wave induced sediment transport and sandbar migration onshore sediment transport and sandbar migration are important to the morphological evolution of beaches but are not well understood here a model that accounts for fluid accelerations in waves predicts the onshore sandbar migration observed on an ocean beach in both the observations and the model the location of the maximum acceleration induced transport moves shoreward with the sandbar resulting in feedback between waves and morphology that drives the bar shoreward until conditions change a model that combines the effects of transport by waves and mean currents simulated both onshore and offshore bar migration observed over a 45 day period

characteristics of turbulent boundary layers over a rough bed under saw tooth waves and its application to sediment transport article i nfo a large number of studies have been done dealing with sinusoidal wave boundary layers in the past however ocean waves often have a strong asymmetric shape especially in shallow water and net of sediment movement occurs it is envisaged that bottom shear stress and sediment transport behaviors influenced by the effect of asymmetry are different from those in sinusoidal waves characteristics of the turbulent boundary layer under breaking waves saw tooth are investigated and described through both laboratory and numerical experiments a new calculation method for bottom shear stress based on velocity and acceleration terms theoretical phase difference and the acceleration coefficient ac expressing the wave skew ness effect for saw tooth waves is proposed the acceleration coefficient was determined empirically from both experimental and baseline k model results the new calculation has shown better agreement with the experimental data along a wave cycle for all saw tooth wave cases compared by other existing methods it was further applied into sediment transport rate calculation induced by skew waves sediment transport rate was formulated by using the existing sheet flow sediment transport rate data under skew waves by watanabe and sato watanabe a and sato s 2004 a sheet flow transport rate formula for asymmetric forward leaning waves and currents proc of 29th icce asce pp 1703 1714 moreover the characteristics of the net sediment transport were also examined and a good agreement between the proposed method and experimental data has been found

la mc icp ms u pb dating of zircons from volcanic rocks and subvolcanic intrusions in ashele cu zn ore district xinjiang and its geological implications the ashele cu zn deposit is representative volcanogenic massive sulfide vms deposit in china s altay region the deposit occurs in the marine volcano sedimentary sequence of the ashele formation in the ashele basin no main ore body occurs in the stratiform form between tuff and basalt and mineralization occurs in massive densely massive banded laminated densely disseminated and veinlet forms the hydrothermal alteration and mineralization also occur in the sub dacite lots of research work has been carried out in the ashele deposit but the ages of its ore hosting volcanic rock subvolcanic rock and mineralization have not yet been clearly determined in this paper la mc icp ms zircon u pb dating was used for studying the tuff and basalt from the direct host rocks of the ore bodies sub dacite and quartz diorite in the asele cu zn district the u pb ages are 387 0 4 2 ma 388 2 3 3 ma 379 4 0 8 ma 378 5 0 9 ma for tuff basalt sub dacite and quartz diorite respectively suggesting that the ashele formation is early middle devonian in age the ashele cu zn deposit is an syngenetic deposit and no main ore body occurs between tuff and basalt the ages of the tuff and basalt suggest that the mineralization in the sedimentary exhalative period occurred in the late early devonian 388 387 ma the u pb age of the sub dacite is 379 4 0 8 ma imrplying that the magmatic hydrothermal mineralization took place in the middle devonian the u pb ages of the older zircons from tuff basalt sub dacite and quartz diorite range from 743 to 2505 ma which represent the forming age of the precambrian crystalline basement in altay region

bed slope effects on turbulent wave boundary layers 2 comparison with skewness asymmetry and other effects 1 a numerical model solving incompressible reynolds averaged navier stokes equations combined with a two equation k model for turbulence closure is used to systematically compare the relative strength of bed shear stress quantities and boundary layer streaming under wave motions from four contributions believed to play a prominent role in cross shore boundary layer and sediment transport processes 1 converging diverging effects from bed slope 2 wave skewness 3 wave asymmetry and 4 waves combined with superposed negative currents intended to loosely represent for example return currents or undertow the effects from each of the four components are isolated and quantified using a standard set of bed shear stress quantities allowing their easy comparison for conditions representing large shallow water waves on steep slopes the results suggest that converging diverging effects from beach slope may make a significant onshore bed load contribution generally however the results suggest wave skewness in addition to conventional steady streaming as the most important onshore contribution outside the surf zone streaming induced within the wave boundary layer is also investigated for each component and skewness and asymmetry are demonstrated to promote largely negative streaming velocities consistent with earlier work for hydraulically smooth cases however a thin region of positive streaming is revealed in the viscous sublayer which is effectively absent in hydraulically rough conditions cross shore boundary layer dynamics are generally acknowledged to be a complicated combination of numerous competing physical processes and this work is among few to systematically compare a number of these it is hoped that the results will be useful in assessing which of the contributions considered will be most prominent for a given set of local wave and beach slope conditions

seabed shear stress and bedload transport due to asymmetric and skewed waves abstract a simple conceptual formulation to compute seabed shear stress due to asymmetric and skewed waves is presented this formulation generalizes the sinusoidal wave case and uses a variable friction factor to describe the physics of the boundary layer and to parameterize the effects of wave shape predictions of bed shear stresses agree with numerical computations using a standard boundary layer model with a k e turbulence closure the bed shear stress formulation is combined with a meyer peter and muller type formula to predict sheet flow bedload transport under asymmetric and skewed waves for a horizontal or sloping bed the predictions agree with oscillatory water tunnel measurements from the literature

petrogenesis and tectonic settings of volcanic rocks of the ashele cu zn deposit in southern altay xinjiang northwest china insights from zircon u pb geochronology geochemistry and sr nd isotopes abstract the early mid devonian ashele formation of the southern margin of the chinese altay hosts the ashele cu zn volcanogenic massive sulfide vms deposit and consists of intercalated volcanic and sedimentary rocks that have experienced regional greenschist facies metamorphism we studied the petrography zircon u pb geochronology geochemistry and sr nd isotopes of dacites and basalts in order to understand the petrogenesis of these rocks and the regional tectonic evolution two dacites yielded la mc icp ms zircon u pb ages of 402 6 ma and 403 2 ma the dacites are calc alkaline and characterized by high na 2 o k 2 o ratios 3 6 9 3 and high mg values 47 63 enrichment in large ion lithophile elements lile and light rare earth elements lree depletion in nb ta ti and p and relatively positive e nd t values 3 6 to 7 5 collectively suggesting a sanukitic magma affinity the variations in the major and trace elements of the dacites indicate that fe ti oxide plagioclase and apatite were fractionated during their petrogenesis the basalts are tholeiitic and are characterized by high mg values 66 73 and negative nb and ta anomalies the geochemical characteristics of the basalts are similar to those of n morb those characteristics together with the positive e nd t values 6 8 to 9 2 of the basalts indicate that the precursor magma was derived mainly from an n morb type depleted asthenospheric mantle in an island arc setting the geochemical similarities between the basalts and dacites indicate that they both originated from a similar depleted mantle source via partial melting under different magmatic conditions in each case possibly related to ridge subduction

discrete particle model for sheet flow sediment transport in the nearshore fully three dimensional discrete particle computer simulations of high concentration sheet flow transport in oscillatory flows quantify the effect of fluid acceleration on bed load transport in highly unsteady flows typical of nearshore marine environments a simple impulse momentum approach explains simulation results and forms the basis for adding an acceleration related term to widely used energetics sediment transport formulae transport predicted by the acceleration term becomes increasingly significant as wave shape approaches the sawtooth profile characteristic of surf zone bores simulations integrate f ma and a corresponding set of equations for the torques for each sphere normal and tangential forces between contacting particles are linear functions of the distance between sphere centers and the relative tangential displacement at the contact point respectively particle interactions are both inelastic and frictional pressure gradient forces generated by the passage of surface gravity waves drive fluid and particle motion in a stack of thin horizontal fluid layers that exchange momentum and exert fluid drag added mass and buoyancy forces on particles transport properties of the simulated granular fluid assemblage are robust to large variations in material properties of the particles simulated transport rates agree with available experimental data for unsteady transport of coarse sands the mode of bed load motion dispersion of bed load particles and particle segregation by size and density are qualitatively consistent with available particle scale observations of bed load transport of natural particles

boundary layer hydrodynamics and bedload sediment transport in oscillating water tunnels oscillating water tunnels are experimental facilities commonly used in coastal engineering research they are intended to reproduce near bed hydrodynamic and sediment transport phenomena at a realistic scale in an oscillating water tunnel a piston generates an oscillatory motion that propagates almost instantaneously to the whole tunnel consequently flow is uniform along the tunnel unlike the propagating wave motion in the sea or in a wave flume this results in subtle differences between the boundary layer hydrodynamics of an oscillating water tunnel and of a propagating wave which may have a significant effect in the resulting sediment transport in this paper we present a zeroth order analytical model of the turbulent boundary layer hydrodynamics in an oscillating water tunnel by using a time varying eddy viscosity and by accounting for the constraints arising from the tunnel s geometry the model predicts the oscillating water tunnel hydrodynamics and yields analytical expressions to compute bed shear stresses for asymmetric and skewed waves both in the absence or presence of an imposed current these expressions are applied to successfully quantify bedload sediment transport in oscillating water tunnel experiments

role of pressure gradients in sheet flow of coarse sediments under sawtooth waves 1 discrete particle model dpm simulations have been performed to directly examine the role of horizontal pressure gradients acting on the wave bottom boundary layer wbbl during the process of sheet flow transport in the surf zone the dpm is a two phase wbbl model that directly couples a one dimensional eddy viscosity fluid flow to a three dimensional particle model newton s third law is enforced at every simulation time step through fluid particle interaction forces of buoyancy drag and added mass simulations are able to reproduce bedload transport rates from a laboratory data set for coarse sediment distributions consequently simulations of a monochromatic sawtooth wave were performed with three coarse grain size distributions to investigate the relative importance of bed shear stresses horizontal pressure forces and fluid particle drag forces on bedload transport processes the simulation results demonstrate that the magnitude of the horizontal pressure force acting directly on sediment embedded in the wbbl is small compared to the magnitude of the particle drag force or particle stress however the phasing of the onshore peak in the horizontal pressure force with respect to the particle drag force is important to sediment mobilization and enhances the observed onshore bias in bed load flux removing the horizontal pressure force on the sediment particles resulted on average in a 30 reduction in net bed load flux in the surf zone free stream fluid accelerations are typically equated to the horizontal pressure gradient thus the simulations may explain why the fluid acceleration can be a successful parameter for aiding in sediment transport predictions in the surf zone

wave induced sediment transport and onshore sandbar migration the 25 m onshore migration of a nearshore sandbar observed over a 5 day period near duck nc is simulated with a simplified computationally efficient wave resolving single phase model the modeled sediment transport is assumed to occur close to the seabed and to be in phase with the bottom stress neglected intergranular stresses and fluid granular interactions likely important in concentrated flow are compensated for with an elevated relative to that appropriate for a clear fluid model roughness height that gives the best fit to the observed bar migration model results suggest that when mean current induced transport is small wave induced transport leads to the observed onshore bar migration based on the results from the simplified phase resolving model a wave averaged energetics type model e g only moments of the near bottom velocity field are required with different friction factors for oscillatory and mean flows is developed that also predicts the observed bar migration although the assumptions underlying the models differ the similarity of model results precludes determination of the dominant mechanisms of sediment transport during onshore bar migration

the predictability of cross shore bed evolution of sandy beaches at the time scale of storms and seasons using process based profile models deterministic and probabilistic profile models have been compared with hydrodynamic and morphodynamic data of laboratory and field experiments on the time scale of storms and seasons the large scale laboratory experiment is a pure 2d case and offers and ideal test case for cross shore profile models as disturbing alongshore non uniformities are absent the field experiments are performed at the egmond site the netherlands during the eu coast3d project and represent storm time scale oct nov 1998 as well as seasonal time scale conditions may 1998 sep 1999 the objective of the paper is to present information of coastal processes on these time scales and to assess the predictive capabilities coastal process based profile models with respect to hydrodynamics and morphodynamics at sandy beaches on the time scales of storms and seasons profile models can quite accurately errors smaller than 10 represent the cross shore significant wave height distribution in the surf zone if the wave breaking model is properly calibrated the wave breaking coefficient should be a function of local wave steepness and bottom slope for most accurate results profile models can reasonably represent the cross shore and longshore currents undertow in a pure 2d case and in 3d field conditions profile models including cross shore mixing effects and breaker delay effects do not produce better predictions of the longshore and cross shore current velocities profile models using default settings can quite reasonably simulate the behaviour of the outer and inner bars on the storm time scale the behaviour of the beach cannot be modelled with sufficient accuracy on the storm time scale profile models can reasonably simulate the post storm onshore bar migration provided that the near bed orbital velocities and wave asymmetry related sand transport are represented in a sufficiently accurate way using non linear wave theories profile models cannot simulate the beach recovery processes on the post storm time scale because these essentially 3d processes are not sufficiently known to be included in the models profile models using default settings cannot simulate the behaviour of the outer and inner bars and the beach on the seasonal time scale the behaviour of the outer bar on the seasonal time scale can only be represented properly after tuning using measured bed profiles the simulation of the inner bar and beach morphology on the seasonal time scale could not be improved by tuning

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 two phase flow model for asymmetric sheetflow conditions abstract a newly developed two phase flow model was applied to simulate the sediment movement under 2nd order stokes wave sheetflow conditions with different sediment sizes and wave periods as for the distribution of eddy viscosity and sediment diffusion coefficient the difference between onshore and offshore phases was considered by using an equivalent sinusoidal velocity amplitude for the asymmetric velocity profile sophisticated comparisons between laboratory measurements o donoghue t wright s 2004b flow tunnel measurements of velocities and sand flux in oscillatory sheetflow for well sorted and graded sands coast eng 51 11 12 1163 1184 and the present numerical simulation were performed for sediment concentration sediment velocity sand flux and net transport rate four existing engineering models together with the present two phase flow model were introduced for net transport rate prediction taking both the net sand transport rate magnitude and direction into account the present process based two phase flow model provided the best estimations which can simulate both the onshore net transport for medium coarse sand cases and offshore net transport for fine sand cases with the agreement by a factor of 2 for almost all the considered cases

measurements of sheet flow transport in acceleration skewed oscillatory flow and comparison with practical formulations near bed oscillatory flows with acceleration skewness are characteristic of steep and breaking waves in shallow water in order to isolate the effects of acceleration skewness on sheet flow sand transport new experiments are carried out in the aberdeen oscillatory flow tunnel the experiments have produced a dataset of net transport rates for full scale oscillatory flows with varying degrees of acceleration skewness and three sand sizes the new data confirm previous research that net transport in acceleration skewed flow is non zero is always in the direction of the largest acceleration and increases with increasing acceleration skewness large transport rates for the fine sand conditions suggest that phase lag effects play an important role in augmenting positive net transport a comparison of the new experimental data with a number of practical sand transport formulations that incorporate acceleration skewness shows that none of the formulations performs well in predicting the measured net transport rates for both the fine and the coarser sands the new experimental data can be used to further develop practical sand transport formulations to better account for acceleration skewness

mineral potential mapping with a restricted boltzmann machine abstract a restricted boltzmann machine can be trained to encode and reconstruct training samples from a training sample population with an unknown complex probability distribution small probability samples can be differentiated from the training sample population due to their comparatively larger encoded and reconstructed errors in mineral potential mapping mineral potential areas usually take up only a small proportion of the whole mineral exploration region and have specific evidence map patterns assume that the whole mineral exploration region is divided into uniform cells and a restricted boltzmann machine is then trained on all the cells as a small proportion of the total training cells mineral potential cells have much larger encoded and reconstructed errors compared to non mineral potential cells based on the encoded and reconstructed errors of the training cells asc and ase are thus defined as two mineral potential indicators for mineral potential mapping with the trained restricted boltzmann machine the altay district in northern xinjiang in china which is linked with a complex geological setting is chosen as a case study area restricted boltzmann machines with 12 visible units and differing hidden units are constructed and trained on 9582 training cells in the study area the asc ase posterior probability and deposit bearing probability are used to predict the mineral potential of each grid cell in the study area the auc area under the curve a measure of aggregated classification performance in machine learning is applied to measure the mineral potential mapping performance of these four mineral potential indicators the results show that the four mineral potential indicators perform similarly well therefore a restricted boltzmann machine can be trained to map mineral potentials and the asc and ase are two feasible indicators for the mineral potential mapping with the trained restricted boltzmann machine

sediment transport under wave groups relative importance between nonlinear waveshape and nonlinear boundary layer streaming 1 sediment transport under nonlinear waves in a predominately sheet flow condition is investigated using a two phase model specifically we study the relative importance between the nonlinear waveshape and nonlinear boundary layer streaming on cross shore sand transport terms in the governing equations because of the nonlinear boundary layer process are included in this one dimensional vertical 1dv model by simplifying the two dimensional vertical 2dv ensemble averaged two phase equations with the assumption that waves propagate without changing their form the model is first driven by measured time series of near bed flow velocity because of a wave group during the sistex99 large wave flume experiment and validated with the measured sand concentration in the sheet flow layer additional studies are then carried out by including and excluding the nonlinear boundary layer terms it is found that for the grain diameter 0 24 mm and high velocity skewness wave condition considered here nonlinear waveshape e g skewness is the dominant mechanism causing net onshore transport and nonlinear boundary layer streaming effect only causes an additional 36 onshore transport however for conditions of relatively low wave skewness and a stronger offshore directed current nonlinear boundary layer streaming plays a more critical role in determining the net transport numerical experiments further suggest that the nonlinear boundary layer streaming effect becomes increasingly important for finer grain when the numerical model is driven by measured near bed flow velocity in a more realistic surf zone setting model results suggest nonlinear boundary layer processes may nearly double the onshore transport purely because of nonlinear waveshape

sediment transport in oscillatory boundary layers in cases of rippled beds and sheet flow an experimental study was focused on the process of sediment transport in unsteady flow conditions due to wave action wave induced oscillatory flow conditions near the seabed were simulated at full scale 1 1 in a new large oscillating water tunnel two sets of experiments series a and b were carried out during series a bed forms and wave cycle averaged suspended sediment concentrations were measured under sinusoidal waves series b focused on measurement of the wave cycle averaged sediment transport rates under regular and random asymmetric oscillatory flows upper shoreface conditions and was aimed at the verification of quasi steady formulas for the description of cross shore sediment transport bedform dimensions appeared to decrease considerably under the influence of wave asymmetry and wave randomness only the measured ripple dimensions under asymmetric waves series b showed good agreement with nielsen s 1979 relations for most of the series b experiments the bed was plane sheet flow the net sediment transport was directed onshore and the measured transport rates showed a strong correlation with the velocity moment an empirical quasi steady transport model is proposed which is based on the new tunnel data and other existing data sets the limitations of the quasi steady model approach became clear in the rippled bed regime and through the presence of a consistent influence of the wave period in plane bed conditions in rippled bed conditions the suspended concentration profiles followed a negative exponential distribution for most of the experiments the measured concentration decay length showed a linear relation with the ripple height in plane bed sheet flow conditions the measured suspended concentration profiles followed a negative power function the power or concentration decay parameter was constant 2 1 for a wide range of velocity conditions it is suggested that the mobile bed sheet flow layer has a strong damping effect on the mixing of suspended sediments turbulence damping

sand transport under combined current and wave conditions a semi unsteady practical model for the general purposes of morphodynamic computations in coastal zones simple formula based models are usually employed to evaluate sediment transport sediment transport rates are computed as a function of the bottom shear stress or the near bed flow velocity and it is generally assumed that the sediment particles react immediately to changes in flow conditions it has been recognized through recent laboratory experiments in both rippled and plane bed sheet flow conditions that sediment reacts to the flow in a complex manner involving non steady processes resulting from memory and settling entrainment delay effects these processes may be important in the cross shore direction where sediment transport is mainly caused by the oscillatory motions induced by surface short gravity waves the aim of the present work is to develop a semi unsteady practical model to predict the total bed load and suspended load sediment transport rates in wave or combined wave current flow conditions that are characteristic of the coastal zone the unsteady effects are reproduced indirectly by taking into account the delayed settling of sediment particles the net sediment transport rates are computed from the total bottom shear stress and the model takes into account the velocity and acceleration asymmetries of the waves as they propagate towards the shore a comparison has been carried out between the computed net sediment transport rates with a large data set of experimental results for different flow conditions wave current flows purely oscillatory flow skewed waves and steady currents in different regimes plane bed and rippled bed with fine medium and coarse uniform sand the numerical results obtained are reasonably accurate within a factor of 2 based on this analysis the limits and validity of the present formulation are discussed

flow tunnel measurements of velocities and sand flux in oscillatory sheet flow for well sorted and graded sands oscillatory flow tunnel measurements of velocities and fluxes for sands in oscillatory sheet flow conditions are presented the experiments involved a range of well sorted and graded sands in two asymmetric flows velocities were measured using an ultrasonic velocity profiler uvp capable of measuring deep within the sheet flow layer velocity profiles are found to be similar for the same flow but different sand beds and display expected features of oscillatory boundary layer flow the near bed velocity leads the main flow velocity by approximately 21 and a small offshore directed current is generated near the bed measures of the boundary layer thickness are in good agreement with those predicted using an equation formulated for the boundary layer thickness over fixed beds velocity data have been combined with concentration data to produce time dependent sand flux profiles covering the sheet flow and suspension regions there are fundamental differences in the transport processes of sands of different size and grading caused by unsteady effects which dominate in the case of fine sand and are largely absent in the case of coarse sand 1 time averaged flux is onshore directed positive in the case of coarse sand and is confined to a region immediately above the bed in contrast time averaged flux in the case of fine sand extends high above the bed is offshore directed negative in the sheet flow layer and becomes onshore directed in the suspension layer 2 net transport in the case of coarse sand is directed onshore as the percentage of fine sand in the bed increases offshore transport becomes increasingly dominant as the percentage of fine sand increases 3 net transport in the suspension layer is onshore while net transport in the sheet flow layer may be onshore or offshore depending on sand size and grading

glacial dynamics in southernmost south america during marine isotope stage 5e to the younger dryas chron a brief review with a focus on cosmogenic nuclide measurements the timing of major glacial changes between marine isotope stage mis 5e and the younger dryas chron yd in southern south america is reviewed focus is placed on studies that use cosmogenic nuclide measurements however other dated records and modelling results are also discussed to provide the broader glacial geological context limits on the state of glacial geologic knowledge are examined and suggestions are made as to how some of these can be addressed in future studies studies show that on the east side of the andes at lago buenos aires 45 s there is evidence indicating that following a mis 6 glaciation ice was less extensive during mis 4 than mis 2 in contrast on the west side of the andes in the chilean lake district area mis 4 ice may have been more extensive than during mis 2 although patagonia experienced an mis 2 glaciation broadly in phase with that in other areas around the globe there are differences in glacial histories between areas on millennial timescales climate reversals are evident in many records between ca 17 and 10 ka the timing of such lateglacial activity which included less extensive advances than during the local last glacial maximum lgm varies somewhat between areas this could be due to the relative influence of middle to high latitude climatic regimes at present chronological uncertainties prevent confident assignment of cosmogenic ages for glacial events at the millennial timescale and defining associated climate variability between different study areas copyright 2008 john wiley sons ltd