibnite pore water in mine tailings is well buffered by the dissolution of carbonates ph values between 6 6 and 7 0 and arsenopyrite grains are surrounded by reaction rims composed of ferric iron minerals based on sequential extraction results most solid phase arsenic is in the reducible fraction i e ferric oxyhydroxides sulfidic fraction and residual fraction distribution of antimony in the solid phase is similar but contents are lower the principal attenuation mechanism for as v is adsorption to ferric oxide and hydroxides but the adsorption seems to be limited by the competition with sb v produced by the oxidation of stibnite for adsorption sites water in mine tailings is at equilibrium with gypsum and calcite but far from equilibrium with any arsenic and antimony minerals the concentrations of arsenic and antimony in the surrounding aquifer are much lower with maximum values of 215 and 426 g l respectively arsenic and antimony are transported by ground water flow towards the blatina creek but their loading from ground water to the creek is much lower compared with the input from the mine adits in the blatina creek arsenic and antimony are attenuated by dilution and by adsorption on ferric iron minerals in stream sediments with resulting respective concentrations of 93 and 45 g l at the site boundary south of mine tailing ponds

a synthesis of the basal thermal state of the greenland ice sheet the basal thermal state of an ice sheet frozen or thawed is an important control upon its evolution dynamics and response to external forcings however this state can only be observed directly within sparse boreholes or inferred conclusively from the presence of subglacial lakes here we synthesize spatially extensive inferences of the basal thermal state of the greenland ice sheet to better constrain this state existing inferences include outputs from the eight thermomechanical ice flow models included in the searise effort new remote sensing inferences of the basal thermal state are derived from holocene radiostratigraphy modern surface velocity and modis imagery both thermomechanical modeling and remote inferences generally agree that the northeast greenland ice stream and large portions of the southwestern ice drainage systems are thawed at the bed whereas the bed beneath the central ice divides particularly their west facing slopes is frozen elsewhere there is poor agreement regarding the basal thermal state both models and remote inferences rarely represent the borehole observed basal thermal state accurately near northgrip and dye 3 this synthesis identifies a large portion of the greenland ice sheet about one third by area where additional observations would most improve knowledge of its overall basal thermal state

the theoretical foundations and potential for large eddy simulation les in fluvial geomorphic and sedimentological research abstract large eddy simulation les is a method for resolving the time dependent structure of high reynolds number turbulent flows with les it is possible to model and track the behaviour of coherent turbulent structures and study their effect on the flow field hence les is potentially an important research tool in the fluvial sciences where flow mixing sediment entrainment and sediment transport are all affected by the presence of coherent vortices and their interactions with channel boundaries and other flow structures this paper introduces the les methodology discusses a variety of ways for representing small scale processes within les the subgrid scale modelling problem and provides some examples of early work into the use of les in a fluvial context a number of advances in computational power and numerical methods are required before les can be effectively applied at the river reach scale this paper considers some recent developments and their potential for providing validated large eddy simulations of river flow at the channel scale

measured basal water pressure variability of the western greenland ice sheet implications for hydraulic potential the gradient of the hydraulic potential field at the ice bedrock interface beneath the greenland ice sheet gris dictates the routing and energetics of subglacial water thereby influencing drainage system characteristics and sliding dynamics in the ablation zone of the gris variable water pressure due to an active subglacial drainage system and basal topography with high relief potentially interact to drive unknown spatial patterns and temporal changes in the hydraulic potential field here we present a suite of water pressure measurements collected in 13 boreholes along a 46 km transect on the western gris to investigate the role of spatial and temporal basal water pressure adjustments in hydraulic potential gradient dynamics all borehole sites show pressures with similar seasonality having relatively steady and high values during winter variable and irregular behavior during spring and fall and diurnal cycles that can persist for multiple weeks during the peak melt season despite much higher variability during the melt season the median pressure of the summer period is nearly the same as the median pressure of the winter period however time variability of water pressure due to basal drainage processes can force changes in the magnitude and orientation of the hydraulic potential field over diurnal periods we find that the basal water pressure across the transect generally mimics the ice thickness field but with superimposed large pressure gradients that develop at shorter scales within the basal drainage system this leads to a complex hydraulic potential field across regions of similar ice thickness

geochemical characterization and modeling of arsenic behavior in a highly contaminated mining soil the environmental assessment and management of historical mining sites contaminated with various inorganic species require a better knowledge of pollutant bearing phases among elements present in mining soils arsenic is a toxic metalloid with potential high content and high mobility capacity into the environment the objective of this paper was to investigate the mobility and fractionation of arsenic as in a highly as contaminated soil ca 3 wt the soil was collected from an old gold mining site in france where mining activities and smelting processes of gold ores took place single and sequential chemical extraction procedures were firstly conducted these leaching tests were used to assess the potential mobility of as depending on its fractionation in the contaminated soil and also on the portion of as sorbed onto soil particles additionally numerical simulations were performed using the usgs software phreeqc 3 in order to evaluate the role of adsorption on as mobilization this multidisciplinary approach provided information on the nature of as fixation in this mining soil moreover the role of adsorption in the control of dissolved as was evidenced by geochemical modeling results showed that as appeared to be mainly ca 72 wt reversibly sorbed to iron fe compounds in the soil in particular fe oxyhydroxides consequently a potential risk of as mobilization exists especially under acidic and or reducing conditions which frequently occurs in mining environments

bed topography in bends of sand silt rivers a mathematical model for defining the lateral bed topography in bends of sand silt rivers is presented the model includes the effects of suspended sediment that have not been considered in the existing models the major agency for defining the lateral bed profile is found to be the force balance between the fluid force and the gravitational force exerting on bed materials the theory suggests that the lateral convective transport of suspended sediment induced by secondary flow may considerably affects the bed profile at the outer region of river bends while the lateral diffusion due to turbulence has negligible effect on the profile everywhere the new model is applied to an actual river suggesting the adequacy of the present model within the possible error

mechanisms of fast flow in jakobshavns isbrae west greenland part i measurements of temperature and water level in deep boreholes several holes were drilled to depths of 1500 1630 m along a profile across jakobshavns isbrae 50 km upstream from the calving front drilling was by hot water and required approximately 20 h the holes were rapidly closed by refreezing but it was possible to instrument them with thermistors and tilt sensors before this occurred near the margins of the ice stream the holes reached the bed and connected with the subglacial drainage system water level changes recorded in these holes are discussed in terms of the basal hydraulic system the temperature measurements show that the glacier is temperate based moreover extrapolation of a measured temperature profile and its curvature suggests that a temperate layer of substantial thickness may exist at the bed near the center of the ice stream there is a striking difference in the shapes of temperature profiles measured at different locations beneath the center line the temperature minimum is at a considerably smaller relative depth than near the margins but it is nearly the same in magnitude 22 1 c this may indicate a disproportionately large vertical stretching of the basal ice in the center of the ice stream since the basal ice is warmer and much less viscous than the ice above a thickening of that layer would cause a corresponding increase of surface velocity we presume that this mechanism contributes to the fast flow of jakobshavns isbrae

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

experiments on the pickup flux of sand at high flow velocities abstracttwo regimes can be distinguished for the pickup flux of sand at a shields parameter of less than about 0 5 corresponding with flow velocities of 0 5 1 m s the erosion process is dominated by the size and density of the grains grain by grain pickup at higher flow velocities the bulk properties of the sand bed start to influence the erosion process dilative behavior results in the inflow of water to the sand bed which reduces the pickup flux dilatancy reduced pickup because of the shearing of layers of sand a pickup function was recently developed for this regime incorporating the effect of bulk properties such as permeability and porosity on the pickup this function agrees well with data of previous erosion experiments in which the permeability and porosity of the sand bed were varied however these experiments just met the condition for dilatancy reduced pickup the flow velocity during these previous experiments was between 1 and 1 5 m s while the shields parameter varied bet

turbulent convection of suspended sediments due to flow reversal 1 we investigate the ejection of sediments from the near bed region of a pulsating boundary layer over a flat bottom the boundary layer flows were generated using large eddy simulation les while the motion of individual particles was calculated using a modified version of the maxey and riley equation the suspension rate of near bed sediment particles sharply increases during decelerating flow phase and peaks near the time of local flow reversals this suspension pattern of sediments was closely related to the near bed turbulent vortex structures which evolve during a wave cycle during period of maximum flow rate the horizontally aligned vortex cores retarded settling of sediment particles as the flow decelerates vertically organized vortices induce an upward flux of particles vertical velocity fluctuations are strongest at the time of flow reversal leading to maximum sediment suspension at this time these results are shown to be incompatible with simple eddy diffusivity models for sediment transport

two dimensional two phase depth integrated model for transients over mobile bed abstractfast geomorphic transients may involve complex scenarios of sediment transport occurring near the bottom as bed load i e saltating sliding and rolling or as suspended load in the upper portion of the flow the two sediment transport modalities may even coexist or alternate each other during the same event especially when the shear stress varies considerably modeling these processes is therefore a challenging task for which the usual representation of the flow as a mixture may result in being unsatisfactory in the present paper a new two phase depth averaged model is presented that accounts for variable sediment concentration in both bed and suspended loads distinct phase velocities are considered for bed load whereas the slip velocity between the two phases is neglected in the suspended load it is shown that the resulting two phase model is hyperbolic and the analytical expression of the eigenvalues is provided the entrainment deposition of sediment between the bottom and the bed

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

sediment transport of fine sand to fine gravel on transverse bed slopes in rotating annular flume experiments large scale morphology in particular meander bend depth bar dimensions and bifurcation dynamics are greatly affected by the deflection of sediment transport on transverse bed slopes due to gravity and by secondary flows overestimating the transverse bed slope effect in morphodynamic models leads to flattening of the morphology while underestimating leads to unrealistically steep bars and banks and a higher braiding index downstream however existing transverse bed slope predictors are based on a small set of experiments with a minor range of flow conditions and sediment sizes and in practice models are calibrated on measured morphology the objective of this research is to experimentally quantify the transverse bed slope effect for a large range of near bed flow conditions with varying secondary flow intensity sediment sizes 0 17 4 mm sediment transport mode and bed state to test existing predictors we conducted over 200 experiments in a rotating annular flume with counterrotating floor which allows control of the secondary flow intensity separate from the streamwise flow velocity flow velocity vectors were determined with a calibrated analytical model accounting for rough bed conditions we isolated separate effects of all important parameters on the transverse slope resulting equilibrium transverse slopes show a clear trend with varying sediment mobilities and secondary flow intensities that deviate from known predictors depending on shields number and strongly depend on bed state and sediment transport mode fitted functions are provided for application in morphodynamic modeling

internal geometry and evolution of moulins storglaciaren sweden depart ment of physical geog raphy university of stoc kholm s 106 91 stockholm sweden abstract the initial conditions needed for formation of moulins are crevasses and a supply of melt water water pouring into a crevasse may fill it until it ove rflows at the lowest point which is normally near the margin however as the crev asse deepens it intersects englacial chann els through which the water can drain these chann els may be finger tip tributaries in a dendritic system such as that described by shreve 1972 and observ ed by raymond and harrison 1975 when the cre vasse closes heat in the melt water keeps the conne ction open and a moulin is formed the englacial channel enlarges rapidly by melt ing utilizing mechanical energy released by the descending water descents into moulins and mapping of stru ctures exposed at the surface after many years of melting demonstrate that the drainage channels leading down from the bottoms of the moulins have incli nations of 0 450 from the vertical these channels trend in the dire ction of the original crevasse but appear to be deeper than the expected depth of the crevasse they have not

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

arsenic behaviour in gold ore mill tailings massif central france hydrogeochemical study and investigation of in situ redox signatures abstract historical au ore exploitation at the cheni mine in the massif central france generated 525 000 tonnes of finely ground mill tailings deposited in a heap that has spread with time into three settling basins the tailings which are rich in quartz 80 mica and clay minerals 10 of illite smectite kaolinite and chlorite feldspars 5 but poor in carbonates e h 700 mv to moderate ph and weakly reducing ph 7 6 e h 15 mv the waters are rich in so 4 and ca and have variable as 0 05 95 mg l 1 and fe concentrations 0 07 141 mg l 1 reduced as iii species predominate over as v species as iii as v up to 21 whereas oxidized forms of fe and s are favoured fe ii fe iii up to 0 5 and s iv s vi up to 1 thermodynamic calculations were performed with the phreeqc and eq3nr codes based on a revised as database to evaluate saturation indices si of the waters in relation to the main minerals and define which redox couples control the redox state of the system the important role of carbonates though only present in small amounts explains the acid buffering generated by the oxidation of sulphides for waters in the ph 7 7 5 range measured e h appears to fall between the calculated e h of the fe ii fe iii couple and that of the as iii as v couple illustrating redox disequilibrium

toward modeling turbulent suspension of sand in the nearshore 1 we present two depth and phase resolving models based on single and two phase approaches for suspended sediment transport under water waves both models are the extension of a wave hydrodynamic model cornell breaking wave and structure cobras in the two phase approach dilute two phase mass and momentum equations are calculated along with a fluid turbulence closure based on balance equations for the fluid turbulence kinetic energy k f and its dissipation rate f in the single phase approach the fluid flow is described by the reynolds averaged navier stokes equations while the sediment concentration is calculated by an advection diffusion equation for the conservation of sediment mass the fluid turbulence is calculated by k f f equations that incorporate the essential influence of sediment which can also be consistently deduced from the two phase theory by adopting a commonly used sediment flux boundary condition near the bed the proposed models are tested against laboratory measurements of suspended sediment under nonbreaking skewed water waves and shoaling broken waves although the models predict wave averaged sediment concentrations reasonably well the corresponding time histories of instantaneous sediment concentration are less accurate we demonstrate that this is due to the uncertainties in the near bed sediment boundary conditions in addition we show that under breaking waves the near bed sediment pickup cannot be solely parameterized by the bottom friction suggesting that other effects may also influence the near bed sediment boundary conditions

automated sediment erosion testing system using digital imaging measurement of vertical profiles of the critical shear stress c and the erosion rate e from the same undisturbed sediment core is crucial for modeling the resuspension of fine grained natural sediments the automated sediment erosion testing system asets was developed to determine profiles of c and e with centimeter spatial vertical resolution in an undisturbed shelby tube sediment core whose surface was eroded by steady turbulent flow through a flume the unique feature of asets is that it is a real time imaging method that accurately determines the position of the core surface during erosion for both calculating the vertical profile of e and controlling a motor driver system that automatically pushes up the core to maintain its surface flush with the flume bottom undisturbed field cores were tested over a range of flow average bed shear stress b conditions the amount of eroded sediment from both optical backscattering measurements and the imaging method were in good agreement which validated asets measured vertical profiles of c and e were similar to those reported in literature e correlated well with b c 2 which agrees with previous results in literature

a two species model of aeolian sand transport the transport of sand by wind results from the equilibrium between the erosion of grains dragged by the flow and the resulting slow down of the wind velocity the dynamical mechanisms governing the saturation of the sand flux are investigated theoretically we first demonstrate that previous models based on the assumption that all the grains have the same trajectory are either not self consistent or lead to unstable solutions a model based on a discrete number of states is derived which solves these problems two well defined species of grain appear which correspond to saltons high energy grains and reptons grains ejected from the sand bed by the impact of saltons they play specific roles the negative feedback of the transport on the wind is limited to the reptation layer while most of the transport is due to saltation the model is further simplified benefiting from the existence of these two species and the dependencies of the threshold velocity the saturated flux the aerodynamic roughness and the saturation length are derived and compared to experimental measurements

sediment transport and morphodynamics induced by a translating monopolar vortex we performed laboratory experiments to describe and quantify the transport of sediment and the changes in the bed due to a generic translating monopolar vortex experiments were performed inside a water filled square tank with a particle bed on the bottom and a vertical plate attached perpendicular to one of the sidewalls the tank was placed on top of a rotating table to create the vortex by changing its rotation rate this change created a current inside the tank that separated at the edge of the vertical plate with the shear layer rolling up into a vortex once the vortex was formed the table was promptly stopped sediment particles are brought into suspension and captured by the vortex forming a conical region that moves with the vortex until the sediment resettles in the bed changing the original bed morphology three different measurement techniques were used to obtain information about the flow velocities the sediment in suspension and the net changes in the bed changes in the bed morphology occur along the trajectory of the vortex where a region of erosion is followed by a region of deposition the strength of a vortex is the main parameter governing the capture and suspension of particles with similar characteristics a power law relationship is found between the vortex strength and the net displaced particle volume experiments were also performed without sediment to determine if the presence of sediment could affect the vortex dynamics however a definitive answer requires more experiments to obtain reliable statistics

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

heat flux variations beneath central greenland s ice due to anomalously thin lithosphere the thermal state of the earth s surface is usually influenced more by climate than by heating from the earth s interior numerical models show that in the oldest and thickest part of the greenland ice sheet geothermal heat flux through an anomalously thin lithosphere leads to strong regional variations in basal melting

bed load at low shields stress on arbitrarily sloping beds failure of the bagnold hypothesis 1 the bagnold hypothesis has been a major tool in the development of mechanistic models of bed load transport according to the hypothesis a necessary constraint for the maintenance of equilibrium bed load transport is that the fluid shear stress at the bed must be reduced to the critical or threshold value associated with incipient motion of grains the constraint determines a functional form for the areal concentration of bed load grains as a function of flow parameters it is shown here however that the bagnold hypothesis breaks down when applied to equilibrium bed load transport on beds with transverse slopes above a relatively modest value that is well below the angle of repose in particular under such conditions it is shown that no areal concentration no matter how large is sufficient to reduce the fluid shear stress at the bed to the critical value this failure motivates the abandonment of the bagnold constraint even for nearly horizontal beds the framework presented here however provides a natural basis for an entrainment based model of sediment transport that neither satisfies nor suffers from the drawbacks of the bagnold constraint