bed material transport estimated from the virtual velocity of sediment this study evaluates the possibility of determining bed material transport using the virtual rate of travel of individual particles dimensions of the active layer of the streambed and porosity and density of streambed material magnetically tagged stones and scour indicators were employed in carnation creek british columbia to quantify transport rates observations cover flows up to 36 m3 s 1 0 081 transport rates ranging from 0 090 to 9 7 kg s 1 0 12 13 2 m3 h 1 display a relatively sensitive trend with maximum stream power as expected error analysis indicates that uncertainty in virtual velocity covers the majority of sample variance an evaluation of the two measurement techniques used to delineate active layer dimensions magnetically tagged stones and scour indicators indicates that they yield comparable depths widths and transport rates over the range of flows observed issues for further study are discussed 1998 john wiley sons ltd

sedimentary characteristics of the gravel sand transition in the river rhine abstract a gravel bed river often changes abruptly into a sand bed river the causes of such so called gravel sand transitions have been elucidated in recent years but detailed observations of gravel sand transitions in large rivers are scarce the present study fills this knowledge gap by investigating the sedimentary characteristics of the gravel sand transition in the river rhine data on bed composition and flow characteristics are used in combination with a novel method for the evaluation of the bed structure the analysis shows that in contrast to common belief the bed structure in the gravel sand transition zone does not change from fully clast supported to fully matrix supported instead there is a strong cross stream variation in bed structure especially upstream of the transition zone the analysis also shows that the downstream decrease in gravel mobility in the gravel sand transition zone which is usually attributed to the change in bed structure and the so called patchiness effect is at least partly caused by the larger scale bend sorting process which concentrates gravel in outer bends where it is only infrequently mobile dune sorting which has been suggested to have an effect on the gravel mobility similar to that of bend sorting was found to be relatively unimportant in the rhine partly because it is strongly counteracted by armoring processes that affect an uncommonly thick sediment layer the gravel sand transition in the rhine with its length of 50 km is much less abrupt than the gravel sand transitions of smaller rivers reported on in the literature although the dependence of the transition length on river size intuitively is correct the exact causes remain unclear

on the true antiquity of eoarchean chemofossils assessing the claim for earth s oldest biogenic graphite in the saglek block of labrador abstract a recent claim to have found traces of earth s earliest life 3 95 ga utilising isotopically light carbon in graphite bearing metapelites from the saglek block of northern labrador canada is re evaluated applying rigorous geological and geochronological criteria the establishment of these criteria in previous evaluations of early life claims from southern west greenland and northern canada is reviewed in order to provide a backdrop to discussion of the saglek claim in particular we emphasise the importance of the scale of lithological continuity in determining the veracity of such claims which are considerably easier to demonstrate from large relatively less tectonised supracrustal remnants like the isua greenstone belt than they are from smaller isolated enclaves of the kind found on akilia or the highly tectonised and imbricated unit that is found in the saglek block unambiguous field relationships between ca 3 9 ga tonalitic gneiss and the graphite bearing metasediments have not been demonstrated in the literature that the saglek claim relies upon and earlier u pb hf isotopic studies on zircon from metasediments at one of the localities used in the claim indicate a mesoarchean to neoarchean time of deposition we conclude that irrespective of the validity of the carbon isotopic evidence field relationships and geochronological evidence fail to demonstrate an age of 3 95 ga for the potential traces of life

infiltration of fine sediment into a coarse mobile bed a phenomenological study experiments were undertaken to study the nature of granular interaction in running water by examining the influence of fine grain inputs to a coarser sediment bed with a mobile surface video recordings of grain sorting by both kinetic sieving and spontaneous percolation are used to diagnose the critical processes controlling the overall bed response kinetic sieving takes place in the mobile bed surface with the finer sediment moving to the bottom of the bedload transport layer at the interface with the underlying quasi static coarse bed we show that the behavior at this interface dictates how a channel responds to a fine sediment input if by spontaneous percolation the fine sediment is able to infiltrate into the underlying quasi static bed the total transport increases and the channel degrades however if the fine sediment input rate exceeds the transport capacity or is geometrically unable to infiltrate into the underlying bed it forms a quasi static layer underneath the transport layer that inhibits entrainment from the underlying bed resulting in aggradation and an increase in bed slope this article is protected by copyright all rights reserved

grain size and topographical differences between static and mobile armour layers a series of laboratory flume experiments under conditions of sediment starvation zero sediment feeding and recirculation were conducted in order to identify the temporal evolution and surface properties of static and mobile armour layers the experiments were carried out in an 8 m long flume using a bimodal grain size mixture d50 6 2 mm and a range of shear stresses ranging from 4 0 to 8 6 n m 2 the results confirm that a static armour layer is coarser than a mobile one and that the grain size of a mobile armour layer is rather insensitive to changes in the imposed flow strength an analysis of laser scan bed surveys revealed the highly structured and imbricated nature of the static armour layer under these conditions the vertical roughness length scale of the bed diminished and it became topographically less complex at higher forming discharges the topography of mobile armour layers created by rising discharges differed they exhibited a greater roughness length scale and were less organized despite the fact that the grain size of the surface material maintained an approximately constant value during recirculation also the mobile armour tended to create larger cluster structures than static armour layers when formed by higher discharges these differences were mainly due to the transport of the coarser fraction of bed sediments which diminished to zero over the static armour because of being hidden within the bed whereas in the mobile armour the coarser particles protruded into the flow and were actively transported increasing the vertical roughness length scale overall the results show that an examination of the grain size characteristics of armour layers cannot be used to infer sediment mobility and bed roughness detailed elevation models of exposed surfaces of gravel bed rivers are required to provide critical insight on the sediment availability and sedimentation processes copyright 2011 john wiley sons ltd

applicability of bed load transport models for mixed size sediments in steep streams considering macro roughness in steep mountain streams macro roughness elements typically increase both flow energy dissipation and the threshold of motion compared to lower gradient channels reducing the part of the flow energy available for bed load transport bed load transport models typically take account of these effects either by reducing the acting bed shear stress or by increasing the critical parameters for particle entrainment here we evaluate bed load transport models for mixed size sediments and models based on a median grain size using a large field data set of fractional bed load transport rates we derive reference shear stresses and bed load transport relations based on both the total boundary shear stress and a reduced or effective shear stress that accounts for flow resistance due to macro roughness when reference shear stresses are derived from the total boundary shear stress they are closely related to channel slope but when they are derived from the effective shear stress they are almost invariant with channel slope the performance of bed load transport models is generally comparable when using the total shear stress and a channel slope related reference shear stress or when using the effective shear stress and a constant reference shear stress however dimensionless bed load transport relations are significantly steeper for the total stress approach whereas they are similar to the commonly used fractional wilcock and crowe wc transport model for the effective stress approach this similarity in the relations allows the wc model developed for lower gradient streams to be used in combination with an effective shear stress approach in steep mountain streams

size and distance of travel of unconstrained clasts on a streambed we have examined the relation between the mean distance of movement during individual flood events and the mean particle size of unconstrained clasts in gravel bed rivers distance of movement was scaled using the mean distance of movement of the median size group of the surface material size was scaled using the median b axis diameter of the subsurface material the scaled data are fitted with a nonlinear function clasts larger than the median of surface material exhibit a steep decline of mobility with an upper limit for mobility near di d50sub 10 smaller materials exhibit a less sensitive relation we suppose that trapping of small clasts affects their travel distance these results indicate that the movement of free surface stones is size preferred a subordinate analysis of free constrained and buried particles reveals that bed surface structure acts to reduce differential movement

grain size distributions of bed load inferences from flume experiments using heterogeneous sediment beds abstract the grain size fractions in the bedload transported over the five heterogeneous sediment beds of different values of bed roughness were computed from the flume experiments the existence of an entrapment factor associated with the sorting observed from the bed to active layer was modeled based on the modified critical shear stress to estimate the grain size fractions in the transport layer under given hydraulic conditions the efficiency of these models was tested with the observed data subsequently the patterns of observed grain size distributions in the transport layer were tested to identify the distributions developed in the active layer due to sorting using three probability density functions pdf such as log normal log hyperbolic and log skew laplace tests indicated that a log skew laplace distribution fitted best for 49 a log hyperbolic for 31 and a log normal for 20 out of forty five bedload samples collected under unidirectional flow with changes in flow discharge and bed roughness the results of this study would be useful to specify the grain size distributions in the bedload formed under different hydrodynamic conditions in various sedimentary environments

time and the rivers flowing fluvial geomorphology since 1960 fluvial geomorphology has been the largest single subdiscipline within geomorphology for many decades fluvial geomorphic expertise is integral to understanding and managing rivers and to developing strategies for sustainable development this paper provides an overview of some of the significant advances in fluvial geomorphology between 1960 and 2010 with respect to conceptual models fluvial features and environments being studied tools used by fluvial geomorphologists geomorphic specialty groups within professional societies journals in which fluvial geomorphic research is published and textbooks of fluvial geomorphology during this half century fluvial geomorphology broadened considerably in scope from a focus primarily on physical principles underlying process and form in lower gradient channels with limited grain size range to a more integrative view of rivers as ecosystems with nonlinear behavior and great diversity of gradient substrate composition and grain size the array of tools for making basic observations analyzing data and disseminating research results also expanded considerably during this period as did the diversity of the fluvial geomorphic community

observations of bedload movement bar development and sediment supply in the braided ohau river relative bedload transport rate and hydraulic parameters were measured on two occasions in a reach of the braided gravel bedded ohau river each reach contained a deep fast flowing chute leading to an area of diverging shallow flow which contained a middle bar the measurements are self consistent and indicate that where flow is concentrated in a deep chute shear stress is high but where flow diverges depth slope and shear stress decrease in the first survey the bed was scoured in the chute and sediment transport rates were high but where flow diverged sediment transport rate decreased it appears that deposition leads to bar growth bar growth in turn reduces slope and depth deposition is encouraged and the bar continues to grow vertically laterally and upstream in the second survey no sediment transport was observed despite hydraulic conditions very similar to the first survey the absence of sediment transport is attributed to the cessation of sediment supply to the river channel

model experiments on mobile paved gravel bed streams laboratory experiments which model streams with poorly sorted gravel beds at reduced scale reveal that pavement is a mobile bed phenomenon it acts to decrease the inherent difference in mobility between large and small grains by overrepresenting the percentage of large grains exposed to the flow pavement can coexist with the motion of all available grain sizes because motion is sporadic so that at any given time only a small percentage of surface grains are actually in motion particles in the immediate subpavement are only occasionally moved and deeper particles are hardly ever moved the experiments were conducted at constant discharges they provide accurate quantitative models of two field streams in that they obey the same bedload law as field data both sediment feed and recirculating configurations were utilized the only systematic difference between the two is in the behavior of the finer grains

equal mobility of gravel in streams the remains of the day 1 the concept of equal mobility of gravel transport is 2 decades old the weak form of the hypothesis states that in order to transport the coarse half of the mean annual gravel load through a river reach at a rate equal to the fine half the coarser material must be overrepresented on the bed surface giving rise to a mobile bed armor the degree of mobile bed armoring necessary to accomplish this diminishes with increasing bed shear stress the strong form of the hypothesis states that the grain size distribution of the gravel portion of the bed load should be similar to that of the substrate and finer than that of the surface layer here the hypothesis is subjected to a rigorous test in the laboratory under controlled conditions which are nevertheless chosen to be as representative as possible of actual field conditions the grain size distributions used in the experiment included both model gravel and model sand at the end of the experiment the entire surface layer and a significant depth of substrate were removed from an entire reach of the channel and sieved the results of the experiment confirmed the weak form of equal mobility the surface layer was significantly coarsened compared with the bed load even when the sand was excluded from the size distributions the strong form of equal mobility was also supported by the experiment in that the size distribution of the gravel substrate was nearly identical to the size distribution of the gravel portion of the load the gravel substrate was however slightly but measurably coarser than the gravel load a tendency that has been observed in the field in cases for which the strong form is not satisfied

incipient motion of sand gravel sediment mixtures experiments on the incipient motion of gravel and sand mixtures of 0 100 10 90 25 75 45 55 and 100 0 percent ratios of gravel and sand respectively were made in a laboratory flume a series of transport experiments was made for each of the five sediment beds and the critical shear stress for motion was calculated for 12 size ranges by interpolating or extrapolating the bed shear stress for a very small transport rate the sand in each of the five bed mixtures began to move at nearly the same bed shear stress all gravel sizes began to move at nearly the same bed shear stress in the 100 gravel experiments but in the sand gravel experiments the gravel showed an increase in critical shear stress with increasing size reasons for this change in the initiation of motion of the gravel from the 100 gravel to the sand gravel mixtures may result from the abundant sand sized sediment inhibiting the formation of a coarse bed surface layer in the sand gravel experiments

bed load transport of mixed size sediment fractional transport rates bed forms and the development of a coarse bed surface layer fractional transport rates bed surface texture and bed configuration were measured after a mixed size sediment had reached an equilibrium transport state for seven different flow strengths in a recirculating laboratory flume fractional transport rates were also measured at the beginning of each run when the bed was well mixed and planar the start up observations allow us to describe the variation of fractional transport rates with bed shear stress for a constant bed surface texture and bed configuration the start up and equilibrium observations together allow for the first time an unambiguous description of the mutual adjustment among the transport the bed configuration and the bed surface as the transport system moves toward equilibrium we find that a substantial interaction exists among the transport bed surface and bed configuration bed forms and a coarse surface layer coexist over a range of bed shear stress under some flow conditions the size and shape of the bed forms are controlled by the presence of the coarse surface layer at higher flows the coarse surface layer is eliminated by scour in the lee of the bed forms if the bed surface is defined as that over which the bed forms move a coherent relation between the bed surface texture and the transport grain size distribution may be defined at equilibrium the transport rates of all fractions were not equally mobile defined as identical transport and bed grain size distributions although equal mobility was approached for runs in which the bed shear stress was more than twice that for initial motion of the mixture under some flow conditions the transport was observed to adjust away from equal mobility as the bed adjusted from a well mixed start up condition to an equilibrium state development of a partial static armor wherein some individual grains become essentially immobile even though other grains in the same fraction remain in transport is suggested to explain these adjustments between the transport and bed surface grain size distributions constraints on equilibrium mixed size sediment transport are defined the special conditions for which equal mobility must hold and the relevance to natural conditions of flume results and the equal mobility concept are discussed

geomorphology and endangered fish habitats of the upper colorado river 2 linking sediment transport to habitat maintenance alluvial reaches of the colorado river near grand junction colorado provide important habitat for the endangered colorado squawfish this paper examines recent changes in the geomorphology of the colorado river and addresses the question of what can be done to improve existing fish habitats observations of channel change during periods of above average runoff from 1993 through 1995 indicate minor scour and fill of the main channel but more significant scour and enlargement of side channel and backwater habitats and flushing of fine sediment from the bed modeled relations between discharge and dimensionless shear stress indicate that the threshold of bed load transport 0 03 occurs at about half the bank full discharge these flows are exceeded about 26 days per year on average the bank full discharge produces an average of 0 047 and is exceeded about 8 days per year the width and depth of the channel thus appear to be set by a discharge that produces an average boundary shear stress of 1 5 times greater than the critical shear stress the effective discharge is slightly less than the bank full discharge and approximately 80 of the total sediment load is carried by the highest 10 of all discharges

analysis of bedload transport characteristics of idaho streams and rivers field data are essential in evaluating the adequacy of predictive equations for sediment transport each dataset based on the sediment transport rates and other relevant information gives an increased understanding and improved quantification of different factors influencing the sediment transport regime in the specific environment data collected for 33 sites on 31 mountain streams and rivers in central idaho have enabled the analysis of sediment transport characteristics in streams and rivers with different geological topographic morphological hydrological hydraulic and sedimentological characteristics all of these streams and rivers have armored poorly sorted bed material with the median particle size of surface layer coarser than the subsurface layer the fact that the largest particles in the bedload samples did not exceed the median particle size of the bed surface material indicates that the armor layer is stable for the observed flow discharges generally bankfull or less and in some cases two times higher than bankfull discharge the bedload transport is size selective the transport rates are generally low since sediment supply is less than the ability of flow to move the sediment for one range of flow discharges or the hydraulic ability of the stream is insufficient for entrainment of the coarse bed material detailed analyses of bedload transport rates bedload and bed material characteristics were performed for each site the obtained results and conclusions are used to identify different influences on bedload transport rates in analyzed gravel bed rivers copyright 2008 john wiley sons ltd

experiments on bar formation in a straight flume 2 graded sediment laboratory experiments have been carried out in a large laboratory flume using a strongly bimodal sediment mixture in a range of flow conditions such that the initially flat bed of the flume became unstable enhancing the development of alternate bars in order to elucidate the effect of grain sorting the present experiments are compared with a previous set of experiments performed in the same flume under similar hydraulic conditions but using a nearly uniform sand with a mean geometric grain diameter equal to that characterizing present experiments the comparison suggests that sediment heterogeneity may appreciably affect bed form characteristics the development of smallscale ripples and mesoscale dunes sediment waves tended to be inhibited thus allowing a decrease in flow resistance owing to the bimodal character of the adopted mixture at low values of the bed shear stress a condition of partial transport was attained for which only the finer grained portion of the mixture was observed to move while the coarsergrained fractions remained essentially immobile throughout the experimental run however complete mobilization of all size fractions was observed to occur in runs carried out at higher slopes i e at higher bed shear stress in order to generate an alternate bar pattern selective transport of individual grain size fractions coupled with the characteristic bar topography pattern led to an intense longitudinal sorting which accreted the coarser particles on bar crests furthermore bar migration caused through scour and fill a significant vertical sorting as a consequence of these sorting processes and in accordance with previous experimental observations bar height turns out to be invariably damped with respect to uniform sediment experiments the trend exhibited by the wavelengths is less clear and suggests that in the present experiments sorting effects do not enhance the clear shortening of bar wavelengths typically observed in other series of flume experiments carried out with weakly bimodal mixtures

experiments on the effect of hydrograph characteristics on vertical grain sorting in gravel bed rivers 1 desert ephemeral gravel bed streams typically have bed surfaces that are relatively unarmored compared to the substrate below while gravel bed streams in humid and snowmelt areas typically have well armored surfaces the degree of armoring can be characterized in terms of an armor ratio defined as the ratio of the surface median size to the substrate median size a set of field data shows desert ephemeral gravel bed streams with armor ratios ranging from 0 5 to 2 4 and with an average value of 1 2 the armor ratio of snowmelt fed gravel bed streams in the same set ranges from 2 to 7 with an average value of 3 4 the reason for this difference is sought in terms of differing hydrological characteristics and sediment supply regimes thirteen experiments were conducted to study the formation of armoring under a range of hydrological conditions the experiments have two limiting cases a relatively flat hydrograph that represents conditions produced by continuous snowmelt and a sharply peaked hydrograph that represents conditions associated with flash floods all constant hydrograph experiments developed a well armored structured surface while short asymmetrical hydrographs did not result in substantial vertical sorting all symmetrical hydrographs show some degree of sorting and the sorting tended to become more pronounced with longer duration sediment supply appears to be a first order control on bed surface armoring while the shape of the hydrograph plays a secondary role

modelling cross shore intensive sand transport and changes of bed grain size distribution versus field data abstract the study is focused on the cross shore transport of size graded sediment under combined wave current flow in the intensive flow regime the mathematical method for the description of hydrodynamic processes and sediment transport is adapted from the approach of kaczmarek and ostrowski coast eng 45 2002 1 for non graded sediment the theoretical model of vertical structure of sediment concentration as well as vertical mixing and sorting is presented the model of transport of graded sediment accounts for two directional cross shore sand flux the first component of this flux is directed onshore and results from wave asymmetry effects while the second one is directed seawards and is caused by undertow the vertical structure of this two directional sediment flux and its variability along a cross shore profile is a reason for segregation of grains in a horizontal direction this horizontal sorting of sand is theoretically modelled using the present approach a concept of the carpet of sorted sediments is implemented to reproduce the segregation of sediment in time and to assess the influence of grain size changes on short term evolution of the cross shore profile the results of computations are compared with the large scale laboratory data from the literature and with field measurements carried out by the authors the agreement between the model results and the experimental data is found to be very good particularly it has been theoretically shown that the observed in situ bimodal grain size distributions result from two directional sediment fluxes on the cross shore profile

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

mineralogy and genesis of cordierite anthophyllite rocks from the sulfide deposit of falun sweden abstract cordierite anthophyllite rocks from the aureole of the falun sulfide deposit are characterized by the assemblages cordierite anthophyllite garnet gahnite quartz dierite staurolite quartz and cordierite andalusite quartz metamorphic conditions are estimated to be 550 50 c 2 5 1 kbar bulk rock chemistry trace element concentration and the variance of the system as defined by the parageneses hint at an origin from acid rocks altered metasomatically at rather low temperatures to chlorite quartz muscovite and subsequently metamorphosed under essentially isochemical conditions

on why gravel bed streams are paved bedload transport in poorly sorted gravel bed streams downstream of dams is considered bedload and typical bed material subpavement size distributions are observed to be similar it follows that the coarse half of the subpavement moves through a reach at a rate near that of the fine half since coarser grains are intrinsically less mobile than fine grains it follows that some mechanism must act to nearly equalize mobility it is hypothesized that the pavement seen in gravel bed streams at low flow is in fact in place during typical transport events capable of moving all available sizes this pavement can provide the equalizing mechanism by exposing proportionally more coarse grains to the flow field data are used to quantify this concept and to develop a predictive relation for river pavement the model indicates that pavement should be absent in most sand bed streams in agreement with observation

mobilization of coarse surface layers in gravel bedded rivers by finer gravel bed load 1 additions of sand to gravel beds greatly increase the mobility and flux of gravel however it is not known how additions of finer gravel to coarser gravel beds will affect the mobility of bed material here we examine the effect of fine gravel pulses on gravel bed material transport and near bed flow dynamics in a series of flume experiments bed material refers exclusively to sediment in the channel prior to the pulse introduction the observations indicate that fine sediment pulses tend to migrate downstream in low amplitude waves as the waves pass over the gravel bed the interstitial pockets in the bed material surface fill and coarse gravel particles are entrained this increases bed material transport rates and causes a distinct shift from a selective mobility transport regime where particles coarser than the bed material median 8 mm make up 30 of the load to an equal mobility transport regime where bed materials coarser than 8 mm and finer than 8 mm are transported in equal proportions the only possible source for this coarser bed load material is the sediment bed suggesting that portions of the coarse surface layer are being mobilized observations of near bed velocity and turbulence suggest that fine gravel pulses cause fluid acceleration in the near bed region associated with a reduction in the level of turbulence produced at the sediment boundary this accelerated fluid at the bed increases drag exerted on coarse surface layer particles promoting their mobilization our findings suggest that in general finer bed sediment not just sand can mobilize coarser sediment and that expressions for the influence of sand on bed mobility need to be generalized on the basis of grain ratios

fluvial transport of sand and gravel mixtures with bimodal size distributions abstract initiation of motion and fractional transport rates of sediments with bimodal size distributions were measured in a laboratory channel and in a natural channel transport experiments were conducted with unimodal 100 sand and 100 gravel bed sediments and three bimodal mixtures of the two sediments 10 gravel 90 sand 25 gravel 75 sand and 45 gravel 55 sand in the bimodal sediment beds the critical shear stress for the initiation of motion showed very little change with grain size for the sand sizes but increased with grain size for the gravel sizes for low flow strengths only the sand sizes were in transport while for the highest flow strengths the bed load sediment size distribution approached that of the bed material

input and output mass flux correlations in an experimental braided stream implications on the dynamics of bed load transport through the development of a model experiment it is shown that there exists a correlation between input and output sediment fluxes in a micro scale braided stream that remains valid regardless of the stability of the braided river this correlation has some important consequences on the mechanics of bed load transport by braided rivers it enables the definition of both a dimensionless stream power and a dimensionless transport efficiency these dimensionless variables in turn permit the definition of a braided river stability criterion with regard to bed load transport the existence of such a correlation also suggests that the average critical shear stress or slope of motion may depend on the flux of mass input to the system using these findings together with a one dimensional exner equation for the conservation of mass a kinematic wave equation for the average evolution of the riverbed is eventually derived and its significance analyzed

frequency distribution of river bed materials the size distribution of river bed material plays an important role in the study of fluvial hydraulic processes it is not always easy to sample the river bed material for the determination of its size distribution but knowledge of the frequency distribution and of bed material sizes can be used to predict its size distribution therefore data on bed material size distributions of 63 streams from 10 different countries have been analysed to determine the frequency distribution which can be best fitted to them the log normal distribution cannot be fitted to the bed material mixtures when the entire range of sizes is considered the method of power transformation is found to normalize these mixtures relationships have been proposed between the parameters of the normalization and the stream slope these relations can be used to predict the size distribution of the river bed material

laboratory simulation of the salt weathering of schist 1 weathering of schist blocks in a seasonally wet tropical environment data describing sediment generation focusing on the temporal evolution of size gradation are required for the prediction of long term landform evolution this paper presents such data for the salt weathering of a quartz chlorite schist obtained from the ranger uranium mine in northern australia rock fragment samples are subjected to three different climate regimes 1 a dry season climate 2 a wet season climate both based on observations at the ranger site and 3 an oven drying sequence designed to test the sensitivity of the weathering process by exposing the rocks to more extreme temperatures two mgso4 salt solutions are applied one being typical of wet season runoff and the other a more concentrated solution salt solution is applied daily in the wet season experiments and once only at the beginning of the dry season experiments results of the experiments reveal four stages of weathering the kinetics of each stage are described and related to the formation of sediment of different sizes wet season climate conditions are shown to produce greater moisture variability and lead to faster weathering rates however salt concentrations in the wet season are typically lower and so when climate is combined with observed salt concentrations the dry and wet season experiments weather at approximately equal rates finally small variations in rock properties were shown to have a large impact on weathering rates leading to the conclusion that rock weathering experiments need to be carefully designed if results are to be used to help predict weathering behaviour at the landscape scale copyright 2006 john wiley sons ltd

breakup and reestablishment of the armour layer in a large gravel bed river below dams the lower ebro changes in armour layer during floods under supply limited conditions are little known this paper describes the breakup and the reestablishment of the bed armour layer in the regulated gravel bed ebro river during a flooding period the study was conducted over a 28 km study reach from 2002 to 2004 the surface subsurface and bed load grain size distribution constitute the bases for the analysis of bed armouring dynamics the results indicate that the magnitude of floods controlled the degree of armouring of the river bed the initial mean armouring ratio was 2 3 with maximum values reaching 4 4 floods in the winter of 2002 2003 q8 caused the breakup of the armour layer in several sections this resulted in the erratic bed load pattern observed during the december 2002 flushing flow and in the increase in bed load transport during successive events most grain size classes were entrained and transported causing river bed incision the mean armouring ratio decreased to 1 9 in contrast during low magnitude floods in 2003 2004 q2 the coarsest fractions 64 mm did not take part in the bed load while finer particles were winnowed thus surface deposits coarsened as a result the armour layer was reestablished i e the mean armouring ratio increased to 2 3 and the supply of subsurface sediment decreased the supply and transport of bed material appear to be in balance in the river reach immediately below the dam in contrast the transport of medium and finer size classes in the downstream reaches was higher than their supply from upstream a phenomenon that progressively reduced their availability in the river bed surface hence the armour layer reworking

tectonic sedimentology sediment systems deciphering global to local tectonics tectonic sedimentology has broad appeal because it can be applied at many time and length scales such as sedimentary consequences of changing rates of plate creation at mid ocean ridges continent continent collisions plateaux uplift active plate margins extensional rift tectonics and the birth growth and death of individual folds and faults tectonic sedimentology deals with the direct influence of neotectonics on sedimentation and basin development and with the inverse problem of reconstructing the order and development of palaeotectonic structures this review attempts to show how the scope and importance of the subject has developed over the last decade and is divided into five themes i at the largest tectonic scale constraints on mid ocean ridge activity and continent continent collisions come from a precise chemical analyses of fluid inclusions in marine halite deposits dating back to ca 550 ma b sr isotopic ratios of marine phanerozoic calcitic fossils and c chemical composition of archaean and proterozoic banded iron formations ii at regional scales constraints on the timing and extent of continental plateau uplift incision and cratonic tilting are given by a palaeoaltimetry estimates from oxygen isotope depletion in carbonate palaeosols b radiometric dating of palaeowater table speleothems and c preferential river migration iii at basin scales catchment processes are emphasized as key controls on sediment flux from tectonic uplands to sedimentary basins the inadequacy of sediment transport algorithms based on tractive stress and flow power to describe erosion incision and sediment transport during the most formative catchment hydrological events is emphasized iv rates of basin scale fault and fold growth displacement death and basement uplift are provided by application of facies analysis and sequence stratigraphy to accurately dated sediments in sedimentary basins v the effects of changing climate and varying basin base level in modifying tectonic influences on erosion and sedimentation are examined in such cases experimental and numerical modelling using multi variate parameters of subsidence rate sediment supply and sea level change can shed light on the problem future developments will undoubtedly improve such models hopefully establishing full linkage and feedback between sediment water supply and changing climate within an overall tectonic framework that may itself be changing

sediment storage partial transport and the evolution of an experimental gravel bed under changing sediment supply regimes abstract the adjustment of a gravel bed during cycles of sediment storage was analyzed for a flume experiment designed to study the effects of episodic sediment supply regimes as the bed aggraded and degraded due to changes in sediment feed it developed a complex topography with bedforms at different scales e g pebble clusters bars sediment inputs increased bedload rates and promoted large changes in bed morphology without an external supply the bed armored which increased bed stability counteracted bed degradation and decreased bedload rates fully mobile gravel 2 8 mm was the only fraction that exhibited a deficit over the experiment preferential storage of coarse grains caused the development of a sediment wedge upstream and downstream fining on the bed surface the storage of sand was also significant 60 of feed probably because of infiltration e g in the upstream wedge and hiding effects promoted by bed armor and structures size selective transport caused a cumulative increase in bed slope which was likely to affect sediment transport capacity the large variability in bedload rates for same levels of bed storage indicated that sediment availability and bed state were the main controls on sediment transport regime we provide empirical evidence that cycles of aggradation and degradation caused by changes in sediment feed upstream condition bed composition and topography and the rate and texture of sediment output