aerodynamic roughness of fixed sandy beds the nature of interactions between surface winds and sand surfaces that can be characterized by aerodynamic roughness length has important implications for aeolian sediment transport here we report the wind tunnel results of systematic tests of the aerodynamic roughness lengths of different sized fixed sand beds at different free stream wind velocities the results suggest that there are complex variations of aerodynamic roughness length wind is an active factor in determining the aerodynamic roughness length of fixed sand beds the so called 1 30 law in aeolian research proposed by bagnold more than a half century ago for sand surfaces is found to suffer some limitations some multivariate models relating aerodynamic roughness length and other factors are provided the differences between the aerodynamic roughness of fixed and mobile beds are discussed and it is implied that mobile surfaces adapt to the wind by changing roughness the similarities between aerodynamic roughness and hydraulic roughness are compared aerodynamic roughness is divided into aerodynamically smooth transitional and completely rough regimes

mapping the interactions between rivers and sand dunes implications for fluvial and aeolian geomorphology article i nfo the interaction between fluvial and aeolian processes can significantly change earth surface morphology when riversandsanddunes meet theinteractionofsedimenttransportbetweenthetwosystemscanleadtochangein eitherorboth systems however these two systemsare usuallystudied independently which leavesmanyques tions unresolved in terms of how they interact this paper carries out a global inventory using satellite imagery to identify 230 sites where there are significant fluvial aeolian interactions at each location key attributes such as wind river direction net sand transport direction fluvial aeolian meeting angle dune type and river channel pattern were identifiedand relationshipsbetween each factorwere analysed from thesedata six different types of interaction were classified that reflect a shift in dominance between the fluvial and aeolian systems results from this classification confirm that only certain types of interaction were significant the meeting angle and dunetype themeeting angle and interaction type and finally thechannel pattern andinteraction type however the findings also indicate the difficulties of classifying dynamic geomorphic systems from snapshot satellite images

provenance and climate change inferred from sr nd pb isotopes of late quaternary sediments in the huanghe yellow river delta china we present a provenance study of core zk2 from the huanghe yellow river delta in order to assess the impacts of climate change on the sediment supplies during the last glacial interglacial cycle facies analysis and sequence stratigraphy methods are used to construct the age model sr isotopic compositions of zk2 range from 0 716389 to 0 723884 with 87sr 86sr increased with decreasing grain size nd and pb isotopic compositions display two large major excursions during marine oxygen isotope stages mis 2 and 4 with less radiogenic end and lower 208pb 204pb 207pb 204pb and 206pb 204pb values during these periods these excursions have been explained in terms of changes in the mixing proportion of sediments from the loess plateau and ordos plateau resulting from east asian monsoon intensity variations the weak summer monsoon precipitation resulted in decreased erosion of loess plateau during mis 2 4 and the middle of mis 3 meanwhile both the intensified east asian winter monsoon and the southward expansions of mu us desert significantly enhanced the eolian sand entering the huanghe therefore our results highlight the impact of monsoon variability on erosion patterns in the huanghe basin

gully annealing by aeolian sediment field and remote sensing investigation of aeolian hillslope fluvial interactions colorado river corridor arizona usa abstract processes contributing to development of ephemeral gully channels are of great importance to landscapes worldwide and particularly in dryland regions where soil loss and land degradation from gully erosion pose long term land management problems whereas gully formation has been relatively well studied much less is known of the processes that anneal gullies and impede their growth this study of gully annealing by aeolian sediment spanning 95 km along the colorado river corridor in glen marble and grand canyon arizona usa employed field and remote sensing observations including digital topographic modelling results indicate that aeolian sediment activity can be locally effective at counteracting gully erosion gullies are less prevalent in areas where surficial sediment undergoes active aeolian transport and have a greater tendency to terminate in active aeolian sand although not common examples exist in the record of historical imagery of gullies that underwent infilling by aeolian sediment in past decades and evidently were effectively annealed we thus provide new evidence for a potentially important interaction of aeolian hillslope fluvial processes which could affect dryland regions substantially in ways not widely recognized moreover because the biologic soil crust plays an important role in determining aeolian sand activity and so in turn the extent of gully development this study highlights a critical role of geomorphic ecologic interactions in determining arid landscape evolution

wind erodibility of soils at fort irwin california mojave desert usa before and after trampling disturbance implications for land management recently disturbed and control i e less recently disturbed soils in the mojave desert were compared for their vulnerability to wind erosion using a wind tunnel before and after being experimentally trampled before trampling control sites had greater cyanobacterial biomass soil surface stability threshold friction velocities tfv i e the wind speed required to move soil particles and sediment yield than sites that had been more recently disturbed by military manoeuvres after trampling all sites showed a large drop in tfvs and a concomitant increase in sediment yield simple correlation analyses showed that the decline in tfvs and the rise in sediment yield were significantly related to cyanobacterial biomass as indicated by soil chlorophyll a however chlorophyll a amounts were very low compared to chlorophyll a amounts found at cooler desert sites where chlorophyll a is often the most important factor in determining tfv and sediment yield multiple regression analyses showed that other factors at fort irwin were more important than cyanobacterial biomass in determining the overall site susceptibility to wind erosion these factors included soil texture especially the fine medium and coarse sand fractions rock cover and the inherent stability of the soil as indicated by subsurface soil stability tests thus our results indicate that there is a threshold of biomass below which cyanobacterial crusts are not the dominant factor in soil vulnerability to wind erosion most undisturbed soil surfaces in the mojave desert region produce very little sediment but even moderate disturbance increases soil loss from these sites because current weathering rates and dust inputs are very low soil formation rates are low as well therefore soil loss in this region is likely to have long term effects published in 2006 by john wiley sons ltd

velocity profile of a sand cloud blowing over a gravel surface particle dynamic analyzer pda measurement technology was used to study the turbulent characteristics and the variation with height of the mean horizontal in the downwind direction and vertical in the upward direction particle velocity of a sand cloud blowing over a gravel surface the results show that the mean horizontal particle velocity of the cloud increases with height while the mean vertical velocity decreases with height the variation of the mean horizontal velocity with height is to some extent similar to the wind profile that increases logarithmically with height in the turbulent boundary layer the variation of the mean vertical velocity with height is much more complex than that of the mean horizontal velocity the increase of the resultant mean velocity with height can be expressed by a modified power function particle turbulence in the downwind direction decreases with height while that in the vertical direction is complex for fine sands 0 2 0 3 mm and 0 3 0 4 mm there is a tendency for the particle turbulence to increase with height in the very near surface layer 4 mm the movement of blown sand particles is very complex due to the rebound of particles on the bed and the interparticle collisions in the air wind starts to accelerate particle movement about 4 mm from the surface the initial rebound on the bed and the interparticle collisions in the air have a profound effect on particle movement below that height where particle concentration is very high and wind velocity is very low

erosion caused by hyperconcentrated flow on the loess plateau of china abstract hyperconcentrated flows are widely observed in the middle yellow river basin they occur as a result of erosion but once they form on slopes they operate as a strong eroding and sediment carrying force and play an important role in drainage basin erosion and sediment production processes since the energy expenditure is less and sediment carrying capacity is greater hyperconcentrated flows have very high eroding and transporting abilities there exists a strong coupling relation between hyperconcentrated flow transport and gravitational erosion which ensures a rapid removal of mass wasted materials hyperconcentrated flows are an important factor responsible for the high intensity erosion and sediment yield in the middle yellow river basin many previous studies have indicated that the sediment delivery ratio on the loess plateau approaches 1 this can be explained by the action of hyperconcentrated flows as hyperconcentrated flows exhibit some particular behaviors in erosion and sediment production processes the present study suggests that the erosion by hyperconcentrated flows be regarded as a special type of erosion accordingly some countermeasures are proposed to control hyperconcentrated flows and the resulting erosion

causes and processes of sandy desertification in guinan county qinghai tibet plateau by means of field investigations interpretation of remote sensing images analysis of a digital elevation model and grain size tests we analyzed the causes and processes responsible for sandy desertification in guinan county on the qinghai tibet plateau the desertified land is mainly distributed on the mugetan region and covered 566 km2 about 96 1 of which distributed on the sandy hills we found that reactivation of the underlying fossil dunes supplied the sand that contributed to modern sandy desertification the surface turf which supports a dense growth of grass and its matted roots covers the underlying cohesive silty sands in the sandy hills and both layers protect the dunes against erosion mechanical destruction of the protective shell leads to exposure of fossil dune sands the exposed loose fossil sands are then carried away by the wind creating scarps followed by lateral recession at the bottom of the scarp leading to its collapse the process then repeats with the expansion of recession caused by wind erosion abundant sands are supplied and aeolian activity intensifies repetition of this process expands the blowouts leading to merger of the blowouts and the evolution of mobile dunes similar processes occur at the top of cliffs above the yellow river and mangla river

temporal variability of ultraviolet cloud features in the venus stratosphere abstract statistics on the temporal variability of uv cloud features on venus during 66 days of nominal mission imaging by the pioneer venus orbiter cloud photopolarimeter reveal at least five types of systematic variability on large scales 1 a low latitude global scale wave of period 3 94 0 1 days corresponding to longitudinal motion of the dark equatorial band and propagating westward relative to the mean flow 2 a midlatitude wave of period 5 20 0 2 days corresponding to wavenumber 1 oscillations of the latitude of the bright polar bands and propagating eastward relative to the mean flow 3 2 to 3 week fluctuations in the slope of longitudinal cloud brightness power spectra at intermediate wavenumbers manifested by variations in the intensity of large bow shaped features 4 2 month variations in polar region brightness consistent with polar brightening episodes observed from earth and 5 a monotonic decrease in the disk integrated brightness of venus during the nominal mission which may be either a true time variation or a solar locked longitudinal dependence of brightness small scale features appear to correlate with large scale albedo patterns specifically cellular features exist primarily where large scale dark material is present while the orientation of streak features with respect to latitude circles oscillates with the same 4 day period as the large scale features at low latitudes the wide range of time scales present in the data suggests the complexity of venus stratospheric dynamics extended observations over many years may be becessary to define the general circulation

comparison of measured wind tunnel and sweep simulated soil losses wind erosion estimates from the single event wind erosion evaluation program sweep model of the wind erosion prediction system weps were compared to wind tunnel experiments the influences of wind speed and soil texture were investigated from a previous study soil losses were measured directly in a wind tunnel using three soil types sandy loam loamy sand and sand each under three free stream wind speed conditions 10 18 and 26 m s 1 a different sand soil from another experiment was also tested under five wind speeds from 10 to 18 m s 1 over intervals of 2 m s 1 using a sediment trap and a flux profile estimating method the comparison of measured and estimated agricultural soil losses under non extreme winds less than 18 m s 1 in the wind tunnel was good the loamy sand comparison had an error less than 6 while the sandy loam soil had an error of about 35 sweep underestimated the amount of erosion with the sand soil however because the estimating equations used in sweep to predict soil parameters for agricultural soils are not directly applicable to pure sand surfaces this was expected when conducting sweep simulations it is recommended to use the actual aggregate size distribution asd data if available rather than relying on sweep s asd parameter values being estimated from other soil properties c 2013 elsevier b v all rights reserved

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

short term dynamics of wind erosion of three newly cultivated grassland soils in northern china this study examined the dynamic nature of short term wind erosion processes of three grassland soils under simulated cultivation in a laboratory wind tunnel soil loss on a sandy loam a loamy sand and a sand soil was measured in six successive 10 3 and 1 min exposures at the speeds of 10 18 and 26 m s 1 respectively erodible soil particle sizes of each interval were determined through direct dry sieving it was observed that increasing blowing duration generally led to rapid decrease of soil loss decrease of the erodible soil particle size from a definitely restricted area by any definite speed of wind and the non erodible particles remaining on the soil surface increased from the first to the last blowing interval soil loss decreased by 86 4 94 8 at 10 m s 1 in 60 min 90 0 95 4 at 18 m s 1 in 18 min and 71 5 97 8 at 26 m s 1 in 6 min the results indicate that wind erosion on the newly cultivated soils is most intense during the initial blowing the decrease of soil loss with time is presumed due to modification of soil surface by blowing wind i e the concentration of non erodible aggregates with the deflation of the erodible particles on the soil surfaces

cassini radar observation of punga mare and environs bathymetry and composition abstract in january 2015 fly by t108 the cassini radar observed punga mare titan s northernmost and third largest sea in altimetry mode during closest approach the ground track intercepted a section of the mare and a system of channels and flooded areas connecting punga to kraken mare we use a processing technique successfully adopted for ligeia mare and ontario lacus for detecting echoes from the sea floor and constraining the depth and composition of these liquid bodies we find that along the radar transect punga mare has a maximum measured depth of 110 m the relative reduction in backscatter of the seafloor as a function of increasing depth suggests a liquid loss tangent of 3 1 10 5 while this value is within the formal uncertainty of the loss tangent derived for ligeia mare the best fit solution is lower and is consistent with a nearly pure binary methane nitrogen liquid with little to no ethane or higher order components the indication of very low amounts of ethane toward the pole suggests that atmospheric processes are controlling the surface liquid composition of titan s seas

tensile test of natural microbiotic crust abstract the mechanical properties of microbiotic crust are important to stabilize sandy surfaces in arid and semi arid regions we developed a new experimental approach to perform the tensile test of natural microbiotic crust the modulus of elasticity ultimate stress and one dimensional stress strain relation was obtained the microbiotic crust we measured exhibits linear elastic behavior firstly and then breaks this mechanical character was applied to the study of the rupture of microbiotic crust under the impact of one saltating grain a very simple dimensionless variable was suggested to quantitatively assess surface stability

characteristics of freshly deposited sand and finer sediments along an island braided gravel bed river the roles of water wind and trees over the past two decades there has been a growing interest in the geomorphological mosaic along large floodplain rivers where channel dynamics are seen to drive habitat patch creation and turnover and to contribute to high biological diversity this has required a new perspective on fluvial geomorphology that focuses on biological scales of space and time this study examines the spatial pattern of surface fine sediment accumulations along a reach of a large gravel bed river the tagliamento river in ne italy an area with a moist mediterranean climate and seasonal flow regime the study investigates changes in sediment characteristics during the summer low flow period between april and september focussing on five areas representing a gradient from open bar braided to wooded island braided morphologies the paper demonstrates the importance of riparian vegetation and aeolian fluvial interactions significant contrasts in particle size distributions and organic content of freshly deposited sand and finer sediments were found between sampling areas geomorphological settings and sampling dates in particular wooded floodplain and established islands supported consistently finer sediment deposits than both open bar surfaces and the lee of pioneer islands and in september significantly finer sediments were also found in deposits located in the lee of pioneer islands than on open bar surfaces overall the september samples had a greater variability in particle size characteristics than those obtained from the same sites in april with a general coarsening of the d5 i e the coarse tail of the particle size distribution also in september crusts of fine sediment 30 m d50 64 m had formed on the surface of some of the open bar and pioneer island deposits within the more open sampling areas along the study reach these crusts possessed similar particle size characteristics to aeolian crusts found in more arid environments they were significantly finer than april samples and september subcrust samples obtained from the same sites and had similar particle size characteristics to some samples taken from wooded floodplain established island surfaces and the lee of pioneer islands that were not crusted local climatological and river level data confirm significant wind and rainfall events during a period of consistently low river levels between the april and september sampling periods these support deflation deposition and rain wash of finer sediment during the summer with windblown sediments being deposited on bar surfaces and in the lee of pioneer islands where wood and young trees provide foci for accelerated sedimentation and island growth as well as on marginal floodplains and established islands we conclude that along braided rivers in moist settings but with a distinct dry season aeolian reworking of sediment deposits may have a more important role in driving habitat dynamics than previously considered

the action of wind and water in a mid cretaceous subtropical erg margin system close to the variscan iberian massif spain aeolian processes and ephemeral water influx from the variscan iberian massif to the mid cretaceous outer back erg margin system in eastern iberia led to deposition and erosion of aeolian dunes and the formation of desert pavements remains of aeolian dunes encased in ephemeral fluvial deposits aeolian pods demonstrate intense erosion of windblown deposits by sudden water fluxes the alternating activity of wind and water led to a variety of facies associations such as deflation lags desert pavements aeolian dunes pebbles scattered throughout dune strata aeolian sandsheets aeolian deposits with bimodal grain size distributions mud playa ephemeral floodplain pebble sand and cobble sand bedload stream pebble cobble sand sheet flood sand bedload stream debris flow and hyperconcentrated flow deposits sediment in this desert system underwent transport by wind and water and reworking in a variety of sub environments the nearby variscan iberian massif supplied quartzite pebbles as part of mass flows pebbles and cobbles were concentrated in deflation lags eroded and polished by wind driven sands facets and ventifacts and incorporated by rolling into the toesets of aeolian dunes the back erg depositional system comprises an outer back erg close to the variscan highlands and an inner back erg close to the central erg area the inner back erg developed on a structural high and is characterized by mud playa deposits interbedded with aeolian and ephemeral channel deposits in the inner back erg area ephemeral wadis desiccated after occasional floods were mud cracked and overrun episodically by aeolian dunes subsequent floods eroded the aeolian dunes and mud cracked surfaces resulting in largely structureless sandstones with boulder size mudstone intraclasts floods spread over the margins of ephemeral channels and eroded surrounding aeolian dunes the remaining dunes were colonized occasionally by plants and their roots penetrated into the flooded aeolian sands upon desiccation deflation resulted in lags of coarser grained sediments a renewed windblown supply led to aeolian sandsheet accumulation in topographic wadi depressions synsedimentary tectonics caused the outer back erg system to experience enhanced generation of accommodation space allowing the accumulation of aeolian dune sands ephemeral water flow to the outer back erg area supplied pebbles eroded aeolian dunes and produced hyperconcentrated flow deposits fluidization and liquefaction generated gravel pockets and recumbent folds dune damming after sporadic rains the case of the namib desert monsoonal water discharge thar desert and meltwater fluxes from glaciated mountains taklamakan desert are three potential non exclusive analogues for the ephemeral water influx and the generation of hyperconcentrated flows in the cretaceous desert margin system an increase in relief driven by the aptian anti clockwise rotation of iberia led to an altitude sufficient for the development of orographic rains and snowfall which fed melt water fluxes to the desert margin system quartzite conglomerates and sands dominantly consisting of quartz and well preserved feldspar grains which are also observed in older cretaceous strata indicate an arid climate and the mechanical weathering of precambrian and palaeozoic metamorphic sediments and felsic igneous rocks unroofing of much of the cover of sedimentary rocks in the variscan iberian massif must therefore have taken place in pre cretaceous times

freeze thaw and soil moisture effects on wind erosion abstract wind erosion is very pronounced in semiarid regions during late winter early spring and has major impacts on regional desertification and agriculture in order to identify the effects of freeze thaw and soil moisture on wind erosion wind tunnel experiments were conducted to compare wind erosion effects under various soil moisture gradients in frozen and thawed soil the variation of surface soil moisture after wind erosion and the effective soil particle size distribution was tested to explain the differences the results showed that surface soil moisture content decreased in thawed soil and increased in frozen soil after wind erosion the mean weight diameter which increased with increasing soil moisture was smaller in thawed soil than in frozen soil the wind driven sediment flux of frozen and thawed soil both decreased with increasing moisture owing to the heavier soil particle weight and stronger interparticle bonding forces the critical soil moisture content for suppressing wind erosion was around 2 34 for frozen soil and around 2 61 for thawed soil the wind driven sediment flux of thawed soil was always larger than that of frozen soil at the same moisture content but this difference became negligible at moisture contents above 3 38 we may speculate that wind erosion will be more severe in the future because of the lower soil moisture content and fewer soil freezing days as a result of global warming

wind streaks on venus clues to atmospheric circulation magellan images reveal surface features on venus attributed to wind processes sand dunes wind sculpted hills and more than 5830 wind streaks have been identified the streaks serve as local wind vanes representing wind direction at the time of streak formation and allowing the first global mapping of near surface wind patterns on venus wind streaks are oriented both toward the equator and toward the west when streaks associated with local transient events such as impact cratering are deleted the westward component is mostly lost but the equatorward component remains this pattern is consistent with a hadley circulation of the lower atmosphere

western boundary currents in the martian atmosphere numerical simulations and observational evidence western boundary currents hereafter wbcs are an intensification of meridional fluid flow along the eastward facing flank of a boundary they occur in the earth s oceans the best known instance being the gulf stream and in the terrestrial atmosphere an example of which is the east african jet we have investigated wbcs in numerical simulations of the martian atmosphere where they occur in the presence of large longitudinal topographical gradients combined with the effect we suggest that wbcs have already been simulated by other martian atmospheric models although not identified as such the intensity of these currents is dependent on basic model parameters notably surface drag we show that for physically reasonable values of drag frictional forces dominate the wbcs behavior the requirement of zero net cross equatorial time mean mass flow produces a return flow in simulations with relatively low surface drag which acts in opposition to the tharsis wbc we also show that the intense flow associated with wbcs advects potential vorticity across the equator although the presence of strong radiative damping inhibits low level inertial instabilities that might result from this slope winds are found to have a profound effect on wbc structure especially where they have a component parallel to the jet in these cases slope winds can cancel out or reinforce wbcs depending on their direction enhanced low level winds associated with wbcs may be a factor that influences the locations of dust storm generation the high vertical shear associated with wbcs may also play a role in the maintenance and subsequent decay of these dust storms some observational evidence may exist for wbcs in the form of the alignment of bright depositional dust streaks wave clouds and in wind measurements taken during the parachute descent phase of viking lander 1 through the planetary boundary layer

a waveform model for near nadir radar altimetry applied to the cassini mission to titan the radar altimeter of the cassini mission to titan operates in a transition region between pulse and beam limited conditions due to the specific observation geometry low values of mispointing angle have been found to significantly affect altimeter impulse response ir this involves a nonconventional formulation of the system response which is the main goal of this paper an analytical model of the average return power waveform valid for near nadir altimetry measurements has been developed in order to cope with the particular operating conditions of cassini mission the model used to approximate the altimeter waveform is based on the same general assumptions of the classical brown s model 1977 but exploits a flat surface response approximation by prony s methods both theoretical considerations and simulated data have been taken into account to support the accuracy of the proposed model to infer the main geophysical parameters describing surface topography from altimetry data a parametric estimation procedure has been used the maximum likelihood estimator procedure has been chosen since in principle it can assure optimal performance as a consequence of the analytical model we used to describe the system ir performances of the implemented method have been numerically evaluated through simulation of data received by cassini in high resolution altimeter mode

is the mean venusian tropospheric circulation unsteady 1 the troposphere of venus or that region between the surface and the sulphuric acid cloud layer is characterised by very low horizontal temperature contrasts of less than 10 k such low thermal gradients will have a large impact on the tropospheric mean circulation using a simplified atmospheric model we show that the mean circulation might change in strength and possibly even reverse in direction on timescales of decades to centuries the phenomenon is associated with the high surface pressure and hence long thermal relaxation time scale of the lower atmosphere inertial oscillations appear to play a role in any circulation reversals that occur we note that wind streak data are consistent with a variable hadley circulation our results imply that the venusian cloud layer could also exhibit significant variability on the same very long timescales consistent with some observations

the contribution of aeolian processes to fluvial sediment yield from a desert watershed in the ordos plateau china in arid zones many active aeolian dunes terminate at ephemeral and perennial desert rivers the desert rivers show very high rates of sediment transport that cause deleterious downstream effects on the river system and ecology high sediment loading has been attributed to severe water erosion of sparsely covered watersheds during infrequent but heavy rainfall although aeolian erosion is known to lead to high rates of wind blown sand transport direct confirmation of whether the aeolian processes accelerate or inhibit fluvial sediment loss is lacking here we show that an aeolian fluvial cycling process is responsible for the high rate of suspended sediment transport in a sudalaer ephemeral desert channel in the ordos plateau of china frequent aeolian processes but low frequency once every 3 years on average flooding occur in this region wind blown saltating grains appeared to be unable to cross the desert channel because of interruption of channel induced recirculating air flow and therefore tended to settle in the channel during the windy seasons leading to channel narrowing during flooding this narrowed channel was found to yield a threefold increase in suspended sediment loading and a 3 4 fold increase in the weight percentage of the 0 08 0 2 mm sediment fraction on 18 july 2012 loss of stored aeolian sand due to channel erosion accounted for about half of the total sediment yield in this watershed these findings show that aeolian processes play an essential role in accelerating the sediment yield from a watershed characterized by aeolian fluvial interplay and also suggest that the drier the region and the greater the aeolian process the more the aeolian process contributes to fluvial sediment yield copyright 2013 john wiley sons ltd

aeolian dust in colorado plateau soils nutrient inputs and recent change in source aeolian dust windblown silt and clay is an important component in arid land ecosystems because it may contribute to soil formation and furnish essential nutrients few geologic surfaces however have been characterized with respect to dust accumulation history and resultant nutrient enrichment we have developed a combination of methods to identify the presence of aeolian dust in arid regions and to evaluate the roles of this dust in ecosystem processes unconsolidated sandy sediment on isolated surfaces in the canyonlands region of the colorado plateau differs greatly in mineralogical and chemical composition from associated bedrock mainly aeolian sandstone detrital magnetite in the surficial deposits produces moderately high values of magnetic susceptibility but magnetite is absent in nearby bedrock a component of the surficial deposits must be aeolian to account for the abundance of magnetite which formed originally in far distant igneous rocks particle size analysis suggests that the aeolian dust component is typically as much as 20 30 dust inputs have enriched the sediments in many elements including p mg na k and mo as well as ca at sites where bedrock lacks calcite cement soil surface biologic crusts are effective dust traps that apparently record a change in dust sources over the past several decades some of the recently fallen dust may result from human disturbance of land surfaces that are far from the canyonlands such as the mojave desert some land use practices in the study area have the potential to deplete soil fertility by means of wind erosion removal of aeolian silt

the effects of plantation development on biological soil crust and topsoil properties in a desert in northern china abstract afforestation was one of most successful measures to rehabilitate desertified lands and to improve regional eco environments in the horqin sand land a field experiment was conducted during 2005 and 2006 in the horqin sand land to investigate the effects of populus simonii plantation growth on soil crust formation and topsoil properties the results showed that plantation establishment promoted the development of biological soil crust and improved properties of topsoil 0 5 cm under the crust in sand dunes as the plantation aged soil crust developed gradually from a physical crust to a lichen crust and then to a moss crust and crust coverage thickness hardness very fine sand content clay silt organic carbon and nutrients increased significantly clay silt organic carbon and nutrients in topsoil 0 2 5 cm and 2 5 5 0 cm under the soil crust increased with plantation age and crust development but the magnitude of changes decreased with increasing soil depth changes in soil physical and chemical properties in the crust had a significant positive correlation with plantation age and changes in physical and chemical properties in the 0 5 0 cm layer of topsoil had a significant positive correlation with soil crust development and plantation age soil crust development and changes in topsoil properties under the soil crust can be attributed primarily to the reestablishment of vegetation and the duration that the vegetation is in place

the behavior of specific sediment yield in different grain size fractions in the tributaries of the middle yellow river as influenced by eolian and fluvial processes based on data from 35 stations on the tributaries of the yellow river annual specific sediment yield y s in eight grain size fractions has been related to basin averaged annual sand dust storm days d ss and annual precipitation p m to reveal the influence of eolian and fluvial processes on specific sediment yield in different grain size fractions the results show that y s in fine grain size fractions has the highest values in the areas dominated by the coupled wind water process from these areas to those dominated by the eolian process or to those dominated by the fluvial process y s tends to decrease for relatively coarse grain size fractions y s has monotonic variation i e with the increase in d ss or the decrease in p m y s increases this indicates that the sediment producing behavior for fine sediments is different from that for relatively coarse sediments the results all show that y s for relatively coarse sediments depends on the eolian process more than on the fluvial process and the coarser the sediment fractions the stronger the dependence of the y s on the eolian process the y s d ss and y s p m curves for fine grain size fractions show some peaks and the fitted straight lines for y d ss and y s p m relationships for relatively coarse grain size fractions show some breaks almost all these break points may be regarded as thresholds these thresholds are all located in the areas dominated by the coupled wind water process indicating that these areas are sensitive for erosion and sediment production to which more attention should be given for the purpose of erosion and sediment control a number of regression equations were established based which the effect of rainfall sand dust storms and surface material grain size on specific sediment yield can be assessed copyright 2007 john wiley sons ltd

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

titan fractals and filtering of cassini altimeter data fractal behavior of one titan profile acquired by the cassini altimeter during its first flyby is demonstrated and quantitatively analyzed the inadequacy of popular nonfractal models to represent scale dependent behavior is also discussed our results lead to the conjecture that a proper geometrical model of the titan surface is provided by the fractional brownian motion stochastic process and that the particular acquired profile has a fractal dimension of about 2 4 in addition use of the developed statistical model allows the design of model based filters for a significant improvement of the measurement accuracy at the expense of the horizontal resolution

grain size characteristics of suspended sediment in the yellow river china abstract based on the data from the yellow river and its tributaries a systematic study has been made of the spatial and temporal variations in grain size feature of suspended sediment the grain size characteristics of suspended sediment in the yellow river basin are closely influenced by precipitation seasonal alternations of wind and water action and the nature of surface materials the lower the mean annual precipitation the stronger the wind action the coarser the surface loess materials the coarser is the suspended sediment in particular grain size characteristics of suspended sediment of the middle yellow river s tributaries are controlled by hyperconcentrated flows with suspended sediment concentrations of 300 000 400 000 mg l or more at a station the relationship between grain size and suspended sediment exhibits two peaks with percentages of the 0 05 mm suspended sediment occurring at both low and very high suspended sediment concentrations based on the data from all the tributaries of the middle yellow river an optimal grain size composition of suspended sediment has been identified that leads the annual suspended sediment concentration to the highest values the long term variation of grain size suspended sediment in the yellow river can be related to variations in precipitation and human activities the 30 year record from longmen station shows that during the 1960s the suspended sediment size increased but since the 1970s it has declined controlled by the influencing factors grain size of suspended sediment in the middle yellow river decreases from northwest to southeast

the flux profile of a blowing sand cloud a wind tunnel investigation abstract the flux profile of a blowing sand cloud or the variation of blown sand flux with height is the reflection of blown sand particles that move in different trajectories and also the basis for checking drifting sand here we report the wind tunnel results of systematic tests of the flux profiles of different sized sands at different free stream wind velocities the results reveal that within the 60 cm near surface layer the decay of blown sand flux with height can be expressed by an exponential function q h a exp h b where q h is the blown sand transport rate at height h a and b are parameters that vary with wind velocity and sand size the significance of coefficient a and b in the function is defined a represents the transport rate in true creep and b implies the relative decay rate with height of the blown sand transport rate the true creep fraction the ratio of the sand transported on the surface h 0 to the total transport varies widely decreasing with both sand size and wind speed the flux profiles are converted to straight lines by plotting sand transport rate q h on a log scale the slope of the straight lines that represents the relative decay rate with height of sand transport rate decreases with an increase in free stream wind velocity and sand grain size implying that relatively more of the blown sand is transported to greater heights as grain size and wind speed increase the average saltating height represented by the height where 50 of the cumulative flux percentage occurs increases with both wind speed and grain size implying that saltation becomes more intense as grain size and or wind velocity increase

biological soil crust development and its topsoil properties in the process of dune stabilization inner mongolia china this study was undertaken at horqin sand land inner mongolia northern china field samples of biological soil crusts bscs and underlying topsoil 0 5 cm under bsc were taken in areas of different dune stabilization stages and their physicochemical properties were analyzed including particle size distribution bulk density organic matter nitrogen phosphorus electrical conductivity ec ph and caco3 content the results revealed that semi mobile dunes semi fixed dunes and fixed dunes had developed a physical crust algae crust and moss crust respectively the thickness hardness water content fine fraction and nutrient contents of bscs were gradually increasing along the dune stabilization gradient meanwhile bsc establishment and development enhanced the bulk density silt and clay content and nutrients of the topsoil under it in an increasing tend from semi mobile dune to fixed dune organic matter concentrations and other nutrients in the 0 5 cm topsoil layer under bscs were significantly higher compared to unconsolidated soil control moreover there were strong significant positive correlations between topsoil and bscs organic matter total nitrogen available nitrogen available phosphorus caco3 and 0 05 mm particle content suggesting that bscs have an influence on some of the properties of the underlying topsoil

a study of physico geographical factors for formation of hyperconcentrated flows in the loess plateau of china semi arid climate poor vegetation cover and highly erodible loess can be regarded as the main natural factors responsible for the formation of hyperconcentrated flows on the loess plateau china the degree to which the hyperconcentrated flows develop especially their extreme suspended concentration shows a significant areal differentiation this is closely related to the grainsize composition of suspended sediment an optimal grainsize composition of suspended sediment has been identified which leads to the highest value of extreme concentration among different river basins this optimal composition is related to the combination of three surface material types i e loess wind blown sand and weathered bedrock and it occurs as a result of seasonally alternating wind and water processes operating in this area

archaeology of the anthropocene in the yellow river region china 8000 2000 cal bp although archaeological analysis emphasizes the importance of climatic events as a driver of historical processes we use a variety of environmental and archaeological data to show that human modif

temporal variability in composition and fluxes of yellow river particulate organic matter this study examines temporal variations of the abundance and carbon isotopic characteristics of particulate organic carbon poc and specific source compounds in the context of hydrological variability in the yellow river the content and bulk carbon isotopic characteristics 13c and 14c of poc were relatively uniform over the hydrologic seasonal cycle we attribute these temporally invariant geochemical characteristics to the dominant contribution of loess material to the suspended particulate matter spm in contrast molecular level signals revealed that hydrologic conditions exert a significant influence on the proportional contributions of petrogenic and especially fresh plant derived oc while pre aged soil oc is mobilized via deeper erosion processes e g gully erosion mudslides and is independent of hydrodynamics and surface runoff a coupled biomarker isotope mixing model was applied to estimate the time varying supply of contemporary modern biomass pre aged soil and fossil oc components to chinese marginal seas from the yellow river we found that natural e g precipitation and human induced e g water and sediment regulation variations in hydrological regime strongly influence the flux with the magnitude of the corresponding annual fluxes of poc ranging between 0 343 0 122 mt yr 1 and 0 581 0 213 mt yr 1 but less strongly infleunce proportions of the different oc constituents inter annual differences in pre aged soil and fossil oc fluxes imply that extreme climate events e g floods modulate the exhumation and export of old carbon to the ocean but the oc homogeneity in the pre aged mineral soil dominated watersheds facilitates robust predictions in terms of oc transport dynamics in the past sediment cores and in the future

assessment of aeolian desertification trends from 1975 s to 2005 s in the watershed of the longyangxia reservoir in the upper reaches of china s yellow river abstract global climate change will affect the ecology and environment of the qinghai tibet plateau thus increasing attention is being paid to the aeolian desertification that is occurring in the watershed that supplies the longyangxia reservoir in the upper reaches of china s yellow river we must assess the aeolian desertification trends before developing a plan to restore the region s degraded eco environment in this study land suffered from aeolian desertification was classified into four levels slight moderate severe and extremely severe using a series of indices interpretation of landsat mss and tm data from 1975 s 1989 s and 2005 s was used to establish databases of aeolian desertified land at these three times we then derived the aeolian desertification trends during the study period by overlaying the consecutive databases and we analyzed the driving factors responsible for the observed aeolian desertification the results show a total of 1 721 478 02 ha of aeolian desertified land in 2005 s accounting for 13 of the region s total area from 1975 s to 1989 s the area of aeolian desertified land increased by 229 307 26 ha which represents a 15 increase compared to the 1975 s area and from 1989 s to 2005 s the area of aeolian desertified land decreased by 19 079 87 ha which represents a 1 decrease compared to the 1989 s area the main driving factors responsible for this increased aeolian desertification were climate factors high wind velocity and an increase in annual temperature combined with low precipitation and high evaporation as well as unsustainable human activities and inappropriate policy measures a series of key national projects initiated to combat degradation of the study area s eco environment led to a decrease of aeolian desertified land through obvious restoration of vegetation

titan dune heights retrieval by using cassini radar altimeter abstract the cassini radar is a ku band multimode instrument capable of providing topographic and mapping information during several of the 93 titan fly bys performed by cassini the radar collected a large amount of data observing many dune fields in multiple modes such as sar altimeter scatterometer and radiometer understanding dune characteristics such as shape and height will reveal important clues on titan s climatic and geological history providing a better understanding of aeolian processes on earth dunes are believed to be sculpted by the action of the wind weak at the surface but still able to activate the process of sand sized particle transport this work aims to estimate dunes height by modeling the shape of the real cassini radar altimeter echoes joint processing of sar altimeter data has been adopted to localize the altimeter footprints overlapping dune fields excluding non dune features the height of the dunes was estimated by applying maximum likelihood estimation along with a non coherent electromagnetic em echo model thus comparing the real averaged waveform with the theoretical curves such analysis has been performed over the fensal dune field observed during the t30 flyby may 2007 as a result we found that the estimated dunes peak to trough heights difference was in the order of 60 120 m estimation accuracy and robustness of the mle for different complex scenarios was assessed via radar simulations and monte carlo approach we simulated dunes interdunes different composition and roughness for a large set of values verifying that in the range of possible titan environment conditions these two surface parameters have weak effects on our estimates of standard dune heights deviation results presented here are the first part of a study that will cover all titan s sand seas

the response of infiltration depth evaporation and soil water replenishment to rainfall in mobile dunes in the horqin sandy land northern china to understand the relationships among rainfall infiltration evaporation replenishment in mobile dunes in the semi arid areas of china we used the container of water distribution 100 100 120 cm3 to examine rainfall infiltration soil water redistribution and soil surface evaporation under natural and simulated rainfall conditions the results showed that infiltration depth was linearly related to rainfall amount and intensity rainfall amounts larger than 13 4 mm could replenish soil water at 60 cm depth after redistribution while with rainfalls larger than 39 8 mm infiltration depth could exceed 120 cm rainfall amounts larger than 50 mm produced saturated soil water at 120 cm depth and replenishment amount accounted for 40 4 of the total amount of rainfall soil surface evaporation exhibited a relatively minor change with increases in rainfall when rainfall was larger than 11 8 mm the amount of evaporation and soil water content were significantly correlated at 0 60 cm soil depth but not below these results suggest that the maximum effective depth of evaporation is 60 cm below the ground surface and that rainfall of 13 4 mm is a threshold distinguishing effective from ineffective rainfall in the mobile dunes of the horqin sandy land

erosion and sediment yields as influenced by coupled eolian and fluvial processes the yellow river china based on data from the middle yellow river a model of erosion and sediment yield is proposed to describe coupled eolian and fluvial processes in a transitional zone from and to sub humid climates and to explain rapid erosion and a high sediment yield in the zone in the study area wind action predominates from march to june which erodes weathered bedrock and transports eolian sand to gullies river channels and floodplains in the following summer especially from july to september rainstorm runoff in gullies and river channels transports large quantities of fine loessic material in the form of hyperconcentrated flow as a result most of the previously stored eolian sand and material supplied by mass wasting of loess can be transported to the major tributaries and the main stream of the yellow river resulting in the high specific sediment yield there exists all optimal grain size composition which maximizes suspended sediment concentration in the study area resulted from the combined wind water processes c 2005 elsevier b v all rights reserved

effects of slope gradient on hydro erosional processes on an aeolian sand covered loess slope under simulated rainfall the aeolian sand covered loess slope of the wind water erosion crisscross region of the loess plateau in china may play a key role in contributing excessive sediment to the yellow river understanding its hydro erosional processes is crucial to assessing controlling and predicting soil and water losses in this region and maintaining the ecological sustainability of the yellow river simulated rainfall intensity 90 mm h 1 was used to investigate the runoff and soil loss from loess slopes with different slope gradients 18 27 36 47 and 58 and overlying sand layer thicknesses 0 5 and 10 cm as compared with uncovered loess slopes an overlying sand layer delayed runoff production reduced cumulative runoff and increased cumulative soil loss as well as enhancing variations among slope gradients cumulative runoff and soil loss from the sand covered loess slopes increased with increasing slope gradients and then slightly decreased with a peak at about 47 gradient they both were greater from the 10 cm sand covered loess slope than from the 5 cm except for with 18 slope gradient in general differences in cumulative runoff between sand layer thicknesses became smaller while those in cumulative soil loss became larger with increasing slope gradient runoff and soil loss rates on the sand covered loess slopes exhibited unimodal distributions during the rainstorms maximum values tended to occur at the same rain duration and increased considerably with increasing slope gradient and sand layer thickness on slopes that were less than 47 liquefaction process might occur on the lower loess slopes covered with thinner sand layers but failures similar to shallow landslides might occur when the sand layer was thicker on steeper slopes the presence of an overlying sand layer changed the relationship between runoff and soil loss rates during intense rainstorms and this change varied with different slope gradients our results demonstrated that the effects of slope gradient on hydro erosional processes on the sand covered loess slopes were important and vary with changing sand thickness these effects should be considered when assessing and predicting soil losses from such slopes in the study region and from similar slopes elsewhere

contrasting styles of ephemeral river systems and their interaction with dunes of the skeleton coast erg namibia abstract the skeleton coast erg forms a prominent nnw trending dune belt 6 22 km wide comprising dunes up to 50 m high sub parallel to the south atlantic margin of namibia to a variable degree along its strike the dune belt dams west southwestward flowing ephemeral river systems on their route towards the atlantic ocean the southern rivers koigab uniab and hunkab affecting the erg are characterized by short infrequent ephemeral flows from restricted catchments whereas northern rivers hoanib and hoarusib are fed by large catchment areas favouring higher discharge and more frequent flows as the intertropical convergence zone and greater likelihood of monsoonal rainfall influence is approached the potential for river damming increases in the same downwind direction through the erg because of increasing dune belt width and height and the change from low barchanoid dune forms in the south to large composite transverse dunes in the north whereas cross sections of the southern part of the erg show considerable asymmetry with low barchans and sinuous crested dune forms eastwards but a high dune wall at the western edge cross sections over the northern erg are more uniformly symmetrical as a consequence the northern rivers are effectively dammed at the eastern erg margin causing flood reservoir basins there in contrast southern rivers are dammed within the erg as the most pronounced and commonly encountered barrier is provided by the dunewall at its western border

atmospheric tides on venus iv topographic winds and sediment transport abstract solar heat absorbed by the soil of venus is rapidly deposited in its atmosphere this exchange drives small diurnal temperature and pressure variations these in turn generate periodic winds of a few meters per second and surface stresses capable of blowing sand size grains along the surface of venus this paper presents a new theory of the venus boundary layer which includes the effects of topography use of the mixing length hypothesis eliminates the unknown eddy viscosity maps of predicted mass flux and erosion deposition rates are presented based on the relief measured by the pioneer venus orbiter regional slopes dominate the wind field and corresponding mass transport typical friction speeds are 19 cm s several times those estimated from venera 9 and 10 anemometer data mean aeolian transport is generally away from the equator contrary to the prevailing direction of wind streaks seen by the magellan orbiter including a steady hadley circulation can correct the wind direction but not the friction speeds

a model to study the grain size components of the sediment deposited in aeolian fluvial interplay erosion watershed abstract aeolian fluvial interplay erosion areas with complex dynamics and physical sources are the main suppliers of coarse sediment in the yellow river understanding the composition distribution and sources of deposited sediments in such areas is of great importance for the control of sediment transport in rivers in this paper a typical aeolian fluvial interplay erosion watershed the dongliu gully was studied and the frequency distribution curves of sediments deposited in the stream channel were fitted using the weibull function sources of deposited sediment in the stream channel were analyzed based on the law of the conservation of matter results showed that the hilly zone accounted for 78 of deposited sediments which were dominated by material with a median grain size d 50 of 0 093 mm and the desert zone accounted for 22 of deposited sediments which were dominated by material with a d 50 of 0 01 mm wind erosion dynamics accounted for 72 of deposited sediments while water erosion dynamics accounted for only 28 this research provides a theoretical basis for the control and management of rivers with high sediment content

characteristics of wind blown sand on gobi mobile sand surface the characteristics of wind blown sand on gobi mobile sand surface have been investigated through field observation and wind tunnel experiments on moving sand surface the pattern of wind speed profile in sand flow follows the power function overline u az b and its power exponent is about 0 20 while on gobi surface due to collision of sand grains with gravels the structure of sand flow differs from that on moving sand surface which decreases exponentially with height the height of blown sand activities on gobi surface is mainly concentrated below 20 cm in addition the structure of sand flow can reach a peak at a certain height and increases with inlet wind velocity

liquid filled canyons on titan in may 2013 the cassini radar altimeter observed channels in vid flumina a drainage network connected to titan s second largest hydrocarbon sea ligeia mare analysis of these altimeter echoes shows that the channels are located in deep up to 570 m steep sided canyons and have strong specular surface reflections that indicate they are currently liquid filled elevations of the liquid in these channels are at the same level as ligeia mare to within a vertical precision of about 0 7 m consistent with the interpretation of drowned river valleys specular reflections are also observed in lower order tributaries elevated above the level of ligeia mare consistent with drainage feeding into the main channel system

controlling windblown sand problems by an artificial gravel surface a case study over the gobi surface of the mogao grottoes abstract in arid regions gravel surfaces are usually known for protecting the soil from wind erosion trapping the sand and dust carried by the wind thereby forming a sink of sediment however gravel surfaces with a suitable gravel size and coverage density can also act as the source of sediment under unsaturated wind flow a dynamically equilibrated gravel surface can be built to prevent potential windblown sand problems in the dunhuang mogao grottoes in northwestern china unlike previous studies that suggested constructing a high coverage 50 or more gravel surface on the gobi land on top of the mogao grottoes a much lower value of 30 is recommended this kind of artificial gravel surface can protect the underlying sand materials from wind erosion and trap the invading westerly windblown sand at the same time the deposited sand over the artificial gravel surface can be transported to the western megadunes by the easterly wind under the multidirectional wind regime the gravel surface can remain from sand burial over the long term