high resolution numerical modelling of three dimensional flows over complex river bed topography this paper describes preliminary results from a method for the treatment of complex bed topography for the understanding of three dimensional flow processes it develops an established porosity based method and couples it to high resolution bed topographical data acquired using digital photogrammetry the results provide quantitative data on flow processes that match and perhaps exceed current measurement capabilities and so raise difficult questions for model validation however the detailed flow fields provided by the method allow us to develop current models for flow form interactions in gravel bed rivers of most importance the method will allow us to enhance significantly the application of computational fluid dynamics to complex river bed morphology for large eddy simulation roughness parameterization sediment entrainment and deposition studies and understanding interactions between flow and vegetation in relation to conveyance studies copyright 2002 john wiley sons ltd

embryo dune development on a large actively accreting macrotidal beach calais north sea coast of france sediment budget data from an 18 month topographic survey were analysed with data from brief experiments on wind parameters beach moisture contents bedforms and sand mobilization in order to monitor conditions and patterns of embryo dune development over a flat 150 1000 m wide accreting upper beach the surface conditions over the upper beach locally affect aeolian transport but net dune development over time depends on sustained strong winds and their orientation incoming marine sand supplied by storms and onshore winds is reorganized by the dominant offshore to longshore winds into elongated embryo dunes over this upper beach imprinting a regional morphology of long term longshore dune ridge development copyright 2006 john wiley sons ltd

simulation and measurement of surface shear stress over isolated and closely spaced transverse dunes in a wind tunnel topographic interactions generate multidirectional and unsteady air ow that limits the application of velocity pro le approaches for estimating sediment transport over dunes results are presented from a series of wind tunnel simulations using irwin type surface mounted pressure sensors to measure shear stress variability directly at the surface over both isolated and closely spaced sharp crested model dunes findings complement existing theories on secondary air ow effects on stoss transport dynamics and provide new information on the in uence of lee side air ow patterns on dune morphodynamics for all speeds investigated turbulent unsteadiness at the dune toe indicates a greater more variable surface shear despite a signi cant drop in time averaged measurements of streamwise shear stress at this location this effect is believed suf cient to inhibit sediment deposition at the toe and may be responsible for documented intermittency in sand transport in the toe region on the stoss slope streamline compression and ow acceleration cause an increase in ow steadiness and shear stress to a maximum at the crest that is double that at the toe of the isolated dune and 60 70 per cent greater than at ow reattachment on the lower stoss of closely spaced dunes streamwise ow accelerations rather than turbulence have greater in uence on stress generation on the stoss and this effect increases with stoss slope distance and with incident wind speed reversed ow within the separation cell generates signi cant surface shear 30 40 per cent of maximum values for both spacings this supports eld studies that suggest reversed ow is competent enough to return sediment to the dune directly or in a de ected direction high variability in shear at reattachment indicates impact of a turbulent shear layer that despite low values of time averaged streamwise stress in this region would inhibit sediment accumulation downwind of reattachment shear stress and ow steadiness increase within 6 h h dune height of reattachment and approach upwind values by 25 h a distance of at least 30 h is suggested for full boundary layer recovery which is comparable to uvial estimates the irwin sensor used in this study provides a reliable means to measure skin friction force responsible for sand transport and its robust simple and cost effective design shows promise for validating these ndings in natural dune settings copyright 2003 john wiley sons ltd

coastal foredune topography as a control on secondary airflow regimes under offshore winds aeolian sediment transport under offshore winds is usually discounted from sediment budget considerations of coastal dunes results presented here indicate however that depending on wind orientation and foredune morphology positive contributions to the sediment budget can arise from offshore winds lee side airflow patterns seaward of the foredune crest under offshore winds were studied at three sites of varying foredune geometry along magilligan strand northern ireland ultrasonic anemometers recorded 1 hz wind velocity data at 1 intervals descriptive statistics and wind rose diagrams were used in the analysis of these data under perpendicularly offshore winds each site exhibited a different type of lee side airflow pattern a tall 11 4 m sharp crested foredune produced flow separation with a recirculation cell a lower 6 6 m more rounded foredune crest exhibited lee side flow that remained attached but was deflected parallel to the crest while flow over a low incipient foredune crest resulted in attached flow with no deflection in the lee the morphology of the lee slopes best explained these airflow adjustments more obliquely offshore winds were also found to affect the secondary airflow patterns with a smooth transition from flow separation to flow attachment as the incident angle decreased at higher wind velocities this smooth transition was replaced with a more abrupt switch between the secondary airflow types this threshold was located at similar approach angles to those recorded for desert dunes 90 20 these findings have significant implications for the post storm recovery and long term evolution of beach dune systems where the predominant winds are offshore and offer an explanation for the presence of many beach dune systems in lee coast locations copyright 2010 john wiley sons ltd

geological control of beach morphodynamic state the concept of beach morphodynamic states has achieved widespread acceptance in the coastal geological literature since its inception in the mid 1980s and expansion in the 1990s much of the pioneering work was undertaken in australia under a range of environmental conditions in microtidal environments and a close empirical relationship between beach 3 dimensional morphology and the dean s parameter h b wst was established subsequently the relative tidal range parameter h b tr was extended to beaches of all tidal ranges in this paper observations are presented from 25 beaches around the north coast of ireland these beaches exist on an environmental gradient that encompasses marked tidal and wave energy variability micro to macrotidal and low to high wave energy each beach was visually categorised into one of several established beach states described in the literature on the basis of field observations for each beach the rtr and dean s parameter were calculated for the immediately antecedent period and used to predict the beach state using published relationships observed and predicted beach states were then compared comparison of observed and predicted beach states showed that while beaches with observed dissipative morphology typically matched the expected criteria most other beach states did not lack of agreement between predicted and observed beach states has been reported elsewhere and attributed to failings in the rtr and dean s parameter in addition this study identifies geological factors as important constraints on actual beach state in the majority of beaches studied inherited geological factors appear to be more important determinants of beach morphology than contemporary dynamics c 2005 elsevier b v all rights reserved

application of the equilibrium planform concept to natural beaches in northern ireland the equilibrium planform concept epc for bayed beaches has achieved wide currency in coastal morphodynamics the north coast of ireland comprises a series of discrete headland embayment beaches within which waves and currents recycle a finite sediment volume it is therefore an ideal setting in which to explore the applicability of the concept application of the approach to 9 embayment beaches on the north coast of ireland provides some insights into the application of the concept the planform of some beaches does correspond to that predicted while others do not those whose measured planform does not correspond to the predicted planform can be interpreted through a difficulty in identifying the wave diffraction point b disequilibrium on the beach sediment scarcity or excess c geological control of beach morphology the subjectivity in selecting the diffraction point renders alternative explanations difficult and reduces the utility of the approach on natural shorelines where significant irregularities render identification of such points difficult

computational fluid dynamics modelling of boundary roughness in gravel bed rivers an investigation of the effects of random variability in bed elevation results from a series of numerical simulations of two dimensional open channel flow conducted using the computational fluid dynamics cfd code fluent are compared with data quantifying the mean and turbulent characteristics of open channel flow over two contrasting gravel beds boundary roughness effects are represented using both the conventional wall function approach and a random elevation model that simulates the effects of supra grid scale roughness elements e g particle clusters and small bedforms results obtained using the random elevation model are characterized by a peak in turbulent kinetic energy located well above the bed typically at y h 0 1 0 3 this is consistent with the field data and in contrast to the results obtained using the wall function approach for which maximum turbulent kinetic energy levels occur at the bed use of the random elevation model to represent supra grid scale roughness also allows a reduction in the height of the near bed mesh cell and therefore offers some potential to overcome problems experienced by the wall function approach in flows characterized by high relative roughness despite these benefits the results of simulations conducted using the random elevation model are sensitive to the horizontal and vertical mesh resolution increasing the horizontal mesh resolution results in an increase in the near bed velocity gradient and turbulent kinetic energy effectively roughening the bed varying the vertical resolution of the mesh has little effect on simulated mean velocity profiles but results in substantial changes to the shape of the turbulent kinetic energy profile these findings have significant implications for the application of cfd within natural gravel bed channels particularly with regard to issues of topographic data collection roughness parameterization and the derivation of mesh independent solutions copyright 2001 john wiley sons ltd

airflow up the stoss slope of sand dunes limitations of current understanding the windward stoss side of a sand dune acts as a streamlined obstacle in the path of the wind continuity principles necessitate compression of the flow field up the stoss slope of a dune and shear stress must progressively increase as the flow accelerates measurements in transverse flow over thirteen dunes at padre island texas the algodones california and white sands new mexico confirm that velocity profiles on the stoss slope are not log linear and that flow acceleration occurs very close to the surface within an internal boundary layer as a consequence in the overlying flow where measurements have historically been made an overall decrease in shear stress occurs up the slope the actual shape of the velocity profiles and the identification of the appropriate segment of the profile from which to derive the shear stress that drives saltation represent major problems not approachable by traditional means

meso scale aeolian sediment input to coastal dunes the nature of aeolian transport events abstract observations of aeolian transport in coastal areas have focused on short term experiments because of limitations imposed by instrumentation this paper uses a case study at greenwich dunes prince edward island national park canada to analyze how sediment transport takes place at the beach over periods of weeks to months a monitoring station provided hourly time series of vegetation cover shoreline position fetch distances surficial moisture content presence of ice and snow wind speed and direction and transport processes over nine months analysis shows that high wind speeds may not generate any net transport into the dunes because of the limitations imposed by snow ice cover moisture and short fetch distances despite extreme winds during intense storms such events often lead to wave scarping rather than aeolian sediment input to the foredunes when sediment was transported on the beach the magnitude was regulated by a combination of factors including angle of wind approach fetch distance moisture content and duration of the wind event in particular angle of wind approach and therefore fetch distance may demote a high magnitude wind event with strong transport potential to one with no transport at all which poses challenges for predicting the effects of individual storms over the course of several months a significant proportion of sediment delivery to the foredunes was associated with wind events of low to medium magnitude it is suggested here that large magnitude wind events have low probabilities of resulting in transport towards the foredune because factors such as wave inundation play an increasing role in preventing sediment movement across the beach this has implications for modelling and management and highlights differences between the magnitude and frequency of aeolian transport events in the coastal environment compared to those in deserts and to fluvial sediment transport

rates of sediment accumulation in pollen cores from small lakes and mires of eastern north america abstract data from 291 small lakes and mires in eastern north america provide information on the natural variability of rates of sediment accumulation in these environments over the last 18 000 yr accumulation rates were calculated by linear interpolation between radiocarbon and biostratigraphic dates from sediment cores taken for pollen analysis within the data set the rates were lognormally distributed with a mean accumulation rate of 91 cm 103 yr and a range from less than 1 to over 3500 cm 103 yr the accumulation rate data were divided into five subsets that were temporally or spatially distinct and therefore represent different geomorphic and climatic conditions at the time of deposition sediments deposited in basins north of 50 n south of 40 n and before 10 000 yr b p accumulated at much slower rates than sediments accumulating in midlatitude basins between 40 and 50 n between 10 000 and 330 yr b p sediment accumulation over the last 330 yr has on average been at rates four to five times faster than any time previously inorganic sediments that could be radiocarbon dated have accumulated at significantly lower rates than organic sediments reflecting differences in depositional processes for midlatitude basins during the holocene the most likely rate of continuous sediment accumulation within our data set is 65 cm 103 yr rates below 10 cm 103 yr are likely to be associated with nonconstant processes of sediment accumulation

the geomorphological significance of airflow patterns in transverse dune interdunes abstract the interdunes between aeolian dunes have been relatively ignored when compared with the research attention on the morphodynamics of the dune bodies themselves this neglect is in spite of the possible significance of interdune dynamics for the geomorphology of the sand dune system as a whole especially with regard to dune spacing this paper considers the mean airflow within four relatively simple transverse dune interdunes the study locations were chosen in order to sample interdunes with different size and surface characteristics the dynamics of which were investigated for when incident flow was normal to the upwind crest the findings confirm existing models of flow reattachment length and recovery for aeolian dune lee side flow and show a consistent pattern of increasing near surface velocity downwind of reattachment that supports a mechanism for interdunes as sand free features flow dynamics are characterised for the different types of interdune observed where two groups are recognised the flow patterns in relatively short interdunes where dunes are closely spaced with a sandy surface were accordant with those of the flow response model in extended interdunes where bounding dunes were spaced with a length well over that for flow separation evidence at the downwind edge of the interdunes suggested that flow reacted to the subsequent dune for the case of these extended interdunes a new descriptive model is presented to characterise their dynamics in this model the variation in near surface flow allowed process zones to be identified through the interdune the geomorphological significance of the processes dominating each zone is discussed and comparisons are made between the flow response case and the new interdune model from this study in a discussion on the controls of spacing between dunes where reattachment length exerts a fundamental control the role of sediment availability is also highlighted as a significant factor the presence of a sandy bed can in some circumstances determine whether dune development and therefore spacing is controlled primarily by elements of flow response

a new instantaneous aeolian sand trap design for field use a new aeolian sediment trap is described which can give up to 1 hz measurement frequency in held conditions the trap adopts a circular horizontal trap design with a load cell connection to give continuous unobtrusive trap measurement of sediment flux simultaneous velocity recording is carried out using an anemometer trap construction costs are approximately pound 200 initial results in held conditions using a direct comparison of wind velocity data sampled at an equivalent frequency have given a first order relationship between sediment flux and velocity the trap enables simultaneous sampling of wind velocity and sediment flux at a sufficiently short interval to enable investigation of sediment transport dynamics under a variety of field conditions

a wind tunnel study of flow structure adjustment on deformable sand beds containing a surface mounted obstacle roughness elements of varied scale and geometry commonly appear on the surfaces of sedimentary deposits in a wide range of planetary environments they perturb the local fluid flow so that the entrainment transport and deposition of particles surrounding each element is fundamentally altered fluid dynamists have expended much effort in examining the flow structures surrounding idealized elements mounted on fixed planar walls however self regulation occurs in sedimentary systems as a result of the bed surface undergoing rapid topographic modification with sediment transport until it reaches a stable form that enhances the net physical roughness the present wind tunnel study examines how the flow pattern surrounding an isolated cylinder a problem extensively studied in classical fluid mechanics is altered through morphodynamic development of a deep well that envelopes the windward face and side walls of the roughness element spatial patterns in the fluid velocity turbulence intensity and reynolds stress obtained from laser doppler anemometer lda measurements suggest that the flow structures surrounding such a cylinder are fundamentally altered through self regulation of the bed topography as it reaches steady state for example flow stagnation and the turbulent dissipation of momentum are substantially increased at selected points surrounding the upwind face and side walls of the cylinder respectively along the center line of the wake flow to the rear of the cylinder several structures arising from flow separation are annihilated by strong upwelling of the airflow exhausted from the terminus of the well feedback plays a complex time dependent role in this system

toward a model for airflow on the lee side of aeolian dunes the interaction between dunes and the primary wind results in a complex pattern of secondary airflow on the lee side of dunes from 15 dunes studied during transverse flow conditions at padre island in texas white sands in new mexico and the algodones in california distinct flow regions can generally be recognized with the overall flow structure comparing favourably to that proposed for subaqueous bedforms downwind of dunes with flow separation is a back flow eddy that extends about four dune brink heights downwind from the brink of the dune beyond the separation cell the velocity profiles can be divided into regions based upon segments separated by kinks in the velocity profiles the interior is an area above the dunes of relative high wind speed but low velocity gradient beneath the interior is the wake which consists of two layers the upper wake exhibits an uppermost portion where the flow decelerates while the remainder exhibits accelerating flow so that the overall velocity gradient decreases downwind the lower wake exhibits low velocity gradients and wind speeds that accelerate downwind at all heights but primarily near the top of the layer thereby causing the velocity gradient to increase downwind at about eight dune heights downwind the upper and lower wakes equilibrate to a single profile with the kink between them no longer apparent the lowest recognizable region is the internal boundary layer it is recognized by a relatively steep velocity gradient below the wake and never exceeds a few tens of centimetres in height for our data set because of acceleration and increasing shear stress within this layer interdune flats are at least potentially erosional overall the wake and internal boundary layer show a downward transfer of momentum from upper regions so that the flow recovers where flow separation does not occur simple flow expansion down the lee face causes flow deceleration

application of sedimentological analysis to correlation of eroded layers under beaches with local and regional pleistocene stratigraphy a contribution to geological dating of palaeolithic sites northern coast of brittany france a distinctive feature of the palaeolithic of western france is that most of the sites are along the present coast line and that the archaeological layers are often partially eroded and contained in very residual pleistocene silty sediments preserved under the beaches in the absence of radiometric dating correlations with local deposits and reference to a regional chronostratigraphic scale allow proposal of a geological age where direct radiometric or related dating i e osl results exist sedimentological analysis i e descriptive sedimentology can be used either to confirm the dating or to extend the discussion this paper is based on examples which have been processed over thirty years but that had never been the subject of an overall methodological presentation

investigation of three dimensional wind flow behaviour over coastal dune morphology under offshore winds using computational fluid dynamics cfd and ultrasonic anemometry the behaviour of offshore directed winds over coastal dune and beach morphology was examined using a combination of modelling 3 d computational fluid dynamics cfd and field measurement both model simulations and field measurements showed reversal of offshore flows at the back beach and creation of an onshore sediment transport potential the influence of flow reversals on the beach dune transport system and foredune growth patterns has previously received little attention detailed wind flow measurements were made using an extensive array of mast mounted 3 d ultrasonic anemometers 50 hz arranged parallel to the dominant incident wind direction large eddy simulation les of the offshore wind flow over the dune was conducted using the open source cfd tool openfoam the computational domain included a terrain model obtained by airborne lidar and detailed ground dgps measurements the computational grid 22 million cells included localized mesh refinement near the complex foredune terrain to capture finer details of the dune morphology that might affect wind flows on the adjacent beach measured and simulated wind flow are presented and discussed the cfd simulations offer new insights into the flow mechanics associated with offshore winds and how the terrain steering of wind flow impacts on the geomorphological behaviour of the dune system simulation of 3 d wind flows over complex terrain such as dune systems presents a valuable new tool for geomorphological research as it enables new insights into the relationship between the wind field and the underlying topography the results show that offshore and obliquely offshore winds result in flow reversal and onshore directed winds at distances of up to 20m from the embryo dune toe the potential geomorphological significance of the findings are discussed and simple calculations show that incoming offshore and obliquely offshore winds with mean velocities over 13m s 1 and 7m s 1 respectively have the potential to create onshore directed winds at the back beach with mean velocities above 3 3m s 1 these are above the threshold of movement for dry sand and support previous conclusions about the significance of offshore winds in dune and beach budget calculations

wind direction and complex sediment transport response across a beach dune system evidence from a field study on wind flow and sediment transport across a beach dune system under onshore and offshore conditions including oblique approach angles indicates that sediment transport response on the back beach and stoss slope of the foredune can be exceedingly complex the upper air flow measured by a sonic anemometer at the top of a 3 5 m tower located on the dune crest is similar to regional wind records obtained from a nearby meteorological station but quite different from the near surface flow field measured locally across the beach dune profile by sonic anemometers positioned 20 cm above the sand surface flow form interaction at macro and micro scales leads to strong modulation of the near surface wind vectors including wind speed reductions due to surface roughness drag and adverse pressure effects induced by the dune and wind speed increases due to flow compression toward the top of the dune as well as pronounced topographic steering during oblique wind approach angles a conceptual model is proposed building on the ideas of sweet and kocurek sedimentology 37 1023 1038 1990 walker and nickling earth surface processes and landforms 28 111 1124 2002 and lynch et al earth surface processes and landforms 33 991 1005 2008 geomorphology 105 139 146 2010 which shows how near surface wind vectors are altered for four regional wind conditions a onshore detached b onshore oblique attached and deflected c offshore detached and d offshore oblique attached and deflected high frequency measurements of sediment transport intensity during these different events demonstrate that predictions of sediment flux using standard equations driven by regional wind statistics would by unreliable and misleading it is recommended that field studies routinely implement experimental designs that treat the near surface wind field as comprising true vector quantities with speed and direction in order that a more robust linkage between the regional upper air wind field and the sediment transport response across the beach dune profile be established copyright 2012 john wiley sons ltd

airflow and aeolian sediment transport patterns within a coastal trough blowout during lateral wind conditions blowouts are depressions that occur on coastal dunes deserts and grasslands the absence of vegetation in blowouts permits high speed winds to entrain and remove sediment whereas much research has examined patterns of wind flow and sediment transport on the stoss slopes and lee of sand dunes no study has yet investigated the connections between secondary air flow structures and sediment transport in a blowout where zones of streamline compression expansion and steering are less clearly delineated in this study we investigated the variability of sediment flux and its relation to near surface wind speed and turbulence within a trough blowout during wind flow that was oblique to the axis of the blowout wind flow was measured using six three dimensional 3d ultrasonic anemometers while sediment flux by eight sand traps all operating at 25 hz results demonstrated that sediment flux rates were highly variable throughout the blowout deflation basin even over short distances 0 5 m where flow was steadiest flux was greatest consequently the highest rates of sediment transport were recorded on the erosional wall crest where flow was compressed and accelerated the strength of correlation between sediment flux and wind parameter improved with an increase in averaging interval from 10 seconds to 1 minute at an interval of 10 seconds however wind speed correlated best with flux at seven of eight traps whereas at an interval of one minute turbulent kinetic energy tke provided the best correlation with flux at six of the eight traps correlation between sediment flux and wind parameters was best in the centre of the blowout and poorest on the erosional wall crest the evidence from this paper suggests for the first time that tke may be a better predictor of sediment transport at minute scale averaging intervals particularly over landforms where wind flow is highly turbulent

island encapsulating eolian sedimentary systems of the canary and cape verde archipelagos abstract eolian dunes are generally absent or poorly developed on oceanic islands yet large scale eolian sedimentary systems characterize the oceanic islands of the canary and cape verde archipelagos these island encapsulating sedimentary systems extend around or across entire islands and comprise upwind source areas eolian transport corridors and downwind sediment depocenters each of which is characterized by distinctive dune forms upwind beaches are denuded of sand while downwind locations exhibit progressive shoreline accretion cross island transport corridors developed in topographic lows on the island surface are characterized by a variety of landforms including sandsheets barchanoid dunes and transverse dunefields depending on topography and local sediment volume and supply circum island transport corridors develop when the island topography is high and sediment transport takes place on the island margins alternating between headland bypass dunes and longshore transport in the littoral zone in the intervening embayments depocenters comprise extensive eolian dunefields prograding beaches or beach ridges depending on local topography recognition of the interconnected nature of the components of these contemporary systems has important management implications the presence of these sedimentary systems in the canary and cape verde chains can be attributed to a particular combination of geological and geographical factors the thick lithosphere in which the island chains occur slows subsidence rates and creates long lived oceanic islands that are exposed to weathering and erosion for several million years during which terrestrial denudation and biogenic sediment production creates a sufficient volume of littoral sediment from a geographical perspective these islands are in arid or semiarid environments with unidirectional or strongly asymmetrical transport capable winds i e trade winds

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

the role of computational fluid dynamics in understanding shipwreck site formation processes studies indicate that physical processes commonly dominate the initial stages of wreck site formation detailed knowledge and understanding of hydro and sediment dynamics are therefore imperative for studies dealing with site formation and in situ preservation in this investigation the results of computational fluid dynamic modelling over a shipwreck site are presented using a high resolution surface derived from multi beam echo sounder data and boundary conditions constrained by field measurements sediment samples and flow measurements simulation of the 3 dimensional flow velocity field around the wreck site and secondary products derived from the computational model confirm that flow velocity and turbulence are both amplified by the presence of the wreck causing changes in the morphology of the flow regime flow contraction the formation of lee wake vortices behind the structure accompanied by vortex shedding and increased turbulence are all observed shear stress and tke amplification three to four times greater than ambient values are recorded downstream of the wreck structure benefits of this approach for studies of site formation and in situ conservation include the inexpensive open source and desk based nature of the investigation

high resolution measured and modelled three dimensional airflow over a coastal bowl blowout abstract blowouts are common landforms found within coastal dunes their dynamics are primarily driven by aeolian transport caused by surface wind stress though patterns of deflation and deposition within blowouts are poorly understood as near surface wind flow is complex three dimensional wind flows around blowouts have yet to be properly quantified especially within zones of separation re attachment and acceleration this has been largely due to inadequate measurement of airflow and a lack of suitable airflow models with this in mind we present results from a study that has quantified alongshore and oblique onshore wind flow dynamics over a bowl blowout on the belmullet peninsula ireland using ultrasonic three dimensional anemometry measuring at 50 hz and three dimensional computational fluid dynamic cfd modelling we measure and model for the first time in 3d a detailed picture of the heterogeneity of wind flow over this type of terrain during alongshore wind conditions wind speeds within the deflation basin were retarded by 50 compared to the foredune zone and flow separation restricted to a small zone in lee of the windward rim wind was directed into the deflation basin through a gap in a western erosional wall termed the blowout throat in oblique onshore wind airflow orientated with the blowout throat remained unchanged in direction and slowed by only 30 compared to wind speed on the foredune in lee of the erosional wall adjacent to the blowout throat small zones of flow separation occurred close to the erosional wall in both cases the highest variation in wind speed and direction occurred in zones of separation and attachment whilst flow increased in steadiness with height over the erosional walls the results illustrate that wind is manipulated according to localised topography within the bowl blowout itself resulting zones of potential sediment transport erosion and deposition are spatially complex and alter with wind direction the presence of a blowout throat has a significant influence on airflow patterns within a deflation basin modelled cfd and measured anemometer data demonstrated excellent comparisons for wind direction and speed allowing much greater spatial measurement resolution than physical instrumentation simulated turbulence did not correlate well with measured data highlighting the requirement for high frequency three dimensional anemometry in areas of complex flow

formation and behavior of aeolian streamers received 5 december 2004 revised 31 march 2005 accepted 9 june 2005 published 7 september 2005 1 field experiments were conducted to determine the characteristic spatial and temporal dimensions and behavior of aeolian streamers and to identify the processes responsible for their formation an instrument array that included anemometer towers piezo electric transport sensors safires and hot film probes was deployed to measure streamers and airflow dynamics on both a coastal dune and a desert sand mound in california aeolian transport occurs predominantly in the form of families of intertwining and bifurcating streamers while under intense wind forcing more complex patterns of nested streamers and clouds with embedded streamers develop the streamers display a characteristic width of approximately 0 2 m and an average lateral spacing of about 1 m these dimensions appear to be independent of mean airflow characteristics the observations and measurements of streamers under different environmental conditions suggest that bed surface control in the form of differentiation in moisture content grain size or microtopography is not a necessary condition for the formation of streamers the results show little correlation between possible streamwise vortices or burst sweep events and streamers it is proposed that streamers are generated by near surface gusts that originate from large eddies propagating to the ground from higher regions of the boundary layer these elongated and stretched eddies scrape across the surface and initiate saltation along their path this concept accounts for the characteristic size and spacing of streamers their rapid propagation and the fast response of saltation to wind speed fluctuations

the role of streamline curvature in sand dune dynamics evidence from field and wind tunnel measurements abstract field measurements on an unvegetated 10 m high barchan dune in oman are compared with measurements over a 1 200 scale fixed model in a wind tunnel both the field and wind tunnel data demonstrate similar patterns of wind and shear velocity over the dune confirming significant flow deceleration upwind of and at the toe of the dune acceleration of flow up the windward slope and deceleration between the crest and brink this pattern including the widely reported upwind reduction in shear velocity reflects observations of previous studies such a reduction in shear velocity upwind of the dune should result in a reduction in sand transport and subsequent sand deposition this is not observed in the field wind tunnel modelling using a near surface pulse wire probe suggests that the field method of shear velocity derivation is inadequate the wind tunnel results exhibit no reduction in shear velocity upwind of or at the toe of the dune evidence provided by reynolds stress profiles and turbulence intensities measured in the wind tunnel suggest that this maintenance of upwind shear stress may be a result of concave unstable streamline curvature these additional surface stresses are not recorded by the techniques used in the field measurements using the occurrence of streamline curvature as a starting point a new 2 d model of dune dynamics is deduced this model relies on the establishment of an equilibrium between windward slope morphology surface stresses induced by streamline curvature and streamwise acceleration adopting the criteria that concave streamline curvature and streamwise acceleration both increase surface shear stress whereas convex streamline curvature and deceleration have the opposite effect the relationships between form and process are investigated in each of three morphologically distinct zones the upwind interdune and concave toe region of the dune the convex portion of the windward slope and the crest brink region the applicability of the model is supported by measurements of the rate of sand transport and the change of the dune surface in the field

aeolian slipface dynamics and grainflow morphologies on earth and mars abstract in 2015 an active dune field on mars was visited up close by the curiosity rover in gale crater providing the first high resolution ground images of fine scale windblown features not previously resolved from orbital based imagery for the first time these images allow for direct comparison with terrestrial aeolian dynamics and provide critical ground truth data to bridge the gap between model predictions and satellite observations the image data from the slipface on the namib dune within the bagnold dune field shows grainflow morphologies that are similar to dunes on earth quantitative estimates of flow thickness based on shadow length are presented for the grainflows on the namib dune slipface and compared to grainflow characteristics measured by terrestrial laser scans from the maspalomas dune field located in gran canaria spain using observations from maspalomas to support interpretations of martian slipface dynamics we discuss implications for the local wind regime style of grainflow seasonal activity and dune migration the presence of multiple large magnitude grainflows on the namib slipface suggests an active aeolian environment capable of delivering enough sediment to the slipface to initiate these flows and transport sediment to the bottom of the lee slope however the thinness of grainflows on the namib dune the formation of smaller grainflows directly below the dune brink and limited grainfall suggest a lower wind energy environment at least for the most recent slipface activity large actively migrating stoss ripples obliquely oriented to the dune crest regularly deposit sediment on to the upper slipface and may be a mechanism in which larger grainflow occur during seemingly low energy wind events this mechanism of sediment delivery may also explain the existence of a variety of slipface morphologies both young and old which are otherwise quickly erased on earth due to sediment redistribution and grainfall

airflow reversal and alternating corkscrew vortices in foredune wake zones during perpendicular and oblique offshore winds on all sandy coastlines fringed by dunes understanding localised air flow allows us to examine the potential sand transfer between the beach and dunes by wind blown aeolian action traditional thinking into this phenomenon had previously included only onshore winds as effective drivers of this transfer recent research by the authors however has shown that offshore air flow too can contribute significantly through lee side back eddies to the overall windblown sediment budget to coastal dunes under rising sea levels and increased erosion scenarios this is an important process in any post storm recovery of sandy beaches until now though full visualisation in 3d of this newly recognised mechanism in offshore flows has not been achieved here we show for the first time this return flow eddy system using 3d computational fluid dynamics modelling and reveal the presence of complex corkscrew vortices and other phenomena the work highlights the importance of relatively small surface undulations in the dune crest which act to induce the spatial patterns of airflow and transport found on the adjacent beach

morphological and sedimentary features of oblique zibars in the kumtagh desert of northwestern china abstract zibars are coarse grain armored low relief aeolian bedforms with a large spacing but without slipfaces little is known of their morphodynamic processes even though they are ubiquitous at upwind desert margins in this paper we describe the morphological and sedimentary features of oblique zibars in the northeastern kumtagh desert of china analyze the effective wind regime and discuss the significance of the coarse grained sediments for zibar morphology and sedimentary structures due to a mantle of coarse grains oblique zibars and nearby linear dunes respond to different effective wind regimes that result in the angle between their geomorphological trends topographic surveys showed that the spacing of the oblique zibars ranged between 130 5 and 357 5 m and that the height ranged between 0 6 and 3 0 m the oblique zibar surface is almost entirely covered by coarse sand and includes gravel with a particle diameter of up to 2 34 the poorly sorted positively to very positively skewed surface sediments with mean grain size ranging between 0 2 and 1 5 were characterized by a bimodal distribution the spacing between the oblique zibars is closely related to the coarsest 5th percentile of the surface sediments and can potentially be explained by a combination of the saturation length and minimum dune size theories in addition the protectionist theory combined with the surface creep and vibration of coarse grains which allows infiltration of finer materials between the grains may account for the alternating coarse and fine laminae in the oblique zibars

variable and conflicting shear stress estimates inside a boundary layer with sediment transport this paper presents a comparison between two methods for estimating shear stress in an atmospheric internal boundary layer over a beach surface under optimum conditions using wind velocities measured synchronously at 13 heights over a 1 7 m vertical array using ultrasonic anemometry the reynolds decomposition technique determines at a point shear stresses at each measurement height while the law of the wall yields a single boundary layer estimate based on fitting a logarithmic velocity profile through the array data analysis reveals significant inconsistencies between estimates derived from the two methods on both a whole event basis and as time series despite a near perfect fit of the law of the wall the point estimates of reynolds shear stress vary greatly between heights calling into question the assumed presence of a constant stress layer a comparison with simultaneously measured sediment transport finds no relationship between transport activity and the discrepancies in shear stress estimates results do show however that reynolds shear stress measured nearer the bed exhibits slightly better correlation with sand transport rate the findings serve as a major cautionary message to the interpretation and application of single height measurements of reynolds shear stress and their equivalence to law of the wall derived estimates and these concerns apply widely to boundary layer flows in general 2015 the authors earth surface processes and landforms published by john wiley sons ltd