field measurements of the flux and speed of wind blown sand a field experiment was conducted to measure the flux and speed of wind blown sand under known conditions in a natural setting the experiment run at pismo beach california involved a tract 100 m long parallel with the wind by 20 m wide the site was instrumented with four arrays of anemometers to obtain wind velocity profiles through the lower atmospheric boundary layer temperature probes to determine atmospheric stability and wind vanes to determine wind direction from these measurements wind friction speeds were derived for each experimental run in order to measure sand saltation flux a trench 3 m long by 10 m wide transverse to the wind direction by 0 5 m deep was placed at the downwind end of the tract and lined with 168 collector bins forming an egg box pattern the mass of particles collected in each bin was determined for four experimental runs in order to assess various sand trap systems used in previous experiments 12 leatherman traps one fryberger trap and one array of ames traps were deployed to collect particles concurrently with the trench collection particle velocities were determined from analysis of high speed 3000 and 5000 frames per second motion pictures and from a particle velocimeter sand samples were collected from the trench bins and the various sand traps and grain size distributions were determined fluxes for each run were calculated using various previously published expressions and then compared with the flux derived from the trench collection results show that bagnold s 1941 model and white s 1979 equation most closely agree with values derived from the trench comparison of the various collector systems shows that the leatherman and ames traps most closely agree with the flux derived from the trench although these systems tended to under collect particles particle speeds were measured from analysis of motion pictures for saltating particles in ascending and descending parts of their trajectories results show that particle velocities from the velocimeter are in the range 0 5 7 0 m s 1 compared to a wind friction velocity of 0 32 0 43 m s 1 and a wind velocity of 2 7 3 9 m s 1 at the height of the particle measurements descending particles tended to exceed the speeds of ascending particles by 0 5 m s 1

environmental impact and geochemistry of old tailing pile from the sanggok mine creek republic of korea this study evaluates the pollution load on a creek based on the physicochemical and mineralogical properties of old tailings the sanggok mine is one of the largest lead zinc producers in the hwanggangri mining district republic of korea the vertical profile of the old tailings in the mine area can be divided into three units based on color change and mineralogical and textural variations as well as physical and chemical properties unit i surface accumulation and oxidized heterogeneous tailing soil has lower ph and higher eh than unit ii originally unoxidized dumped tailing soil and unit iii pebble bearing bottom soil the conductivity data indicates that unit i and ii have very high values compared to unit iii and basement the mine area consists mainly of carbonate rocks however mineral constituents of tailing soil and sediments near the mine were mainly composed of quartz mica feldspar amphibole calcite dolomite magnesite and clay minerals units i and ii are characterized by high abundances of siderite locally pyrite and dolomite precipitates in the mining drainage mainly included smectite illite berthierine quartz siderite hexahydrite and ca ferrate among the separated metallic minerals tailing soils and sediments of highly concentrated toxic metals are found some pyrite arsenopyrite chalcopyrite sphalerite galena malachite goethite various hydroxide and uncertain secondary minerals units i and ii are characterized by relatively high concentrations of ca fe mn and low contents of al mg k na ti rare earth elements rees that correlated with the proportion of secondary minerals potentially toxic elements such as ag as cd cu pb sb and zn are highly enriched in the upper two units this metal concentration can be influenced by changes in the depth because of oxic and suboxic zonal distribution the removal zone unit i has probably migrated below the elevation of the maximum enrichment layer due to deepening of the oxic suboxic boundary in most of the materials the enrichment index is higher than 3 62 the highest value of 42 55 is found in the oxidation surface soils of the tailing pile an average enrichment index of the profiles and precipitates are 27 62 and 22 62 respectively rocky basement soils have an average enrichment index of 6 63 which is influenced by overlying the tailing pile the water quality and habitat of the sanggok creek are severely polluted polluted surface water may also negatively impact the agricultural soil and groundwater

the physics of wind blown loess implications for grain size proxy interpretations in quaternary paleoclimate studies abstract loess deposits are recorders of aeolian activity during past glaciations since the size distribution of loess deposits depends on distance to the dust source and environmental conditions at the source during transport and at deposition loess particle size distributions and derived statistical measures are widely used proxies in quaternary paleoenvironmental studies however the interpretation of these proxies often only considers dust transport processes to move beyond such overly simplistic proxy interpretations and toward proxy interpretations that consider the range of environmental processes that determine loess particle size distribution variations we provide a comprehensive review on the physics of dust particle mobilization and deposition furthermore using high resolution bulk loess and quartz grain size datasets from a last glacial interglacial sequence we show that because grain size distributions are affected by multiple often stochastic processes changes in these distributions over time allow multiple interpretations for the driving processes consequently simplistic interpretations of proxy variations in terms of only one factor e g wind speed are likely to be inaccurate nonetheless using loess proxies to understand temporal changes in the dust cycle and environmental parameters requires i a careful site selection to minimize the effects of topography and source distance and ii the joint use of bulk and quartz grain size proxies together with high resolution mass accumulation rate calculations if possible

reconstructing the vertical distribution of the aeolian saltation mass flux based on the probability distribution of lift off velocity the probability distribution of lift off velocity of the saltating grains is a bridge to linking microscopic and macroscopic research of aeolian sand transport the lift off parameters of saltating grains i e the horizontal and vertical lift off velocities resultant lift off velocity and lift off angle in a wind tunnel are measured by using a phase doppler particle analyzer pdpa the experimental results show that the probability distribution of horizontal lift off velocity of saltating particles on a bed surface is a normal function and that of vertical lift off velocity is an exponential function the probability distribution of resultant lift off velocity of saltating grains can be expressed as a log normal function and that of lift off angle complies with an exponential function a numerical model for the vertical distribution of aeolian mass flux based on the probability distribution of lift off velocity is established the simulation gives a sand mass flux distribution which is consistent with the field data of namikas namikas s l 2003 field measurement and numerical modelling of acolian mass flux distributions on a sandy beach sedimentology 50 303 326 therefore these findings are helpful to further understand the probability characteristics of lift off grains in aeolian sand transport c 2007 elsevier b v all rights reserved

the occurrence and dispersion of potentially toxic elements in areas covered with black shales and slates in korea abstract potentially toxic heavy metals together with other elements are present in some natural geological materials and the okchon black shale in korea provides an important example of this the dispersion of these elements in the rocks and soils derived from this shale are examined geochemical surveys were undertaken in 11 study areas in the okchon zone underlain by black shales slates phyllites and limestones after appropriate preparation of rocks and soils samples were analysed for multi elements by inaa icp aes and icp ms some potentially toxic elements are highly enriched in the okchon black shales and soils developed from these shales in the dukpyungri and majeonri areas in particular mean concentrations in soils in the dukpyungri area are 34 g g as 43 g g mo and 3 4 g g se which are significantly higher than the worldwide average for soils the degree of enrichment decreases in the order forest upland farm paddy playground soils and discriminant analysis by geochemical characteristics separates soils in the black shale area from those in other rock areas in terms of se zn mo and cd

migration of radionuclides in fissured rock the influence of micropore diffusion and longitudinal dispersion the migration of radionuclides in the fissures in the bedrock surrounding a repository is discussed a one dimensional transport model is presented it includes diffusion of the nuclides into the microfissures of the rock and linear sorption and longitudinal dispersion in the bedrock an analytical solution to the model is given in terms of an infinite integral the integrand is a sometimes highly oscillatory function of the system parameters a special integration method is developed to evaluate the infinite integral the method utilizes the oscillatory behavior of the integrand the assessment of input parameters is discussed in some detail dimensionless breakthrough curves are given for the approximate range of variation of the input parameters calculations are made for a repository of spent fuel surrounded by fissured but fairly good rock kp 10 9 m s and fissure spacing s 50 m longitudinal dispersion may significantly affect the amount of radioactive material reaching the biosphere radionuclides which would decay completely without longitudinal dispersion may arrive in nonnegligible concentrations dispersion effects of the magnitude considered in this study can significantly diminish the retardation effects of matrix diffusion

statistical analysis of sand grain bed collision process recorded by high speed digital camera a high speed digital camera was employed to record the sand grain bed collision process with image processing and a statistical method a series of parameters of the collision process were obtained the results show that the collision process of a grain with rebounding can be represented by two parameters the kinetic energy restitution coefficient and the collision angle both parameters satisfy a normal distribution and they are dependent on one another with an increase of the collision angle the distribution of the kinetic energy restitution gradually reduces from a broad to a narrow range with low values the percentage of vertical velocity restitution coefficients greater than 1 can reach 70 or more which ensures that the settling time of the sand grains in the air increases and that they receive more energy from the air to progress the saltation movement

adaptation of the near surface wind to the development of sand transport a model of wind blown sand transport is described with particular emphasis on the feedback between the grain cloud and the near surface wind the results from this model are used to develop owen s 1964 hypothesis that the grain layer behaves so far as the flow outside it is concerned as increased aerodynamic roughness whose height is proportional to the thickness of the layer the hypothesis is developed to show the influence this dynamic roughness has on the turbulent boundary layer above the saltation layer two processes are identified which influence the path of the system towards equilibrium the first is the feedback between the near surface wind and the grain cloud in which the quantity of sand transported is limited by the carrying capacity of the wind the second is due to the temporal development of an internal boundary layer in response to the additional roughness imposed on the flow above the grain layer by the grain cloud a similarity is noted between the temporal response of a turbulent boundary layer to sand transport and the spatial response of a turbulent boundary layer downstream of a step increase in surface roughness finally it is noted that the work may have important implications for transport rate prediction in unsteady winds

wind regime sediment transport and landscape dynamics at a mars analogue site in the andes mountains of northwestern argentina abstract the puna plateau of northwestern argentina is a promising region for analogue investigations of martian aeolian processes owing to its high altitude low atmospheric pressure aridity geology and widespread granular and bedrock aeolian landforms despite a growing body of research about the region s enigmatic aeolian landforms little is known about the contemporary aeolian environment processes and landscape dynamics to address this gap we used a combination of modelled weather data satellite imagery and field measurements to characterize the wind regime aeolian sediment transport and allied surface changes the study focused on the campo de piedra pomez cpp a volcanic landscape with a variety of mars analogue landforms gravel mantled megaripples yardangs ventifacts periodic bedrock ridges and aeolian rat tails modelled weather data from the european center for medium range forecasting s era interim reanalysis dataset confirm the contemporary dominance of northwesterly winds in this region consistent with the primary orientation of yardangs these data also indicate the presence of less frequent southeasterly winds which may explain why re entrant profiles are observed on the southeast flanks of a small portion of the yardang population and why some aeolian rat tails point to the northwest observations from multi temporal satellite imagery indicate that deposition and displacement of small sediment patches overlying ignimbrite bedrock is relatively common across the region samples retrieved from sediment traps deployed over one year in the region suggest a broad range of particle densities are mobilized by wind which implies a wide range of wind speed for fluid entrainment conventional aeolian transport models do not consider the effects of particle density variations on transport processes however in areas with multiple density sediment present our results point towards a need for aeolian models to consider density when quantifying and qualifying sediment transport

the effects of slope and slope position on local and upstream fluid threshold friction velocities in deserts dunes are common aeolian landforms and parallel ridges are common in cultivated land a computational fluid dynamics cfd model is used to simulate a stable wind blowing over slope beds of varying height and coupled with the slope compensating fluid threshold friction velocity formula the model accurately reproduced patterns of flow deceleration at the slope toe and stoss flow acceleration based on the cfd based model quantitative analyses of slope gradient and particle position on the initiation of particle movement are performed results indicate that the slope has a great influence on particle saltation in the windward slope and the initiation of particle movement is particularly sensitive to particle position with respect to the slope copyright 2008 john wiley sons ltd

aeolian and subaqueous bedforms in shear flows a sediment bed sheared by an unbounded flow is unconditionally unstable towards the growth of bedforms called ripples under water and dunes in the aeolian case we review here the dynamical mechanisms controlling this linear instability putting the emphasis on testing models against field and laboratory measurements we then discuss the role of nonlinearities and the influence of finite size effects namely the depth of the atmospheric boundary layer in the aeolian case and the water depth in the case of rivers

the geochemistry of co and cu in the kafue river as it drains the copperbelt mining area zambia abstract samples of the dissolved 0 45 m phases have been collected in the kafue river during a 1 year cycle within the mining area the concentrations of co cu and s in the river occasionally increase more than 100 times compared to concentrations upstream from the mining area the highest concentrations of dissolved cu 3 4 m and fe 4 2 m are found during high water discharge probably indicating a washout of leached weathering products from spoil heaps high levels of co appear to originate from one point source the location where the co ore is treated in the kafue river secondary mn and fe rich particles are formed on which co and cu respectively are enriched the elements associated to secondary fe and mn particles are enriched at the sediment surface in the river due to redox processes hence secondary particles and sorbed trace elements may be resuspended and transported further downstream in the river system however very high concentrations of cu 1 and co 0 1 in the sediment are caused by primary sulphides

experimental investigation of mass flux and transport rate of different size particles in mixed sand transport by wind abstract sand transport by wind in arid regions is a geomorphic process affected by the grain size distribution knowledge of the transport behavior of each size group in mixed sand transport is important for understanding the saltation dynamics in dune migration this paper focuses on the characteristics of mass flux mass concentration horizontal velocity and transport rate of different particle size groups and the relation to their mass proportion in air experiments were carried out to analyze these relations in a wind tunnel by particle tracking velocimetry the mass flux of different size particles usually decays exponentially with height for larger size groups and deviates from exponential decay for smaller size groups the trend of mass concentration of different size groups with height is similar to the mass flux the mean horizontal velocity of different size groups generally increases with increasing height and decreases with the increase of particle size at the same height with increasing height the ratio of mass flux of each size group to the total mass flux increases for the smaller size group but decreases for the larger size group and the transition diameter of particles is about 0 14 mm for the 0 16 mm sand sample and about 0 21 0 27 mm for the 0 24 mm sand sample for the smaller size group the ratio of the mass weighted average horizontal velocity of each size group to that of all particle sizes is 1 0 and the ratio of the transport rate of each size group to the total transport rate is usually larger than its mass proportion in air this is the opposite for the larger size groups the maximum deviation of mass flux proportion of each size group from its mass proportion in air is about 15 which is determined by the mass weighted average horizontal velocity of each size group

effects of the magnus and saffman forces on the saltation trajectories of sand grain abstract saltating sand grains are the primary component of airborne sand and account for 75 of all sand transport flux the saltation height and horizontal distance traveled by sand grains are key factors in sand control engineering in addition to gravity and aerodynamic drag the magnus and saffman forces also play important roles in saltation to quantify the magnitudes of these forces in saltation we used high speed multi flash photography to observe the movement of saltating sand grains in a wind tunnel this proved to be an efficient technique for determining the movement and rotational velocities of grains of natural sand with grain sizes ranging from 0 2 to 0 3 mm and shear velocities u of 0 67 0 83 and 0 87 m s 1 the rotational speed of saltating sand grains varied between 200 and 800 rev s 1 mean clockwise and anticlockwise rotational speeds were nearly identical and both increased with increasing saltation height with saltation heights divided into 1 cm intervals the rotational speeds followed a lorentzian distribution calculations based on a saltation model showed that the maximum increases in saltation height and in horizontal distance due to the magnus force were 10 2 and 24 9 respectively the rate of increase of both parameters increased with increasing lift off angle the maximum increases in saltation height and horizontal distance of sand grains caused by the saffman force were only 4 6 and 3 7 respectively

an experimental study of multiple grain size ejecta produced by collisions of saltating grains with a flat bed collision data are presented from coloured high speed films of three size fractions of sand grains saltating over a bed of the total grain population each fraction was colour tagged and the proportion of each size ejected by grains colliding with the surface was recorded on a number of films taken as the bed was progressively eroded the results confirm earlier findings that v3 v1 0 5 0 6 vn v1 08 and the rebound angle increases with decreasing grain size ejected grains are examined in relation to their size the impactor size ejection speed and angle and the number of ejecta per collision in addition changes in grain parameters are observed with time for fine impactors ejection speeds generally increase with a decrease in ejecta size but the fine fraction does not follow this trend for the coarse and medium impactors ejection angles are typically between 40 and 60 with coarse grains having shallower mean angles than fine ejecta the number of ejections per collision increases with a decrease in particle size for each impactor size the general tendency for coarse particles to be ejected at lower speeds and shallower angles than fine particles will lead to sorting of the grain sizes there is poor correlation between the forward momentum loss of the saltating grams at collision and both the forward momentum of the ejected grains and the number of ejected grains much of the forward momentum of the saltating grains is transfered to creeping grains the composition and geometry of the bed are considered to be important factors in the evolution of the saltation cloud

aeolian sediments on the north eastern tibetan plateau abstract aeolian sediments on the tibetan plateau are an important archive of palaeoclimatic information this study presents a detailed analysis of sediments from the donggi cona catchment on the north eastern part of the tibetan plateau long and short distance sediment transport leads to a complex pattern of aeolian sediment deposition that depends on climatic changes as well as on the availability of sediments based on the largest dataset of osl datings 51 from a single catchment on the tibetan plateau so far different periods of increased sediment transport have been reconstructed increased aeolian deposition in this high elevation environment started in the early holocene with the accumulation of sands from around 10 5 to 7 ka loess sediments have been preserved from a period from 10 5 to 7 5 ka both archives are related to the strengthening of the asian summer monsoons characterized by wetter and warmer climate this change in climate supported the trapping of aeolian sediments under full monsoon conditions from around 9 ka onwards fluvial processes resulted in erosion of the aeolian archives and the formation of colluvial sediments until 6 ka a dry and cooler climate resulted in the reactivation of dune sands from 3 ka to present possibly in combination with stronger human influence aeolian sediments on the tibetan plateau therefore indicate two different climatic modes during the early holocene wetter conditions were favourable to retain aeolian sediments the reactivation of sediment in the late holocene due to small scale disturbances in the vegetation cover points to a cooler and drier climate

steady state saltation in air coupled equations of motion for steady state saltation over an infinite plane are derived and solved for a simplified model of the grain surface impact process experimentally observed features of the wind velocity profile in saltation are qualitatively reproduced including a diminution of the sub saltation layer mean wind speed as the friction speed increases in this model the surface impact velocity of the saltating grains remains relatively constant over a wide range of free stream shear stresses and the grain mass flux increases with friction speed uf less rapidly than uf3

large eddy simulation of sand transport under unsteady wind abstract aeolian sand movement contributes to evolution of surface landforms on earth and mars as well as on venus and titan most natural landforms in arid regions are molded by wind with a general feature of unsteadiness many researches have improved our cognition of saltation in unsteady flow but it is probably true that this issue is not yet fully analysed in this paper we conducted three dimensional numerical simulations of wind blown sand under unsteady wind conditions the trajectories of sand particles are simulated by using a lagrangian model particle motion particle bed interaction and wind modification have been taken into account results indicate that the characteristics of sand transport in unsteady and steady wind conditions profoundly differ the sediment transport in unsteady conditions is significantly enhanced and increases with the amplitude of the sinusoidal wind fluctuations the time series of sediment transport reveals a sine like variation which lags behind the variation of the wind with a time delay of about 1 s response time of saltation to wind variation in unsteady conditions sand transport shows an overshoot which is embodied in the initial wave of the sediment transport the impact of unsteady sediment transport should be paid more attention in future aeolian research

saltating particles over flat beds measurements of ejection and impact velocities trajectory lengths and maximum rise heights of sand grains median diameters 118 and 188 m in saltation over a flat sand bed in a wind tunnel have been obtained from the digitization of multiple image photo graphs the mean angle of ejection is found to be about 30 o from the horizontal rather than 90 o with mean vertical ejection velocity of about 2u where u is the friction velocity trajectories of saltating grains have been computed using the measurements of the initial ejection velocities and the mean velocity profile of the air flow

a comprehensive numerical model of steady state saltation comsalt 1 the blowing of sand by wind known as saltation ejects dust aerosols into the atmosphere creates sand dunes and erodes geological features we present a comprehensive numerical model of steady state saltation comsalt that in contrast to most previous studies can reproduce a wide range of measurements and can simulate saltation over mixed soils comsalt calculates the motion of saltating particles due to gravity fluid drag particle spin fluid shear and turbulence and explicitly accounts for the retardation of the wind due to drag from saltating particles furthermore we included a novel physically based parameterization of the ejection of surface particles by impacting saltating particles which matches experimental results comsalt is the first numerical saltation model to reproduce measurements of the wind shear velocity at the impact threshold i e the lowest shear velocity for which saltation is possible and of the aerodynamic roughness length in saltation it also reproduces a range of other saltation processes including profiles of the wind speed and particle mass flux and the size distribution of saltating particles as such comsalt is the first physically based numerical model to reproduce such a wide range of experimental data since we use a minimum of empirical relations comsalt can be easily adapted to study saltation under a variety of physical conditions such as saltation on other planets saltation under water and saltating snow

the effect of wind speed and bed slope on sand transport this paper reports on a wind tunnel study of the effects of bed slope and wind speed on aeolian mass transport the use of a sloping wind tunnel has enabled estimation of the friction angle to be about 40 for saltating particles in the range 170 540 m a formula relating dimensionless mass transport to friction speed and bed slope is proposed and mass transport data for five uniform sand samples and one non uniform sand sample are shown to fit the equation well in particular the relationship reveals an overshoot in mass transport slightly above threshold collisions a feature also evident when previous experimental data is re examined as the number of mid air collisions between the saltating particles increases greatly with wind speed the overshoot may occur as a result of increasing energy losses resulting from the collisions finally it is demonstrated that data for saltating snow shows a similar overshoot in the dimensionless transport rate

eolianite grain size distributions as a proxy for large changes in planetary atmospheric density a digitized version of the ahlbrandt 1979 global dune dataset and data for distributions in figure are available at https github com erikgoosmann aeoliandata

analysis of some laboratory tracer runs in natural fissures tracer tests in natural fissures performed in the laboratory are analyzed by means of fitting two different models in the experiments sorbing and nonsorbing tracers were injected into a natural fissure running parallel to the axis of a drill core the models take into account advection dispersion diffusion into the rock matrix and sorption onto the surface of the fissure and on the microfissures inside the matrix for the second mechanism one of the models considers hydrodynamic dispersion while the other model assumes channeling dispersion the models take into account time delays in the inlet and outlet channels the dispersion characteristics and water residence time were determined from the experiments with nonsorbing tracers surface and volume sorption coefficients and data on diffusion into the rock matrix were determined for the sorbing tracers the results are compared with values independently determined in the laboratory good agreement was obtained using either model when these models are used for prediction of tracer transport over larger distances the results will depend on the model the model with channeling dispersion will show a greater dispersion than the model with hydrodynamic dispersion assuming constant dispersivity

sediment transport by wind toward a general model a general model of eolian sediment transport by both saltation and suspension is developed saltation is analyzed through calculations of single trajectories given initial conditions of liftoff speed angle and spin profiles of particle concentration and mass flux generated by assuming that all trajectories are identical display distinct maxima at the top of the trajectory by incorporating the realistic distribution of trajectories that arises from the stochastic nature of grain impacts with a granular bed the model yields monotonic decreases in particle concentration and mass flux with height in accordance with published empirical data the analysis of suspension as the balance between downward advective flux as a result of the settling of grains and their upward diffusive flux as a result of turbulence results in concentration profiles that fall off as power laws with height also in accordance with empirical data a relation for reference level concentrations is presented for both blowing snow and dust profiles the solutions for saltation and suspension are combined to yield mass flux profiles for the entire range of grain sizes in the bed the saltation layer emerges naturally as that region where the total flux of saltating grains exceeds that of suspended grains the model points clearly to the need for further research on the stochastic grain bed interactions which control both the probability distribution of liftoff velocities in saltation and the production of fine particles in suspension

on the effect of mid air collisions on aeolian saltation the effect of mid air collisions on aeolian saltation is investigated using concentration profiles and grain velocities predicted by a numerical saltation model the probability of a mid air collision is found to be greater at high wind speeds it is also found that mid air collisions tend to reduce the number of grain bed impacts and thus reduce the number of ejecta near the bed this in turn reduces the intensity of mid air collisions it is suggested that this feed back mechanism significantly influences transport rates at high wind speeds

collisions of quartz grains with a sand bed the influence of incident angle the velocities with which grains were observed to emerge from a sand bed after an intersaltation collision at u 40 cm s 1 are reported for four bed attitudes from horizontal bed to adverse bed slope 15 the principal effect of bed angle is to alter the magnitude and direction of the ricochet velocity however emergent velocities of dislodged grains are consistent with reptation path lengths comparable to the length of the upwind face of ripples in the corresponding wind calculations of the loss of forward momentum at collision using the data for the range of bed attitudes studied suggest that creep is most vigorous on the sloping upwind face of the ripple and diminishes at the crest as a result the crest would be expected to accumulate the coarse material which moves predominantly by creep the saltations originating in ricochet from the sloping back of the ripple are more vigorous and more concentrated in plan than are those originating at the crest however the saltation path length is at least an order of magnitude greater than the ripple wavelength and the probability distribution of path lengths is quite dispersed consequently it is very unlikely that these spatial patterns of ricochet are preserved sufficiently distinctly in the saltation cloud and subsequent collision distribution to be the agent of ripple development this study therefore supports a view of moving grain interaction with the bed in which saltation provides the power to mobilize grains but ripple growth is associated with reptation and particularly with a pattern of impact which develops with the bed relief creep is more active on upwind facing slopes than at the crest which therefore is a zone of net creep grain deposition

the characteristic of streamwise mass flux of windblown sand movement abstract two patterns have been reported in previous literature about the streamwise mass flux of windblown sand movement in steady state namely the exponential pattern and the stratification pattern although the exponential pattern has been verified by some experimental measurements and numerical simulations an agreed conclusion is not reached yet re evaluating the previous model it can be found that the pattern of the pdf probability density function distribution of the initial liftoff velocity is the key factor that determines whether the stratification happens or not if the number of liftoff grains decreases with the increase in liftoff velocity such as in the case of the exponential distribution the stratification pattern will not appear if the number of liftoff grains increases first and decreases later with the increase in liftoff velocity such as in the case of the log normal distribution gamma distribution and gaussian distribution the stratification pattern will come into existence in addition the hop height for the initial liftoff velocity corresponding to the peak value of its pdf distribution equals the height of the maximum streamwise mass flux on the basis of some deterministic laws from experimental measurements and numerical simulations of grain bed impact a qualitative understanding about the pdf distribution of the liftoff velocity is obtained and the rayleigh distribution is used for reptating grains also included in this paper is a model in which grain bed impact is discussed and the interaction between the grains and the wind is considered it is shown that the stratification pattern composed of a linear increment layer a saturation layer and a monotonic decrement layer indeed exists in the streamwise mass flux of windblown sand movement further as with the average velocity and pdf distribution of the liftoff velocity of the reptating grains which is determined by the characteristics of grains the height of the peak value of the streamwise mass flux is also determined by the property of the grains and will be independent of the wind intensity

aeolian saltation on mars at low wind speeds laboratory experiments indicate that the fluid threshold friction speed u tf required to initiate fully developed aeolian saltation is much higher on mars than on earth a discrepancy exists between mars climate models that do not predict winds this strong and observations that sand sized particles are indeed moving this paper describes how wind friction speeds well below u tf but above the impact threshold u ti required to sustain saltation can initiate sustained saltation on mars but at relatively low flux numerical experiments indicate that a sand grain on mars mobilized sporadically between u ti and u tf will develop over fetch lengths longer than generally available within low pressure wind tunnels trajectories capable of splashing grains that propagate saltation and collectively form a cluster of saltating grains that migrate downwind together the passage of a saltation cluster should leave behind a narrow zone of affected surface grains the cumulative effect of many clusters represents a low flux phenomenon that should produce slow changes to aeolian bedforms over periods in which winds remain close to u ti and never or rarely reach u tf field evidence from small impact ripples along rover traverses is consistent with effects of saltation at these low friction speeds without obvious evidence for events u tf the potential utility of this grain mobility process is that it can operate entirely at more common winds well below u tf and so help explain widespread sand movements observed on mars wherever evidence might be mostly absent for u tf being exceeded

an equilibrium relationship for shear velocity and apparent roughness lenght in aeolian saltation abstract an equilibrium relationship between shear velocity and apparent surface roughness is established for aeolian saltation velocity profiles of wind over blowing sand were digitized from eleven published data sets the 106 profiles were analyzed to obtain estimates of shear velocity and apparent surface roughness lenghts these values were used to test charnock s relationship for suitability in aeolian environments the results indicate that z 0 0 0091 u 2 g modifying charnock s model to describe wind over an equilibrium saltation field yields z 0 2d 50 30 0 0252 u u t 2 g the latter result is used to demonstrate that the focal point concept proposed by bagnold stems from the increase in apparent roughness with increased shear velocity the results demonstrate an excellent example of threshold controlled equilibrium in dynamic systems

a simple model to estimate emission of wind blown particles from a granular bed in comparison to wind tunnel experiments dust emissions due to aeolian erosion of exposed granular materials are strongly influenced by grain size distribution non erodible particles that are too heavy to be lifted into the air play a protective role in the aeolian erosion process attenuating emission which is known as the pavement phenomenon to date there is no approach that reliably predicts the reduction in emissions caused by their presence on an aggregate surface in this work an analytical model was developed to quantify emissions from particle beds with a wide size distribution as non erodible particles accumulate changes in surface characteristics create increasing shelter for the erodible portion of the bed until the shear on the erodible surface reaches a minimum and emissions cease the proposed emission model describes the relationship between this minimum value of wind shear and the eroded depth of the bed after the pavement which in turn gives the emitted mass in addition wind tunnel experiments were carried out in order to broaden knowledge of the pavement phenomenon and validate the modelling a bimodal particle size distribution of sand with erodible and non erodible particles was used for the tested velocities three experimental measurements were carried out i continuous weighing of the emitted mass ii eroded depth of the bed at regular time intervals and iii final cover rates of the non erodible particles using digital analysis of sand bed pictures after experiments good agreement between the modelling and experimental results was found the emission model proposed herein is a simple algebraic expression that demands low computational effort this approach may serve as a base for an emission model for application in granular materials stockpiles 2019 elsevier b v

aerodynamic roughness lengths over movable beds comparison of wind tunnel and field data 1 we evaluate the increase in apparent roughness length during aeolian saltation using a data set comprising 291 wind profiles measured in wind tunnels or in the field we tested the charnock 1955 modified charnock sherman 1992 and raupach 1991 relationships for the entire data set and for segregated wind tunnel and field data sets we assessed the abilities of the models to predict enhanced roughness and investigated scaling differences between wind tunnels and field environments for the entire data set the charnock relationship worked best with an r2 of 0 25 for the segregated data sets the charnock relationship also worked best with an average r2 of 0 675 as opposed to 0 66 for the modified charnock and 0 61 for the raupach model for conditions with shear velocity 1 0 ms 1 the comparable average values of r2 are 0 54 0 625 and 0 645 respectively there was an order of magnitude difference in the roughness length responses for wind tunnel and field data for each model evaluated convincing evidence of a fundamental scaling constraint in the wind tunnel data the scaling differences are attributed to conceptual and bias errors that include the use of the law of the wall versus the wake defect law or differences in turbulence characteristics especially regarding the role of large coherent structures raupach s 1991 a was found to be an extremely volatile constant making the modified charnock relationship most suitable for predicting aerodynamic roughness lengths over movable sand beds

on the rate of aeolian sand transport a simple explicit formula for the transport rate of windblown sand is derived based on physical reasoning the curve relating the dimensionless transport rate to the dimensionless friction speed exhibits the empirically well established peak in fact the theory developed in the paper can explain the peaked shape of this curve three empirically determined coefficients in the formula can be given a physical interpretation the formula is shown to fit transport rates measured in wind tunnel experiments well except for very coarse sand formulae for the wind profile in the saltation layer and for the grain dislodgement rate in dependence on the friction speed are obtained as part of the theory

radionuclide transport in fast channels in crystalline rock recent field investigations in crystalline rock give strong indications that water flows in largely isolated channels in fissured rock the present paper sets out to investigate radionuclide transport in such channels including diffusion into the rock matrix it is shown that the uptake from a cylindrical hole in a matrix is much more effective per unit contact area than a flat surface semi infinite solid comparison of diffusion from cylindrical and slit formed channels shows that the differences in interfacial flux are minor a slit formed channel may therefore be approximated by a cylindrical one diffusional transport in the matrix is then treated as one dimensional instead of two dimensional which gives a considerable numerical simplification a simple estimate of the penetration depth into the cylindrical region i e the location of the diffusional front is proposed by using the integrated finite difference method a number of radionuclide transport calculations are performed for the case of flow and dispersion in a cylindrical channel coupled to diffusion and sorption in the matrix

giant saltation on mars saltation the motion of sand grains in a sequence of ballistic trajectories close to the ground is a major factor for surface erosion dune formation and triggering of dust storms on mars although this mode of sand transport has been matter of research for decades through both simulations and wind tunnel experiments under earth and mars conditions it has not been possible to provide accurate measurements of particle trajectories in fully developed turbulent flow here we calculate the motion of saltating grains by directly solving the turbulent wind field and its interaction with the particles our calculations show that the minimal wind velocity required to sustain saltation on mars may be surprisingly lower than the aerodynamic minimal threshold measurable in wind tunnels indeed mars grains saltate in 100 times higher and longer trajectories and reach 5 10 times higher velocities than earth grains do on the basis of our results we arrive at general expressions that can be applied to calculate the length and height of saltation trajectories and the flux of grains in saltation under various physical conditions when the wind velocity is close to the minimal threshold for saltation

effect of advective flow in fractures and matrix diffusion on natural gas production although hydraulic fracturing has been used for natural gas production for the past couple of decades there are significant uncertainties about the underlying mechanisms behind the production curves that are seen in the field a discrete fracture network based reservoir scale work flow is used to identify the relative effect of flow of gas in fractures and matrix diffusion on the production curve with realistic three dimensional representations of fracture network geometry and aperture variability simulated production decline curves qualitatively resemble observed production decline curves the high initial peak of the production curve is controlled by advective fracture flow of free gas within the network and is sensitive to the fracture aperture variability matrix diffusion does not significantly affect the production decline curve in the first few years but contributes to production after approximately 10 years these results suggest that the initial flushing of gas filled background fractures combined with highly heterogeneous flow paths to the production well are sufficient to explain observed initial production decline lastly these results also suggest that matrix diffusion may support reduced production over longer time frames

field measurement and numerical modelling of aeolian mass flux distributions on a sandy beach the vertical and horizontal distributions of aeolian mass flux were measured at oceano dunes california and these data were used to evaluate a numerical model of saltation grain size analyses showed that the distributions of the modal sediment size class corresponded closely to those of the total sediment population and modelling thus focused on replicating the distributions of the mean grain size although much previous work has assumed that the mean launch speed of saltating particles varies in proportion to shear velocity simulations using a constant mean launch speed were found to yield the closest approximations to the mass flux distributions observed in the field both exponential and gamma distributions of launch velocity produced realistic simulations although the latter approach required the inclusion of an additional reptation component to achieve good results a range of mean launch angles and an equivalent sphere correction were also found to generate comparable results providing the other input parameters could be varied freely all the modelling approaches overestimated the proportion of mass flux occurring at the bottom of the vertical distributions and underestimated the proportion occurring at the upwind end of the horizontal distributions no theoretical shortcoming that would account for these small but systematic discrepancies could be identified and experimental error thus represents a more plausible explanation the conclusion that mean grain launch speeds are essentially constant and independent of shear velocity suggests that the additional kinetic energy extracted by grains under more energetic wind conditions is largely transferred to the bed and that increases in the transport rate are therefore driven primarily by the ejection of additional grains it is suggested that the kinetic energy of rebounding grains is constrained by the ability of the bed to resist deformation equivalent to a plastic limit hence grains of larger mass diameter rebound from the bed at lower speeds and follow shorter lower trajectories as has been widely observed previously

the effect of surface slope on saltation threshold a new wind tunnel has been constructed to study the mass transport properties of wind blown sand this report on the first set of experiments in the new wind tunnel concerns the effect of slope on threshold friction speed the results of this series of static threshold experiments and one dynamic threshold experiment for a range of particle diameters and bed slope angles show that provided the effects of reynolds number variation and interparticle cohesive force are accounted for the static friction angle is independent of slope and close in value to the measured static angle of response

transverse instability of megaripples as a result of their inherent differences in stability sand ripples and megaripples exhibit variations in terms of their wavelengths and grain size distributions unimodal for sand ripples and bimodal for megaripples while sand ripples form almost straight lines megaripples have greater sinuosity due to their transverse instability a property that causes small megaripple undulations to grow with time the origin of the instability is due to variations in megaripple height variations that do not diminish over time and due to the inverse dependence of ripple drift velocity on the height thus the taller regions of ripples will move more slowly than the adjacent shorter portions an outcome that promotes further perturbation growth we show an example based on fi eld work of the transverse instability of megaripples the instability growth rate depends on the difference between the heights of the different segments of the megaripple in contrast to the underlying instability of megaripples normal sand ripples are essentially stable and are not affected by transverse perturbations instead reacting quickly to the wind which tends to smooth ripple height irregularities the transverse instability of megaripples derives from the composition of their crests which comprise coarse particles that allow initial perturbations in ripple height to grow further the results suggest a physical mechanism for the transverse instability of megaripples and new insight into the spatial patterns of sand ripples

prediction of water soluble metal concentrations in fluvially deposited tailings sediments upper clark fork valley montana u s a abstract mine tailings deposited by historic floods contaminate large areas of the upper clark fork floodplain metal sulfates precipitate on the floodplain surface as byproducts of sulfide weathering and are concentrated by evaporation of soil moisture these salts dissolve readily releasing high concentrations of al as cd cu fe mn zn and h to rainwater and cause periodic fish kills when contaminated runoff reaches the river a pollution index is proposed to quantify the average enrichment of water soluble metals over aquatic hazard levels which occur in floodplain surface sediments a strong correlation between ph and the pollution index was observed because the pollution index can be predicted from ph reconnaissance mapping of metal contamination in surface sediments on the clark fork floodplain and in other contaminated river systems can be conducted simply with a ph meter

observations of collisions of saltating grains with a granular bed from high speed cine film high speed photography was used to record saltating sand grains colliding with a horizontal noncohesive bed of similarly sized grains impacting grain bed interaction is discussed in general the process as observed from the films is then described in terms of the apparent bed contact length abcl and various parameters of the impacting grains and any ejected grains examples are given of typical behaviour of bed grains in response to impacting grains of different sizes saltating grains that are large in comparison to the bed grains they encounter at collision can churn up the surface layers of soils and sediments so that previously buried grains become available for entrainment this process is discussed in relation to the potential release of dust particles into the airflow

solute transport in fracture channel and parallel plate models many studies of flow and solute transport in fractured rocks are based on a conceptual model whereby flow occurs between parallel plates which approximate the fracture walls recently it has been observed that this representation is not consistent with actual fractures real fractures are actually composed of a complex system of void spaces of varying aperture and contact areas which are closed to flow in such fractures flow takes place through a network of channels and dead end regions the present investigation analyzes and compares the behavior of solute breakthrough curves in these channels and parallel plate representations numerical experinents show that breakthrough curves obtained with channel models are characterized by a long tail and jumps in the solute concentration consistent with those observed experimentally it is concluded that the considered channel models provide a sound explanation for the behavior of real breakthrough curves which cannot be reproduced by parallel plate models

energy and momentum conserving model of splash entrainment in sand and snow saltation despite being the main sediment entrainment mechanism in aeolian transport granular splash is still poorly understood we provide a deeper insight into the dynamics of sand and snow ejection with a stochastic model derived from the energy and momentum conservation laws our analysis highlights that the ejection regime of uniform sand is inherently different from that of heterogeneous sand moreover we show that cohesive snow presents a mixed ejection regime statistically controlled either by energy or momentum conservation depending on the impact velocity the proposed formulation can provide a solid base for granular splash simulations in saltation models leading to more reliable assessments of aeolian transport on earth and mars

assessment of contamination load on water soil and sediment affected by the kongjujeil mine drainage republic of korea environmental pollution in the kongjujeil mine creek was determined on the basis of physicochemical and mineralogical properties for various kinds of waters soils precipitates and sediments collected in august and december 1998 the hydrochemistry of water is characterized by an enrichment in concentrations of ca2 si alkali ions no3 and cl in ground and surface water where relatively the mine waters are significantly enriched in ca2 mg2 al heavy metals and so42 concentrations the mine waters have lower ph 3 24 and higher ec 613 s cm compared with those of ground and surface water the ranges of d and 18o values smow in the water are 50 2 to 61 6 and 7 0 to 8 6 using a computer code the saturation indices of albite calcite and dolomite in the mine water show that it is undersaturated and has progressively evolved toward the equilibrium state ground and surface water are nearly saturated the gibbsite kaolinite and smectite are supersaturated in the surface and groundwater geochemical modeling shows that mostly toxic metals exist largely in the form of metal sulfates and free metals in mine water these metals in the surrounding fresh water could be formed of carbonate or hydroxide complex ions minerals within the soil and sediment near the mining area were partly variable consisting of quartz mica alkali feldspar plagioclase chlorite vermiculite berthierine and clay minerals the separated heavy minerals soil and sediment are composed of some pyrite arsenopyrite chalcopyrite sphalerite galena malachite goethite and various hydroxide minerals some potentially toxic elements as cd cu pb sb and zn are found in extremely high concentrations in the surface soils in the vicinity of the mine the enrichment index of heavy metals in sediment and surface soil of the mine drainage was very severe while it was not so great in the cultivated soil

a steady state model of wind blown sand transport a model for steady state eolian saltation is presented in which computation of sand grain trajectories in the wind and of the wind velocity profile modified by saltating grain drag forces is combined with experimental data on grain bed collisions in an iterative simulation scheme which resembles the time development of natural saltation qualitative features of eolian saltation are reproduced in the simulations including a height in the saltating layer at which the wind velocity remains roughly constant with changing free stream friction velocity and an approximate separation of the saltating population into successively hopping grains and reptating or creeping grains the numerical solutions give rise to more general arguments in support of the conclusions that fluid entrainment of grains is unimportant in steady state saltation that the mass flux profile obeys roughly an inverse power law dependence on height and that the vertically integrated mass flux dependence on the free stream friction velocity

saltation threshold for pyroclasts at various bedslopes wind tunnel measurements abstract pyroclastic density currents represent one of the most destructive hazards associated with explosive volcanism this destructive nature does not only urge the need for but also prevents the obtainment of in situ measurements of their physical characteristics the resulting deposits offer however evidence of the physics of their sedimentation phase deposits of dilute pyroclastic density currents frequently exhibit repeated cycles of deposition and erosion yielding insights into the turbulent shearing along the ground the utilization of such field observations can be greatly enhanced by the calibration of physical properties of such flows under well constrained laboratory conditions here wind tunnel measurements were performed using pyroclastic particles the saltation threshold and surface roughness length were calculated for wind above a pyroclastic bed the results serve as an aid in linking field observations to quantitative values of turbulent shear at the base of a flow scoria and pumice particles were investigated as a function of grain size 1 fractions between 0 125 and 4 mm as well as the influence of bedslope 20 to 25 in 10 steps the results point to the dominant control of density grain size and contrary to previous assumptions differ moderately from results obtained for round beads properly utilized the dataset enables the establishment of a link between the grain size of natural deposits and the shearing extant during their emplacement depending on the type of sedimentary structure observed in the field the saltation threshold can be used as a minimal or a maximal shearing limit during emplacement of dilute pyroclastic density current deposits stoss aggrading laminations likely involve the saltation threshold as an upper limit whereas for truncation events it must have been overcome the effect of particle concentration within the flow a critical parameter for pyroclastic density currents and the extent of validity of the data are discussed

on the efficiency of vertical array aeolian field traps the efficiency of three vertical array field traps for measuring the distribution of aeolian mass transport with height was compared with measurements with an isokinetic trap the vertical traps seem to work adequately efficiency 80 at heights greater than 15 mm above the bed closer to the bed however the open array trap catches about 70 the two continuous arrays only about 50 because most of the transport takes place close to the surface the overall efficiency of the field traps ranges from 50 to 70 based on these wind tunnel tests we have developed a low single compartment wedge shaped trap its shape in combination with flow straighteners at the entrance minimizes stagnation effects so that the efficiency is 80 our data indicate that with the wedge trap used in combination with the vertical array aberdeen trap we can sample mass transport in the field during periods with unidirectional winds with an overall efficiency of the order of 80

experimental evidence for the formation of liquid saline water on mars evidence for deliquescence of perchlorate salts has been discovered in the martian polar region while possible brine flows have been observed in the equatorial region this appears to contradict the idea that bulk deliquescence is too slow to occur during the short periods of the martian diurnal cycle during which conditions are favorable for it we conduct laboratory experiments to study the formation of liquid brines at mars environmental conditions we find that when water vapor is the only source of water bulk deliquescence of perchlorates is not rapid enough to occur during the short periods of the day during which the temperature is above the salts eutectic value and the humidity is above the salts deliquescence value however when the salts are in contact with water ice liquid brine forms in minutes indicating that aqueous solutions could form temporarily where salts and ice coexist on the martian surface and in the shallow subsurface

geochemical response to variable streamflow conditions in contaminated and uncontaminated streams 1 seasonal variations in stream inorganic geochemistry are not well documented or understood we sampled two mining impacted and two relatively pristine streams in western montana over a 12 month period collecting samples every 4 weeks with supplemental sampling at least weekly during spring runoff we analyzed all samples for dissolved operationally defined as 0 2 m and total recoverable concentrations generally the trace elements al as cu fe mn and zn did not correlate linearly with streamflow while the major elements e g ca k and mg did suspended sediment total recoverable metals and h followed clockwise hysteresis rotations driven by short term flushing events during the very early stages of spring runoff mining impacted sites had higher concentrations of many trace elements than did relatively pristine sites one of the mining impacted sites exhibited strong geochemical responses to spring rain events in the basin the results underscore the need to sample streams frequently during changing hydrologic and climatic conditions in order to accurately monitor surface water quality and to determine solute and particulate loads both contaminant and noncontaminant

impact of coating and weathering on the properties of chalk fracture surfaces the surface topography of a natural fracture intersecting a chalk formation was mapped using a high resolution laser scanning device and its roughness was evaluated using five different criteria two coated and two uncoated slices of the natural fracture surface were encased in flow cells and exposed to short 24 and 8 hours interactions with percolating synthetic rainwater and industrial wastewater followed by long drying periods weeks these flow experiments simulated the intermittent infiltration of surface runoff and industrial effluents typical of the study area and resulted in erosion of the fracture surfaces and modification of their roughness the temporal variations in surface roughness were evaluated using three commonly used criteria standard deviation from mean heights differences between maximum and minimum heights and the root mean square roughness and two newly developed measures namely the slopes on the surfaces and a calculated roughness related ratio rrr the mean slope maps and rrr calculations were found to be good criteria for evaluating surface topography and its uniformity across the fracture surface the coated surfaces were significantly rougher had greater relief more heterogeneous topography and a larger surface area than the uncoated surfaces the results suggest that coating and fast weathering caused by intermittent flow events significantly change roughness surface area relief and the heterogeneity of a fracture surface these in turn may affect the spatial distribution of flow paths across that fracture surface consequently when exploring the properties of fracture surfaces and fracture flow the impact of surface skin and variations of the surface properties over short timescales should be taken into account

unsteady saltation on mars abstract saltation is an important process on mars as it contributes to dust raising bedform dynamics and aeolian abrasion lander measurements and mesoscale meteorological models suggest that winds in the martian atmosphere rarely exceed the fluid threshold value that is necessary to aerodynamically initiate saltation a fact in stark contrast to the existence of dunes and ripples on the planet many of which are in an active state of migration in an attempt to reconcile these observations we perform an unsteady simulation with a simple turbulence model to calculate the saltation transport rate sinusoidal wind variations are imposed on the saltation layer the numerical simulations verify that gusty transport is one of the main manifestations of martian sediment transport events a formula for the saltation transport rate is reported q m u u it p where u and u it are the friction velocity and impact threshold friction velocity the power p varies in the range of 0 7 1 8 on mars and 1 5 on earth depending on the period and amplitude of the gusty inflow wind our results show that the law of martian and terrestrial transport rate are not universal and hence one should be cautious when trying to extrapolate existing terrestrial results to mars

arsenic mobilization in the hyporheic zone of a contaminated stream arsenic behavior was examined in a contaminated stream by sampling the dissolved 0 45 m arsenic and metals in surface water shallow hyporheic zone water and adjacent ground water surface water was oxic and slightly basic and ground water was anoxic and acidic hyporheic zone water had ph values of 6 7 dissolved oxygen concentrations mostly between 0 and 3 mg l 1 and mean concentrations of most metals inbetween surface and ground water sample concentrations however arsenic and iron were enriched in the hyporheic zone most of the hyporheic zone dissolved arsenic was in the form of as iii which is considered to be more toxic to some organisms than as v in the oxic surface water 20 of the total dissolved as was found to occur in its reduced form we hypothesize that upon burial and reduction of fe oxyhydroxides in the streambed sediment bound arsenic is transferred into the dissolved phase as as iii and it is subsequently released into the surface water where it does not immediately reoxidize a continual flux of reduced as to the surface water maintains as iii concentrations above that expected in oxygenated surface waters

constitutive relationships and pore structure of undisturbed fracture zone samples with cohesionless fault gouge layers multiphase flow processes in fractured rocks are of major importance for the remediation of subsurface contamination for engineering petroleum reservoirs and for the safety analysis of nuclear waste repositories we developed procedures for determining the water retention curve gas permeability function and pore structure of undisturbed fracture zone samples with cohesionless fault gouge layers in the laboratory mylonitic samples were taken at grimsel test site switzerland intrinsic permeabilities of the fault gouge layers were 5 orders of magnitude higher and significant desaturation occurred at capillary pressure heads about 10 times lower than in the surrounding granodiorite thus showing that at this site gas flow would take place mainly in the fracture zone the measured water retention and gas permeability data were well represented by parametric models designed for porous media gas flow could only be detected at water saturations below about 0 8 thus showing strong phase interference at high water saturations to relate these findings to the pore structure of the samples a qualitative and quantitative description of the pore space was obtained at different scales using fluorescent resin imbibition and image analysis techniques results show that the fracture zone consists of a continuous and interconnected fracture network that is filled with a porous medium like material thus explaining the applicability of the above mentioned models and the rather strong phase interference

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

a numerical study of particle motion and two phase interaction in aeolian sand transport using a coupled large eddy simulation discrete element method wind blown sand movement considered as a particle laden two phase flow was simulated by a new numerical code developed in the present study the discrete element method was employed to model the contact force between sand particles large eddy simulation was used to solve the turbulent atmospheric boundary layer motions of sand particles were traced in the lagrangian frame within the near surface region of the atmospheric boundary layer interparticle collisions will significantly alter the velocity of sand the sand phase is quite dense in this region and its feedback force on fluid motion cannot be ignored by considering the interparticle collision and two phase interaction four way coupling was achieved in the numerical code profiles of sand velocity from the simulations were in good agreement with experimental measurements the mass flux shows an exponential decay and is comparable to reported experimental and field measurements the turbulence intensities and shear stress of sand particles were estimated from particle root mean square velocities distributions of slip velocity and feedback force were analysed to reveal the interactions between sand particles and the continuous fluid phase

experimental assessment of owen s second hypothesis on surface shear stress induced by a fluid during sediment saltation a widely used yet thus far unproven fluid dynamical hypothesis originally presented by p r owen 50years ago states that the surface shear stress induced by a fluid on the ground during equilibrium sediment saltation is constant and independent of the magnitude of the fluid velocity and consequently the particle mass flux this hypothesis is one of the key elements in almost all current model descriptions of sediment erosion we measured the surface shear stress in a drifting sand wind tunnel and found owen s hypothesis being merely an approximation of the real situation a significant decrease of the fluid stress with increasing wind velocities was measured for low to intermediate particle mass fluxes for high particle mass fluxes owen s hypothesis essentially holds although a slight increase of the fluid stress was measured

grain scale simulations of loose sedimentary beds the example of grain bed impacts in aeolian saltation sediment transport by wind is one of many processes of interest to the geomorphologist in which grain to grain contacts play an important role in order to illustrate the modelling of collections of frictional inelastic sedimentary grains with the particle dynamics method pdm we use the grain impact process in aeolian saltation as a specific example in pdm all the forces on each particle are evaluated at a sequence of small time steps and the newtonian equations of motion are integrated forward in time interparticle forces at grain contacts are treated as springs with prescribed stiffness normal force and by a coulomb friction law tangential force particle inelasticity is represented by spring damping the granular splash resulting from saltation impacts is assessed for sensitivity to the choice of grain properties and the integration time step we find that for the range of impact speeds and impactor masses relevant to aeolian settings grain splashes are relatively insensitive to grain stiffness grain inelasticity and grain friction and that the pattern of ejection from the bed is largely controlled by bed microtopography a large set of impact realizations involving a variety of impact points on a small set of target beds is used to collect the appropriate statistics for describing the stochastic splash process the splash function representing these statistics is then available for use in calculations over longer time scales such as the evolution of the saltation curtain the details given here will enable the interested reader to adapt pdm modelling to other types of clastic sedimentary systems

modeling saltation intermittency 1 in order to investigate the intermittency of the aeolian saltation a saltation model forced with instantaneous velocity fields has been introduced in a large eddy simulation airflow model the coupled model is evaluated on a flat erodible surface under various wind conditions and soil particle size distribution it is first shown that the model is able to simulate a well developed saltation layer in equilibrium with the turbulent flow the main characteristics of the saltation layer and their sensitivity to wind conditions are in good agreement with previous data set then the saltation intermittency is visualized through the presence of blowing sand structures near the surface known as aeolian streamers this is the first time that such structures are reproduced numerically from a correlation analysis we confirm previous thoughts that these sand structures are a visual footprint of past turbulent eddies propagating in the surface boundary layer the streamers appear to be embedded in larger saltation structures with increasing wind conditions the spatial scales of these streamers change with wind conditions and soil particle size distribution this is explained by two mechanisms 1 the modification of eddy structures with the main characteristics of the saltation layer and 2 the reduction of saltating particle sensitivity to the near surface eddies with increasing wind condition and soil median particle diameter as the eddy lifetime decreases within the saltation layer and the particle response time increases respectively the standard deviation of the saltation flux associated to these saltation patterns represents about 10 to 20 of the mean saltation flux

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