sediment motion and velocity in a glacier fed stream current understanding of coarse sediment transport e g threshold for motion travel length and virtual velocity in mountain rivers is still quite limited and even less is known about glacial streams however the hydrological characteristics of these systems strong daily discharge fluctuations high water turbidity pose challenges to the use of tracers to monitor bed sediment dynamics as tagged clasts are usually located after bedload events when flow stage has receded e g by means of portable antennas in the case of passive integrated transponders pit the use of stationary antennas still scarcely in use worldwide to detect pit tagged particles has potential advantages in glacier fed streams if water discharge is monitored continuously a stationary antenna provides real time data on the actual discharge at the moment of tracer particles passage this study focuses on incipient motion and virtual velocity of bed particles measured by a stationary antennas system in a steep mountain channel saldur river drainage area 18 6 km2 italian alps where significant daily discharge fluctuations and bedload transport occur as a result of a nivo glacial regime four stationary antennas were installed 50 m apart in the study reach a total of 629 pit tagged clasts were inserted in the studied reach between 2011 and 2014 ranging in size from 35 mm to 580 mm with an overall recovery rate of around 44 critical discharge for sediment entrainment was obtained by detecting the movement of tracers placed immediately upstream of antennas virtual velocity was derived by knowing distances between the antennas and travel time of tracers results on initiation of motion show that the relationship between the size of transported tracers and the discharge measured at the time clasts were passing the stationary antenna is very weak the influence of antecedent flows on incipient motion was thus investigated by dividing the highest discharge recorded between each pit deployment and the subsequent entrainment by the actual critical discharge at the time of movement ratio qmax qc results show that approximately 50 of tracers moved at qmax qc 1 2 and that 73 of tracers moved at qmax qc 1 5 therefore about 30 of tracers had to previously experience a discharge substantially greater than the one that actually mobilized them also coarser particles moved at higher qmax qc ratios suggesting that higher antecedent flows may be needed to destabilize bed clustering results on the virtual velocity of the pit tagged clasts employed in the field show that the virtual velocity turned out to be highly variable ranging from 101 to 10 5 m min 1 and weakly related to either particle size or flow discharge however virtual velocity was well correlated with the highest flow discharge experienced by each tracer normalized by a percentile of the flow duration curve this evidence further stresses the importance of flow history on sediment entrainment and transport finally the pros and cons of the deployed monitoring technology are discussed

the infiltration of fine matrices into coarse grained alluvial sediments and its implications for stratigraphical interpretation traps designed to simulate the framework gravel of natural streams and installed in a coarse grained channel allow the identification and differentiation of the processes governing the infiltration of fines into bed interstices vertical patterns of matrix distribution reflect the relative importance of variables acting at both the surface of the channel bed and within the bed sediments differences in grain size and therefore pore size of the framework exercise a strong controlling influence an armour layer of coarse particles superimposed on comparatively finer sub surface bed material common to many coarse grained rivers is shown to encourage the clogging of near surface pores with matrix fines below the obstruction interstices may be protected from incursion and the gravel framework is often left open this is the reason for patchy concentrations of matrices often reported in the stratigraphical literature in contrast a uniform size grading of the bed sediment or an upwards fining leads to a more uniform packing of the interstices with matrix flood history is shown to be an important determinant of both the size distribution and the spatial distribution of matrices and is useful in providing a dynamic explanation of the variability of matrices observed from place to place in ancient deposits

experimental study of incipient motion in mixed size sediment transport rates of five sediments were measured in a laboratory flume three of these sediments had the same mean size the same size distribution shape and different values of grain size distribution standard deviation the critical shear stress for incipient motion of the individual size fractions within these sediments was estimated as that shear stress that produced a small dimensionless transport rate the sorting of the sediment mixture had little effect on the critical shear stress of individual fractions once the median size d50 of the mixture and a fraction s relative size di d50 are accounted for our data combined with previously published data show a remarkably consistent relation between the critical shear stress of individual fractions and the fraction s relative grain size despite a broad variation in the available data of mixture sorting grain size distribution shape mean grain size and grain shape all fractions in a size mixture begin moving at close to the same value of bed shear stress during steady state transport conditions this result is apparently true for transport systems where the transport rates of individual fractions are determined solely by the flow and bed sediment recirculating systems as well as for systems where the fractional transport rates are imposed on the system feed systems this equivalence in initial motion results is important because natural transporting systems often show attributes of both types of behavior in an unknown combination

the effects of flood history on sediment transport in gravel bed rivers abstract the transport of coarse sediment during floods often exhibits hysteresis patterns from changes in flow fields channel geometry bedforms or sediment supply conditions flume experiments that simulate hydrographs tend to confirm that hysteresis is a consequence of the progressive organization of surface sediments in terms of grain protrusion imbrication orientation and roughness hysteretic patterns are also highly dependent on the kind of sediment supply conditions and the type of simulated hydrograph a factor that has not been investigated extensively is the effect of the timing and sequencing of floods on bedload transport depending on its magnitude and duration each flood leaves the channel bed in a different condition which influences the bedload transport of the next event representing the river bed s memory of past floods which can determine future responses to natural disturbances in this study i investigated the effects of different sequences of events i e the flood history on sediment transport through a series of flume experiments that simulated three types of stepped and symmetrical hydrographs ranging from short duration high magnitude to long duration low magnitude events under sediment recirculation conditions hydrographs were simulated as a sequence of the same event and with events in different sequences in order to explore the effects of different antecedent conditions on sediment transport the results show that a previous event decreases the rates of sediment transported by a certain hydrograph by around 40 if a high magnitude event precedes another one and around 70 if a low magnitude event precedes another event of similar magnitude a low magnitude event does not affect the rate of sediment transported by a subsequent high magnitude flood but a high magnitude event reduces the sediment transported by a subsequent long duration low magnitude event

fluvial origin of the valley system in northern victoria land antarctica from quantitative geomorphic analysis a network of sinuous valleys with typical dendritic pattern characterizes northern victoria land nvl in antarctica subparallel to parallel and angular to rectangular patterns are also present quantitative geomorphic analysis of the valley network has been carried out utilizing gis spatial analysis while drainage densities and drainage frequencies show low values segments of the nvl valley network are substantially well organized as indicated by bifurcation ratio r b and direct bifurcation ratio r bd parameters all basins faithfully adhere to horton s laws of drainage network composition quantitative geomorphic analysis suggests that the valley system can be ascribed to fl uvial origin and that consequently a morphoclimatic system completely different from that of present day must have driven its carving the resulting data provide indications about the origin of the valley network and this invaluable information can be used for the reconstruction of earlier phases of glacial history and climatic and tectonic evolution of this signifi cant antarctic region fluvial erosion enhanced the denudation of the transantarctic mountains from at least 55 ma to at least the eocene oligocene boundary ca 34 ma fluvial basins adapted to the tectonic structure following the main regional fault systems a well developed alpine topography postdates the fl uvial morphology temperate glaciers were responsible for denudation until the late miocene parasitic glaciers presently mantle the previously sculpted topography present day glacial erosion is negligible and denudation has been exceedingly slow since 7 5 ma

the evolution of the subglacial landscape of antarctica the aim is to investigate the evolution of the subglacial landscape of antarctica using an ice sheet and erosion model we identify different stages of continental glaciation and model the erosion processes associated with each stage the model links erosion to the basal thermal regime and indicates that much of the antarctic interior may have been subject to less than 200 m of erosion the depth of erosion reflects the presence or absence of warm based ice and the consistency of ice flow direction this information linked with knowledge about landscapes of glaciation in the northern hemisphere and some simple but robust assumptions about initial topography is used to generate a map of the subglacial antarctic landscape in which much of the lowland interior resembles the landscapes of areal scouring typical of the laurentian and scandinavian shields near the continental margins selective linear erosion has overdeepened pre existing river valleys by as much as 2 8 km high elevation plateaus adjacent to such drainage systems have survived largely unmodified under cold based ice high erosion rates result from steep thermal gradients in basal ice mountain regions such as the gamburtsev mountains uplands in dronning maud land and massifs in west antarctica are likely to bear features of local alpine glaciation such landscapes may have been protected under cold based ice for the last 34 myrs or possibly longer

channel adjustments to a succession of water pulses in gravel bed rivers gravel bed rivers commonly exhibit a coarse surface armor resulting from a complex history of interactions between flow and sediment supply the evolution of the surface texture under single storm events or under steady flow conditions has been studied by a number of researchers however the role of successive floods on the surface texture evolution is still poorly understood an experimental campaign in an 18 m long 1 m wide flume has been designed to study these issues eight consecutive runs each one consisting of a low flow period of variable duration followed by a sudden flood water pulse lasting 1 5 h have been conducted the total duration of the experiment was 46 h the initial bed surface was created during a 280 h long experiment focused on the influence of episodic sediment supply on channel adjustments our experiments represent a realistic armored and structured beds found in mountain gravel bed rivers the armor surface texture persists over the duration of the experiment the experiment exhibits downstream fining of the bed surface texture it was found that sorting processes were affected by the duration of low flow between flood pulses since bed load transport is influenced by sediment sorting the evolution of bed load transport is impacted by the frequency of the water pulses short interpulse durations reduce the time over which fine material transported as bed load can be winnowed this in turn contributes to declining reduction of the bed load transport over time while the sediment storage increases

antarctic bedrock topography uncertainty and ice sheet stability antarctic bedrock elevation estimates have uncertainties exceeding 1 km in certain regions bedrock elevation particularly where the bedrock is below sea level and bordering the ocean can have a large impact on ice sheet stability we investigate how present day bedrock elevation uncertainty affects ice sheet model simulations for a generic past warm period based on the mid pliocene although these uncertainties are also relevant to present day and future ice sheet stability we perform an ensemble of simulations with random topographic noise added with various length scales and with amplitudes tuned to the uncertainty of the bedmap2 data set total antarctic ice sheet retreat in these simulations varies between 12 6 and 17 9 m equivalent sea level rise after 3 kyrs of warm climate forcing this study highlights the sensitivity of ice sheet models to existing uncertainties in bedrock elevation and the ongoing need for new data acquisition

structural properties of mobile armors formed at different flow strengths in gravel bed rivers differences in the structure of mobile armors formed at three different flow strengths have been investigated in a laboratory flume the temporal evolution of the bed surfaces and the properties of the final beds were compared using metrics of surface grain size microtopography and bed organization at both grain and mesoscales measurements of the bed condition were obtained on nine occasions during each experiment to describe the temporal evolution of the beds structured mobile armors formed quickly in each experiment at the grain scale 1 45 mm 9 ds50 17 mm where ds50 is the median surface particle size surface complexity decreased and bed roughness increased in response to surface coarsening and the development of the mobile armor particles comprising the armor also became flow aligned and developed imbrication at a larger scale 100 200 mm the surface developed a mesoscale topography through the development of bed patches with lower and higher elevations metrics of mobile armor structure showed remarkable consistency over prolonged periods of near constant transport demonstrating for the first time that actively transporting surfaces maintain an equilibrium bed structure bed structuring was least developed in the experiments conducted at the lowest flow strength however little difference was observed in the structural metrics of the mobile armors generated at higher flows although the range of transport rates studied was limited the results suggest that the structure of mobile armors is insensitive to the formative transport rate except when rates are low 0 03 where is the dimensionless shear stress

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

early pliocene marine sediments coastline and climate of east antarctica we record the first onshore late tertiary fossiliferous marine deposit from the 8000 km long coastline of east antarctica glaciomarine sediments containing abundant diatoms and molluscs were deposited in shallow waters off an open coast during the early pliocene 4 5 3 5 ma and are now exposed less than 15 m above sea level on marine plain in the vestfold hills lat 68 359s long 78 009e marine diatoms suggest early pliocene as the most probable age of the sediments fossil sand wedges show that the deposit was above sea level at least briefly before it was covered with water and subsequently capped with glaciomarine till the coastline at the time of deposition of the marine sediments is inferred to have been close to but farther inland than that of today the ice margin may have been 50 km farther inland considerably reducing the ice volume of antarctica climate at the time of deposition was interglacial and perhaps warmer than the present

ice distal upper miocene marine strata from inland antarctica abstract glacimarine strata of the battye glacier formation 130 m thick pagodroma group exposed in the amery oasis of east antarctica provide a record of late miocene palaeoenvironmental conditions in an ice distal setting the formation overlies the amery erosion surface 300 m to 270 m above sea level that formed during an advance of the lambert glacier into prydz bay odp site 739 at least 750 km further north than today two lithological members a grey and muddier lower member and a brown sand rich upper member reflect variation in proximity to the terminus of the lambert glacier ice distal glacimarine diatom bearing mud up to 12 biogenic silica and in situ articulated molluscs occur in the lower member the battye glacier formation is significant because of its inland location which indicates that ice distal marine conditions existed 250 km inland from the current amery ice shelf edge similar neogene strata are known on land only from the pliocene sorsdal formation in the vestfold hills near the antarctic coast three stratigraphic intervals of diatom bearing mud are recognized from glacially reworked clasts and from in situ strata informally referred to as the mcleod beds and bed a the diatom bearing mud also contains sponge spicules and minor silicoflagellates and ebridians marine diatom biostratigraphy constrains the age of the beds to between 10 7 and 9 0 ma late miocene abundant benthic diatoms suggest deposition within shallow euphotic waters the high abundance of intercalary valves of eucampia antarctica from an interval of the mcleod beds suggests that there was less winter sea ice than in prydz bay today it is unlikely that sea ice was perennial because the presence of thalassionema spp and stellarima stellaris roper hasle et sims suggests that summer sea surface temperatures were too warm 0 c and 3 c respectively the palaeoclimate at the time of deposition appears to have been analogous to that in modern fjords of east greenland e g kangerdlugssuaq fjord which is consistent with the depositional model proposed previously for the pagodroma group the three diatom bearing mud intervals were deposited in the amery oasis 250 km inland of the current amery ice shelf edge when the east antarctic ice sheet was reduced in size relative to today

stabilizing self organized structures in gravel bed stream channels field and experimental observations stable reticulate structures which we call stone cells have been observed in cobble gravel channel beds with low bed material transport rates experiments show that such structures develop simultaneously with the armor layer during an extended period when flows do not exceed the shields threshold by more than 2 times so that bed material transport is low they are constructed by particles moving from less stable positions into more stable configurations against each other intermediate developments include clusters and stone lines they reduce sediment transport by orders of magnitude and are evidently a major stability promoting mechanism in gravel channels the timescale for their development suggests that the boundaries of many gravel bed channels are not in equilibrium with recent competent flows but reflect the history of recent dominant flows

reconstructions of antarctic topography since the eocene oligocene boundary abstract accurate models of past antarctic ice sheet behaviour require more realistic reconstructions of the evolution of bedrock topography however other than a preliminary attempt to reconstruct antarctic topography at the eocene oligocene boundary the long term evolution of antarctica s subglacial topography throughout its glacial history has not previously been quantified here we derive new reconstructions of antarctic topography for four key time slices in antarctica s climate and glacial history the eocene oligocene boundary ca 34 ma the oligocene miocene boundary ca 23 ma the mid miocene climate transition ca 14 ma and the mid pliocene warm period ca 3 5 ma to reconstruct past topography we consider a series of processes including ice sheet loading volcanism thermal subsidence horizontal plate motion erosion sedimentation and flexural isostatic adjustment and validate our models where possible using onshore and offshore geological constraints our reconstructions show that the land area of antarctica situated above sea level was 25 larger at the eocene oligocene boundary than at the present day offshore sediment records and terrestrial constraints indicate that the incision of deep subglacial topographic troughs around the margin of east antarctica occurred predominantly in the oligocene and early miocene whereas in west antarctica erosion and sedimentation rates accelerated after the mid miocene changes to the topography after the mid pliocene were comparatively minor our new palaeotopography reconstructions provide a critical boundary condition for models seeking to understand past behaviour of the antarctic ice sheet and have implications for estimating changes in global ice volume temperature and sea level across major cenozoic climate transitions

the effect of hydrographs on bed load transport and bed sediment spatial arrangement 1 field measurements of sediment transport in gravel bed rivers often reveal hysteretic effects due to differences in sediment availability between the rising and falling limbs of a flood hydrograph however only a small number of flume studies have analyzed the dynamics of sediment transport during hydrographs three types of stepped hydrographs with contrasting durations and magnitudes are simulated here under sediment recirculation conditions bed load transport rate and grain size have been measured continuously the dynamic behavior of the surface armor layer has been explored by analyzing digital photographs and laser scanner surveys of the bed surface taken during hydrographs the results indicate that sediment transport during the falling limb was lower than during the rising limb in all of the three types of hydrographs this reduction is more evident for the low magnitude hydrographs the grain size of the bed remained virtually constant throughout the hydrographs but the grain size of transported sediments exhibited a counterclockwise hysteresis also a significant increase in the reference shear stress for sediment entrainment was measured during the falling limb of hydrographs additionally a detailed analysis of partial transport dynamics of the bed surface sediments reveals a reduction in sediment mobility during the falling limb of the hydrographs the difference in sediment entrainment and transport before and after the peak of the hydrographs appears to be caused by a change in the organization of the surface sediments an analysis of detailed laser scan bed surveys reveals a phase of bed restructuring lower vertical roughness clast rearrangement during the falling limb of hydrographs consequently changes in the degree of organization and complexity of the bed surface are likely the cause of the reduced mobility of sediments and thus of the reduced sediment transport rate during the falling limb of the hydrographs

taking the river inside fundamental advances from laboratory experiments in measuring and understanding bedload transport processes bedload transport in gravel bed rivers impacts channel stability the lifespan of hydraulic structures physical components of aquatic habitat and long term channel evolution field measurements of bedload transport are notoriously difficult which precludes understanding many of the processes and mechanics associated with grain motion such uncertainties are exacerbated when using bedload transport equations most of which were derived using data from a single river or set of laboratory flume experiments recently laboratory experiments have focused on better quantifying the processes that impact bedload fluxes which can then be used to improve sediment transport predictions we highlight recent advances in laboratory instrumentation that can be used in bedload transport studies in particular more accurate ways to measure bedload fluxes near bed turbulence bed grain sizes and topography hold great promise laboratory experiments have also fundamentally improved our understanding of the influence of sediment supply and armoring processes on bedload fluxes and channel conditions the importance of flow hydrographs in controlling total bedload transport rates and bedload hysteresis has also been demonstrated using flume experiments finally many details about the mechanics of grain motion including flow turbulence bed arrangement and particle transport statistics are only possible through laboratory investigations and we feature key knowledge gaps that can be improved with further study

potential seaways across west antarctica the west antarctic ice sheet wais has long been considered vulnerable to rapid retreat and today parts are rapidly losing ice projection of future change in wais is however hampered by our poor understanding of past changes especially during interglacial periods that could be analogs for the future but which undoubtedly provide an opportunity for testing predictive models we consider how ice loss would open seaways across wais these would likely alter southern ocean circulation and climate and would broadly define the de glacial state but they may also have left evidence of their existence in the coastal seas they once connected we show the most likely routes for such seaways and that a direct seaway between weddell and ross seas which did not pass through the amundsen sea sector is unlikely continued ice loss at present rates would open seaways between amundsen and weddell seas a w and amundsen and bellingshausen seas a b in around one thousand years this timescale indicates potential future vulnerability but also suggests seaways may have opened in recent interglacial periods we attempt to test this hypothesis using contemporary bryozoan species assemblages around antarctica concluding that anomalously high similarity in assemblages in the weddell and amundsen seas supports recent migration through a w other authors have suggested opening of seaways last occurred during marine isotope stage 7a 209 ka bp but we conclude that opening could have occurred in mis 5e 100 ka bp when antarctica was warmer than present and likely contributed to global sea levels higher than today

spatial variations in surface sediment structure in riffle pool sequences a preliminary test of the differential sediment entrainment hypothesis dseh riffle pool sequences are maintained through the preferential entrainment of sediment grains from pools rather than riffles this preferential entrainment has been attributed to a reversal in the magnitude of velocity and shear stress under high flows however the differential sediment entrainment hypothesis dseh postulates that differential entrainment can instead result from spatial sedimentological contrasts here we use a novel suite of in situ grain scale field measurements from a riffle pool sequence to parameterise a physically based model of grain entrainment field measurements include pivoting angles lift forces and high resolution dems acquired using terrestrial laser scanning from which particle exposure protrusion and surface roughness were derived the entrainment model results show that grains in pools have a lower critical entrainment shear stress than grains in either pool exits or riffles this is because pool grains have looser packing hence greater exposure and lower pivoting angles conversely riffle and pool exit grains have denser packing lower exposure and higher pivoting angles a cohesive matrix further stabilises pool exit grains the resulting predictions of critical entrainment shear stress for grains in different subunits are compared with spatial patterns of bed shear stress derived from a 2d computational fluid dynamics cfd model of the reach the cfd model predicts that under bankfull conditions pools experience lower shear stresses than riffles and pool exits however the difference in sediment entrainment shear stress is sufficiently large that sediment in pools is still more likely to be entrained than sediment in pool exits or riffles resulting in differential entrainment under bankfull flows significantly this differential entrainment does not require a reversal in flow velocities or shear stress suggesting that sedimentological contrasts alone may be sufficient for the maintenance of riffle pool sequences this finding has implications for the prediction of sediment transport and the morphological evolution of gravel bed rivers

cenozoic landscape evolution of an east antarctic oasis radok lake area northern prince charles mountains and its implications for the glacial and climatic history of antarctica abstract ice free areas antarctica reveal a multi million year history of landscape evolution but most attention up to now has focused on the transantarctic mountains the amery oasis in the northern prince charles mountains borders the lambert glacier amery ice shelf system that drains 1 million km2 of the east antarctic ice sheet and therefore provides a record of fluctuations of both local and regional ice since the ice sheet first formed in early oligocene time this glacial record has been deciphered by i geomorphological mapping from aerial photographs and on the ground ii documenting the relationship between thick well dated uplifted glaciomarine strata and the underlying palaeolandscape iii examining surficial sediment facies and iv surface exposure dating using 10be and 26al the se amery oasis records at least 10 million years of landscape evolution beginning with a pre late miocene phase of glacial erosion followed by deposition of glaciomarine strata of the battye glacier formation pagodroma group in late miocene time a wet based ice sheet next expanded over the se amery oasis following which deposition of the glaciomarine pliocene bardin bluffs formation pagodroma group took place both formations were uplifted by at least 500 and 200 m respectively their tops are characterised by geomorphological surfaces upon which intensive periglacial activity took place higher level bedrock areas were subjected to deep weathering and tor formation early pleistocene time was characterised by expansion of a cold based ice sheet across the whole area but it left little more than patches of sandy gravel and erratic blocks late pleistocene expansion of local ice the battye glacier saw deposition of moraine mound complexes on low ground around radok lake and ice dammed lake phenomena subglacial drainage of the lake escaped to the east exhuming the sediment filled gorges holocene landscape modification has been relatively superficial overall the landscape of the amery oasis evolved primarily under the influence of wet based probably polythermal glaciers in miocene and pliocene times whereas the quaternary period was characterised mainly by cold based glaciers that had comparatively little impact on the landscape

critical conditions for particle motion in coarse bed materials of nonuniform size distribution initiation of particle motion in a bed material of nonuniform size distribution may be quantified by qci qcr di dr b where qci is the critical unit discharge at which particle size di enters motion qcr is the critical condition for a reference size dr unaffected by the hiding exposure effects associated with nonuniform size distributions i and r refer to percentiles of the distribution and b varies from 0 equal mobility in entrainment of all particle sizes to 1 5 2 5 full size selective transport currently there is no generally accepted method for predicting the value of b flume and field data are therefore combined to investigate the above relationship thirty seven sets of flume data quantify the relationship between critical unit discharge and particle size for bed materials with uniform size distributions used here to approximate full size selective transport field data quantify the relationship for bed materials of nonuniform size distribution at 24 sites with b ranging from 0 15 to 1 3 intersection of the two relationships clearly demonstrates the hiding exposure effect in some but not all cases dr is close to the median size d50 the exponent has two clusters of values b 1 for sites subject to episodic rain fed floods and data collected by bedload pit trap and tracers and b 1 sites with relatively infrequent bedload transport where particle embedding and consolidation could reduce the mobility of coarser particles and for b 0 7 a looser bed structure with frequent transport events allowing hiding exposure and size selection effects to achieve their balance as yet there is no firm evidence for such a dependency on bed structure but variations in b could potentially be caused by factors outside those determining equal mobility or size selection but appearing to affect b in the same way

detection of overpressure zones and a statistical model for pore pressure estimation from well logs in the krishna godavari basin india abnormally high pressures measured by repeat formation tester rft and detected by well log data from 10 wells in the krishna godavari k g basin occur in the vadaparru shale of miocene and raghavapuram shale of early cretaceous age overpressures generated by disequilibrium compaction and pore pressures have been estimated using the conventional eaton sonic equation with an exponent of 3 0 the observed abnormal pore pressure gradient ranges from 11 85 to 13 10 mpa km whereas fracture pressure gradient varies from 17 40 to 19 78 mpa km the magnitude of vertical stress sv has a gradient from 21 00 to 23 10 mpa km the minimum horizontal principal stress sh magnitude is found to vary from 64 to 77 of the sv in normally pressured to overpressured sediments a multiple linear regression model with a squared multiple correlation coefficient r2 of 0 94 is proposed for pore pressure prediction from gamma ray density and sonic logs to focus on efficient drilling operations and to prevent borehole instability the statistical model has been calibrated with the rft data from five wells covering about 3400 sq km area of the onshore k g basin the model predicted pore pressure values are in close agreement with the actual rft data for another four wells including a well in the offshore k g basin hence the proposed regression model may be useful for predicting pore pressure from other well logs in the k g basin

extremely low long term erosion rates around the gamburtsev mountains in interior east antarctica the high elevation and rugged relief 3 km of the gamburtsev subglacial mountains gsm have long been considered enigmatic orogenesis normally occurs near plate boundaries not cratonic interiors and large scale tectonic activity last occurred in east antarctica during the pan african 480 600 ma we sampled detrital apatite from eocene sands in prydz bay at the terminus of the lambert graben which drained a large pre glacial basin including the northern gamburtsev mountains apatite fission track and u th he cooling ages constrain bedrock erosion rates throughout the catchment we double dated apatites to resolve individual cooling histories erosion was very slow averaging 0 01 0 02 km myr for 250 myr supporting the preservation of high elevation in interior east antarctica since at least the cessation of permian rifting long term topographic preservation lends credence to postulated high elevation mountain ice caps in east antarctica since at least the cretaceous and to the idea that cold based glaciation can preserve tectonically inactive topography

dynamic behaviour of the east antarctic ice sheet during pliocene warmth warm intervals within the pliocene epoch 5 33 2 58 million years ago were characterized by global temperatures comparable to those predicted for the end of this century1 and atmospheric co2 concentrations similar to today2 3 4 estimates for global sea level highstands during these times5 imply possible retreat of the east antarctic ice sheet but ice proximal evidence from the antarctic margin is scarce here we present new data from pliocene marine sediments recovered offshore of adelie land east antarctica that reveal dynamic behaviour of the east antarctic ice sheet in the vicinity of the low lying wilkes subglacial basin during times of past climatic warmth sedimentary sequences deposited between 5 3 and 3 3 million years ago indicate increases in southern ocean surface water productivity associated with elevated circum antarctic temperatures the geochemical provenance of detrital material deposited during these warm intervals suggests active erosion of continental bedrock from within the wilkes subglacial basin an area today buried beneath the east antarctic ice sheet we interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the east antarctic ice sheet was sensitive to climatic warmth during the pliocene

minimal pliocene pleistocene uplift of the dry valleys sector of the transantarctic mountains a key parameter in ice sheet reconstructions we propose that there has been little or no pliocene pleistocene uplift of the dry valleys sector of the transantarctic mountains on the basis of isotopic dating and mapping of in situ cinder cone deposits on the walls of taylor valley twenty seven 40ar 39ar incremental heating analyses on whole rock samples from subaerially erupted olivine basanite volcanic outcrops of known elevations define 14 eruptions ranging in age from 3 89 to 1 50 ma because taylor valley opens directly onto the ross sea these results show that any surface uplift during the past 2 57 m y was 300 m our conclusion of minimal uplift contradicts previous models of dramatic uplift up to 3000 m since 3 ma and associated hypotheses that uplift caused climatic cooling and growth of a polar east antarctic ice sheet

west antarctic paleotopography estimated at the eocene oligocene climate transition 1 one generally recognized limitation of models for rapid growth of antarctic ice near the eocene oligocene transition is that they are based on present topography corrected only for removal of modern ice for west antarctica this results in large areas below sea level that would not readily host ice in the recently active west antarctic rift system other factors may have contributed to significant vertical motions since the eocene additional corrections for thermal contraction resulting from tectonic extension and for erosion and sedimentation since 34 ma restore most of west antarctica to above sea level increasing total antarctic land area by 10 20 because ice sheets have convex slopes the potential increase in ice volume is larger than the increase in land area accounting for large changes in west antarctic topography may resolve conflicts between ice models and data by demonstrating the possibility of an early large west antarctic ice sheet

age provinces in the antarctic craton evidence from detrital zircons in permian strata from the beardmore glacier region antarctica abstract the antarctic gondwana sequence crops out along the transantarctic mountains permian strata at mt bowers and mt weeks in the central part of the range were mainly derived from the ice covered east antarctic craton for which the geology is inferred from coastal outcrops and the miller range in the transantarctic mountains analysis of detrital zircons from permian sandstones at those two localities demonstrate a slowly changing zircon age probability distribution for four samples from the lower part of the sequence with an abrupt change for the upper buckley formation sandstone the stratigraphically lowest sample from a unit informally designated the mt bowers sandstone is dominated by zircons in the age range 610 540 ma with minor components at 1 0 ga and 2 7 ga upward the pagoda formation sandstone is likewise dominated by zircons of 600 550 ma age together with a significant grenville age cluster 1 3 1 0 ga and a minor 1 5 1 4 ga cluster the fairchild formation sandstone has a preponderance of grains in the range 600 530 ma with a scatter of older ages zircon grains in the lower buckley formation sandstone are principally in the range 575 520 ma with another cluster at 470 450 ma and a scattering of older ages most zircons in the upper buckley formation sandstone are permian in age but with a very small component in the range 650 475 ma and a trace of older ages archean to early mesoproterozoic zircon grains are few in number and may have been recycled from distal outcrops the 1 5 1 4 ga grains suggest an unexposed mesoproterozoic source within the east antarctic craton which could have been linked to laurentian north america the grenville age source is considered to be similarly a sub glacial belt in the interior of east antarctica zircons with a late neoproterozoic to ordovician signature 600 460 ma were derived from a ross orogen foreland sequence and or an early and inland extension of the orogen itself permian zircons in the upper buckley sandstone reflect the development of a magmatic arc on the gondwana pacific margin

ice flow of the antarctic ice sheet we present a reference comprehensive high resolution digital mosaic of ice motion in antarctica assembled from multiple satellite interferometric synthetic aperture radar data acquired during the international polar year 2007 to 2009 the data reveal widespread patterned enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent this view of ice sheet motion emphasizes the importance of basal slip dominated tributary flow over deformation dominated ice sheet flow redefines our understanding of ice sheet dynamics and has far reaching implications for the reconstruction and prediction of ice sheet evolution

the spatial distribution of coarse surface grains and the stability of gravel river beds previous studies of surface particle structures in gravel bed rivers in particular coarse grain clusters conclude that these bedforms increase bed stability and reduce sediment transport rates however few studies have quantitatively analysed the effect of the surface distribution of coarse grains in isolation or arranged into distinct bedforms on particle entrainment focussing on descriptions of bedform formation and mechanical behaviour a novel image analysis technique was employed that allowed recognition of coarse grains and calculation of particle cluster areas under laboratory conditions increasing discharges were applied to a unimodal sand gravel bed the size class containing the d90 size was painted in ultraviolet paint image analysis software was used to identify this size class on digital images of the bed surface taken under ultraviolet light both the total surface area occupied by ultraviolet grains and the area of accumulations of connected grains were related to the threshold shear stress for entrainment as discharge magnitude increased coarse grains actively grouped together forming fewer larger accumulations of coarse particles lower values of critical bed shear stress occurred for beds with higher degrees of clustering beds are more stable when coarse grains are distributed more evenly over the bed surface this implies that using bed surface composition as a descriptor of bed resistance to entrainment may need to be complemented by a descriptor of the spatial distribution of the coarsest grains

the trouble with shear stress abstract predicted bedload fluxes often have large errors partly because calculations usually do not include spatial and temporal flow variability sediment motion is driven by a temporal distribution of applied fluid forces which are often simplified into time averaged flow velocities or shear stresses in sediment transport equations spatial variations in these flow parameters are also often neglected given the nonlinearities in the relation between flow and sediment flux the reach averaged sediment flux calculated with an average velocity or shear stress will not necessarily equal the measured spatially averaged bedload flux such spatial and temporal flow variations are ignored with the commonly used reach averaged shear stress ds that is a function of the flow depth and channel slope to demonstrate the uncertainties with using reach averaged shear stresses and even local shear stresses to predict bedload transport rates we have three goals first we outline the derivations and assumptions involved with commonly used estimates of shear stress second we summarize the literature on the uncertainties involved with using shear stress and other space and time averaged flow parameters to predict sediment flux third we use a new data set from experiments to add further support to a growing body of literature that suggests ds may not be linked to the mechanics of bedload transport we show considerable uncertainties exist in estimating a reach averaged shear stress by comparing ds and near bed shear stresses calculated from velocity profiles reynolds stresses and local turbulence for example ds was systematically greater than these near bed stresses even for experiments without large bed roughness we also find that correlations between local time averaged sediment fluxes and local reynolds stresses or turbulence intensities are relatively poor the near bed time averaged local flow velocity has the strongest relation with the time averaged local bedload flux because it is closely related to the forces that actually drive sediment transport however sediment transport rates in individual experiments could still vary by orders of magnitude for a given value of this flow velocity suggesting that additional work is needed to identity a parameter or distributions of parameters that will best predict sediment fluxes

critical shear stress of natural sediments the critical shear stress of individual fractions ci in unimodal and weakly bimodal sediments shows little variation with grain size and depends only on the mean grain size bf the mixture for strongly bimodal sediments ci increases with grain size an apparent result of a lateral segregation of the finer and coarser fractions on the bed surface that causes ci to deviate from size independence in the direction of unisize shields values a quantitative definition of mixture bimodality may be used to estimate the degree of mixture bimodality beyond which a substantial size dependence of ci is observed and to predict the variation of ci with grain size in bimodal sediments because properties of sediment grain size distributions other than bimodality appear to have little influence on ci the trends presented here for 14 unimodal and bimodal sediments may be quite general

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

critical shear stress for incipient motion of sand gravel streambeds results of an experimental study of the incipient motion of streambeds composed of sand gravel sediment mixtures are reported and compared with the earlier findings for uniform sediments the experiments were conducted in an 8 m long by 0 30 m wide glass walled tilting flume and an 18 m long by 0 80 1 10 m wide trapezoidal concrete channel a reference transport method is used to define the beginning of bed material movement the experiments demonstrate that the incipient motion of individual size fractions within a mixture is controlled by their relative size with respect to median size intergranular effects mixture standard deviation effect of the shape of grain size distribution absolute value of median size absolute size effect and bed slope effect of relative depth on overall flow resistance the shear stress at incipient motion of median sized grains in mixtures is found to be the same as for uniform sediment of this size the present findings are consistent with available flume and field data a technique for calculating the critical shear stress of different grain sizes in coarse uniform sediments and unimodal weakly bimodal sediment mixtures is proposed

a systematic analysis of eight decades of incipient motion studies with special reference to gravel bedded rivers data compiled from eight decades of incipient motion studies were used to calculate dimensionless critical shear stress values of the median grain size t c 50 calculated t c 50 values were stratified by initial motion definition median grain size type surface subsurface or laboratory mixture relative roughness and flow regime a traditional shields plot constructed from data that represent initial motion of the bed surface material reveals systematic methodological biases of incipient motion definition t c 50 values determined from reference bed load transport rates and from visual observation of grain motion define subparallel shields curves with the latter generally underlying the former values derived from competence functions define a separate but poorly developed field while theoretical values predict a wide range of generally higher stresses that likely represent instantaneous rather than time averaged critical shear stresses the available data indicate that for high critical boundary reynolds numbers and low relative roughnesses typical of gravel bedded rivers reference based and visually based studies have t c50 ranges of 0 052 0 086 and 0 030 0 073 respectively the apparent lack of a universal t 50 for gravel bedded rivers warrants great care in choosing defendable t c50 values for particular applications

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

evidence against a young volcanic origin of the gamburtsev subglacial mountains antarctica 1 the gamburtsev subglacial mountains of east antarctica are among earth s most enigmatic mountain ranges they are situated in the middle of antarctica buried under hundreds of meters of ice and reach an elevation of more than 3000 m these characteristics have given rise to speculation about their origin and composition in particular whether they are a hotspot or remnants of ancient orogenic events we studied fluvio deltaic sands from odp site 1166 in prydz bay which were deposited prior to the onset of east antarctic glaciation to address the question of their origin results for u pb dating of detrital zircons reveal an important age population of 530 ma which is accompanied by a dominant 40ar 39ar age population of 519 ma for detrital hornblendes the data show no sign of young volcanic contributions suggesting an old continental origin of the mountains leaving as enigmatic the cause of their great height and size

influence of the sediment supply texture on morphological adjustments in gravel bed rivers the role played by the texture of the sediment supply on channel bed adjustments in gravel bed rivers is poorly understood to address this issue an experimental campaign has been designed flume experiments lasting 96 h in a 9 m long 0 60 m wide have been performed with different sand gravel mixtures as feed textures the response of the surface texture has been found to be highly dependent on the grain size distribution of the feed when the feed texture included gravel the finest fractions of the sediment supply infiltrate beneath the surface conversely sand remains on the surface when the feed texture lacks gravel this different textural response becomes obscured when water discharge increases further the sediment transport rate approaches the feed rate differently depending on the content of gravel in the feed texture when a small proportion of gravel is part of the feed texture bed load transport rate asymptotically approaches the feed rate however when a significant fraction of gravel is part of the feed grain size distribution bed load transport rate approaches the feed rate by following an oscillatory path these findings have been verified in terms of a one dimensional numerical model this modeling reveals that the higher the differences in mobility among the grain sizes contained in the feed texture the more evident is the nonasymptotic transient trend toward equilibrium

bedrock platforms within the ross embayment west antarctica hypotheses for ice sheet history wave erosion cenozoic extension and thermal subsidence ice penetrating radar mostly airborne and marine seismic surveys have revealed plateaus and terraces about 100 350 m below sea level beneath parts of the ross embayment including the west antarctic ice sheet the ross ice shelf and the eastern ross sea these surfaces cover many thousands of square kilometers and are separated by bedrock troughs occupied by the west antarctic ice streams prominent plateaus are under edward vii peninsula siple dome and roosevelt island marine seismic data and gravity data over the buried plateaus support an interpretation that they were caused by erosion into basement the flat and level nature of the surfaces that were formed by erosion are near the same depth over large distances and fringe the buried rugged bedrock topography of marie byrd land supports an interpretation of marine rather than glacial erosion marine seismic reflection profiles over one of the plateau remnants show it as an angular unconformity cut into gently dipping sediments of late oligocene age draped with thin flat lying sediments implying that the plateau is early miocene or younger the younger limit for plateau erosion follows from the interpretation of the mechanism erosion must predate permanent ice along the coast associated with the growth of the west antarctic ice sheet probably prior to 10 ma and possibly prior to 14 ma the plateaus along the siple coast with depths around 350 meters do not rebound to close to sea level and wave base for models of removing past and present ice load this discrepancy can be explained if ross embayment lithosphere has been cooling and subsiding since significant extension in eocene to oligocene time our interpretation requires crustal subsidence in the ross sea which in turn implies higher bedrock elevations in the past within this region higher standing topography presented an opportunity for the accumulation of local ice sheets and caused sea level fluctuation prior to late cenozoic time

major neogene fluctuations of the east antarctic ice sheet stratigraphic evidence from the lambert glacier region stratigraphic and sedimentological data are presented from a region likely to directly record the evolution of the east antarctic ice sheet along the western margin of the lambert graben which now drains 1 106 km2 or one eighth of the total area of the east antarctic ice sheet extensive remnants of cenozoic glaciomarine fjordal sediment known as the pagodroma group are preserved as far as several hundred kilometers inland from the open coast the sediments resemble those produced by tidewater glaciers in the arctic rather than those of modern antarctica four separate formations of the pagodroma group spanning the interval from early miocene or older to pliocene or early pleistocene are preserved the oldest and highest crop out at nearly 1500 m above sea level each formation was deposited in close proximity to an ice margin grounded on the fjord bottom during major recessional phases of the lambert glacier underlying each formation is a glacially cut erosion surface each surface records a separate stage of fjord excavation when ice expanded onto the continental shelf in prydz bay evidence from offshore drilling in prydz bay and these data indicate fluctuations of the lambert glacier terminus in excess of 500 km in neogene time thereby reflecting large changes in the volume of the ice sheet depositional episodes were succeeded by phases of uplift totalling more than 1500 m

the impact of stress history on bed structure recent research has started to focus on how prolonged periods of sub threshold flows may be capable of imparting structural changes that contribute to increased bed stability to date this effect termed stress history has been found to be significant in acting to increase a bed s critical shear stress at entrainment threshold however it is supported by only limited qualitative and often speculative information on the mechanisms of this stabilisation process in grade specific studies as such this paper uses high resolution laser scanning to quantitatively ascertain the granular mechanics underpinning the relationship between stress history and entrainment threshold for beds of a range of grain size distributions employing a bed slope of 1 200 three grain size distributions with median grain sizes d50 of 4 8mm uniform g d84 d16 0 5 1 13 bimodal g 2 08 and unimodal g 1 63 were exposed to antecedent stress histories of 60 and 960 minutes duration antecedent shear stress magnitude was set at 50 of the critical shear stress for the d 50 when no stress history period was employed two laser displacement scans of the bed surface approximate area 100 x 117mm were taken one prior to the antecedent period and one after this period so that changes to surface topography could be quantified resolution of x 0 10mm y 0 13mm and z 0 24mm rearrangement of bed surface structure is described using statistical analysis and 2d semi variograms to analyse scaling behaviour results reveal vertical settlement changes to bed roughness and particle repositioning however the bed grain size distribution influences the relative importance of each mechanism in determining stress history induced bed stability this is the focus of discussion in this paper

effect of changes in fine grained matrix on bedload sediment transport in a gravel bed river while clay and silt matrices of gravel bed rivers have received attention from ecologists concerned variously with the deteriorating environments of benthic and hyporheic organisms their impact on sediment entrainment and transport has been explored less a recent increase of such a matrix in the bed of nahal eshtemoa an ephemeral river of the northern negev has more than doubled the boundary shear stress needed to initiate bedload from 7 n m 2 0 027 during the flash floods of 1991 2001 to 15 n m 2 0 059 during those of 2008 2009 the relation between bedload flux and boundary shear stress continues to be well defined but it is displaced the matrix now contains a significant amount of silt and clay size material the reasons for the increased entrainment threshold of bedload are explored large scale laser scanning of the dry bed reveals a reduction in grain scale morphological roughness while artificial in situ tests of matrix integrity indicate considerable cohesion the implications for adopting bed material sampling strategies that account for matrix development are assessed copyright 2012 john wiley sons ltd

increase in coarse sediment transport associated with disturbance of gravel river beds by signal crayfish pacifastacus leniusculus there is growing acknowledgement of the interaction between animals and the river bed on which they live and the implications of biological activity for geomorphic processes it has been observed that signal crayfish pacifastacus leniusculus disturb gravel substrates potentially promoting sediment transport and impacting ecological communities however the mechanisms involved and the extent of their impact remain poorly understood especially in relation to other processes that affect grain mobility in gravel bed rivers a series of flume experiments using loose and water worked gravel beds of narrowly graded grain sizes that were exposed to 6 h of crayfish activity under low velocity flows showed a substantial increase in the number of grains entrained by subsequent higher velocity flows when compared with control runs in which crayfish were never introduced crayfish alter the topography of their substrate by constructing pits and mounds which affect grain protrusion when walking and foraging they also alter gravel fabric by reorienting and changing the friction angle of surface grains in water worked surfaces this fabric rearrangement is shown to lead to a statistically significant partial reversal of the structuring that had been achieved by antecedent flow for these previously water worked surfaces the increase in entrainment arising from disturbance by crayfish was statistically significant with grain transport nearly twice as great this suggests that signal crayfish an increasingly widespread invasive species in temperate latitudes beyond their native nw north america have the potential to enhance coarse grained bedload flux by altering the surface structure of gravel river beds and reducing the stability of surface grains this study illustrates further the importance of acknowledging the impact of mobile organisms in conditioning the river bed when assessing sediment entrainment mechanics in the context of predicting bedload flux

the incidence and nature of bedload transport during flood flows in coarse grained alluvial channels a continuous record reveals that the incidence of bedload in a coarse grained river channel changes from flood to flood long periods of inactivity encourage the channel bed to consolidate sufficiently so that bedload is largely confined to the recession limb of the next flood wave but when floods follow each other closely the bed material is comparatively loose and offers less resistance to entrainment in this case substantial amounts of bedload are generated on the rising limb this is confirmed by values of bed shear stress or stream power at the threshold of initial motion which can be up to five times the overall mean in the case of isolated floods or those which are the first of the season this produces a complicated relationship between flow parameters and bedload and explains some of the difficulties in establishing bedload rating curves for coarse grained channels besides this the threshold of initial motion is shown to occur at levels of bed shear stress three times those at the thresholds of final motion this adds further confusion to attempts at developing predictive bedload equations and clearly indicates at least one reason why equations currently in use are unsatisfactory bedload is shown to be characterized by a series of pulses with a mean periodicity of 1 7 hours in the absence of migrating bedforms it is speculated that this well documented pattern reflects the passage of kinematic waves of particles in a slow moving traction carpet the general pattern of bedload including pulsations is shown to occur more or less synchronously at different points across the stream channel

capturing the spatiotemporal variability of bedload transport a time lapse imagery technique monitoring sediment transport in morphologically complex and labile channels remains a difficult task even at the laboratory scale to address this challenge a fully automated imagery technique for continuously mapping the spatial and temporal variability of bedload transport is proposed this method uses differentiated time lapse imagery taken from a fixed camera to detect bed variations induced by grain displacement the technique is not based on tracking the individual particles rather it evaluates macroscopic colour changes within a region that contains several grains which depend on the occurrence and intensity of the bedload transport image derived data were compared with the sediment flux measured during four flume experiments and produced good correspondence the method provides continuous tracking of the location of the transporting channels and enables estimation of local variations in the magnitude of the bedload flux moreover the spatial extent of the monitoring area offers an unprecedented opportunity to aggregate spatially dense and continuous data at the reach scale as needed to properly capture the full range of variability of morphologically complex and rapidly evolving gravel bed rivers despite being limited to laboratory scale physical experiments the method provides useful data to investigate fundamental morphodynamic processes such as bar migration bank erosion anabranches opening closure and the associate spatial and temporal scales further the data obtained have the potential to enhance numerical model calibration and improve our understanding of the complex dynamics of real world settings copyright 2017 john wiley sons ltd