influence of cell size on volume calculation using digital terrain models a case of coastal dune fields abstract in this work we analyze how variation in cell size influences the volume calculated from digital terrain models dtms derived from a lidar light detection and ranging survey in two coastal late holocene dune fields in southern brazil cell size varied from 1 to 100 m rmse root mean square error of the resampled dtms from the original lidar with 0 5 m resolution increases linearly with cell size while r 2 coefficient of determination decreases following a second order trend the volume does not show simple linear or exponential behavior but fluctuates with positive and negative deviations from the original dtm this can be explained by a random factor in the position of the cell with regard to landforms and a relationship between cell and landform size wherein a small change in cell size can lead to an under or overestimation of volume the aster gdem global digital elevation model and x sar srtm shuttle radar topography mission 1 digital elevation models dems were not considered viable volume sources due to large deviations from the reference data either as a consequence of noise in the srtm x sar data or lack of bias elevation correction to a common reference base in the gdem processing chain volumes from a 3 arcsec sir c srtm deviated around 5 from the reference data and are considered suitable input for numerical simulations of quaternary dune field evolution models because these values should be within the expected range of sediment volume changes over hundreds to millions of years

regional aeolian dynamics and sand mixing in the gran desierto evidence from landsat thematic mapper images spatial variations in sand composition were mapped on a regional scale in a terrestrial sand sea the gran desierto of sonora mexico mesoscale mapping on a satellite image base allowed quantitative interpretation of the dynamic development of sand sheets and dunes the results were used to interpret the quaternary geologic history of the tectonically active region at the mouth of the colorado river landsat thematic mapper multispectral images were used to predict the abundance of different mineralogies of sand grains in a mixed aeolian terrain a spectral mixing model separated the effects of vegetation and topographically induced shading and shadow from the effects produced by different mineral and rock types compositions determined remotely agreed well with samples from selected areas within the spectral limitations of the thematic mapper a simple discrimination capability for active versus inactive sand surfaces is demonstrated based upon differences in the percentage of low albedo accessory grains occurring on dormant aeolian surfaces a technique for discriminating between low albedo materials and macroscopic shade is implemented by combining thermal images with the results of the spectral mixing model the image analysis revealed important compositional variations over large areas that were not readily apparent in the field

spatial analysis of sand dunes with a new global topographic dataset new approaches and opportunities on june 29 2009 version 1 of the aster gdem advanced spaceborne thermal emission and reflection radiometer global digital elevation model was made available at no cost or restrictions to users worldwide via electronic download the aster gdem provides expanded spatial coverage and better resolution than other global digital elevation models dems in this paper we demonstrate how the aster gdem provides new opportunities for investigating large aeolian sand dunes in three dimensions two dune specific spatial analysis methods are presented to illustrate potential applications of these data for discriminating dune generations and quantifying spatial variations of sediment supply moreover we review how existing and emerging fields of dune pattern analysis and simulation modeling will be able to make significant advances through application of these data potentially leading to future progress in studies of dune morphodynamics environmental controls and paleoenvironmental reconstructions copyright 2010 john wiley sons ltd

biogeomorphic model of dunefield activation and stabilization on the northern great plains abstract a conceptual model is proposed for the activity of sand dune systems on the northern great plains that incorporates vegetation growth theory and geomorphic system theory dunefield activity is modeled as a cyclic phenomenon alternating between active and stable states with the latter as the system state attractor the model is divided into two constituent parts an activation model and a stabilization model the activation model is qualitative and describes the transition from stable to active dunes as the result of a climatic perturbation such as drought that decreases vegetation cover the intensity and duration of the climatic perturbation determines the rate of decline of vegetation cover the stabilization model is quantitative and describes the transition from active to stable dunes using a logistic model of vegetation growth small perturbations during stabilization can prolong the duration of recovery enabling dunes to remain active well after the initial perturbation despite the geographic focus of this study the model appears applicable to a variety of environments where dune activity is limited in part by vegetation cover

recent stabilization of active sand dunes on the canadian prairies and relation to recent climate variations the historical activity of sand dunes on the southern canadian prairies was investigated in order to determine the relation with recent climate variations changes in dune activity were determined from historical aerial photographs at seven sites with active parabolic dunes in saskatchewan and manitoba the methodology developed combines digital image processing and geographical information system gis analysis to measure changes in dune activity from the aerial photographs as well as correlation analysis to determine the relation between dune activity and climate variations overall dune activity has been decreasing since the early to mid 1900s as evidenced by greater vegetation colonization than sand dune migration or reactivation the decrease in dune activity is significantly correlated with decadal scale variations in aridity and is coincident with a decrease in annual wind speed evidence suggests that this response is superimposed on a longer trend towards stabilization possibly in place since the late 1700s taken together the effect of this complex response is that dune recovery on the southern canadian prairies is prolonged well after an initial disturbance and therefore gives the impression of anomalous levels of activity for extended periods thereafter for this reason dune mobility indices predicated on short term climate variations years to decades do not fully describe the present level of dune activity on the southern canadian prairies

mapping the iron oxide content of dune sands namib sand sea namibia using landsat thematic mapper data abstract a linear mixture model was applied to landsat thematic mapper data to map iron oxide content over the northern part of the namib sand sea namibia field samples were collected to calibrate the remotely sensed iron oxide proportions to dithionite extractable fe in mg g 1 the in situ proportions correlating strongly with the remotely sensed estimates r 0 91 the results reveal a region of high fe oxide concentration in the east an area of low fe oxide concentration in the west separated by a mixing zone we interpret this to indicate that there is more than one sand source contributing to the sand sea

stress history effects on graded bed stability this paper presents the first detailed examination of the dependence of graded bed stability on antecedent flow conditions stress history thirty three experiments including repetitions were undertaken where a bimodal sediment bed d50 4 8 mm g 2 1 was conditioned for between 30 and 5 760 min the antecedent shear stress ranged from 53 to 91 of the critical shear stress for the d50 of the sediment bed data indicate that higher antecedent shear stresses reduce bed stability due to selective entrainment of the fine matrix conversely extending the duration of the antecedent conditioning phase increases bed stability due to local particle rearrangement analysis of the competitive effects indicates that particle rearrangement may be of greater relative importance than compositional change overall the paper demonstrates the significance of antecedent flow conditions for hydraulic engineering and research including the modeling of bed load transport during flood events and the need for standardizing the flume based experimental procedure

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

effects of river regulation on aeolian landscapes colorado river southwestern usa 1 connectivity between fluvial and aeolian sedimentary systems plays an important role in the physical and biological environment of dryland regions this study examines the coupling between fluvial sand deposits and aeolian dune fields in bedrock canyons of the arid to semiarid colorado river corridor southwestern usa by quantifying significant differences between aeolian landscapes with and without modern fluvial sediment sources this work demonstrates for the first time that the flow and sediment limiting effects of dam operations affect sedimentary processes and ecosystems in aeolian landscapes above the fluvial high water line dune fields decoupled from fluvial sand supply have more ground cover biologic crust and vegetation and less aeolian sand transport than do dune fields that remain coupled to modern fluvial sand supply the proportion of active aeolian sand area also is substantially lower in a heavily regulated river reach marble grand canyon arizona than in a much less regulated reach with otherwise similar environmental conditions cataract canyon utah the interconnections shown here among river flow and sediment aeolian sand transport and biologic communities in aeolian dunes demonstrate a newly recognized means by which anthropogenic influence alters dryland environments because fluvial aeolian coupling is common globally it is likely that similar sediment transport connectivity and interaction with upland ecosystems are important in other dryland regions to a greater degree than has been recognized previously

discrimination of active and inactive sand from remote sensing kelso dunes mojave desert california abstract landsat tm images field data and laboratory reflectance spectra were examined for the kelso dunes mojave desert california to assess the use of visible and near infrared vnir remote sensing data to discriminate aeolian sand populations on the basis of spectral brightness results show that areas of inactive sand have a larger percentage of dark fine grained materials compared to those composed of active sand ehich contain less dark fines and a higher percentage of quartz sand size grains both areas are spectrally distinct in the vnir suggesting that vnir spectral data can be used to discriminate active and inactive sand populations in the mojave desert analysis of laboratory spectra was complicated by the presence of magnetite in the active sands which decreases their laboratory reflectance values to those of inactive sands for this application comparison of tm and laboratory spectra suggests that less than 35 vegetation cover does not influence the tm spectra

predictability of dune activity in real dune fields under unidirectional wind regimes we present an analysis of 10 dune fields to test a model derived hypothesis of dune field activity the hypothesis suggests that a quantifiable threshold exists for stabilization in unidirectional wind regimes active dunes have slipface deposition rates that exceed the vegetation deposition tolerance and stabilizing dunes have the opposite we quantified aeolian sand flux slipface geometry and vegetation deposition tolerance to directly test the hypothesis at four dune fields bigstick white sands stable white sands active and cape cod we indirectly tested the hypothesis at six additional dune fields with limited vegetation data hanford ano nuevo skagen odde salton sea oceano stable and oceano active inverse calculation sites we used digital topographic data and estimates of aeolian sand flux to approximate the slipface deposition rates prior to stabilization results revealed a distinct quantifiable and consistent pattern despite diverse environmental conditions the modal peak of prestabilization slipface deposition rates was 80 of the vegetation deposition tolerance at stabilized or stabilizing dune fields results from inverse calculation sites indicate deposition rates at stabilized sites were near a hypothesized maximum vegetation deposition tolerance 1 m a 1 and active sites had slipface deposition rates much higher overall these results confirm the hypothesis and provide evidence of a globally applicable simple and previously unidentified predictor for the dynamics of vegetation cover in dune fields under unidirectional wind regimes

fluvial aeolian interactions part i modern systems two modern fluvial aeolian depositional systems great sand dunes national monument colorado and the mojave river wash california are remarkably similar in spite of different climates sizes fluvial sediment textures and relative directions of aeolian and fluvial transport dune growth and migration and deflation of blowouts create 8 10 m of local relief in unflooded aeolian landscapes there are six prominent fluvial aeolian interactions 1 fluvial flow extends into the aeolian system until it is dammed by aeolian landforms 2 interdune areas overbank interdunes upstream of aeolian dams and alongside channels are flooded 3 water erodes dunes alongside channels and interdunes 4 flood waters deposit sediment in interdune areas 5 fluvially derived groundwater floods interdunes interdune playas 6 wind erodes fluvial sediment and redeposits it in the aeolian system unique and characteristic sediments are deposited in overbank interdunes and in interdune playas reflecting alternate fluvial and aeolian processes and rapidly changing flow and salinity conditions these fluvial aeolian interdune deposits are characterized by irregular concave up bases and flat upper surfaces containing mudcracks or evaporite cement characteristic low relief surfaces form in aeolian systems as an effect of flooding fluvial deposits are resistant to aeolian deflation aeolian sand is preserved when flood sediments are deposited around the bases of the dunes thus repetitive fluvial and aeolian aggradation tends to be stepwise as interdune floors are suddenly raised during floods the effects of flooding should be easy to recognize in ancient aeolianites even beyond the area covered with overbank muds

dune dammed paleovalleys of the nebraska sand hills intrinsic versus climatic controls on the accumulation of lake and marsh sediments although running water is the dominant geomorphic agent on earth eolian processes can gain ascendancy in regions where the climate is arid vegetation is sparse and abundant sand is available for transport with climate change the boundaries between fluvial dominated and eolian dominated areas may shift although there have been few reports in the north american literature of river systems blocked by dune sand our work in the nebraska sand hills provides evidence of multiple episodes of such blockage events during prolonged arid intervals in latest pleistocene and middle holocene time eolian dune sand blocked two large valley systems in western nebraska these blockages raised the water table of the high plains aquifer as much as 25 m over an area of 7000 km2 and created over one thousand lakes wetlands far removed from the discharge points of the buried paleovalley system are strongly alkaline exceeding 250 000 mg l total dissolved solids tds relatively fresh 280 mg l tds flow through lakes are present at the distal end of the system where the gradient of the water table is steep and the cross section of the buried valley is large anomalously thick marsh and lake sediments accumulated in deep paleovalleys upstream of dune dams near the southern margin of the sand hills our cores and radiocarbon dates from blue and crescent lakes reveal their histories to be quite distinct from adjacent swan lake these differences are best explained by multiple blockage events our work explains why lakes are most abundant in the driest part of the sand hills it also provides another line of evidence for major dune activity in the sand hills region during holocene time and shows that factors other than regional climate specifically location height and hydraulic conductivity of dune dams can control the rise and fall of the ground water table and the chemistry of lakes

optimisation of uavs sfm data collection in aeolian landform morphodynamics a case study from the gonghe basin china uavs sfm unmanned aerial vehicles structure from motion systems can generate high resolution 3d topographic models of aeolian landforms to explore the optimisation of uavs sfm for use in aeolian landform morphodynamics this study tested flight parameters for two contrasting aeolian landform areas free dune and blowout to assess the 3d reconstruction accuracy of the uavs survey compared with field point measurements using differential rtk gps real time kinematic global positioning system the results reveal the optimum uavs sfm flight set up at the free dune site was flying height 74 m camera tilt angle 90 photo overlap ratio 85 70 heading sideways the horizontal vertical location error was around 0 028 0 055 m and 0 053 0 069 m respectively and a point cloud density of 463 m3 was found to generate a clear texture using these flying parameters for the 20m deep blowout the optimum set up with highest accuracy and the lowest cliff texture distortion was flying height 74 m combined camera tilt angle 90 and 60 photo overlap ratio 85 70 heading sideways and an evenly distributed gcps ground control points density of 42 km2 using these flying parameters when the depth of the blowouts exceeded 40 m the optimum flight survey parameters changed slightly to account for more challenging cliff texture generation flying height 80 m with 90 and 60 combined camera tilt angle gcps density 63 km2 to generate horizontal and vertical location error of 0 024 m and 0 050 m respectively and point cloud density of 2597 11 m3 the main external factors that affect the successful 3d reconstruction of aeolian landforms using uavs sfm are the weather conditions manipulation errors and instrument system errors the uavs sfm topographic monitoring results demonstrate that uavs provide a viable and robust means for aeolian landform morphodynamics monitoring importantly the rapid and high precision 3d reconstruction processes were significantly advanced using the optimal flight parameters reported here

field observations of the threshold of sediment motion by wave action two field experiments were carried out to determine critical conditions at the threshold of sand motion beneath irregular sea waves the experiments were performed outside the breaker zone at blackpool sands start bay devon in waters of depth 4 10 m from synchronous video and near bed velocity records critical conditions at the threshold of motion have been established in terms of the measured free stream velocity amplitude despite the irregular nature of the swell waves and the mixture of grain sizes on the bed agreement between the present field results and previous laboratory results is reasonable provided that proper allowance is made for the presence of sand ripples in order to define threshold motion conditions on a more rational basis than in terms of the free stream velocity amplitude calculations of the bottom stress have been made on the basis of laboratory derived wave drag coefficients the threshold motion conditions thus established from the field data are in good agreement with sediment threshold values from shields curve derived from laboratory work at least for cases in which it has been possible to calculate the skin friction contribution to the total bed shear stress

wind waves and moveable bed bottom friction abstract effects of moveable bed bottom friction for wave observations and wave modeling are investigated using a state of the art bottom friction model this model combines the hydrodynamic friction model of madsen et al with a moveable bed roughness model based on grant and madsen analyzing the present model for idealized swell cases it is shown that swell might result in wave generated sand ripples the large change of roughness corresponding to initial ripple formation results in a preferred wave height for swell related to bathymetric scales as generally occur in shelf seas away from the coast the corresponding wave generated bottom roughness is not defined by the local wave conditions but is related to the overall energy balance of the wave field sediment data thus is imperative for the interpretation of observed decay rates and friction factors for swell for idealized depth limited wind seas near bottom wave motion is expected to generate partially washed out ripples and moderate sheet flo

geochemical evidence for an eolian sand dam across the north and south platte rivers in nebraska abstract geochemical and geomorphic data from dune fields in southwestern nebraska provide new evidence that the nebraska sand hills once migrated across the north and south platte rivers and dammed the largest tributary system to the missouri river the lincoln county and imperial dune fields which lie downwind of the south platte river have compositions intermediate between the nebraska sand hills quartz rich and northeastern colorado dunes k feldspar rich the most likely explanation for the intermediate composition is that the lincoln county and imperial dunes are derived in part from the nebraska sand hills and in part from the south platte river the only mechanism by which the nebraska sand hills could have migrated this far south is by complete infilling of what were probably perennially dry north platte and south platte river valleys such a series of events would have required an extended drought both for activation of eolian sand and decreased discharges in the platte river system a nearby major tributary of the north platte river is postulated to have been blocked by eolian sand about 12 000 14c yr b p we propose that an eolian sand dam across the plattes was constructed at about this same time

wind forces and related saltation transport the effect of several wind characteristics on sand transport was studied in three experiments in north burkina faso west africa the first experiment is used to analyse the relation between wind speed and shear stress fluctuations across height the second experiment is used to study the relation of these wind characteristics with saltation transport for fourteen convective storms registered during the rainy seasons of 2002 and 2003 the effect of sampling time is studied for two of these convective storms the third experiment relates the turbulent structures of four convective storms to saltation transport wind speed measurements were undertaken with two sonic anemometers and sediment transport was measured by two saltiphones the sampling frequency was either 8 or 16 hz the sonic frame of reference was rotated according to a triple rotation horizontal fluctuations showed a fairly good correlation with height because the wind speed at both sensors was affected by the same vortices the correlation coefficients ranged from 0 42 when the distance between the sensors was 1 75 m to 0 92 when the distance was 0 25 m the instantaneous reynolds stress had the weakest correlation correlation coefficient of 0 05 at 1 75 m between the sensors and 0 56 at 0 25 m between the sensors because the momentum at 2 m above the soil surface is transported by different eddies than those close to the ground this also explains the fairly good correlation coefficients between the horizontal components of the wind and saltation compared to the poor correlations between instantaneous reynolds stress and saltation an increase in sampling time did not have much impact on these correlation coefficients up to sampling periods of about 30 s however this sampling interval would be too coarse to describe the vertical wind component adequately the classification of the moments of shear stress into the turbulent structures sweeps ejections inward and outward interactions showed that the mean saltation flux is higher at sweeps and outward interactions than at ejections and inward interactions also saltation occurred more often during sweeps and outward interactions than during ejections and inward interactions

using remote sensing to quantify aeolian transport and estimate the age of the terminal dune field dunas pampa blanca in southern peru abstract aeolian dunes are widely used to reconstruct paleoenvironmental conditions however terminal dune fields ergs in the coastal desert of southern peru where information regarding quaternary paleoenvironmental conditions is very limited have until now not been used for paleoenvironmental reconstructions and the time depth of their accumulation is unknown here different estimates are derived to constrain the time depth recorded in the dunas pampa blanca a terminal dune field in coastal southern peru dune field age is calculated using the volume of the dunas pampa blanca and i recent aeolian transport rate in migrating transverse dunes feeding the dunas pampa blanca derived from digital processing of sequential landsat and quickbird images and ii limitations posed by recent fluvial sediment supply to the source of aeolian transport the resulting maximum age estimate of 70 8 ka from aeolian transport compares with a minimum age estimate of 4 75 ka from sediment supply however a minimum age estimate of 110 450 ka is deduced from the tectonic and topographic evolution of the region this discrepancy contradicts the hypothesis of late quaternary stability in the peruvian coastal desert and indicates that recent conditions of aeolian sediment supply and transport are not representative for the late quaternary

large scale laboratory investigation into the effect of varying back barrier lagoon water levels on gravel beach morphology and swash zone sediment transport abstract it is generally accepted that the effect on beach morphology of the interactions between swash motion and the beach groundwater table depends on the elevation of the latter relative to that of the sea specifically a low beach groundwater table is considered to enhance onshore sediment transport and beach accretion while the reverse is thought to hold for a high beach groundwater table here we use the results of a carefully designed series of tests conducted in the delta flume the netherlands as part of the barrier dynamics experiment bardex to unequivocally demonstrate the validity of this assertion during the experiment a 4 m high and 50 m long gravel barrier d 50 11 mm was constructed within the central region of the 250 m long and 7 m deep wave flume enabling a back barrier lagoon to be located at its landward side the groundwater table in the beach was manipulated by lowering and raising the lagoon level and the gravel beach was subjected to variable wave conditions and sea lagoon levels using as the initial beach profile the morphology resulting from 90 min of wave forcing with the sea and lagoon at the same level the identical wave forcing with a low lagoon level consistently resulted in onshore sediment transport in the swash zone and beach accretion whereas the identical wave forcing with a high lagoon level consistently caused offshore sediment transport in the swash zone and beach erosion the divergent beach morphological responses for the low and high lagoon levels could not be attributed to changes in the bulk swash hydrodynamics i e based on single point velocity measurements arising from a difference in the amount of swash infiltration into the unsaturated beach instead application of a sediment transport model that accounts for the effects of in exfiltration suggested that the onshore sediment transport and beach accretion for the low lagoon tests mainly resulted from enhanced bed shear stresses during the wave uprush due to infiltration into the saturated part of the beachface due to the large hydraulic conductivity of gravel k o 0 1 m s 1 the effect of altered shear stresses due to in exfiltration may be an important factor in sediment transport in the swash zone of gravel beaches

wave friction factor as related to the shields parameter for steady currents abstract the wave friction factor fw is an important dimensionless parameter used to estimate wave induced bed shear stress which together with current induced bed shear stress controls sediment transport in the marine and lacustrine environment however fw is either overestimated or underestimated by existing equations the matter is complicated by the fact that different equations must be used for hydrodynamically smooth or rough flows but the limit between these two boundary conditions is still poorly defined some equations also require estimated values for the nikuradse roughness length and the wave boundary layer thickness neither of which can be derived accurately it is therefore not surprising that fw values as calculated by existing equations differ by as much as a factor of 3 in the present paper fw is related to the shields parameter for unidirectional currents which not only facilitates the direct comparison and summation of bed shear stresses but also yields a more accurate equation valid for grains of different density in any fluid irrespective of the boundary condition

responses of the braided channel to reduced discharge and lateral inputs of aeolian sand in the ulan buh desert reach of the upper yellow river the ulanbuh desert reach belongs to the upper reaches of the yellow river located in inner mongolia autonomous region china which has developed a sandy bed this reach that flows across aeolian dunes field of the ulanbuh desert has caused large lateral infusion of aeolian sands into riverbed an abrupt addition of the bedload and a sharp channel widening forming a typical braided channel in addition to traditional driving factors such as discharge suspended sediments and slope here we also focus on the lateral infusion of aeolian sands into the yellow river which may have a significant impact on channel form to further recognize the desert braided channel change here based on a long time series of field dataset from 1966 to 2013 results show that lateral infusion of aeolian sand is the same as discharge as a significant factor to channel form which is mainly controlled by aeolian activity and discharge conditions before the early 1990s higher discharge and greater intensity of aeolian activity caused a frequent lateral movement and large lateral inputs of aeolian sands into river this reach showed an unsteady and wider braided channel with a higher braiding intensity from the early 1990s to 2013 a reduced discharge that caused a decreasing lateral movement coupled with the decreasing aeolian activity have resulted in the main flow of the yellow river far away from sand dunes which led to a reduction in lateral inputs of aeolian sands thus the braided channel of the ulanbuh desert reach presented a shrinkage state gradually changing from a wider and unsteady braided channel to a narrower and relative steady channel form

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

mapping and measuring aeolian sand dunes with photogrammetry and lidar from unmanned aerial vehicles uav and multispectral satellite imagery on the paria plateau az usa abstract the paria plateau is a potentially important but relatively unstudied aeolian sand source area in the grand canyon region of arizona usa this study used unmanned aerial vehicle uav based lidar and structure from motion sfm photogrammetry to produce high resolution topographic models of aeolian dunes on the plateau we combined the dune topography data with a high resolution satellite image maximum likelihood classification producer s accuracy 87 2 to quantify potential aeolian sand source areas across the 958 km2 plateau we mapped all the unvegetated active aeolian dunes on the plateau and estimate they contain 24 tg of sand and could therefore be a proportionately important regional sand source considering the annual sand loads of the downwind paria river at its confluence with the colorado river are generally

heavy metal contamination in overbank sediments of the geul river east belgium its relation to former pb zn mining activities overbank sediments of the geul river east belgium are highly contaminated by the heavy metals pb zn and cd due to former pb zn mining activities in the drainage basin geochemical variations in vertical overbank sediment profiles sampled 1 km north of the mine tailings of plombieres allow metal fluxes back to the 17th century to be reconstructed the vertical profiles are subdivided into three major units corresponding to different industrial periods based on sedimentological criteria as well as on the distribution of contaminants alluvial sediments with the highest heavy metal concentrations correspond to the major period of mining activity of the 19th century the fact that zn mining at the la calamine open mine started before large scale mining of the pbs zns subsurface exploitations is reflected in the vertical profiles by an increase in zn content before a marked increase in pb and cu the regional extent of contamination in the alluvial deposits was evaluated on the basis of the geochemical analysis of sediments at depths of the 0 20 cm and 80 100 cm most of the upper samples are extremely contaminated significant local variations in heavy metal concentration in the lower samples are interpreted in terms of which overbank sediment horizon has been sampled at a depth of 80 100 cm this indicates that blind sampling of overbank sediments to characterize the degree of contamination in shallow boreholes can give very erratic results

the impact of tailings dam spills and clean up operations on sediment and water quality in river systems the rios agrio guadiamar aznalcollar spain the aznalcollar tailings dam at boliden apirsa s aznalcollar los frailes ag cu pb zn mine 45 km west of seville spain was breached on 25 april 1998 flooding approximately 4600 hectares of land along the rios agrio and guadiamar with approximately 5 5 million m3 of acidic water and 1 3 106 m3 of heavy metal bearing tailings most of the deposited tailings and approximately 4 7 106 m3 of contaminated soils were removed to the aznalcollar open pit during clean up work undertaken immediately after the spill until january 1999 detailed geomorphological and geochemical surveys of the post clean up channel floodplain and valley floor and sediment and water sampling were carried out in january and may 1999 at 6 reaches representative of the types of river channel and floodplain environments in the rio guadiamar catchment affected by the spill the collected data show that the clean up operations removed enough spill deposited sediment to achieve pre spill metal ag as cd cu pb sb tl zn concentrations in surface sediment these concentrations however are still elevated above pre mining concentrations and emphasise that mining continues to contaminate the agrio guadiamar river system dilution by relatively uncontaminated sediment appears to reduce metal concentrations downstream but increases in metal and as concentrations occur downstream presumably as a result of factors such as sewage and agriculture river water samples collected in may 1999 have significantly greater dissolved concentrations of metals and as than those from january 1999 probably due to greater sulphide oxidation from residual tailings with concomitant release of metals in the warmer early summer months these concentrations are reduced downstream probably by a combination of dilution and removal of metals by mineral precipitation single chemical extractions de ionised water cacl2 0 01 mol l 1 ch3coonh4 1 m ch3coona 1 m and ammonium oxalate 0 2 m on alluvial samples from reaches 1 and 6 the tailings pre spill alluvium and marl have shown that the order of sediment borne contaminant mobility is generally zn cd cu pb as pb and as are relatively immobile except possibly under reducing conditions much of the highly contaminated sediment remaining in the floodplain and channel still contains a large proportion of tailings related sulphide minerals which are potentially reactive and may continue to release contaminants to the agrio guadiamar river system our work emphasises the need for pre mining geomorphological and geochemical data and an assessment of potential contributions of contaminants to river systems from other non mining sources

concepts in gravel beach dynamics abstract the dominant processes in gravel beach dynamics are reviewed highlighting some common themes which unify the various components of the gravel beach system the repercussions of which impart on how gravel beach dynamics might be understood conceptually in particular gravel beach dynamics are thought to be highly dependent on the temporal and spatial variation in grain size and the continual adjustments made by an active beach step both of which act not only as the expression of changing morphodynamic conditions but also as a controlling influence morphodynamics the notion that the exchanges on beaches between the hydrodynamics sediment transport and morphological change takes the form of reciprocal relationships which are mediated through feedback mechanisms in such a way that they cannot be thought of or studied independently is not a new one yet it appears that for the gravel beach morphodynamics must be re defined to describe conditions where variations in sediment size are thought to deserve parity rather than as merely a sequent entity or boundary condition morpho sedimentary dynamics is a phrase coined to intuit such cause and effect detailing the co evolution of morphology hydro hydraulics and sediment properties whilst acknowledging causative pluralism feedbacks and multiplier effects this is the recommended conceptual framework within which to crystallise thought and organise further research for the gravel beach essentially it increases the minimum number of parameters needed to describe the state of the gravel beach as a physical system therefore it is advised that simplicity will be most expedient in our future modelling efforts if complexity is to be adequately encapsulated

sand grain threshold in relation to bed stress history an experimental study besides particle size density and shape the erodibility of a sediment bed depends also upon the exposure to prethreshold velocities in the overlying flow such flow effectively rearranges the grains at and below the bed surface causing them to become more resistant to subsequent erosion the effects of the stress history leading up to the critical condition for sediment movement are investigated for unidirectional flows generated in a recirculating laboratory flume the sediment beds investigated consisted of cohesionless quartz sand grains with mean grain diameters of 0 194 mm fine sand 0 387 mm medium sand and 0 774 mm coarse sand with narrow particle size distributions the critical threshold shear velocity target value for the three beds was established within 2 5 min of increasing the flow from zero velocity the subsequent experiments were performed under prethreshold velocities at 70 for 5 10 20 40 and 80 min exposure duration 80 for 5 10 20 40 and 80 min exposure duration 90 and 95 for 5 10 20 40 80 and 120 min exposure duration of the target value following exposure to these different prethreshold conditions the flow was increased then to reach actual critical conditions within a period of 2 5 min the critical condition for the initiation of sediment movement was established using visual observation supplemented by video recordings according to the yalin criterion the results show that if the exposure duration to prethreshold velocities remains constant then the critical shear velocity increases with increasing prethreshold velocity likewise if the prethreshold velocity remains constant then the critical shear velocity increases with increasing exposure duration in some circumstances the critical shear velocity was found to increase by as much as 27 an empirical formula is proposed to account for the exposure correction to be applied to the critical shear velocities of sand sized sediment beds this is prior to their inclusion into bedload transport formulae for an improved prediction of the magnitude and nature of transport

uav based remote sensing of the super sauze landslide evaluation and results unmanned aerial vehicles uavs equipped with digital compact cameras can be used to map landslides quickly and at a high ground resolution images taken by a radio controlled mini quad rotor uav of the super sauze france landslide have been used to produce a high resolution ortho mosaic of the entire landslide and digital terrain models dtms of several regions the uav capability for imaging fissures and displacements on the landslide surface has been evaluated and the subsequent image processing approaches for suitably georectifying the data have been assessed for super sauze horizontal displacements of 7 to 55 m between a high resolution airborne ortho photo of may 2007 and a uav based ortho mosaic of october 2008 have been measured fixed areas of persistent deformation have been identified producing fissures of different distributions and orientations comparable to glacial crevasses and relating directly to the bedrock topography the uav has demonstrated its capability for producing valuable landslide data but improvements are required to reduce data processing time for the efficient generation of ortho mosaics based on photogrammetric dtms in order to minimise georeferencing errors

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

high frequency sediment transport responses on a vegetated foredune wind flow and sand transport intensity were measured on the seaward slope of a vegetated foredune during a 16 h storm using an array of sonic anemometers and wenglor laser particle counters the foredune had a compound seaward slope with a wave cut scarp about 0 5 m high separating the upper vegetated portion from the lower dune ramp which was bare of vegetation wind direction veered from obliquely offshore at the start of the event to obliquely onshore during the storm peak and finally to directly onshore during the final 2 h as wind speed dropped to below threshold sand transport was initially inhibited by a brief period of rain at the start of the event but as the surface dried and wind speed increased sand transport was initiated over the entire seaward slope transport intensity was quite variable both temporally and spatially on the upper slope as a result of fluctuating wind speed and direction but overall magnitudes were similar over the whole length ten minute average transport intensity correlates strongly with mean wind speed measured at the dune crest and there is also strong correlation between instantaneous wind speed and transport intensity measured at the same locations when the data are smoothed with a 10 s running mean transport on the beach for onshore winds is decoupled from that on the seaward slope above the small scarp when the wind angle is highly oblique but for wind angles 45 from shore perpendicular some sand is transported onto the lower slope copyright 2012 john wiley sons ltd

turbulence based measurements of wave friction factors under irregular waves on a gravel bed very few studies have quantified the wave friction factor fw for coarse sediments at field scale to address this shortcoming high frequency measurements of turbulence obtained within the boundary layer of irregular waves over gravel in the delta flume have been used to calculate values of fw using different evaluation methods in the field scale laboratory experiments reported here three velocimeters were deployed on the seaward side of a 4 m high 5 m wide and 55 m long gravel barrier subject to a jonswap spectrum of waves with significant wave heights ranging from 0 8 m to 1 3 m and peak periods of 3 0 s to 10 s and offshore water depths ranging from 1 75 m to 3 75 m the deployment area was essentially flat with little or no predicted or observed sediment movement under the wave conditions investigated the turbulent kinetic energy method was found to be the most suitable approach for calculating the bed shear stress which can be related to fw wave friction factor values under the conditions tested here fell in the range 0 01 and 0 27 although fw predicted by an existing equation agrees well with the mean measured fw value the application of a new predictor for fw is recommended for improved parameterisation of skin friction over the range of relative roughness values encountered in this study this approach combines the wave reynolds number wave steepness and relative depth to provide a simple expression to assist assessments of coarse sediment transport by waves for uses within a range of practical engineering applications

colorado river sediment transport 1 natural sediment supply limitation and the influence of glen canyon dam analyses of flow sediment transport bed topographic and sedimentologic data suggest that before the closure of glen canyon dam in 1963 the colorado river in marble and grand canyons was annually supply limited with respect to fine sediment i e sand and finer material furthermore these analyses suggest that the predam river in glen canyon was not supply limited to the same degree and that the degree of annual supply limitation increased near the head of marble canyon the predam colorado river in grand canyon displays evidence of four effects of supply limitation 1 seasonal hysteresis in sediment concentration 2 seasonal hysteresis in sediment grain size coupled to the seasonal hysteresis in sediment concentration 3 production of inversely graded flood deposits and 4 development or modification of a lag between the time of a flood peak and the time of either maximum or minimum depending on reach geometry bed elevation analyses of sediment budgets provide additional support for the interpretation that the predam river was annually supply limited with respect to fine sediment but it was not supply limited with respect to fine sediment during all seasons in the average predam year sand would accumulate and be stored in marble canyon and upper grand canyon for 9 months of the year from july through march when flows were dominantly below 200 300 m3 s this stored sand was then eroded during april through june when flows were typically higher after closure of glen canyon dam because of the large magnitudes of the uncertainties in the sediment budget no season of substantial sand accumulation is evident because most flows in the postdam river exceed 200 300 m3 s substantial sand accumulation in the postdam river is unlikely

internal boundary layer model for the evolution of desert dune fields dune fields often show abrupt changes in morphology over short distances but the mechanism driving the changes has been unclear physical modelling and airborne altimetry from white sands new mexico show that the development of an internal boundary layer is linked to the vegetation and hydrologic patterns observed there desert dunes often exhibit remarkable changes in their morphology over short distances for example sediment rich dunes can break up into smaller isolated features and then become stabilized by plants over distances of kilometres1 2 3 4 5 6 these pattern transitions often coincide with spatial variations in sediment supply1 3 5 transport rate6 7 hydrology8 and vegetation9 10 11 but these factors have not been linked mechanistically here we hypothesize that the abrupt increase in roughness at the upwind margins of dune fields triggers the development of an internal boundary layer12 13 14 15 16 17 18 that thickens downwind and causes a spatial decrease in the surface wind stress we demonstrate that this mechanism forces a downwind decline in sand flux at white sands new mexico using a combination of physical theory14 15 16 17 18 19 repeated airborne altimetry surveys and field observations the declining sand flux triggers an abrupt increase in vegetation density which in turn leads to changes in groundwater depth and salinity showing that aerodynamics sediment transport and ecohydrology are tightly interconnected in this landscape we conclude that despite the documented complex climatic and geologic history of white sands20 internal boundary layer theory explains many of the observed first order patterns of the dune field

on the cross shore profile change of gravel beaches abstract this paper investigates cross shore profile changes of gravel beaches with particular regard to discussing the tendency for onshore transport and profile steepening in the swash zone the discussion includes observed morphological changes on a gravel beach from experimental investigations at the large wave flume gwk in hanover germany during the tests all the profile changes occurred in the swash zone resulting in erosion below the still water line swl and formation of a berm above the swl we investigate the profile evolution evaluating the transport rates from a bed load sediment transport formulation coupled with velocities calculated from a set of boussinesq equations that have been validated for its use in the surf and swash zones lynett p j wu t r and liu l f p 2002 modelling wave runup with depth integrated equations coastal engineering 46 89 107 otta a k and pedrozo acuna a 2004 swash boundary and cross shore variation of horizontal velocity on a slope in j m smith editor proceedings 29th international conference on coastal engineering world scientific lisbon portugal pp 1616 1628 we discuss the influence of bottom friction on the predicted profiles using reported friction factors from experimental studies it is shown that the use of a different friction factor within a realistic range in each phase of the swash uprush and backwash improves prediction of the beach profiles although quantitative agreement between the measured and computed profile evolutions is not satisfactory furthermore if the friction factor and the transport efficiency c of the sediment transport formulation are kept the same in the uprush and backwash accurate representation of profile evolution is not possible indeed the features of the predicted profiles are reversed however when the c parameter is set larger during the uprush than during the backwash the predicted profiles are closer to the observations differences between the predicted profiles from setting non identical c values and friction factors for the swash phase are believed to be linked to both the infiltration effects on the flow above the beachface and the more accelerated flow in the uprush

spectral wave flow attenuation within submerged canopies implications for wave energy dissipation 1 communities of benthic organisms can form very rough surfaces canopies on the seafloor previous studies have shown that an oscillatory flow induced by monochromatic surface waves will drive more flow inside a canopy than a comparable unidirectional current this paper builds on these previous studies by investigating how wave energy is attenuated within canopies under spectral wave conditions or random wave fields defined by many frequencies a theoretical model is first developed to predict how flow attenuation within a canopy varies among the different wave components and predicts that shorter period components will generally be more effective at driving flow within a canopy than longer period components to investigate the model performance a field experiment was conducted on a shallow reef flat in which flow was measured both inside and above a model canopy array results confirm that longer period components in the spectrum are significantly more attenuated than shorter period components in good agreement with the model prediction this paper concludes by showing that the rate at which wave energy is dissipated by a canopy is closely linked to the flow structure within the canopy under spectral wave conditions wave energy within a model canopy array is dissipated at a greater rate among the shorter period wave components these observations are consistent with previous observations of how wave energy is dissipated by the bottom roughness of a coral reef

seabed stress determinations using the inertial dissipation method and the turbulent kinetic energy method direct measurements of seabed stress are difficult especially in field conditions several methods for estimating these stresses using current meter data are available two of these methods the inertial dissipation method and the turbulent kinetic energy method are described below and a matlab program is used to analyse data from a wave current environment

wave friction factors in nearshore sands abstract wave friction factors are estimated from vertical profiles of near bed turbulence and horizontal velocity spanning the wave bottom boundary layer measured values are partitioned by bed state which ranged from irregular ripples to flat bed and are examined as a function of two traditionally selected parameters physical bed roughness and outer flow reynolds number the measurements are from two field experiments in very different nearshore environments a relatively protected unbarred pocket beach and a linear barred beach exposed to the open shelf duck measured wave friction factors are remarkably similar for the two beaches and are highest for low energy rippled beds and lowest for the high energy flat bed conditions the reduction in the friction factor for high energy conditions corresponds to a decrease in the physical roughness of the bed as wave energy increases as a function of relative roughness measured friction factors are generally consistent with previous laboratory results and

geomorphological mapping with a small unmanned aircraft system suas feature detection and accuracy assessment of a photogrammetrically derived digital terrain model abstract small unmanned aircraft systems suas are a relatively new type of aerial platform for acquiring high resolution remote sensing measurements of earth surface processes and landforms however despite growing application there has been little quantitative assessment of suas performance here we present results from a field experiment designed to evaluate the accuracy of a photogrammetrically derived digital terrain model dtm developed from imagery acquired with a low cost digital camera onboard an suas we also show the utility of the high resolution 0 1 m suas imagery for resolving small scale biogeomorphic features the experiment was conducted in an area with active and stabilized aeolian landforms in the southern canadian prairies images were acquired with a hawkeye rq 84z areohawk fixed wing suas a total of 280 images were acquired along 14 flight lines covering an area of 1 95 km2 the survey was completed in 4 5 h including gps surveying suas setup and flight time standard image processing and photogrammetric techniques were used to produce a 1 m resolution dtm and a 0 1 m resolution orthorectified image mosaic the latter revealed previously un mapped bioturbation features the vertical accuracy of the dtm was evaluated with 99 real time kinematic gps points while 20 of these points were used to quantify horizontal accuracy the horizontal root mean squared error rmse of the orthoimage was 0 18 m while the vertical rmse of the dtm was 0 29 m which is equivalent to the rmse of a bare earth lidar dtm for the same site the combined error from both datasets was used to define a threshold of the minimum elevation difference that could be reliably attributed to erosion or deposition in the seven years separating the suas and lidar datasets overall our results suggest that suas acquired imagery may provide a low cost rapid and flexible alternative to airborne lidar for geomorphological mapping

dune mobility and vegetation cover in the southwest kalahari desert as part of a wider project investigating the palaeoenvironmental significance of partially vegetated linear dunes in the southwest kalahari data collected in the latter part of 1992 concerning dune movement and vegetation cover suggest that sediment transport is occurring on some dune surfaces and that the majority of surface activity occurs on the crests and upper slopes of the dunes the data suggest that the limiting variables on surface sediment movement vary on different parts of a dune on interdunes and lower dune slopes the primary limiting variable is available wind energy while on dune crests and upper slopes it is vegetation cover ground cover by litter has much greater importance in protecting the surface sediment from erosion than rooted vegetation from individual data points no evidence is found to support a threshold vegetation cover below which sediment movement occurs rather a gradient of activity is suggested whereby a reduction in vegetation cover increases the potential for sediment movement and surface change however dunes with differing amounts of mean vegetation cover display differing degrees of surface activity and at this scale a vegetation cover threshold in the region of 14 per cent may be recognized

identification of sand sources and transport pathways at the kelso dunes california using thermal infrared remote sensing the kelso dune field is located in the eastern mojave desert california at the terminus of a sand transport pathway which has its primary source at the mojave river wash 50 km to the west initial examination of 1984 airborne thermal infrared multispectral scanner tims data showed significant spectral variations that indicate potential mineralogic heterogeneities within the active dunes this result prompted the collection of a suite of 48 sand samples in 1990 and the acquiring of new tims data in 1995 this new data set was used to test a newly developed linear spectral retrieval algorithm in conjunction with a spectral library of end member minerals results of this analysis produced images of end member minerals that showed marked variations within the dunes in addition standard petrographic techniques revealed that the dunes contain mineralogic variations and were much less quartz rich 42 than previously reported 70 90 point count results agreed with the spectral data to within an average of 5 3 for tims derived and 3 1 for laboratory derived mineralogic abundances high concentrations of several of the end member minerals on the surrounding alluvial fans indicate a potential nearby source for these minerals most evident is the presence of potassium feldspar from the fan that emanates from the providence mountains east of the dunes this previously unidentified potential sand input is not visible with other remote sensing techniques and was confirmed with additional field sampling much of the quartz and some plagioclase feldspar however appear to have been transported from the mojave river wash source as previously reported this study also validates the potential of using thermal remote sensing from future satellite based instruments to globally monitor desert fringe areas susceptible to the changing conditions of sand encroachment

the effects of topographic surveying technique and data resolution on the detection and interpretation of geomorphic change abstract change detection of high resolution topographic data is commonly used in river valleys to quantify reach and site scale sediment budgets by estimating the erosion deposition volume and to interpret the geomorphic processes driving erosion and deposition field survey data are typically collected as point clouds that are often converted to gridded raster datasets and the ultimate choice of grid resolution is left to the user this choice may have important implications for both the quantification and interpretation of geomorphic change here we used concurrent topographic data collected by terrestrial laser scanning tls and structure from motion sfm photogrammetry to quantify the influence of grid resolution and sampling technique on a the sediment budget and b the presence and role of geomorphic processes i e alluvial colluvial aeolian and fluvial transport driving topographic change at four sites along the colorado river in grand canyon arizona usa we found that while both techniques produced similar estimates for site scale sediment budgets the magnitude of detected topographic change was dampened at coarser pixel resolutions an overall decrease in the areal extent of erosion and deposition were observed respectively when coarsening pixel size from 5 cm to 1 m among all sites coarser resolution data tended to affect interpretation of landscape change along the margins of river valleys for example when changing from 5 cm to 1 m pixel resolution the inferred contribution of aeolian changes to total site scale geomorphic change increased in area by 7 9 whereas the inferred contribution of alluvial and colluvial processes decreased in area by 97 9 and 88 2 respectively more generally we found that coarsening pixel sizes disproportionately attributed geomorphic change to one or more of the most common processes operating at a site we also found that coarsening pixel resolution amplified the net sediment imbalance at the site scale driving the imbalance at erosional sites further into erosion and vice versa for depositional sites our results have implications both for point cloud data collection and for raster dataset processing we argue that selecting the finest obtainable resolution is not always warranted to accurately quantify and interpret geomorphic change because remote sensing technique topographic data resolution and analysis procedure can be optimized to capture the spatial scale of those processes driving landscape change however in landscapes at or near sediment equilibrium i e equal amounts of erosion and deposition the finest obtainable topographic data resolution is warranted to avoid amplifying sediment imbalance and erroneously inferring that sites are trending toward erosion or deposition

the effects of surface moisture on aeolian sediment transport threshold and mass flux on a beach this paper presents results from a study designed to explore the effects of beach surface moisture and fetch effects on the threshold of movement intensity of sand transport by wind and mass flux the experiment was carried out over a period of five weeks at greenwich dunes prince edward island canada in may and june 2002 moisture content was measured with a delta t moisture probe over a 50 m by 25 m grid established on the beach measurements of wind speed and direction were made with arrays of cup anemometers and a two dimensional sonic anemometer transport intensity was measured at a height of 2 4 cm above the bed using omnidirectional saltation probes which count the impact of saltating grains on a piezoelectric crystal anemometers and saltation probes were sampled at 1 hz sand transport was measured with vertical integrating sand traps over periods of 10 20 minutes results show that where there is a considerable supply of dry sand the saltation system responds very rapidly 1 2 s to fluctuations in wind speed i e to wind gusts where sand supply from the surface is limited by moisture mean transport rates are much lower and this reflects in both a reduction in the instantaneous transport rate and in a transport system that becomes increasingly intermittent threshold wind speed is significantly correlated with an increase in surface moisture content near the upwind end of the beach fetch but the relationship is not significant at the downwind end where sediment transport is initiated primarily by saltation impact from upwind mass flux increases with increasing fetch length and the relationship is described best by a power function further work is necessary to develop a theoretical function to predict the increase in transport with fetch distance as well as the critical fetch distance copyright 2007 john wiley sons ltd

wind blown sand on beaches an evaluation of models five models for predicting rates of aeolian sand transport were evaluated using empirical data obtained from field experiments conducted in april 1994 at a beach on inch spit co kerry republic of ireland measurements were made of vertical wind profiles to derive shear velocity estimates beach slope and rates of sand transport sediment samples were taken to assess characteristics of grain size and surface moisture content estimates of threshold shear velocity were derived using grain size data after parsing the field data on the basis of the quality of shear velocity estimation and the occurrence of blowing sand 51 data sets describing rates of sand transport and environmental conditions were retained mean grain diameter was 0 17 mm surface slopes ranged from 0 02 on the foreshore to about 0 11 near the dune toe mean shear velocities ranged from 0 23 m s 1 just above the observed transport threshold to 0 65 m s 1 rates of transport ranged from 0 02 kg m 1 h 1 to more than 80 kg m 1 h 1 these data were used as input to the models of bagnold bagnold r a 1936 the movement of desert sand proc r soc london a157 594 620 kawamura kawamura r 1951 study of sand movement by wind translated 1965 as university of california hydraulics engineering laboratory report hel 2 8 berkeley zingg zingg a w 1953 wind tunnel studies of the movement of sedimentary material proc 5th hydraulics conf bull 34 iowa city inst of hydraulics pp 111 135 kadib kadib a a 1965 a function for sand movement by wind university of california hydraulics engineering laboratory report hel 2 8 berkeley and lettau and lettau lettau k and lettau h 1977 experimental and micrometeorological field studies of dune migration in k lettau and h lettau eds exploring the world s driest climate university of wisconsin madison ies report 101 pp 110 147 correction factors to adjust predictions of the rate of transport to account for the effects of slope and moisture content were calculated using the models of bagnold bagnold r a 1973 the nature of saltation and bed load transport in water proc r soc london ser a 332 473 504 and belly belly p y 1964 sand movement by wind u s army corps eng cerc tech mem 1 washington d c 38 pp respectively none of the models was able to produce a strong correspondence between measured and predicted rates of transport best results were obtained using the bagnold and zingg models and the kadib model was the least viable of this group the influence of sediment moisture content appeared to be the critical factor in degrading model viability overall none of the models is adequate for general applications to coastal aeolian environments where moisture content complications tend to override the predictive competence of the simple transport formulations c 1998 elsevier science b v