the effect of sparse vegetation on the transport of dune sand by wind the precise effect of a sparse plant cover on the transport of dune sand by wind is a critical factor in understanding the morphology evolution and global distribution of aeolian dunes1 3 it is also of considerable practical importance in sand stabilization rehabilitation and restoration ecology here i report the first detailed experimental quantification of this effect using living plants in patterns approximating natural vegetation for wind velocities v at 0 5 m elevation up to 15 m s 1 and plant covercup to 17 the rate of aeolian sand transport q g cm 1 s 1 is closely approximated by q b v 1 kc vt 3 where b is bagnold s constant4 vt is a threshold velocity and k is a constant dependent on plant geometry for typical small erect or spreading herbaceous dune plants k 0 018 for small rounded stemless plants k 0 046

probabilistic design of dunes an example from the netherlands abstract dunes act as primary sea defences in some regions over the world and they have then the same function as common sea dikes they prevent flooding and protect people against drowning e g in the netherlands in other regions dunes form only the transition zone between sea and land and are sometimes part of important holiday resorts in those cases high investment costs have been made frequently in building houses and hotels close to the edge of the sea under storm surge conditions however dunes can be damaged by the sea knowing the amount of retreat of the dune s toe is in both cases important a design method for dunes primarily directed at the problem of the loss of life safety has been developed in the netherlands in recent years due to the large number of factors determining dune erosion a probabilistic design method was developed

incipient granular mass flows at the base of sediment laden floods and the roles of flow competence and flow capacity in the deposition of stratified bouldery sands extraordinary floods commonly produce thick deposits as a result of the entrainment and transport often at high concentrations of large volumes of clastic detritus this paper describes the sedimentology of a stratified bouldery sand deposit generated by a 20 km3 breakout flood from intracaldera lake taupo following the 1 8 ka taupo eruption the proximal deposit is characterised by a strongly bimodal grain size distribution with downstream fining boulders enclosed in a poorly sorted and weakly bedded coarse sand to gravel matrix this combination of characteristics is inferred to reflect simultaneous deposition of small and large particles by two distinct mechanisms i accretion of the sandy matrix from an incipient basal granular mass flow as the flood lost capacity and ii progressive emplacement of the boulders as the flood lost the competence to roll them along the channel floor the first mechanism is a product of a nonlinear particle concentration gradient in the sediment laden flow which caused it to segregate into a basal incipient granular mass flow that formed the transient depositional system indicated by the lithofacies the second mechanism is a function of the superjacent turbulent turbid flow that acted as the primary transporting system this pairing of transport and depositional systems is likely to characterise many sediment laden aqueous flows with clay mineral concentrations too low to develop non newtonian rheologies such as jokulhlaups and lahars that entrain unweathered pyroclastic material qualitative and quantitative differences in the way bedload is transported in the presence of this basal granular mass flow as compared to simple water make impossible accurate estimates of flow competence based on shields entrainment functions for beds of both uniform and mixed grain size distribution

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

evidence for a new sand transport process from experiments on saharan dunes sediment transport functions relate the rate of movement of granular solids per unit width of bed to some characteristics of the shearing fluid1 3 many have been applied to sand transport over aeolian dunes4 6 these were developed for horizontal beds however whereas in natural environments there are often appreciable slopes on transport paths7 theoretical analyses have usually been adopted8 10 to account for the effect of bedslope on the threshold of sediment transport11 12 and on the transport rate13 we report results from 462 experiments in the north west saharan sand seas in which we measured the sand transport rate for a range of wind speeds on a variety of up and down sloping dune surfaces the results confirm the theoretical analyses for threshold criteria but reveal transport rates related to the seventh power of the bedslope considerably greater than those predicted by existing theory this suggests that when grains land on the surface they induce surface gravity flow in a process which has not previously been fully recognized

problems of scale in the modeling and interpretation of coastal dunes abstract coastal dune systems are studied at time scales from seconds to millennia and space scales from millimeters to kilometers present approaches to the study of coastal dunes make it difficult to integrate models and interpretations of these systems over these scale ranges and arrive at reasonable conclusions it is argued that identification of key controls on dune development measurement of those controls and synthesis of data describing past and present conditions and used as calibration points will improve the viability of coastal dune models theoretical and empirical advances are necessary to improve the reliability of predictions across a range of geomorphological scales attempts at linking theoretical systematic models process synoptic measurement and historical or paleoenvironmental synthetic approaches make explicit the recognition that at time scales of more than a few hours and space scales greater than a few hundred meters deterministic models become unstable vis a vis prototype environments process climatologies provide one means to link process based work with broader scaled analysis as scales increase such climatologies will become less appropriate as the data become less reliable or as the systems change or as the scales become too large relative to the process record lengths in these conditions specific data i e samples representing points in time and space become check points for calibrating models it should be possible ideally to integrate both up and down time and space scales this is not yet possible

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

aalenian early bathonian middle jurassic radiolarian assemblages in the tavas nappe within lycian nappes in the western taurides sw turkey the first dating of carbonate platform drowning abstract stratigraphic sections kizilca and kizilca north in the tavas nappe western taurides turkey records the event of carbonate platform drowning in the western tethyan realm our detailed biostratigraphic study of radiolarians and other microfossils places the important temporal constraints on this event and indicates that drowning occured in the geochronological interval from early jurassic hettangian sinemurian through to middle jurassic early bathonian the basal part of the kizilca section is represented by platform carbonates with abundant benthic foraminifera and algae of hettangian sinemurian to pliensbachian age toward the upper part of the section the occurrence of brecciated limestones with some ammonites and belemnites reveals that the drowning event began in the pliensbachian the first radiolarian assemblages of early middle to late aalenian age were obtained from the overlying units characterized by pelagic limestones and chert alternation just after the subsidence of the platform ribbon chert sedimentation began in the late aalenian as indicated by the radiolarians successively early late bajocian and latest bajocian early bathonian radiolarian assemblages were obtained from overlying chert with mudstone silicified mudstones similar to that observed in the kizilca section the kizilca north section include successively pelagic limestones pelagic limestone chert alternation and chert mudstone alternation of late aalenian to early middle bajocian age according to radiolarian biostratigraphy all of these observations indicate that a continuous stratigraphy recorded the drowning event without a large gap from hettangian sinemurian to early bathonian in the tavas nappe this drowning event has close similarities with coeval events in other tethyan realms in terms of mechanism facies characteristics and fossil assemblages therefore this study can aid correlation studies of the tavas nappe with the jurassic paleogeography worldwide

a semianalytical model for sheet flow layer thickness with application to the swash zone a new semianalytical model for the time dependent thickness of the sheet flow layer that includes the effects of pressure gradients bed slope boundary layer growth and bore turbulence is presented the shear stress and boundary layer growth are computed using the boundary layer integral method the model is expressed as two coupled ordinary differential equations that are solved numerically given a prescribed time series of free stream velocity horizontal pressure gradient and bore turbulence which together represent the hydrodynamic forcing the model was validated against two data sets of sheet flow layer thickness collected in oscillatory flow tunnels and one data set collected in the swash zone of a prototype scale laboratory experiment in the oscillatory flow tunnel data sets sheet flow is mostly generated by shear stress with pressure gradients providing an important secondary forcing around flow reversal in the swash zone pressure gradients and shear stresses alone are not sufficient to generate the large sheet flow layer thickness observed at the initial stages of uprush bore turbulence is most likely the dominant generation mechanism for this intense sheet flow

global radiolarian zonation for the pliensbachian toarcian and aalenian jurassic radiolarians from 220 samples in queen charlotte islands b c williston lake b c east central oregon baja california sur southern spain austria slovenia turkey oman japan and argentina were studied in order to construct global zonation for the pliensbachian toarcian and aalenian stages well preserved faunas from continuous stratigraphic sections in queen charlotte islands provide the most detailed record for this time interval and all collections are tied to north american ammonite zones or assemblages collections from nearly all other areas lack independent dating except for early toarcian carbon isotope dating in slovenia and late aalenian ammonites in spain a database of 197 widely distributed updated taxonomic species was used to construct a unitary association ua zonation for the interval a global sequence of 41 uas was obtained for the top of the sinemurian to the base of the bajocian the first and the last uas represent the late sinemurian and the early bajocian respectively the remaining 39 uas were merged into nine zones four early pliensbachian one late pliensbachian one early toarcian one middle late toarcian and two aalenian according to prominent radiolarian faunal breaks and ammonite data the new zones are the canutus tipperi katroma clara zone latest sinemurian earliest pliensbachian zartus mostleri pseudoristola megaglobosa hsuum mulleri trillus elkhornensis and gigi fustis lantus sixi zones early pliensbachian eucyrtidiellum nagaiae praeparvicingula tlellensis zone late pliensbachian napora relica eucyrtidiellum disparile zone early toarcian elodium pessagnoi hexasaturnalis hexagonus zone middle and late toarcian higumastra transversa napora nipponica zone early aalenian and mirifusus proavus transhsuum hisuikyoense zone late aalenian these zones can be correlated worldwide and link previously established ua zonations for the hettangian sinemurian and the middle to upper jurassic the new zonation allows high resolution dating in the studied interval and provides a solid basis for analyzing faunal turnovers and the paleobiogeography of jurassic radiolarians

field observations of bedforms and sediment transport thresholds of fine sand under combined waves and currents abstract seabed video images and s4 wave current meter data collected during the build up of a moderate storm on the scotian shelf are analysed for bedform development and sediment transport threshold of fine sand under combined waves and currents as the storm built up the following sequence of bedforms was observed 1 relict wave dominant ripples with worm tubes and animal tracks during the preceding fairweather period 2 irregular sinuous asymmetrical current dominant and intermediate wave current ripples under bedload transport 3 regular nearly straight or sinuous asymmetrical to slightly asymmetrical wave dominant ripples under saltation suspension 4 upper plane bed under sheet flow conditions 5 small crest reversing transitory ripples at the peak of the storm and 6 large scale lunate megaripples which developed when the storm decayed these data also show that only single sets of asymmetrical intermediate wave current ripples will form when waves and currents are co linear the development of the crest reversing transitory ripples indicates a high energy transition stage under quasi sheet flow conditions a direct comparison of the skin friction combined shear velocity and the critical shear velocities for bedload suspension and sheet flow transport under estimated the onset of these sediment transport modes as the presence of ripples causes the shear stress to increase from ripple trough to ripple crest the ripple enhanced skin friction shear velocity must be used to determine properly the initiation of bedload transport at high transport stages the boundary layer dynamics is controlled mainly by the thickness of the bedload transport layer thus a transport related bedload shear velocity predicted based upon the sum of the grain roughness and bedload roughness has to be compared against the conventional threshold criterion to properly define the onset of suspension and sheet flow transport modes

sediment suspension in oscillatory flow measurements of instantaneous concentration at high shear abstract different syphon type suspended load probes were used together with a specially developed carousel sampler for measurements of the instantaneous sediment concentration in turbulent oscillatory flow over a sand bed shields parameters were well above the ripple flat bed transition region resulting in intense sediment transport over a flat bed the measurements were performed at different levels in a large oscillating water tunnel they showed some characteristic features of the temporal concentration variation at fixed levels including a pronounced effect of the orientation of the suction tube relative to the flow the variation with height of the average concentration is reasonably well described assuming a constant turbulent diffusivity and the magnitude of this can be predicted relatively well using simple turbulence arguments two empirical formulae for the extrapolated bed concentration are also presented the analysis is partly based on wilson s finding that in sheet flow the equivalent bed roughness is nearly proportional with the shields parameter resulting in a roughness grain diameter ratio much larger than 2 5 the figure often adopted for a flat bed but without sheet flow

the blown sand flux over a sandy surface a wind tunnel investigation on the fetch effect abstract detailed wind tunnel tests were conducted to examine the fetch effect of a sandy surface on a sand cloud blowing over it the results suggest that the fetch length of a sandy surface has a significant effect on both the vertical flux profile and total horizontal flux the sand flux over a sandy surface increases with height in the very near surface layer but then decays exponentially in agreement with the widely accepted conclusion the decay function can be expressed by q aexp h b where q is the sand flux at height h coefficient a that tends to increase with wind speed implies the influence of wind while coefficient b that defines the relative decay rate shows the influence of both the fetch and wind the relative decay rate increases with fetch when the fetch length is short then becomes constant when the fetch reaches a certain length the threshold fetch length over which the relative decay rate keeps constant increases with wind speed the average saltation height generally increases with fetch both the relative decay rate and average saltation height show that the fetch effect on the flux profile becomes more significant when the wind speed increases the total sand transport equation for the total fetch can be expressed by q c 1 ut u 2u3 g where q is the total sand transport rate u and ut are the wind velocity and threshold wind velocity at the centerline height of the wind tunnel respectively g is gravitational acceleration is the density of air and c is a proportionality coefficient that increases with the fetch length implying that the total sand flux increases with the fetch length

understanding the geological record of carbonate platform drowning across rifted tethyan margins examples from the lower jurassic of the apennines and sicily italy abstract in the geological record a drowning process is documented by various types of shallow water to pelagic or shallow water to mixed benthic pelagic carbonate transitions drowning unconformities are paraconformities to disconformities to angular unconformities and their drowning surfaces range from planar to highly irregular morphologies drowning successions display a mix of products of both the benthic and pelagic carbonate factories these successions can be also bounded by unconformities drowning unconformities and drowning successions are contrasted through a description and discussion of examples of escarpment bounded platforms from the jurassic of the northern apennines and subordinately from sicily and other tethyan sectors the areal distribution of drowning unconformities and successions is discussed with reference to a complex depositional system whose architecture was the product of the rift induced fragmentation of a regional hettangian carbonate megabank the examples in this study show drowning unconformities to be exclusive to intrabasinal highs while drowning successions are found both on highs and in hangingwall basins drowning unconformities with their long associated hiatuses and drowning successions are often seen to merge laterally into one another over very short distances on the same intrabasinal high the deposits of the drowning succession are sometimes missing on the top of the platform while they are found forming clinoforms along its flanks evidence that sediment could be permanently swept from the highs in these depositional systems at this stage

are coarse grained sediment waves formed as downstream migrating antidunes insight from an early pleistocene submarine canyon on the boso peninsula japan abstract gently undulating waveforms were identified in conglomerates and pebbly sandstones of the lower pleistocene higashihigasa formation which represents an infill of a submarine canyon on the boso peninsula japan on the basis of dimension geometry and texture these waveforms are interpreted as bedforms that are analogous to coarse grained sediment waves in modern deep water environments the studied waveforms exhibit symmetrical or dune like asymmetrical forms in association with minor antidune like asymmetrical forms with the lee sides being longer than the stoss sides the waveforms are also characterized internally by bedding gently inclined in the downstream direction to the northeast laterally washout dune and humpback dune deposits are locally developed in association with planar bedding the coarse grained sediment wave deposits are interpreted to have developed as downstream migrating antidunes in the upper flow regime condition of turbidity currents on the basis of the empirical relationship between the wavelengths and mean flow depths of downstream migrating gravel antidunes the waveforms are interpreted to have been formed by waves at the interface between the denser bottom flow and the less dense upper flow within a turbidity current it is possible that some of the coarse grained sediment waves in modern deep water environments may have been formed as downstream migrating antidunes regardless of their plan view geometry

surf zone cross shore boundary layer velocity asymmetry and skewness an experimental study on a mobile bed 1 an experimental study on a physical model of a beach in a two dimensional wave flume was designed to investigate velocity nonlinearities in the wave boundary layer the cross shore velocity was measured in the surf zone along a vertical profile every 3mm from free stream elevation down to the still bed level the skewness and the asymmetry of the phase averaged velocity were computed at each elevation observations indicate that the free stream asymmetry transforms into bottom velocity skewness a linear experimental relation between free stream asymmetry to skewness ratio and bottom skewness to free stream skewness ratio is established a theoretical linear relationship is discussed which predicts the phase lead of the bottom velocity this phase lead is also determined by fourier analyzing the velocity time series the first two fourier components yield the same phase lead at the bed that is found to be about 30 and nearly constant over all the experiments made

mobile bed friction at high shear stress analysis demonstrates and experiments confirm that the frictional behavior of mobile beds at high shear stress is inherently different from either of the two classical cases smooth wall and rough wall for those two cases the characteristic lengths for friction are based on viscosity and grain size respectively for the new mobile bed friction relation this length varies with the thickness of the shear layer occupied by the moving bed load particles this thickness is itself directly related to shear stress giving rise to the prediction that at high shear stress shields ordinate greater than unity the effective roughness ratio effective roughness particle diameter should be approximately five times the shields ordinate the high shear stress experimental results show a variation in accord with the prediction

a rouse based method to integrate the chemical composition of river sediments application to the ganga basin 1 the ganga river is one of the main conveyors of sediments produced by himalayan erosion determining the flux of elements transported through the system is essential to understand the dynamics of the basin this is hampered by the chemical heterogeneity of sediments observed both in the water column and under variable hydrodynamic conditions using acoustic doppler current profiler adcp acquisitions with sediment depth profile sampling of the ganga in bangladesh we build a simple model to derive the annual flux and grain size distributions of the sediments the model shows that ca 390 30 mt of sediments are transported on average each year through the ganga at haring bridge bangladesh modeled average sediment grain size parameters d 50 and d 84 are 27 4 and 123 9 mm respectively grain size parameters are used to infer average chemical compositions of the sediments owing to a strong grain size chemical composition relation the integrated sediment flux is characterized by low al si and fe si ratios that are close to those inferred for the himalayan crust this implies that only limited sequestration occurs in the gangetic floodplain the stored sediment flux is estimated to c a 10 of the initial himalayan sediment flux by geochemical mass balance the associated globally averaged sedimentation rates in the floodplain are found to be ca 0 08 mm yr and yield average himalayan erosion rate of ca 0 9 mm yr this study stresses the need to carefully address the average composition of river sediments before solving large scale geochemical budgets citation lupker m c france lanord j lave j bouchez v galy f metivier j gaillardet b lartiges and j l mugnier 2011 a rouse based method to integrate the chemical composition of river sediments application to the ganga basin

stably stratified shear flow over low hills summary an analysis is presented for the mean flow over hills with low slopes for various kinds of stable stratification in the approach flow the froude number f based on the height is always greater than unity the analysis is based on dividing up the flow into different regions with different dynamics we concentrate on the flow in the inviscid outer region of the flow it is shown that in the lower part of the outer region the middle layer where the shear is large the upwind velocity profile and the shape of the hill rather than the upwind density profile largely determine the vertical perturbation velocity in the upper layer the structure of the flow depends largely on the form of the upwind density profile for example this largely determines the location of maximum surface wind new solutions for stable conditions are obtained when there is a constant density gradient when n ub 0 z2 and when there is an elevated inversion layer in the first and third of these cases we compare the results with the hydrostatic approximation and also obtain new general formulae for the near surface winds an approximate formula is developed for surface winds at arbitrary values of f 1 for uniform stable stratification

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

biochronology of jurassic and early cretaceous radiolarites from the lycian melange sw turkey and implications for the evolution of the northern neotethyan ocean new radiolarian ages for blocks of radiolarian cherts associated with other blocks of distal pelagic facies and ophiolitic lithologies within the lycian melange sw turkey indicate deposition during mid jurassic to early cretaceous time radiolarites overlying pink pelagic limestones of an allochthonous carbonate unit accumulated during the midto late jurassic on the basis of structural evidence the lycian melange is inferred to have been rooted within the northern neotethys to the north of the tauride anatolide microcontinent the lycian radiolarites can be compared with other dated radiolarites from the izmir ankara suture the root zone of the northern neotethyan ocean based on all the available radiolarian data it is inferred that radiolarites accumulated within the northern neotethys in western turkey from late triassic mid carnian to late norian to midcretaceous cenomanian time the radiolarites were later detached from their inferred oceanic basement and accreted within a subduction complex during the late cretaceous turonian maastrichtian and emplaced over the northern margin of the tauride anatolide continent together with slices of continental margin and ophiolitic lithologies following the development of mesozoic radiolarian biostratigraphical schemes during the last 25 years radiolarian biochronology has become invaluable for reconstructing the palaeogeography palaeoceanography and tectonic evolution of tethyan oceanic basins and margins de wever 1989 robertson et al 1991 de wever et al 1994 danelian robertson 1997 2001 radiolarites in the tethyan realm commonly occur within melanges that are interpreted as parts of accretionary prisms related to subduction of ocean crust robertson 2002 2004 radiolarian ages from such melanges provide valuable age constraints on related geological processes including spreading intra plate volcanism and tectonic accretion e g al riyami et al 2001 beccaletto et al 2005 here we will present the first radiolarian evidence from the lycian melange an east west trending late mesozoic accretionary complex in sw turkey collins robertson 1997 fig 1 this melange forms part of the wellknown lycian nappes in sw turkey de graciancky 1972 poisson 1977 1984 collins robertson 1998 the root zone of the melange is considered to lie to the north of the regional basement represented by the tauride anatolide platform collins robertson 1998 2003 and is inferred to lie within the izmir ankara suture zone to the north of the menderes massif robertson pickett 2000 robertson et al 2004 we will also review the limited available data for radiolarites from comparable tectonic units within the izmir ankara suture zone and the bey daglari we conclude by considering the implications of the available radiolarian evidence for the evolution of the mesozoic tethyan ocean

near bed cross shore velocity profiles bed shear stress and friction on the foreshore of a microtidal beach abstract new high resolution acoustic doppler current profilers are used to quantify the vertical structure of cross shore fluid velocities in the very inner surf and swash zones on two west central florida beaches field data are collected at an unprecedented 0 001 m vertical resolution over the lower 0 02 m of the water column and at up to 100 hz swash events defined based on the timing of sensor submergence and emergence and inner surf zone flow cycles defined based on the timing of zero upcrossings are normalized around flow reversal and ensemble averaged to investigate the vertical profiles of cross shore flow the ensemble averaged cross shore velocity profile is generally well represented by the logarithmic model r2 0 9 within 0 02 m of the bed the maximum elevation over which the model was applied the logarithmic model fails near flow reversal when velocities are weak friction velocities are used to estimate the corresponding bed shear stress with maximum values of 6 45 and 4 25 n m 2 for swash events and inner surf zone wave cycles respectively friction coefficient estimates adopting the quadratic drag law and the velocity at 0 02 m above the bed are 0 024 0 008 and 0 022 0 007 mean standard deviation for onshore directed motion and 0 034 0 005 and 0 027 0 006 for offshore directed motion for swash zone events and inner surf zone flow cycles respectively

the motion of sediment water mixtures during intense bedload transport computer simulations a new model which couples fluid and particle dynamics has been developed to study the motion of the sediment water mixture during intense bedload transport including the velocity profiles of both sediment and water the roughness length of an upper plane bed and the thickness of moving sediment layers standard mixing length theory is used to model the motion of water above the boundary between the overlying water and the sediment water mixture the turbulent flow within the moving sediment layers is described by a shear stress model in which the effective viscosity of the flowing water is proportional to the velocity difference between the fluid and the sediment the particle dynamics method in which the equations of motion of each of many particles are solved directly is applied to model the movement of sediment particles the particle fluid interaction is expressed by a velocity squared fluid drag force exerted on each sediment particle both computer simulation results and theoretical analysis have shown that the velocities of both sediment and fluid during intense sediment transport decrease exponentially with depth in the top layers of a fast moving sediment water mixture the thickness of the moving sediment layers obtained from the computer simulation results is proportional to the shear stress which agrees with previous experimental observations

experimental evidence for turbulent sediment flux constituting a large portion of the total sediment flux along migrating sand dunes accurate estimation of sediment transport is critical for many fluvial processes but remains challenging due to high frequency dynamics using novel acoustic flow instrumentation we quantified the contribution of turbulent bed and suspended sediment fluxes to the total sediment fluxes along an entire dune profile and over the full flow depth we found that over the dune stoss side and in the bed load layer the turbulent mean streamwise flux is negative and reaches up to 40 of the total mean streamwise flux over the lee side where turbulent intensities are highest the contribution of the turbulent mean streamwise flux to the total mean streamwise flux is larger and reaches up to 50 the mean vertical turbulent flux along the entire dune bed and in the bed load layer reaches nearly 30 of the total mean vertical flux turbulent sediment flux may thus constitute a large component of the total flux

aeolian sand transport a wind tunnel model wind sand transport is an important geological process on earth and some other planets formulating the wind sand transport model has been of continuing significance majority of the existing models relate sand transport rate to the wind shear velocity based on dynamic analysis however the wind shear velocity readapted to blown sand is difficult to determine from the measured wind profiles when sand movement occurs especially at high wind velocity moreover the effect of grain size on sand transport is open to argument detailed wind tunnel tests were carried out with respect to the threshold velocity threshold shear velocity and transport rate of differently sized loose dry sand at different wind velocities to reformulate the transport model the results suggest that the relationship between threshold shear velocity and grain size basically follow the bagnold type equation for the grain size d 0 1 mm however the threshold coefficient a in the equation is not constant as suggested by bagnold but decreases with the particle reynolds number the threshold velocity at the centerline height of the wind tunnel proved to be directly proportional to the square root of grain diameter attempts have been made to relate sand transport rate to both the wind velocity and shear velocity readapted to the blown sand movement the reformulated transport model for loose dry sand follows the modified o brien rindlaub type equation q f1 d 1 ru 2 g v3 or the modified bagnold type equation q f2 d 1 rt 0 25 g u 3 where q is the sand transport rate the sand flux per unit time and per unit width in kg m 1 s 1 is the air density 1 25 kg m 3 g is the acceleration due to gravity 9 81 m s 2 ru vt v rt u t u v is the wind velocity at the centerline of the wind tunnel in m s 1 vt is the threshold velocity measured at the same height as v in m s 1 u is the shear velocity with saltating flux in m s 1 u t is threshold shear velocity in m s 1 f1 d 1 475 24 93 62d d f2 d 1 41 4 98exp 0 5 ln d 1 55d 0 57 2 d is the grain diameter in mm and d is the reference grain diameter equals 0 25 mm the bagnold s equation that asserts for a given wind drag the rate of movement of a fine sand is less than that of a coarse sand is not supported by the reformulated models

analysis of bed load motion at high shear stress recent pipeline experiments performed in saskatchewan show the existence of a shear layer in which the solids concentration decreases linearly with height this finding has already been used to calculate the velocity distribution within a constant stress shear layer the analysis has now been extended to obtain the solids discharge per unit breadth of bed the result agrees with the modified meyer peter and muller equation and with the writer s sand data for larger nylon particles the solids discharge per unit breadth fell below that expected on the basis of the sand data and the new analysis shows the reason for this apparent anomaly it also shows that a shear layer several grain diameters thick will not be uncommon in open channel flow contrary to the conventional wisdom the new analysis predicts that the threshold of motion curve on the shields diagram must approach a constant value at sufficiently small abscissae a finding which appears to be in accord with recent experimental evidence

turbulent velocity profiles and boundary shear in gravel bed rivers vertical profiles of turbulent streamwise velocities in several new zealand gravel bed rivers are investigated field measurements made at high and low flows with electronic pitot tubes show logarithmic velocity profiles to extend over much of the flow depth for the gravel bed rivers studied the velocity at 0 6 of the total depth was generally a good indicator of depth averaged flow velocity an unambiguous definition of flow depth is adopted to deal with situations where the bed is uneven or moving when hydraulic roughness z sub 0 is defined as a fitted parameter of a logarithmic velocity profile the river data indicate that the profile origin displacement below the tops of roughness elements scales with z sub 0 no direct relation between z sub 0 and bed material size is evident under mobile bed conditions for these conditions a relation between hydraulic roughness and u squared is identified with u also derived as a log profile parameter a flow resistance equation using this relation is verified by comparison with mobile bed laboratory measurements in which u is not fitted from velocity profiles

underwater sand bed erosion and internal jump formation by travelling plane jets theory and experiments are used to investigate the water and sediment motion induced along a sea bed by travelling plane jets steadily moving jets are considered and represent an idealization of the tools mounted on ships and remotely operated vehicles rovs for injection dredging and trenching the jet induced turbulent currents simultaneously suspend sand from the bed and entrain water from the ambient to describe these processes a shallow flow theory is proposed in which the turbulent current is assumed stratified into sediment laden and sediment free sublayers the equations are written in curvilinear coordinates attached to the co evolving bed profile a sharp interface description is then adopted to account rigorously for mass and momentum exchanges between the bed current and ambient including their effects on the balance of mechanical energy travelling wave solutions are obtained in which the jet induced current scours a trench of permanent form in a frame of reference moving with the jetting tool depending on the operating parameters it is found that the sediment laden current may remain supercritical throughout the trench or be forced to undergo an internal hydraulic jump these predictions are confirmed by laboratory experiments for flows with or without jump in which the current remains attached to the bed bottom profiles computed by the theory compare favourably with imaging measurements

a general framework for modeling sediment supply to coastal dunes including wind angle beach geometry and fetch effects a series of spatially explicit equations are derived that form the foundation of a modeling framework that provides insight into how the interaction of the fetch effect and angle of wind approach leads to tradeoffs that govern the magnitude of aeolian sediment transport across beaches of different geometry the spatial distribution of sediment transport rate per unit width at any point on the beach is shown to vary predictably as a function of wind angle critical fetch and beach geometry and this has evident implications for the total volume and distribution of sediment transport into the dunes behind the beach as well as the proportion of sediment lost from the beach dune system at the downwind margin as the wind field shifts from onshore shore perpendicular to oblique shore parallel approach angle total sediment transport rate across a dune line segment will reflect a tradeoff between transport reduction because of the cosine effect and transport enhancement because of potentially longer fetch distances traversed by the wind prior to encountering the dune line this tradeoff is most evident on long narrow beaches when beach width is less than the critical fetch for such beaches and with onshore winds the total sediment transport rate across the dune line will be less than that predicted for a wide beach because of the constraint imposed by the fetch effect however as the angle of wind approach becomes oblique the available fetch becomes progressively longer transport limitations imposed by the fetch effect are negated and transport enhancement across the dune line is to be expected with very large angles of wind approach the cosine effect dominates the interaction and transport reductions across the dune line occur until the wind is shore parallel and sediment supply to the dunes ceases altogether this sequence of adjustments and tradeoffs were only partially understood prior to this study and yet they form the foundation of coastal dune modeling the framework proposed in this paper serves to place future studies of process form interaction in beach dune systems on a robust theoretical foundation it also facilitates the testing of various alternative hypotheses regarding the uneven spatial and temporal distribution of dune height and growth rate in coastal environments

aeolian sand transport an optimized model consideration of the available equations for prediction of aeolian sand transport led to the development of a model which relies on optimization techniques for the production of improved performance the model has been applied to the characterization of dunesand movement in coastal environments in eastern australia

numerical simulation of time dependent beach and dune erosion a computational procedure is developed for predicting the time dependent two dimensional beach and dune erosion during severe storms due to elevated water levels and waves the model employs the equation of sediment continuity and a dynamic equation governing the cross shore sediment transport due to a disequilibrium of wave energy dissipation levels these equations are solved numerically by an implicit double sweep procedure to determine the change in position of elevation contours in the profile given sufficient time the profile will evolve to a form where the depth h in the surf zone is related to the distance seaward of the waterline by the relationship h ax23 which is consistent with many natural profiles and in which a depends on sediment characteristics the model is verified qualitatively and quantitatively through application to several idealized cases and through a preliminary simulation of erosion during hurricane eloise in general the time scales for shoreline response were found to be quite long relative to natural storm systems and erosion in the early response stages was found to be sensitive to storm surge height but much less sensitive to wave height the model response characteristics for simulation of erosion due to time varying storm conditions show a lag between the maximum storm surge elevation and maximum erosion with the maximum erosion rate occurring at the time of the peak surge for the simulated erosion due to hurricane eloise reasonable agreement was found between the post hurricane dune profiles and those calculated however the eroded volumes were in better agreement than the profile forms as the steepening of the natural dune profiles was not reproduced in the model

the fluid dynamics of river dunes a review and some future research directions 1 dunes are present in nearly all fluvial channels and are vital in predicting flow resistance sediment transport and deposition within many rivers progress in understanding the fluid dynamics associated with alluvial dunes has been significant in the last 15 years and has witnessed huge advances in field laboratory and numerical investigations progress has been made in detailing the principal features of mean and turbulent flow over asymmetric dunes that possess flow separation in their leesides and how these forms affect both downstream boundary layer structure and stress partitioning over the dune additionally the links between sediment transport over dunes and instantaneous coherent flow structures are being increasingly understood with the feedback of dune three dimensionality upon flow and sediment dynamics over these bed forms beginning to be recognized as vital such research now provides an outstanding background for beginning to address areas of greater complexity that will enable a fuller understanding of these important natural features this review paper summarizes the principal features of mean and turbulent flow over alluvial sand dunes five areas are then highlighted and discussed as a possible focus for future research 1 the influence of dune leeside angle upon flow processes in the dune wake and downstream flow field 2 the influence of three dimensionality in dune shape upon the generation of turbulence and distribution of bed shear stress 3 flow field modification resulting from bed form superimposition and amalgamation 4 the scale and topology of dune related turbulence and its interactions with sediment transport and the flow surface and 5 the influence of suspended sediment on the dune flow field and dune morphology

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

evaluation of aeolian sand transport equations using intertidal zone measurements saunton sands england sand transport rates were measured using a vertical sand trap along the intertidal zone of a beach in north devon england together with simultaneous monitoring of the wind speed on the beach and moisture levels in the surface layers of sand the results of 88 sand trap samples in a wide range of wind speeds showed that moisture levels up to 14 in the top 1 2 mm of the beach sand have no discernible effect on the transport rates transport rates measured from areas of the beach where the moisture was below this level are compared with the rates predicted by seven expressions based on theoretical and wind tunnel research together with the empirical results of other published research measured transport rates range from 0 0001 to 0 22 kg m 1 s 1 the results indicate that expressions based on a power relation between the wind speed and the transport rate and which include a threshold velocity term provide the best estimates of the observed transport rates

aeolus ii an interactive program for the simulation of aeolian sedimentation abstract a computer program has been developed to simulate two or three dimensional topographic change associated with aeolian sediment transport because predictions generated by available models of aeolian transport can vary by about an order of magnitude for a given set of environmental conditions selection of an appropriate model is problematic this program includes a number of models and provides for interactive selection of a desired model combination s to allow for comparison between model predictions topography represented by a set of coordinates in two or three dimensions is defined by bins of sediment differential rates of transport between adjacent bins resulting from variations in grain size slope and surface moisture content are used to determine mass flux and to adjust the topography in an iterative fashion sub routines allow the simulation of temporally varying levels of surface moisture resulting from evaporation and periodic restoration of upwind boundary conditions the wind field can be represented by a constant shear velocity by a spatial cross shore distribution of shear velocities or by a time series of values representing multiple wind events output is in the form of a graphic display or tabulated results written to disk example results are presented which qualitatively suggest that simulated topographic changes are reasonable areas where further refinement is needed to improve correspondence with reality are identified and discussed

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

a sand budget for the alexandria coastal dunefield south africa the sand in the alexandria coastal dunefield is derived from the sandy beach which forms the seaward boundary of the dunefield sand is blown off the beach onto the dunefield by the high energy onshore directed dominant wind the dunefield has been forming over the past 6500 years sand transport rates calculated from dune movement rates and wind data range from 15 to 30 m3 m 1 yr 1 in an ene direction the sand transport rate decreases with increasing distance from the sea due to a reduction in wind speed resulting from the higher drag imposed upon the wind by the land surface aeolian sand movement rates of this order are typical of dunefields around the world the total volume of sand blown into the dunefield is 375 000 m3 yr 1 sand is being lost to the sea by wave erosion along the eastern third of the dunefield at a rate of 45 000 m3 yr 1 the dunefield thus gains 330 000 m3 of sand per year this results in dunefield growth by vertical accretion at about 1 5 mm yr 1 and landward movement at about 0 25 m yr 1 the dunefield is a significant sand sink in the coastal sand transport system the rate of deposition in coastal dunefields can be 10 times as high as rates of deposition in continental sand seas the higher rate of deposition may result from the abundant sand supply on sandy beaches and the higher energy of coastal winds wind transport is slow and steady compared to fluvial or longshore drift transport of sediment and catastrophic aeolian events do not seem to be significant in wind laid deposits

field evaluation of some sand transport models fluorescent tracer procedures originally developed for research on fluvial sediment movement were used to monitor the movement of three commercially purchased sands in a natural dune environment results were compared with estimates of transport rates from three theoretical models estimates from models by bagnold 1941 and hsu 1971 were larger by as much as one order of magnitude than the rates observed in the tracer study the model of a a kadib 1965 provided closer correspondence to observed transport rates for medium sand mean diam 0 653 mm but underestimated rates for coarse sand mean diam 0 992 mm

simple models for the shape and symmetry of tidal sand waves 3 dynamically stable asymmetrical equilibrium forms without flow separation abstract the complex interaction between the local steepness of a sand bed and the tidally induced bedload transport over it is theoretically such that dynamically stable sand waves of asymmetrical cross section can exist beneath a tidal current in which one stream dominant exceeds in peak speed the other subordinate calculations based on a mathematical model embodying these effects show that as with naturally occurring sand waves the degree of sand wave morphological asymmetry increases with growing hydraulic asymmetry it being supposed as a compromise and for simplicity that the streams are of equal duration and simple harmonic in variation but of different peak speeds the calculated sand waves are translatory and their steeper side faces in the direction of the dominant tidal stream and the net bedload transport as would appear to be the case for naturally occurring forms however the precise form of the increase of morphological asymmetry with hydraulic asymmetry together with the bounds on the existence field for sand waves is influenced by the magnitude of the bed material entrainment threshold relative to the peak speeds of the tidal streams the main limitations on the model are its severely simplified treatment of flow and bedload transport over sand waves and the lack of empirical data by which to test the proposed bed steepness effects

emplacement age and direction of the lycian nappes in the soke selcuk region western turkey in the soke selcuk region western turkey the northernmost exposures of the lycian nappes are found as tectonic slices on the menderes massif the menderes massif is represented by a continuous platform sequence and a blocky unit the lower parts of the menderes platform sequence is composed of triassic jurassic marbles and an alternation of calcschists and micaschists however the upper parts are composed of emery and rudist bearing massive marbles along a gradational boundary a blocky unit is found on top of the platform sequence and it comprises blocks of metaophiolite and emery bearing marble set in garnet micaschists matrix along a low angle fault marked by thin slices of red green phyllites tectonic slices of the lycian nappes overlay garnet micaschists of the massif the lycian nappes are represented mainly by a carbonate sequence which consists of dolomites oncoidal limestones intraformational limestone conglomerates and cherty limestones in the carbonate sequence of the lycian nappes undeformed primary structures are clearly observed just several meters above the sole fault indicating a metamorphic break between the lycian nappes and the menderes massif the linear fabric in red green phyllites at the sole of the lycian nappes trends nne ssw gently plunges to ssw and nne and is parallel to the linear fabric of the neotectonic period in the western turkey s c relation suggests top to the ssw sense of shear in red green phyllites the deformation localized along the sole of the tectonic slices indicates that the red green phyllites acted as a decollement surface the deformational features stratigraphic relations orientation of linear fabric and metamorphic break reveal that lycian nappes were emplaced on the menderes massif along a low angle normal fault after the early to middle eocene main menderes metamorphism and prior to the deposition of the middle miocene sedimentary cover

the concept of transport capacity in geomorphology the notion of sediment transport capacity has been engrained in geomorphological and related literature for over 50 years although its earliest roots date back explicitly to gilbert in fluvial geomorphology in the 1870s and implicitly to eighteenth to nineteenth century developments in engineering despite cross fertilization between different process domains there seem to have been independent inventions of the idea in aeolian geomorphology by bagnold in the 1930s and in hillslope studies by ellison in the 1940s here we review the invention and development of the idea of transport capacity in the fluvial aeolian coastal hillslope debris flow and glacial process domains as these various developments have occurred different definitions have been used which makes it both a difficult concept to test and one that may lead to poor communications between those working in different domains of geomorphology we argue that the original relation between the power of a flow and its ability to transport sediment can be challenged for three reasons first as sediment becomes entrained in a flow the nature of the flow changes and so it is unreasonable to link the capacity of the water or wind only to the ability of the fluid to move sediment secondly environmental sediment transport is complicated and the range of processes involved in most movements means that simple relationships are unlikely to hold not least because the movement of sediment often changes the substrate which in turn affects the flow conditions thirdly the inherently stochastic nature of sediment transport means that any capacity relationships do not scale either in time or in space consequently new theories of sediment transport are needed to improve understanding and prediction and to guide measurement and management of all geomorphic systems

neotethyan closure history of western anatolia a geodynamic discussion this paper addresses the lithosphere scale subduction collision history of the eastern termination of the aegean retreating subduction system i e western anatolia although there is some general consensus on the protracted subduction evolution of the aegean since the early cenozoic at least correlation with western anatolia has been widely debated for more than several decades in western anatolia three main tectonic configurations have been envisaged in the past years to reconstruct slab dynamics during the closure of the neotethyan oceanic realm since the late cretaceous some authors have suggested an aegean type scenario with the continuous subduction of a single lithospheric slab punctuated by episodic slab roll back and trench retreat whereas others assumed a discontinuous subduction history marked by intermittent slab break off during either the campanian ca 75 ma or the early eocene ca 55 50 ma the third view implies three partly contemporaneous subduction zones our review of these models points to key debated aspects that can be re evaluated in the light of multidisciplinary constraints from the literature our discussion leads us to address the timing of subduction initiation the existence of hypothetical ocean basins the number of intervening subduction zones between the taurides and the pontides the palaeogeographic origin of tectonic units and the possibility for slab break off during either the campanian or the early eocene thence we put forward a favoured tectonic scenario featuring two successive phases of subduction of a single lithospheric slab and episodic accretion of two continental domains separated by a continental trough representing the eastern end of the cycladic ocean of the aegean the lack of univocal evidence for slab break off in western anatolia and southward younging hp lt metamorphism in continental tectonic units from 85 70 to 50 ma in the late cretaceous palaeogene period suggests continuous subduction since 110 ma marked by roll back episodes in the palaeocene and the oligo miocene and slab tearing below western anatolia during the miocene

disturbance caused by bed sills on the slopes of steep streams live bed tests on steep bed slopes are run in a laboratory flume to investigate the slope of equilibrium the tests simulate a general degradation until a new equilibrium is reached subsequently different bed sill settings are tested as a countermeasure against degradation evidence is presented that in some cases the bed slope with sills is milder than the one without sills under the same flow and sediment rates this fact implies that the efficiency of the bed sill system to stop degradation decreases as the sills are placed closer together tests are on the verge of sheet flow and friction factors are heavily dependent on sediment transport reaches in uniform and gradually varied flow behave very differently bed profiles are not straight and grain size is linked to this fact other detailed information on testing equipment experimental program time development and local scour in a total number of 111 tests is given

numerical simulation of dune flat bed transition and stage discharge relationship with hysteresis effect 1 this work presents recent advances on morphodynamic modeling of bed forms under unsteady discharge this paper includes further development of a morphodynamic model proposed earlier by giri and shimizu 2006a this model reproduces the temporal development of river dunes and accurately replicates the physical properties associated with bed form evolution model results appear to provide accurate predictions of bed form geometry and form drag over bed forms for arbitrary steady flows however accurate predictions of temporal changes of form drag are key to the prediction of stage discharge relation during flood events herein the model capability is extended to replicate the dune flat bed transition and in turn the variation of form drag produced by the temporal growth or decay of bed forms under unsteady flow conditions some numerical experiments are performed to analyze hysteresis of the stage discharge relationship caused by the transition between dune and flat bed regimes during rising and falling stages of varying flows the numerical model successfully simulates dune flat bed transition and the associated hysteresis of the stage discharge relationship this is in good agreement with physical observations but has been treated in the past only using empirical methods a hypothetical relationship for a sediment parameter the mean step length is proposed to a first level of approximation that enables reproduction of the dune flat bed transition the proposed numerical model demonstrates its ability to address an important practical problem associated with bed form evolution and flow resistance in varying flows

bed load motion at high shear stress dune washout and plane bed flow sediment motion at high shear stress is investigated in a pressurized conduit system the bed materials include three sands and bakelite as the dimensionless shear stress was increased toward unity the steepness of the bedforms disappeared abruptly this behavior is indicative of a sudden shift from the bedform regime to the upper plane bed regime not a gradual transition the results for the upper plane bed regime reveal that this type of flow has a larger frictional resistance than that of a conventional rough boundary also determined is that frictional characteristics of the bedform regime cannot be expressed solely in terms of dimensionless shear stress the observed behavior also suggests that as a solid transport mechanism sand waves may be more efficient than upper plane bed flow

boundary layer dynamics and sediment transport under storm and non storm conditions on the scotian shelf abstract near bed measurements of waves currents seabed responses and ripple migration rates were obtained using an instrumented tripod at a water depth of 39 m on the scotian shelf during the winter of 1992 93 these data and the grant and madsen s 1986 grant w d madsen o s 1986 the continental shelf bottom boundary layer annu rev fluid mech 18 265 305 combined flow boundary layer model are used to examine wave current interaction various sediment dynamic thresholds and sediment transport on an exposed high energy continental shelf the seabed was found to be rippled for most time of the deployment and thus the ripple enhanced combined skin friction shear velocity had to be used to determine the initiation of bedload transport under combined flows this indirectly indicates adequate predictions of the skin friction shear velocities inside the wave boundary layer by the grant and madsen model at high transport stages bedload roughness must be added to the grain size roughness to obtain a transportrelated combined shear velocity in order to predict correctly the onsets of saltation suspension and sheet flow transports otherwise the initiation of suspended load transport and the total sediment transport rates will be severely under estimated the comparison between the prediction by the grant and madsen 1986 model and the calculation of a quadratic stress law suggests that the total current shear velocity was enhanced by a factor of 2 3 due to the wave current interaction during storms while the apparent bottom roughness was increased by more than an order of magnitude the non linear coupling between waves and currents also causes a 20 increase of the combined skinfriction shear velocity inside the wave boundary layer this non linear coupling is most important when waves and currents are roughly equal in magnitude and the angles between them are less than 30 four sediment transport formulae were tested while the engelund hansen total load and yalin bedload methods did not perform well the einstein brown and bagnold formulae were found to respectively give reasonable predictions of the bedload and total load sediment transport rates under the observed combined flow conditions the predicted sediment transport direction is also in good agreement with the observed ripple migration direction the gsc sediment transport model sedtrans92 predicts that the net daily transport rates during the storms reached 822 kg m 1 day 1 and were 2 3 orders of magnitude higher than the non storm transport suggesting the dominance of storm processes in sediment transport on the scotian shelf these values are in good agreement with the results from sand tracer experiments conducted in this region we thus conclude that sedtrans92 can properly simulate boundary layer dynamics and sediment transport on continental shelves

lateral and vertical facies relationships of bedforms deposited by aggrading supercritical flows from cyclic steps to humpback dunes abstract the preservation of bedforms related to supercritical flows and hydraulic jumps is commonly considered to be rare in the geologic record although these bedforms are known from a variety of depositional environments this field based study presents a detailed analysis of the sedimentary facies and stacking pattern of deposits of cyclic steps chutes and pools antidunes and humpback dunes from three dimensional outcrops the well exposed middle pleistocene successions from northern germany comprise glacilacustrine ice contact subaqueous fan and glacial lake outburst flood deposits the studied successions give new insights into the depositional architecture of bedforms related to supercritical flows and may serve as an analogue for other high energy depositional environments such as fluvial settings coarse grained deltas or turbidite systems deposits of cyclic steps occur within the glacial lake outburst flood succession and are characterised by lenticular scours infilled by gently to steeply dipping backsets cyclic steps formed due to acceleration and flow thinning when the glacial lake outburst flood spilled over a push moraine ridge these bedforms are commonly laterally and vertically truncated and alternate with deposits of chutes and pools and antidunes the subaqueous fan successions are dominated by laterally extensive sinusoidal waveforms which are interpreted as deposits of aggrading stationary antidunes which require quasi steady flows at the lower limit of the supercritical flow stage and high rates of sedimentation humpback dunes are characterised by downflow divergent cross stratification displaying differentiation into topsets foresets and bottomsets and are interpreted as deposited at the transition from subcritical to supercritical flow conditions or vice versa gradual lateral and vertical transitions between humpback dunes and antidune deposits are very common the absence of planar parallel stratification in all studied successions suggests that the formation of these bedforms is suppressed in flows characterised by hydraulic jumps under highly aggradational conditions the large scale lateral and vertical successions of bedforms are interpreted as representing the temporal and spatial evolution of the initial supercritical flows which was strongly affected by the occurrence of hydraulic jumps small scale facies changes and the formation of individual bedforms are interpreted as controlled by fluctuating discharge bed topography and pulsating unstable flows

understanding river dune splitting through flume experiments and analysis of a dune evolution model forecasts of water level during river floods require accurate predictions of the evolution of river dune dimensions because the hydraulic roughness of the main channel is largely determined by the bed morphology river dune dimensions are controlled by processes like merging and splitting of dunes particularly the process of dune splitting is still poorly understood and as a result not yet included in operational dune evolution models in the current paper the process of dune splitting is investigated by carrying out laboratory experiments and by means of a sensitivity analysis using a numerical dune evolution model in the numerical model we introduced superimposed trias ripples i e triangular asymmetric stoss side ripples on the stoss sides of underlying dunes as soon as these stoss sides exceed a certain critical length simulations with the model including dune splitting showed that predictions of equilibrium dune characteristics were significantly improved compared to the model without dune splitting as dune splitting is implemented in a parameterized way the computational cost remains low which means that dune evolution can be calculated on the timescale of a flood wave subsequently we used this model to study the mechanism of dune splitting literature showed that the initiation of a strong flow separation zone behind a superimposed bedform is one of the main mechanisms behind dune splitting the flume experiments indicated that besides its height also the lee side slope of the superimposed bedform is an important factor to determine the strength of the flow separation zone and therefore is an important aspect in dune splitting the sensitivity analysis of the dune evolution model showed that a minimum stoss side length was required to develop a strong flow separation zone

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

origin of the allochthons in the lycien belt southwest turkey abstract the lycien belt of southwest turkey lies between the menderes metamorphic massif to the northwest and the bey da lari carbonate platform to the southeast the belt is characterized by thrust faults melanges and peridotites stratigraphic and structural relationships suggest that the allochthons of the lycien belt were derived from two distinct tectonic terrains the koyce iz and elmali thrust slices were from south of the massif the tefenni nappe originated far north of the menderes massif the latter incorporates platform sediments melanges and ophiolites represent the edge of a continental platform opening into the tethys oceanic realm correlation of the elmali and koyce iz thrust slices and autochthonous tectonic elements shows that the lycien belt between the menderes massif and the bey da lari was a tectonically active zone of weakness the belt which may be at the extension of the ionian zone was subjected to repeated cycles of deep basin subsidence and intense deformation in triassic jurassic early cretaceous and tertiary times the tefenni nappe passed over the menderes massif and emplaced onto the lycien terrain in the late eocene the lycien terrain was subsequently fragmented and overthrusted southeastward onto the bey da lari shelf sediments in late miocene time

transition between two bed load transport regimes saltation and sheet flow in the saltation regime where bed shear stress is low bed load moves by sliding rolling and saltating along the bed while in the sheet flow regime where bed shear stress is high it travels by a combination of saltation and sheet flow in this paper a theoretical model is developed for predicting the onset of the sheet flow regime as shear stress increases this model is based on a new variable pb representing the proportion of grains on the bed that are entrained as bed load the model yields the equation pb 2 56g 3 in which g 1 c dimensionless bed shear stress and c critical value of at which grains begin to move the equation shows that t which is the value of at the onset of the sheet flow regime and is assumed to occur when pb 1 is around 0 5 with the exact value controlled by c for example when c 0 045 t 0 52 the theoretical model is verified by performing a nonlinear regression analysis on data from 285 flume experiments additional flume experiments with a high speed video hsv system result in consistent values of for the onset of the sheet flow regime which support the theoretical model the hsv images further reveal that 1 the sheet flow regime is characterized by granular sheets or laminations and 2 a zone of mixed saltation and rolling grains exists not only in the saltation regime but also in the sheet flow regime

a simple model of unsteady sheet flow sediment transport a simple quasi steady one dimensional vertical 1dv model of unsteady sheet flow is presented the central aim is to provide greater realism in the near bed high concentration layer than is possible using models based on the classical referenceconcentration approach this is achieved by tracking erosion and deposition at the bottom of the mobile sediment layer in relation to the amount of sediment present in the sheet flow and suspension layers the model relies on empirical assumptions for the time varying sheet flow layer thickness d and time varying equivalent bed roughness ks the formulations adopted yield realistic instantaneous vertical profiles of velocity and sediment concentration from the stationary bed through the highconcentration sheet flow layer up into the outer suspension layer the suspension layer itself is modelled using a standard k e turbulence closure scheme together with the sediment continuity equation matching conditions are applied at the interface between the sheet flow and suspension layers preliminary results presented here include initial validation comparisons with the data set of horikawa et al horikawa k watanabe a katori s 1982 sediment transport under sheet flow conditions proceedings of the 18th international conference on coastal engineering cape town asce reston va usa 1335 1352 further comparisons with the experiments of dohmen janssen et al j geophys res 106 2001 27103 cover a wide range of wave current conditions and sand grain sizes the results are satisfactory with respect to the measured velocity and concentration profiles apart from cases involving fine sand for which the effects of flow unsteadiness are not accounted for in the formulation in addition the new model provides satisfactory predictions of sand transport rates d 2003 elsevier science b v all rights reserved

cross shore suspended sediment transport in the surf zone a field based parameterization existing cross shore sediment transport models for two dimensional surf zone bathymetries almost invariably predict offshore directed sand transports and bar migrations during storm conditions however onshore directed suspended sediment fluxes and associated nearshore bar migration were observed during recent field experiments on a gently sloping beach on the danish north sea coast field measurements of suspended sediment flux obtained during three experiments on two different beaches are used to parameterize the observed fluxes this parameterization predicts suspended sediment transport due to incident waves and undertow across bars in two dimensional surf zones first a non dimensional sediment flux index is formulated which describes the tendency towards net onshore or offshore transport and the strength of that tendency the non dimensional formulation circumvents the problem of measurement inconsistencies due to varying elevations of sediment concentration sensors relative to the bed the index is found to depend upon the undertow velocity the incident wave skewness and the cross correlation between orbital velocity and sediment concentration however some of these parameters are difficult to predict particularly in barred surf zones and therefore the independent variables are recast in terms of a set of more easily obtainable parameters the sediment flux index depends on a combination of the following non dimensional bed shear stress the shields parameter relative water depth wave orbital velocity relative wave height and bed slope finally a formulation of suspended sediment transport across bars is obtained by linking the flux index with a parameterization of the sediment concentration distribution in the water column these concentrations are found to depend on non dimensional bed shear stress relative wave height and water depth the formulation predicts a tendency for onshore directed sediment transport due to incident waves on gently sloping beaches and or with large bed shear stresses on steeply sloping beaches and or in the inner part of the surf zone there is a tendency towards offshore sediment transports due to the undertow

behavious of mobile beds at high shear stress beds of granular material show various types of behaviour as the dimensionless shear stress or shields ordinate y is increased this quantity is defined as r pg s l d where r is boundary shear stress p is fluid density g is gravitational acceleration s is the ratio of solids density to fluid density and d is particle diameter no movement occurs until y exceeds a critical value as y is increased beyond the critical sand waves form first increasing and then decreasing in steepness with successive increases in y finally in the highshear stress region say y 0 8 the bed becomes plane or exhibits antidunes in cases of critical or supercritical free surface flow this high stress condition sometimes called the upper plane bed region may be encountered for rivers in flood large flows in estuaries and closures or breaches of cofferdams or dykes because of the very high rates of sediment transport this type of flow has a disproportionate effect on both natural topographic features and engineering works it is not easy to investigate this behaviour by traditional flume experiments but the use of enclosed pressurised conducts can eliminate many of the experimental difficulties wilson 1966

comparisons of sidewall correction of bed shear stress in open channel flows when investigating sediment transport in laboratory open channel flows it is often necessary to remove sidewall effects for computing effective bed shear stress previous sidewall correction methods are subject to some assumptions that have not been completely verified and different values of the bed shear stress may be obtained depending on the approach used in making sidewall corrections this study provides a quantitative assessment of the existing correction procedures by comparing them to a new sidewall correction model proposed in this study the latter was derived based on the shear stress function and equivalent roughness size for both rigid and mobile bed conditions which were obtained directly from experimental measurements the comparisons show that the einstein correction formula and the vanoni and brooks method generally predict relatively lower and higher bed shear stresses respectively while the williams empirical function leads to more scatter this study also demonstrates that the widely used vanoni and brooks approach can be well approximated by a simple formula derived based on the blasius resistance function the sidewall effects when removed in the different ways would consequently affect the presentation of the bedload function experimental results of bedload transport when plotted as the dimensionless transport rate against the dimensionless shear stress with the latter being corrected using the present model exhibit less scatter than those associated with the previous procedures

toarcian radiolaria from mt mangart slovenian italian border and their paleoecological implications abstract diverse and well preserved toarcian radiolarians have been recovered from a succession of organic rich shale with intercalations of siliceous limestone the succession is located at the slovenian italian border in the julian alps and was deposited on a subsided block pertaining to the south tethyan passive continental margin twenty spumellarian and 17 nassellarian genera were found in total thirty six taxa were identified to species level and one new species bistarkum mangartense n sp is described the assemblages show a high predominance of spumellarians over nassellarians spongy spumellarians especially orbiculiforma are markedly abundant pantanelliidae are generally rare but reach a pronounced peak of 13 in one stratigraphic level among nassellarians parahsuum is the most abundant but members belonging to syringocapsidae are scarce to absent in addition to paleolatitude and water column depth ecological conditions accompanying the early toarcian global anoxic event may have to a considerable extent determined the specific taxonomic composition of these radiolarian faunas

literature review of sand transport by wind on a dry sand surface abstract a critical and comprehensive literature survey of sand transport by wind on a dry sand surface is made from the perspective of engineering use principal findings are 1 most predictive expressions for the sand transport rate show a cubic dependence on the shear velocity or obey a similar power law 2 some difference is found in the value of the multiplicative empirical coefficient in the various formulas and much of the scatter may be ascribed to relative trap efficiency 3 verification of predictive formulas has mainly rested on laboratory measurements and reliable but limited field verification has not been made until recently 4 the laboratory and field data indicate that both the bagnold and the kawamura formulas are applicable to a well sorted sand and can be used for estimation of wind blown sand transport on dry natural beaches modifications have been made for a widely distributed sand and for fluctuating wind velocity

the effect of surface moisture on the entrainment of dune sand by wind an evaluation of selected models reliable predictions of wind erosion depend on the accuracy of determining whether erosion occurs or not among the several factors that govern the initiation of soil movement by wind surface moisture is one of the most significant some widely used models that predict the threshold shear velocity for particle detachment of wet soils by wind were critically reviewed and evaluated wind tunnel experiments were conducted on pre wetted dune sand with moisture contents ranging from 0 00 to 0 04 kg kg 1 sand samples were exposed to different wind speeds for 2 min moisture content was determined gravimetrically before and after each experiment and the saltation of sand particles was recorded electronically with a saltiphone shear velocities were deduced from the wind speed profiles for each moisture content the experiments were repeated at different shear velocities with the threshold shear velocity being determined by least squares analysis of the relationships between particle number rates and shear velocity within the 2 min test runs temporal changes in particle number rates and moisture contents were detected a steep increase in the threshold shear velocity with moisture content was observed when comparing the models large differences between the predicted results became apparent at a moisture content of 0 007 kg kg 1 which is half the moisture content retained to the soil matrix at a water tension or matric potential of 1 5 mpa the increase in wet threshold shear velocity predicted with the different models relative to the dry threshold shear velocity ranged from 117 to 171 the highest care should therefore be taken when using current models to predict the threshold shear velocity of wet sediment nevertheless the models of chepil 1956 proc soil sci soc am 20 288 292 and saleh fryrear 1995 soil sci 160 304 309 are the best alternatives available